Editing IPCC:AR6/WGII/Chapter-2 (section)

== 2.6 Climate Change Adaptation for Terrestrial and Freshwater Ecosystems ==

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Adaptation to reduce the vulnerability of ecosystems and their services to climate change has been addressed in previous IPCC reports, with AR4 and AR5 recognising both autonomous adaptation and human-assisted adaptation to protect natural species and ecosystems. In AR5, Ecosystem-based Adaptation (EbA), adaptation for people, based on the better protection, restoration and management of the natural environment, was identified as an area of emerging opportunity, with a dedicated Cross-Chapter Box on the topic. In the SRCCL, conservation, EbA and related concepts were integrated throughout; SR1.5 also noted the role of EbA. Since the last assessment report, the scientific literature has expanded considerably, with growing interest in the concept of Nature-based Solutions (NbS). This section assesses this new literature and its implications for the implementation of climate change adaptation.

Previous sections of this chapter have set out the vulnerability of natural and semi-natural ecosystems to climate change, and the risks this poses to both biodiversity and ecosystem services (also sometimes described as ‘Nature’s Contributions to People’). Natural systems respond to climatic and other environmental changes in a variety of ways. Individual organisms can respond through growth, movement and developmental processes. Species and populations genetically adapt to changing conditions and evolve over successive generations. Geomorphological features, such as the path of watercourses, can also change naturally in response to climate change. However, there is a limit to which these natural processes can maintain biodiversity and the benefits people derive from nature, partly due to intrinsic limits, but also because of the pressures that people exert on the natural environment.

Most of this section therefore focusses on human interventions to build the resilience of ecosystems, enable species to survive or to adjust management to climate change. Vulnerability is, in many cases, exacerbated by the degraded state of many ecosystems as a result of human exploitation and LUC, leading to the fragmentation of habitats, the loss of species and impaired ecosystem function. This interaction between climate change and environmental degradation means that protecting ecosystems in a natural or near-natural state will be an important pre-requisite for maintaining resilience and give many species the best chance of persisting in a changed climate ( [[#Belote--2017|Belote et al., 2017]] ; [[#Arneth--2020|Arneth et al., 2020]] ; [[#Ferrier--2020|Ferrier et al., 2020]] ; [[#França--2020|França et al., 2020]] ). Protection from degradation, deforestation and exploitation is also essential to maintain critical ecosystem services, including carbon storage and sequestration and water supply ( [[#Dinerstein--2020|Dinerstein et al., 2020]] ; [[#Pörtner--2021|Pörtner et al., 2021]] ).

It is worth briefly considering some key concepts that are relevant to adaptation in ecosystems. Adaptation for biodiversity and ecosystems can encompass both managing change and building resilience. We use the definition of ‘resilience’ set out Chapter 1: ‘the capacity of social, economic and environmental systems to cope with a hazardous event or trend or disturbance, responding or reorganising in ways that maintain their essential function, identity and structure while also maintaining the capacity for adaptation, learning and transformation’. This includes the concept of ‘resistance’, which is used in some ecological literature to distinguish systems which are resistant to change from those that recover quickly from change. We consider both interventions designed primarily to protect biodiversity and those intended to reduce the risks of climate change to people.

A variety of terms are used to describe using environmental management to reduce the impacts of climate change on people in ways that also benefit biodiversity in the scientific literature, particularly EbA and NbS (see also [[IPCC:Wg2:Chapter:Chapter-1#1.4|Section 1.4]] ). EbA is the use of biodiversity and ecosystem services as part of an overall adaptation strategy to help people to adapt to climate change ( [[#Secretariat%20of%20the%20Convention%20on%20Biological%20Diversity--2020|Secretariat of the Convention on Biological Diversity, 2020]] ). EbA aims to maintain and increase the resilience and reduce the vulnerability of ecosystems and people in the face of the adverse effects of climate change ( [[#Vignola--2009|Vignola et al., 2009]] ). NbS is a broader term which is not restricted to climate change, and is also often used to refer to climate change mitigation; it has been defined by the IUCN as ‘Actions to protect, sustainably manage and restore natural or modified ecosystems that address societal challenges effectively and adaptively, simultaneously providing human well-being and biodiversity benefits’ ( [[#Cohen-Shacham--2016|Cohen-Shacham et al., 2016]] ). This widely accepted definition excludes actions which use the natural environment to solve human problems but do not provide benefits for biodiversity, and is closely linked to the concept of the Ecosystem Approach. NbS is not a universally accepted term, but it is being increasingly used in the scientific literature. It is a concept which recognises the importance of biodiversity in ecosystem service provision, and offers the opportunity to address climate change and loss of biodiversity together in an efficient integrated way ( [[#Chong--2014|Chong, 2014]] ; [[#Seddon--2020a|Seddon et al., 2020a]] ; [[#Ortiz--2021|Ortiz et al., 2021]] ). Given that the focus of this chapter is on adaptation, we primarily use the term EbA as it is more specific, but we do so understanding that it can be regarded as a subset of NbS. The wider concept of NbS for climate change adaptation and mitigation is covered in a cross-chapter box on the topic (see Cross-Chapter Box NATURAL in this chapter).

Whilst we distinguish between adaptation for biodiversity and EbA, it is important to recognise that the two are linked in that, if ecosystems themselves are not resilient to climate change, they will not be able to provide adaptation benefits for people. The case for resourcing biodiversity conservation and building the resilience of ecosystems is also strengthened when there are direct benefits for people in addition to the more general benefits of biodiversity.

Ecosystems are specifically included in the adaptation goals set out in the Paris Agreement and are addressed in most national adaptation plans ( [[#Seddon--2020b|Seddon et al., 2020b]] ). There are also now a large number of adaptation programmes and plans for local governments and governmental and non-governmental conservation organisations. Adaptation for and by ecosystems needs to be understood and developed in the wider contexts of conservation, climate resilient development and sustainable development. There are significant potential synergies but also conflicts between different objectives which require an integrated approach (covered further in 2.6.7).

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=== 2.6.1 Limits to Autonomous (Natural) Adaptation ===

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Natural ecosystems often have a high degree of resilience and can, to some extent, adjust to change. Species can adjust through evolutionary adaptation, distribution change, behavioural change, developmental plasticity and ecophysiological adjustment. There are, however, limits to autonomous adaptation, because of intrinsic limitations, the rate at which the climate is changing and the degraded state of many ecosystems.

None of the evolutionary changes either documented or theorised would enable a species to survive and reproduce in climate spaces that it does not already inhabit. It is very improbable that evolutionary responses would be sufficient to prevent species extinctions in the case of that species losing its climate space entirely on a regional or global scale (section 2.4.2.8) ( [[#Parmesan--2015|Parmesan and Hanley, 2015]] ). At the highest risk are the world’s most cold-adapted species (whose habitats are restricted to polar and high mountain-top areas). Examples include the polar bear ( [[#Regehr--2016|Regehr et al., 2016]] ), ‘sky-island’ plants in the Tropics ( [[#Kidane--2019|Kidane et al., 2019]] ), mountain-top amphibians in Spain ( [[#Enriquez-Urzelai--2019|Enriquez-Urzelai et al., 2019]] ), mountain-top lichens in the Appalachians (USA) ( [[#Allen--2016|Allen and Lendemer, 2016]] ) and silverswords in Hawaii ( [[#Krushelnycky--2013|Krushelnycky et al., 2013]] ). However, there is potential for using evolutionary changes to enhance the adaptive capacity of target species, as is being done on the Great Barrier Reef by translocating symbionts and corals that have survived recent intense heat-induced bleaching events into areas that have had large die-off ( [[#Rinkevich--2019|Rinkevich, 2019]] ). Multiple studies have assessed when and how evolution might be able to help wild species adapt to climate change ( [[#Ratnam--2011|Ratnam et al., 2011]] ; [[#Sgro--2011|Sgro et al., 2011]] ).

Some of the reasons cited in the literature as limits to autonomous adaptation are:

# Genetic changes in populations require many generations and, for many species, operate on longer timescales than those on which the climate is currently changing. In addition, experiments indicate there are strong constraints to ability to evolve beyond current climatic limits.
# Many species are moving to higher latitudes as the climate warms, but not all are keeping pace with changes in suitable climate space ( [[#Valladares--2014|Valladares et al., 2014]] ; [[#Mason--2015|Mason et al., 2015]] ). Such ‘climate debt’ (see sections 2.4.2.3.1, 2.4.2.8, 2.5.1.3.1) indicates an inability for non-genetic autonomous adaptation (e.g., evidence of limited ability for plastic responses, like those stemming from dispersal limitations, behavioural restrictions or physiological constraints).
# Some species have a low capacity for dispersal, which, combined with increased fragmentation of habitats, creates barriers to range shifts to match climate warming. Studies have shown that changes in the distribution of species and composition of communities are limited by the presence of intensively managed agricultural land fragmenting natural habitats ( [[#Oliver--2017|Oliver et al., 2017]] ).

There are a variety of mechanisms which promote the resilience of ecosystems through persistence, recovery and reorganisation ( [[#Falk--2019|Falk et al., 2019]] ). Changes in the balance of different plant species within a community can maintain the persistence of the community itself, maintaining its value as a habitat for other species and providing ecosystem services. In some cases, there are negative feedback mechanisms between biological and physical processes; for example, in peatlands, lowered water tables resulting from drier conditions can lead to reduced permeability of peat, increasing rates of water loss ( [[#Page--2016|Page and Baird, 2016]] ). There are limits to this resilience and the concept of tipping points beyond which ecosystems change state, and returning to the original state has been subject of much recent research ( [[#van%20Nes--2016|van Nes et al., 2016]] ). There is clear evidence that the degradation of ecosystems has reduced their resilience and that restoration can help to reduce risks to biodiversity and ecosystem services, discussed below (see [[#2.6.2|Section 2.6.2]] , 2.6.3). However, as the rate of climate change increases, the limits of this approach will start to be reached, and losses (including some with potentially catastrophic consequences) cannot be prevented; this is discussed further in [[#2.6.6|Section 2.6.6]] .

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=== 2.6.2 Adaptation for Biodiversity Conservation ===

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A variety of approaches have been identified as potential adaptation measures which people can take to reduce the risks of climate change to biodiversity. ( [[#Heller--2009|Heller and Zavaleta, 2009]] ), quoted in AR5, identified 113 categories of recommendation for adaptation from a survey of 112 papers and reports. Since then, the literature has expanded with thousands of relevant publications. Whilst there is increasing interest in adaptation for biodiversity conservation and a wide range of plans and strategies, there is less evidence of these plans being implemented. Since AR5, a number of studies, predominantly from Europe and North America, have investigated the extent to which adaptation has been integrated into conservation planning and is being implemented on a local and regional scale ( [[#Macgregor--2014|Macgregor and van Dijk, 2014]] ; [[#Delach--2019|Delach et al., 2019]] ; [[#Prober--2019|Prober et al., 2019]] ; [[#Clifford--2020|Clifford et al., 2020]] ; [[#Barr--2021|Barr et al., 2021]] ; [[#Duffield--2021|Duffield et al., 2021]] ). A common pattern in these studies is that vulnerability has been assessed and potential adaptation actions identified, but implementation has been limited beyond actions to improve ecological conditions which may increase resilience on a local scale.

To date, most scientific literature on adaptation to reduce the risks to biodiversity from climate change has been based on ecological theory rather than on observations or practical experience. A recent review ( [[#Prober--2019|Prober et al., 2019]] ) concluded that out of 473 papers on adaptation, only 16% presented new empirical evidence and very few assessed the effectiveness of actual adaptation actions. It is also the case that relatively little research is focused on local-scale management interventions rather than on larger-scale strategies ( [[#Ledee--2021|Ledee et al., 2021]] ), although there are some exceptions ( [[#Duffield--2021|Duffield et al., 2021]] ).

Although direct assessments of the effectiveness of adaptation actions are rare, since AR5, there have been an increasing number of empirical analyses of how different land use and management can influence the vulnerability of species and habitats. As climate change often interacts with other factors including ecosystem degradation and fragmentation ( [[#Oliver--2015a|Oliver et al., 2015a]] ), actions to address these other interacting factors is expected to build resilience to climate change. Table 2.6 summarises evidence that supports the main categories of proposed adaptation measures. We have taken an inclusive approach and included studies that address extreme weather events such as droughts, which may be exacerbated by climate change, as well as long-term changes in climate variables. We have not distinguished between studies in which climate change adaptation was an explicit focus and those in which lessons for adaptation can be learnt, that is, when studies were conducted for other reasons but inform the assessment of the impacts of actions identified as potential adaptation measures.

'''Table 2.6 |''' Evidence to support proposed climate change adaptation measures for biodiversity. The evidence highlights that adaptation for biodiversity conservation is a broad concept, encompassing a wide range of actions. It includes targeted interventions to change the microclimate for particular species (e.g., by creating shade) to changing national conservation objectives to take account of changing distributions of species and communities. It includes targeted actions addressing both climate change and the protection and restoration of ecosystems, with multiple additional benefits including reduced vulnerability to climate change. Most of the studies are not direct tests of the impacts of adaptation actions which, as noted above, is an important gap in the evidence. There is also a major limitation in that reported studies are predominantly from Europe, North America and Australasia, with little research in other regions.

{| class="wikitable"
|-
! '''Proposed adaptation measures for biodiversity'''

! '''Uncertainty Assessment'''

! '''Comment'''

! '''Selected references'''

|-
| ''Protect large areas of natural and semi-natural habitat''

| ''robust evidence,''

''high agreement''

| There is considerable evidence that: intact systems provide better quality and quantity of ecosystem services; larger intact areas provide better ecosystem services; the risk of species’ extinctions from disturbances including climate change, is reduced by having large, connected populations; more biodiverse systems provide higher levels of ecosystem services and are more resilient to climate change than degraded systems that have lost species

| ( [[#Pimm--2018|Pimm et al., 2018]] ; [[#Dinerstein--2019|Dinerstein et al., 2019]] ; [[#Woodley--2019|Woodley et al., 2019]] ; [[#Brooks--2020|Brooks et al., 2020]] ; [[#Hannah--2020|Hannah et al., 2020]] ; [[#Luther--2020|Luther et al., 2020]] ; [[#Zhao--2020|Zhao et al., 2020]] ; [[#Sala--2021|Sala et al., 2021]] );

|-
| ''Increase connectivity in terrestrial habitats: corridors, stepping stones''

| ''medium evidence,''

''medium agreement''

| There is good evidence that some species move more quickly in more connected landscapes. However, not all species do and some of those that benefit are invasive/pest/disease species; to date, empirical evidence showing that connectivity has reduced climate change impacts on species is limited.

| ( [[#Keeley--2018|Keeley et al., 2018]] ; [[#Stralberg--2019|Stralberg et al., 2019]] ; [[#von%20Holle--2020|von Holle et al., 2020]] )

|-
| ''Increase connectivity in river networks''

| ''limited evidence,''

''high agreement''

| Connectivity is needed to maintain the movement of species and populations, but river reaches and catchments lack integrated protection

| ( [[#Hermoso--2016|Hermoso et al., 2016]] ; [[#Thieme--2016|Thieme et al., 2016]] ; [[#Abell--2017|Abell et al., 2017]] ; [[#Brooks--2018|Brooks et al., 2018]] )

|-
| ''Increase habitat patch size and expand protected areas''

| ''limited evidence,''

''high agreement''

| Generally increases resilience because of functioning natural processes, large species populations and refugial areas

| ( [[#Eigenbrod--2015|Eigenbrod et al., 2015]] ; [[#Oliver--2015a|Oliver et al., 2015a]] )

|-
| ''Increase replication and representation of protected areas''

| ''limited evidence,''

''high agreement''

| Various benefits inferred, including a wider range of climatic and other conditions and less risk of extreme events affecting many rather than few areas. More sites available for colonisation by range-expanding species and better conditions to maintain species ''in situ'' under range contraction.

| ( [[#Mawdsley--2009|Mawdsley et al., 2009]] ; [[#Thomas--2012|Thomas et al., 2012]] ; [[#Virkkala--2014|Virkkala et al., 2014]] ; [[#Gillingham--2015|Gillingham et al., 2015]] ; [[#Pavón-Jordán--2020|Pavón-Jordán et al., 2020]] )

|-
| ''Protect microclimatic refugia''

| ''medium evidence,''

''high agreement''

| Locally cool areas can be identified and there is evidence that species can survive better in such areas

| ( [[#Haslem--2015|Haslem et al., 2015]] ; [[#Suggitt--2015|Suggitt et al., 2015]] ; [[#Isaak--2016|Isaak et al., 2016]] ; [[#Morelli--2016|Morelli et al., 2016]] ; [[#Merriam--2017|Merriam et al., 2017]] ; [[#Bramer--2018|Bramer et al., 2018]] ; [[#Suggitt--2018|Suggitt et al., 2018]] ; [[#Massimino--2020|Massimino et al., 2020]] )

|-
| ''Creating shade to lower temperatures for vulnerable species''

| ''limited evidence,''

''high agreement''

| Creating shade (e.g., of watercourses) has been used as an adaptation strategy, but improvements in species survival under warming conditions have yet to be demonstrated

| ( [[#Broadmeadow--2011|Broadmeadow et al., 2011]] ; [[#Lagarde--2012|Lagarde et al., 2012]] ; [[#Patino-Martinez--2012|Patino-Martinez et al., 2012]] ; [[#Thomas--2016|Thomas et al., 2016]] )

|-
| ''Restoring hydrological processes of wetlands, rivers and catchments, including by raising water tables and restoring original channels of watercourses''

| ''medium evidence,''

''high agreement''

| Wetland restoration is well established as a conservation measure in some countries. It can reduce vulnerability to drought with climate change, but evidence to demonstrate effectiveness as an adaptation measure is limited and requires the long-term monitoring of a range of sites. There is little restoration of degraded tropical peatlands to date

| ( [[#Carroll--2011|Carroll et al., 2011]] ; [[#Hossack--2013|Hossack et al., 2013]] ; [[#Dokulil--2016|Dokulil, 2016]] ; [[#Timpane-Padgham--2017|Timpane-Padgham et al., 2017]] ; [[#Moomaw--2018|Moomaw et al., 2018]] )

|-
| ''Restoration of natural vegetation dynamics''

| ''medium evidence,''

''medium agreement''

| Includes reintroduction of native herbivores and reversing woody encroachment of savannas. Benefits for biodiversity are well established in a wide range of different regions

| ( [[#Coffman--2014|Coffman et al., 2014]] ; [[#Valkó--2014|Valkó et al., 2014]] ; [[#Batáry--2015|Batáry et al., 2015]] ; [[#Smit--2016|Smit et al., 2016]] ; [[#Stevens--2016|Stevens et al., 2016]] ; [[#Hempson--2017|Hempson et al., 2017]] ; [[#Bakker--2018|Bakker and Svenning, 2018]] ; [[#Cromsigt--2018|Cromsigt et al., 2018]] ; [[#Fulbright--2018|Fulbright et al., 2018]] ; [[#Olofsson--2018|Olofsson and Post, 2018]] )

|-
| ''Reduce non-climatic stressors to increase resilience of ecosystems''

| ''limited evidence,''

''medium agreement''

| As a general principle, climate change is recognised as a ‘threat multiplier’ but specific details are often unclear

| ( [[#Oliver--2017|Oliver et al., 2017]] ; [[#Pearce-Higgins--2019|Pearce-Higgins et al., 2019]] )

|-
| ''Assisted translocation and migration of species''

| ''limited evidence,''

''medium agreement''

| Assisted translocation has been commonly suggested as an adaptation measure, but there have been very few examples of this being trialled. Translocations have been carried out for other reasons and lessons for climate change adaptation have been inferred.

| ( [[#Willis--2009|Willis et al., 2009]] ; [[#Brooker--2018|Brooker et al., 2018]] ; [[#Skikne--2020|Skikne et al., 2020]] )

|-
| ''Intensive management for specific species''

| ''medium evidence,''

''medium agreement''

| A variety of approaches including manipulating microclimate and competition between species to improve chances of survival under climate change

| ( [[#Angerbjörn--2013|Angerbjörn et al., 2013]] ; [[#Greenwood--2016|Greenwood et al., 2016]] ; [[#Pearce-Higgins--2019|Pearce-Higgins et al., 2019]] )

|-
| ''Ex situ conservation (seedbanks/genetic stores, etc.)''

| Not possible to assess at present

| Seed banks have been established but their long-term effectiveness can only be evaluated at a later point

| ( [[#Christmas--2016|Christmas et al., 2016]] )

|-
| ''Adjusting conservation strategies and site objectives to reflect changing species’ distributions and habitat characteristics''

| ''robust evidence,''

''high Agreement''

| Conservation management will need to take account of changes that cannot be prevented (e.g., the distribution of species and composition of communities) to protect and manage biodiversity as effectively as possible in a changing climate

| ( [[#Stein--2013|Stein et al., 2013]] ; [[#Rannow--2014|Rannow et al., 2014]] ; [[#Oliver--2016|Oliver et al., 2016]] ; [[#Stralberg--2019|Stralberg et al., 2019]] ; [[#Duffield--2021|Duffield et al., 2021]] )

|-
| ''Softening the matrix of unsuitable habitats between patches to increase permeability for the movement of species in response to climate change''

| ''limited evidence''

| There is potential for agri-environment schemes to do this in hostile farmed landscapes

| ( [[#Donald--2006|Donald and Evans, 2006]] ; [[#Stouffer--2011|Stouffer et al., 2011]] )

|}

Many climate adaptation actions for biodiversity operate on the landscape scale ( [[#von%20Holle--2020|von Holle et al., 2020]] ). The total area of habitat, how fragmented it is, the size of habitat patches and the connectivity between them are inter-linked properties on this scale. A growing number of studies have investigated how these properties affect species ability to persist ''in situ'' and colonise new areas. Overall, larger areas of semi-natural habitat are associated with increased resilience to ongoing climate change and extreme events as well as the capacity to colonise new areas ( [[#Haslem--2015|Haslem et al., 2015]] ; [[#Oliver--2017|Oliver et al., 2017]] ; [[#Papanikolaou--2017|Papanikolaou et al., 2017]] ). Larger habitat patches can support larger populations of a given species, which are more likely to maintain themselves and recover from periods of adverse conditions. Inhabiting a large patch size has been found to increase the resilience of some populations of species to extreme events such as droughts ( [[#Oliver--2015b|Oliver et al., 2015b]] ). They are also more likely to provide a range of different resources and microclimate conditions, which may increase the chances of the persistence of species under climate change. A larger area of habitat may also enable greater connectivity between patches and increase the chances of species colonising new areas as they track climate change ( [[#Oliver--2015b|Oliver et al., 2015b]] ).

Protecting and restoring natural processes is a general principle for maintaining and building resilience to climate change for biodiversity ( [[#Timpane-Padgham--2017|Timpane-Padgham et al., 2017]] ). One element of this is ensuring naturally functioning hydrology for wetlands and river systems (Table 2.6), which is particularly important in a context of changing rainfall patterns and increased evapotranspiration. An important development in approaches to conservation over recent decades has been the concept of re-wilding ( [[#Schulte%20To%20Bühne--2021|Schulte To Bühne et al., 2021]] ); this encompasses a number of elements of restoring natural processes, including the reintroduction of top predators, larger conservation areas, and less prescriptive outcomes than many previous conservation measures. There are elements of re-wilding which may well contribute to building resilience to climate change, but it will be increasingly important to factor climate change adaptation into the planning of re-wilding schemes ( [[#Carroll--2021|Carroll and Noss, 2021]] ).

The most consistently cited climate change adaptation measure for species is increasing connectivity to facilitate the colonisation of new areas. This reflects the fact that many species’ habitats are highly fragmented in areas with more intensive land management, which prevents them naturally changing their range to track changing climatic conditions. Advances and innovations in modelling techniques can support decision-making about connectivity ( [[#Littlefield--2019|Littlefield et al., 2019]] ). There is evidence from empirical and modelling studies that species can disperse more effectively in better-connected areas in terrestrial habitats ( [[#Keeley--2018|Keeley et al., 2018]] ). The issues are different in more natural landscapes—species may still be threatened in intrinsically isolated habitats, such as mountain tops, but connectivity cannot be created here in the same way. Evidence suggests that increased connectivity will only benefit a subset of species, probably those which are intermediate-habitat specialists that are able to disperse ( [[#Pearce-Higgins--2014|Pearce-Higgins and Green, 2014]] ). Generalists do not require corridors or stepping stones, while many corridors or stepping stones will not be of sufficient quality to be used by most habitat specialists. There should also be a caveat to the general principle that increasing connectivity is a benefit for climate change adaptation. It can increase the spread of invasive, pest and disease-causing species into newly suitable regions. In some places, isolated refugia may better allow vulnerable species and biological communities to survive.

There are many different approaches to increasing connectivity, ranging from increasing the overall area of suitable habitat to ‘corridors’ and ‘stepping stones’, with different strategies likely to be more effective for different species and circumstances ( [[#Keeley--2018|Keeley et al., 2018]] ). Connectivity can also be important in increasing the resilience of populations to extreme climatic events ( [[#Newson--2014|Newson et al., 2014]] ; [[#Oliver--2015b|Oliver et al., 2015b]] ). Within freshwater environments, the connectivity of watercourses is essential. Fluvial corridors are necessary to ensure the survival of migrating fish populations, even without climate change; with climate change, connectivity becomes crucial for relatively cold-adapted organisms to migrate upstream to colder areas. Connectivity is also important for the larvae of benthic invertebrates to be able to drift downstream and hence to disperse ( [[#Brooks--2018|Brooks et al., 2018]] ); for adult benthic invertebrates, riparian and terrestrial habitat features can potentially affect dispersal. Connectivity within river and wetland systems for some species can also mediated by more mobile animal species such as fish and birds ( [[#Martín-Vélez--2020|Martín-Vélez et al., 2020]] ). Which factors are the most important in either promoting their colonisation of new sites or persisting ''in situ'' will differ between species and locations. Some general principles have been recognised and can guide conservation policy and practice ( [[#Natural%20England%20and%20RSPB--2020|Natural England and RSPB, 2020]] ; [[#Stralberg--2020|Stralberg et al., 2020]] ), but this will often require additional investigation and planning based on an individual understanding of the niches of specific species.

Managed translocation, that is, moving species from areas where the climate is becoming unsuitable to places where their persistence under climate change is more likely , has been discussed as an adaptation option for many years. So far, there have been very few examples of this and it is likely to be a last resort in most cases, as it usually requires a large investment of resources, outcomes are uncertain and there may be adverse impacts on the receiving sites. Nevertheless, there are cases where it may be a be a viable option ( [[#Stralberg--2019|Stralberg et al., 2019]] ). This is discussed in more detail as a case study in [[#2.6.5.1|Section 2.6.5.1]] .

The evidence that species can persist in microclimatic refugia where suitable conditions for them are maintained locally (e.g., because of variations in topography) has increased in recent years. This has opened up the potential to include refugia in conservation plans and strategies to facilitate the local survival of species ( [[#Jones--2016|Jones et al., 2016]] ; [[#Morelli--2016|Morelli et al., 2016]] ; [[#Morelli--2020|Morelli et al., 2020]] ), for example, targeting management actions ( [[#Sweet--2019|Sweet et al., 2019]] ) aimed at supporting populations of species. This is likely to become an important aspect of climate change adaptation for biodiversity conservation in future. It is also possible to manipulate microclimate, for example, by creating shelters for birds’ nests; see Case Study in 2.6.5.5 of African penguins; ( [[#Patino-Martinez--2012|Patino-Martinez et al., 2012]] ). One specific approach of this sort is the planting or retention of trees and wooded corridors to shade watercourses ( [[#Thomas--2016|Thomas et al., 2016]] ). Riparian shading can also possibly help to reduce phytoplankton and benthic diatom growth in smaller streams and rivers ( [[#Halliday--2016|Halliday et al., 2016]] ).

Refugia often refer to locally cool places in a landscape, such as shaded slopes or high elevations, but they can also include places where the supply of water may continue during dry periods ( [[#Morelli--2016|Morelli et al., 2016]] ). Monitoring can reveal which streams, wetlands, springs and other aquatic resources retain suitable discharges, water quality, wetland area and ecological integrity, especially during dry years ( [[#Cartwright--2020|Cartwright et al., 2020]] ). Measures to conserve drought refugia may include protecting springs and other groundwater-fed systems from groundwater extraction, contamination, salinisation, surface-water diversion, channelisation of streams, trampling by livestock, recreation activities and invasive species and the effects of disturbances in the surrounding landscape ( [[#Cartwright--2020|Cartwright et al., 2020]] ; [[#Krawchuk--2020|Krawchuk et al., 2020]] ). Restoration of degraded aquatic ecosystems can include removing flow-diversion infrastructure, excluding livestock, reducing other human impacts, geomorphic restructuring, removing invasive species and planting native riparian vegetation.

In fire-prone areas, fire suppression and management are a key element of protecting refugia ( [[#2.6.5.8|Section 2.6.5.8]] below). In ecosystems in which a natural fire regime has been suppressed, restoration practices such as prescribed fires, thinning trees and allowing some wildfire where it benefits the ecosystem can be introduced to reduce increasing risks from severe wildfires ( [[#Meigs--2020|Meigs et al., 2020]] ).

Protected areas—areas of land set aside for species and habitat protection with legal protection from development or exploitation—have been a cornerstone of nature conservation for many years. Their effectiveness under a changing climate has been the subject of debate and investigation. There is now a large body of evidence demonstrating that colonisations by range-shifting species are more likely to occur at protected sites than at non-protected sites for a wide range of taxa (e.g., [[#Thomas--2012|Thomas et al., 2012]] ; [[#Gillingham--2015|Gillingham et al., 2015]] ) including across continents ( [[#Pavón-Jordán--2020|Pavón-Jordán et al., 2020]] ). This is probably because, by protecting large areas of natural and semi-natural habitats, they provide suitable places for colonising species ( [[#Hiley--2013|Hiley et al., 2013]] ) which may not be available in the surrounding landscape. Although the evidence for protected areas being associated with reduced extinctions is weaker, the finding by Gillingham et al. ( [[#Gillingham--2015|Gillingham et al., 2015]] ) that protected sites were associated with reduced extinction rates at low latitudes and elevations is strongly suggestive that they can help species’ persistence in the face of climate change.

It is intrinsically difficult to assess the effectiveness of climate change adaptation measures, the benefit of which will be realised in the years and decades ahead ( [[#Morecroft--2019|Morecroft et al., 2019]] ). Nevertheless, taking into account the wide range of evidence reported above, including the theory, modelling and observations of the impacts of climate change in contrasting circumstances, it is possible to make an overarching assessment that appropriate adaptation measures can reduce the vulnerability of many aspects of biodiversity to climate change ( ''robust evidence'' , ''high agreement'' ). It is also clear, however, that to be most effective and avoid unintended consequences, measures need to be carefully implemented by taking into account specific local circumstances ''(robust evidence, high agreement)'' and include the management of inevitable changes ( ''robust evidence, high agreement'' ). It is also clear that while there are now many plans and strategies for adapting biodiversity conservation to climate change, many have yet to be implemented fully ( ''medium evidence, high agreement'' ).

<div id="2.6.3" class="h2-container"></div>

<span id="ecosystem-based-adaptation"></span>
=== 2.6.3 Ecosystem-Based Adaptation ===

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A study published in 2020 found that, out of 162 intended nationally determined contributions (covering 189 countries) submitted to the United Nations Framework Convention on Climate Change (UNFCCC), as commitments to action under the Paris Agreement, 109 indicated ‘ecosystem-orientated visions’ for adaptation, but only 23 used the term ‘ecosystem-based adaptation’ ( [[#Seddon--2020b|Seddon et al., 2020b]] ).

EbA includes a range of different approaches. Examples include restoring coastal and river systems to reduce flood risk and improve water quality, and the creation of natural areas within urban areas to reduce temperatures through shading and evaporative cooling. EbA is closely linked with a variety of other concepts such as ecosystem services, natural capital and disaster risk reduction (DRR). EbA was becoming a well-recognised concept at the time of AR5 but implementation was still at an early stage in many cases. Since then, pilot studies have been assessed and EbA projects have been initiated around the world. The evidence base continues to grow (Table 2.7), and this has led to increasing confidence in approaches which have been shown to work leading to further expansion in some countries (Table 2.7). However, this is not uniform and there is relatively little synthesis across disciplines and regions ( [[#Seddon--2020a|Seddon et al., 2020a]] ). [[#Chausson--2020|Chausson et al. (2020)]] used a systematic mapping methodology to characterise 386 published studies. They found that interventions in natural or semi-natural ecosystems ameliorated adverse climate change impacts in 66% of cases, with fewer trade-offs than for more artificial systems such as plantation forest. However, the evidence base has substantial gaps. Most of the evidence has been collected in the Global North, and there is a lack of robust, site-specific investigations into the effectiveness of interventions compared to alternatives and more holistic appraisals that account for broader social and ecological outcomes.

Restoring coasts, rivers and wetlands to reduce flood risk have probably seen the largest investment in EbA and it is becoming an increasingly accepted approach in some places (e.g., case studies in Sections 2.6.5.2, 2.6.5.7), although significant social, economic and technical barriers remain ( [[#Wells--2020|Wells et al., 2020]] ; [[#Bark--2021|Bark et al., 2021]] ; [[#Hagedoorn--2021|Hagedoorn et al., 2021]] ). Natural flood management (NFM) encompasses a wide range of techniques in river systems and at the coast and has been used in varied locations around the world. In tropical and subtropical areas, the restoration of mangroves to reduce the risk of coastal flooding is a widely advocated, evidence-based approach (e.g., ( [[#Høye--2013|Høye et al., 2013]] ; [[#Sierra-Correa--2015|Sierra-Correa and Kintz, 2015]] ; [[#Powell--2019|Powell et al., 2019]] )). In temperate regions, salt marsh is a similarly important habitat ( [[#Spalding--2014|Spalding et al., 2014]] ). Both provide buffering against SLR and storm surges. Managed realignment of the coast, by creating new habitats, can lead to a loss of terrestrial and freshwater ecosystems, but it can protect them and the services they provide by reducing the risks of catastrophic failure from hard-engineered sea defences.

'''Table 2.7 |''' Examples of key EbA measures with assessments of confidence. Note only adaptation-related services are shown; many measures also provide a range of other benefits to people. All also provide benefits for biodiversity.

{| class="wikitable"
|-
! '''EbA measures'''

! '''Confidence assessment'''

! '''Ecosystem services for climate change adaptation'''

! '''Climate change impact addressed'''

! '''Social benefits from adaptation'''

! '''Relevant ecosystems and contexts'''

! '''Selected references'''

|-
| '''''Natural flood risk management in river systems: restoring natural river courses (removing canalisation), restoring and protecting wetlands and riparian vegetation'''''

| ''medium evidence,''

''medium agreement''

| Flood regulation; sediment retention; water storage; water purification

| Increased rainfall intensity

| Reduction of flood damage

Increased water security (quality and supply)

| Multiple

| ( [[#Iacob--2014|Iacob et al., 2014]] ; [[#Meli--2014|Meli et al., 2014]] ; [[#Dadson--2017|Dadson et al., 2017]] ; [[#Rowiński--2018|Rowiński et al., 2018]] ; [[#Burgess-Gamble--2021|Burgess-Gamble et al., 2021]] )

|-
| '''''Shade rivers and streams by restoration of riparian vegetation or trees.'''''

| ''medium evidence,''

''high agreement''

| Provision of fish stocks

| Warmer water temperatures

| Food security;

income benefits

| Multiple

| ( [[#Broadmeadow--2011|Broadmeadow et al., 2011]] ; [[#Isaak--2015|Isaak et al., 2015]] ; [[#Williams--2015b|Williams et al., 2015b]] ; [[#Thomas--2016|Thomas et al., 2016]] )

|-
| '''''Managed realignment of coastlines; re-establishing and protecting coastal habitats including mangroves, saltmarshes, coral reefs and oyster reefs'''''

| ''robust evidence,''

''high agreement''

| Coastal storm and flood protection;

coastal erosion control;

prevention of intrusion of salt water

| SLR;

increasing storm energy

| Protection of life, property and livelihoods;

water security

| Coastal

| ( [[#Høye--2013|Høye et al., 2013]] ; [[#Spalding--2014|Spalding et al., 2014]] ; [[#Narayan--2016|Narayan et al., 2016]] ; [[#Morris--2018|Morris et al., 2018]] ; [[#Chowdhury--2019|Chowdhury et al., 2019]] ; [[#Powell--2019|Powell et al., 2019]] )

|-
| '''''Agro-forestry and other agro-ecological/conservation practices on agricultural land'''''

| ''medium evidence,''

''medium agreement''

| Local climate regulation; soil conservation; soil nutrient regulation; water conservation; pest control; food provisioning

| High temperature or changing temperature regimes;

changing precipitation regimes

| Food security;

income benefits

| Multiple

| ( [[#Vignola--2015|Vignola et al., 2015]] ; [[#Torralba--2016|Torralba et al., 2016]] ; [[#Paul--2017|Paul et al., 2017]] ; [[#Blaser--2018|Blaser et al., 2018]] ; [[#Nesper--2019|Nesper et al., 2019]] ; [[#Verburg--2019|Verburg et al., 2019]] ; [[#Aguilera--2020|Aguilera et al., 2020]] ; [[#Tamburini--2020|Tamburini et al., 2020]] )

|-
| '''''Restore and maintain urban and peri-urban green space: trees, parks, local nature reserves, created wetlands'''''

| ''robust evidence,''

''high agreement''

| Local climate regulation;

flood regulation;

water purification;

water storage;

erosion control

| Higher temperatures and heat waves;

increased or reduced rainfall intensity

| Cooler micro-climate;

reduced flood damage;

water security

| Urban areas

| ( [[#Norton--2015|Norton et al., 2015]] ; [[#Liquete--2016|Liquete et al., 2016]] ; [[#Liu--2016|Liu, 2016]] ; [[#Bowler--2017|Bowler et al., 2017]] ; [[#Aram--2019|Aram et al., 2019]] ; [[#Stefanakis--2019|Stefanakis, 2019]] ; [[#Ziter--2019|Ziter et al., 2019]] )

|-
| '''''Ecological restoration for reducing fire risk by restoring natural vegetation and herbivory and reinstating natural fire regimes'''''

| ''medium evidence,''

''high agreement''

| Regulation of wildfires

| Mega-fires from increases in drought and heat

| Reduce deaths and infrastructure damage from fires

| Fire-adapted ecosystems

| ( [[#Waldram--2008|Waldram et al., 2008]] ; [[#Stephens--2010|Stephens et al., 2010]] ; [[#van%20Mantgem--2016|van Mantgem et al., 2016]] ; [[#Boisramé--2017|Boisramé et al., 2017]] ; [[#Johnson--2018|Johnson et al., 2018]] ; [[#Parisien--2020a|Parisien et al., 2020a]] ; [[#Parisien--2020b|Parisien et al., 2020b]] ; [[#Stephens--2020|Stephens et al., 2020]] )

|-
| '''''Invasive non-native aquatic plant control to improve water security'''''

| ''robust evidence,''

''high agreement''

| Water provision

| Increasing droughts

| Water security

| Water-scarce regions prone to an increase in droughts

| ( [[#van%20Wilgen--2016|van Wilgen and Wannenburgh, 2016]] )

|-
| '''''Woody plant control (of encroaching biomass) in open grassy ecosystems to restore and maintain grassy vegetation (see 2.4.3.5)'''''

| ''medium evidence,''

''medium agreement''

| Fodder biomass production

| Elevated CO 2 and increased rainfall promoting tree growth

| Income through bush clearing, fuelwood supplies, restore grazing

| Savanna and grasslands

| ( [[#Haussmann--2016|Haussmann et al., 2016]] )

|-
| '''''Rangeland rehabilitation and management e.g. introducing livestock enclosures, appropriate grazing management, reintroducing native grassland species'''''

| ''medium evidence,''

''medium agreement''

| Fodder biomass production; soil erosion control; soil formation; nutrient cycling; water retention

| Changing precipitation and temperature regimes including prolonged dry seasons and increased drought frequency

| Food security Water security, income benefits

| Rangelands

| ( [[#Descheemaeker--2010|Descheemaeker et al., 2010]] ; [[#Wairore--2016|Wairore et al., 2016]] ; [[#Kimiti--2017|Kimiti et al., 2017]] )

|-
| '''''Sustainable forestry of biodiverse managed forests, maintaining forest cover and protecting soils'''''

| ''medium evidence,''

''medium agreement''

| Timber production

| Increased frequency and severity of storms;

higher temperatures;

changing precipitation regimes (more intensive wet and dry periods);

increased incidents of wildfire, pest and disease outbreaks

| Livelihood and income benefits

| Boreal, temperate, subtropical, tropical forests

| ( [[#Gyenge--2011|Gyenge et al., 2011]] ; [[#Barsoum--2016|Barsoum et al., 2016]] ; [[#Jactel--2017|Jactel et al., 2017]] ; [[#Cabon--2018|Cabon et al., 2018]] )

|-
| '''''Watershed reforestation and conservation for hydrological services'''''

| ''medium evidence,''

''medium agreement''

| Flood control; erosion control; water provisioning; water purification

| Changing precipitation regimes

| Food security; Water security; Flood Protection

| Boreal, temperate, subtropical, tropical forests

| ( [[#Filoso--2017|Filoso et al., 2017]] ; [[#Bonnesoeur--2019|Bonnesoeur et al., 2019]] )

|-
| '''''Multi-functional forest management and conservation to provide climate-resilient sources of food and livelihoods and protect water sources'''''

| ''medium evidence,''

''medium agreement''

| Timber and non-timber forest production; fuel wood production; water provisioning; water purification

| Multiple

| Food security; Water security; income benefits

| Boreal, temperate, subtropical, tropical forests

| ( [[#Lunga--2016|Lunga and Musarurwa, 2016]] ; [[#Strauch--2016|Strauch et al., 2016]] ; [[#Adhikari--2018|Adhikari et al., 2018]] )

|-
| '''''Slope re-vegetation for landslide prevention and erosion control'''''

| ''robust evidence,''

''high agreement''

| Soil retention; slope stabilisation

| Increased rain frequency

| Reduced landslide damage; prevention of loss of life

| Montane and other steep-sloped regions

| ( [[#Fox--2011a|Fox et al., 2011a]] ; [[#Krautzer--2011|Krautzer et al., 2011]] ; [[#Osano--2013|Osano et al., 2013]] ; [[#Bedelian--2017|Bedelian and Ogutu, 2017]] ; [[#Getzner--2017|Getzner et al., 2017]] ; [[#de%20Jesús%20Arce-Mojica--2019|de Jesús Arce-Mojica et al., 2019]] )

|}

In river systems ( [[#Iacob--2014|Iacob et al., 2014]] ), management of both the catchments and the channel itself is important: restoring natural meanders in canalised watercourses and allowing the build-up of woody debris can slow flows rates; restoring upstream wetlands or creating them in urban and peri-urban situations can store water during flood events if they are in the right place in a catchment ( [[#Acreman--2013|Acreman and Holden, 2013]] ; [[#Ameli--2019|Ameli and Creed, 2019]] ; [[#Wu--2020|Wu et al., 2020]] ). There is less data on the potential for NFM in tropical compared to temperate catchments. However, ( [[#Ogden--2013|Ogden et al., 2013]] ) showed that flooding was reduced from a secondary forested catchment area compared to those which were pasture or a mosaic of forest, pasture and subsistence agriculture. EbA approaches to reduce flooding can be applied within urban areas as well as in rural catchments, as in Durban, South Africa ( [[#2.6.5.7|Section 2.6.5.7]] ), but effectiveness will depend on EbA being implemented at a sufficient scale and in the right locations ( [[#Hobbie--2020|Hobbie and Grimm, 2020]] ; [[#Costa--2021|Costa et al., 2021]] ). This may, in turn, provide protection to downstream urban communities.

Protecting and restoring natural river systems and natural vegetation cover within catchments as well as integrating agro-ecological techniques into agricultural systems can also help to maintain and manage water supplies for human use, under climate change, including during periods of drought, by storing water in catchments and improving water quality ( [[#Taffarello--2018|Taffarello et al., 2018]] ; [[#Agol--2021|Agol et al., 2021]] ; [[#Khaniya--2021|Khaniya et al., 2021]] ). [[#Lara--2021|Lara et al. (2021)]] showed that replacing a non-native ''Eucalyptus'' plantation in Chile with native forest caused base flow to increase by 28–87% during the restoration period compared to pre-treatment, and found that it remained during periods with low summer precipitation.

EbA can operate on a range of different scales, from local to catchment to region. On the local scale, there is a variety of circumstances in which microclimates can be managed and local temperatures lowered by the presence of vegetation (Table 2.7), and these EbA techniques are now being used more widely. In both urban and agricultural situations, shade trees are a traditional technique which can be applied to contemporary climate change adaptation. As reported in [[#2.6.2|Section 2.6.2]] above, shading of watercourses can lower temperatures, which can allow species to survive locally; as well as supporting diversity, it can help to maintain important fisheries, including those of salmonid fish ( [[#O’Briain--2020|O’Briain et al., 2020]] ). Within cities, green spaces, including parks, local nature reserves and green roofs and walls can also provide cooling as a result of evapotranspiration ( [[#Bowler--2010a|Bowler et al., 2010a]] ; [[#Aram--2019|Aram et al., 2019]] ; [[#Hobbie--2020|Hobbie and Grimm, 2020]] ), although this may be reduced in drought conditions.

Wildfire is an increasing risk for people as well as to ecosystems in many parts of the world. As discussed in [[#2.4.4.2|Section 2.4.4.2]] , this is the result not just of climate change but also past management practices, including fire suppression. Better fire management including reinstating more natural fire regimes can reduce risks.

EbA is usually a place-specific approach and a number of studies have documented how attempts to implement it without an understanding of local circumstances and the full engagement of local communities have been unsuccessful ( [[#Nalau--2018|Nalau et al., 2018]] ). Since AR5, a number of studies have considered the factors that are important for environment adaptation programmes and projects ( [[#UNFCCC--2015|UNFCCC, 2015]] ; [[#Nalau--2018|Nalau et al., 2018]] ; [[#Duncan--2020|Duncan et al., 2020]] ; [[#EPA%20Network%20and%20ENCA--2020|EPA Network and ENCA, 2020]] ; [[#Townsend--2020|Townsend et al., 2020]] ). Considering these sources, others described above and the case studies presented in [[#2.6.5|Section 2.6.5]] , a number of requirements for effective implementation of EbA can be identified, including the following:

* Targeting of the right EbA measure in the right location
* Decision-making at the appropriate level of governance with participation from all affected communities
* Integration of IKLK and capacity into decision-making and the management of projects
* Involvement of government and non-government stakeholders
* Full integration of EbA with other policy areas including agriculture, water resources and protection of natural resources
* Protection and, if possible, improvement of incomes of local people
* Effective institutional support to manage finances and the implementation of projects and programmes
* Time—many EbA interventions take time to establish, for example, for trees to grow and wetlands to recover
* Monitoring of intended outcomes and other impacts and the communication of results

Whilst it is essential to develop place-specific EbA measures with the full engagement of local communities, it is worth noting that new opportunities may emerge that would not have been possible in the past. As the climate changes, novel ecosystems may emerge (with no present day analogue) which have the potential to provide different adaptation benefits, and societies may be more willing to adopt transformative approaches ( [[#Colloff--2017|Colloff et al., 2017]] ; [[#Lavorel--2020|Lavorel et al., 2020]] ).

Increasingly, it is essential to integrate adaptation and the protection of biodiversity with land-based initiatives to mitigate climate change; this is discussed in more detail in Cross-Chapter Box NATURAL in this chapter. The new IUCN standard ( [[#IUCN--2020|IUCN, 2020]] ) offers a basis for assessing whether actions are true NbS and take into account the wider factors necessary for success.

Whilst policy interest is growing and there is an increasing deployment of EbA, there is still a long way to go in delivering its full potential ( [[#Huq--2015|Huq and Stubbings, 2015]] ) and significant institutional and cultural barriers remain ( [[#Huq--2017|Huq et al., 2017]] ; [[#Nalau--2018|Nalau et al., 2018]] ). Nevertheless, it is increasingly clear that EbA can offer a portfolio of effective measures to reduce the risks for people of climate change at the same time as benefitting biodiversity ( ''robust evidence'' , ''high agreement'' ), providing that such measures are deployed with careful planning in a way that is appropriate for local ecological and societal contexts ( ''robust evidence'' , ''high agreement'' ). This chapter has identified risks to species, communities, ecosystems and ecosystem services from climate change, all of which increase with each increment of Global Warming Level (2.5.1, 2.5.2, 2.5.3, 2.5.4). There is therefore a risk to Ecosystem-based Adaptation measures in some circumstances and this risk increases progressively above 1.5°C of warming.

<div id="2.6.4" class="h2-container"></div>

<span id="adaptation-for-increased-risk-of-disease"></span>
=== 2.6.4 Adaptation for Increased Risk of Disease ===

<div id="h2-19-siblings" class="h2-siblings"></div>

Low-probability events can have a very high impact (e.g., the transmission of SARS-CoV-2 from wild animals to humans, causing the Covid-19 pandemic ). A robust disease risk reduction policy would include utilising One Biosecurity ( [[#Meyerson--2002|Meyerson and Reaser, 2002]] ; [[#Hulme--2020|Hulme, 2020]] ; [[#MacLeod--2020|MacLeod and Spence, 2020]] ) or One Health ( [[#Monath--2010|Monath et al., 2010]] ; [[#Deem--2018|Deem et al., 2018]] ; [[#Destoumieux-Garzón--2018|Destoumieux-Garzón et al., 2018]] ; [[#Zinsstag--2018|Zinsstag et al., 2018]] ) approaches with actions to reduce disease risk across multiple sectors and from a variety of anthropogenic drivers, including climate change, even if there is high uncertainty in projected risk (see Cross-Chapter Boxes ILLNESS in this chapter, COVID in [[IPCC:Wg2:Chapter:Chapter-7|Chapter 7]] and DEEP in Chapter 17). [[#Kraemer--2019|Kraemer et al. (2019)]] found that vector importation was a key risk factor and that the focus should be on preventing the introduction of invasive species. Furthermore, many neglected tropical diseases (NTDs) are also VBDs, and the UN SDG of good health and well-being explicitly calls for increased control and intervention with a focus on emergency preparedness and response ( [[#Stensgaard--2019a|Stensgaard et al., 2019a]] ).

Online tools are being developed to warn conservation biologists when species of conservation concern are at a greater risk of disease outbreaks due to environmental changes, for example, for Hawaiian honeycreepers and avian malaria ( [[#Berio%20Fortini--2020|Berio Fortini et al., 2020]] ) and coral diseases ( [[#Caldwell--2016|Caldwell et al., 2016]] ). Forecasting models to warn of human disease outbreaks like malaria and dengue are also now available, with findings that multiple-model ensemble forecasts outperform individual models ( [[#Lowe--2013|Lowe et al., 2013]] ; [[#Lowe--2014|Lowe et al., 2014]] ; [[#Lowe--2018|Lowe et al., 2018]] ; [[#Zhai--2018|Zhai et al., 2018]] ; [[#Johansson--2019|Johansson et al., 2019]] ; [[#Tompkins--2019|Tompkins et al., 2019]] ; [[#Muñoz--2020|Muñoz et al., 2020]] ; [[#Colón-González--2021|Colón-González et al., 2021]] ; [[#Petrova--2021|Petrova et al., 2021]] ). Improving VBD and NTD public health responses will require multi-disciplinary teams capable of interpreting, analysing, and synthesising diverse components of complex ecosystem-based studies for effective intervention ( [[#Mills--2010|Mills et al., 2010]] ; [[#Rubin--2014|Rubin et al., 2014]] ; [[#Valenzuela--2018|Valenzuela and Aksoy, 2018]] ), broad epidemiological and entomological surveillance ( [[#Depaquit--2010|Depaquit et al., 2010]] ; [[#Lindgren--2012|Lindgren et al., 2012]] ; [[#Springer--2016|Springer et al., 2016]] ) as well as community-based disease control programmes that build local capacity ( [[#Andersson--2015|Andersson et al., 2015]] ; [[#Jones--2020b|Jones et al., 2020b]] ).

<div id="cross-chapter-box-illness" class="h2-container box-container"></div>

'''Cross-Chapter Box ILLNESS | Infectious Diseases, Biodiversity and Climate: Serious Risks Posed by Vector- and Water-Borne Diseases'''
<div id="h2-32-siblings" class="h2-siblings"></div>

Authors: Marie-Fanny Racault (UK/France, Chapter 3), Stavana E. Strutz (USA, Chapter 2), Camille Parmesan (France/UK/USA, Chapter 2), Rita Adrian (Germany, Chapter 2), Guéladio Cissé (Mauritania/Switzerland/France, Chapter 7), Sarah Cooley (USA, Chapter 3), Meghnath Dhimal (Nepal), Luis E. Escobar (Guatemala/USA), Adugna Gemeda (Ethiopia, Chapter 9), Nathalie Jeanne Marie Hilmi (Monaco/France, Chapter 18), Salvador E. Lluch-Cota (Mexico, Chapter 5), Erin Mordecai (USA), Gretta Pecl (Australia, Chapter 11), A. Townsend Peterson (USA), Joacim Rocklöv (Germany/Sweden), Marina Romanello (UK/Argentina/Italy), David Schoeman (Australia, Chapter 3), Jan C. Semenza (Italy, Chapter 7), Maria Cristina Tirado (USA/Spain, Chapter 7), Gautam Hirak Talukdar (India, Chapter 2), Yongyut Trisurat (Thailand, Chapter 2)

''Climate change is altering the life cycles of many pathogenic organisms and changing the risk of transmission of vector- and water-borne infectious diseases to humans ('' high confidence ''). The rearrangement and emergence of some diseases are already observed in temperate-zone and high-elevation areas and coastal areas ('' medium confidence to high confidence, depending upon region ''). Shifts in the geographic and seasonal range suitability of pathogens and vectors are related to climatic-impact drivers (warming, extreme events, precipitation and humidity) ('' very high confidence ''), but there are substantial non-climatic drivers (LUC, wildlife exploitation, habitat degradation, public health and socioeconomic conditions) that affect the attribution of the overall impacts on the prevalence or severity of some vector- and water-borne infectious diseases over recent decades ('' high confidence ''). Adaptation options that involve sustained and rapid surveillance systems as well as the preservation and restoration of natural habitats with their associated higher levels of biodiversity, both marine and terrestrial, will be key to reducing the risk of epidemics and the large-scale transmission of diseases ('' medium confidence '').''

Since AR5, further evidence is showing that climate-related changes in the geographic and seasonal range suitability of pathogens and vectors and the prevalence or new emergence of vector- and water-borne infectious diseases have continued across many regions worldwide and are sustained over decadal timescales ( ''low confidence to high confidence,'' depending upon region)(Sections 2.4.2.5, 3.5.5.3, 7.2, 7.3, 9.10.1.2.1) ( [[#Harvell--2009|Harvell et al., 2009]] ; [[#Garrett--2013|Garrett et al., 2013]] ; [[#Burge--2014|Burge et al., 2014]] ; [[#Guzman--2015|Guzman and Harris, 2015]] ; [[#Baker-Austin--2018|Baker-Austin et al., 2018]] ; [[#Watts--2019|Watts et al., 2019]] ; [[#Semenza--2020|Semenza, 2020]] ; [[#Watts--2021|Watts et al., 2021]] ). Ecosystem-mediated infectious diseases at risk of increase from climate change include water-borne diseases associated with pathogenic ''Vibrio'' spp. (e.g., those causing cholera and vibriosis) and harmful algal blooms (e.g., ciguatera fish poisoning) (Sections 3.5, 5.12, Table SM3.3) ( [[#Bindoff--2019|Bindoff et al., 2019]] ); ( [[#Baker-Austin--2013|Baker-Austin et al., 2013]] ; [[#Levy--2015|Levy, 2015]] ; [[#Trtanj--2016|Trtanj et al., 2016]] ; [[#Ebi--2017|Ebi et al., 2017]] ; [[#Mantzouki--2018|Mantzouki et al., 2018]] ; [[#Nichols--2018|Nichols et al., 2018]] ), and VBDs associated with arthropods (e.g., malaria, dengue, chikungunya, Zika virus, West Nile virus and Lyme disease), helminths (e.g., schistosomiasis) and zoonotic diseases associated with cattle and wildlife (e.g., leptospirosis) ( ''low confidence to very high confidence'' , depending upon disease and region) (Sections 2.4.2.7, 3.5, 7.2, 7.3, 9.10.1.1.1, 13.7.1.2, 14.4.6, Cross-Chapter Box COVID in Chapter 7; Table Cross-Chapter Box ILLNESS.1) ( [[#Hoegh-Guldberg--2018|Hoegh-Guldberg et al., 2018]] ; [[#Ebi--2021|Ebi et al., 2021]] ).

The attribution of observed changes in disease incidence, partly or fully, to climatic-impact drivers remains challenging because of the difficulty of accurately capturing the contributions of multiple, interacting and often nonlinear underlying responses of host, pathogen and vector, which can be influenced further by non-climate stressors and the long history of anthropogenic disturbance. Disease emergence in new areas requires independent drivers to coincide (i.e., increasing climate suitability for pathogen or vector survival and competence/capacity, and introduction of the pathogen, that is often via the mobility of human populations). Furthermore, the extent to which changes in ecosystem-mediated diseases impact human health is highly dependent on local socioeconomic status, sanitation, medical systems and practices ( [[#2.4.2.5|Section 2.4.2.5]] , Figure FAQ2.3.1) ( [[#Gething--2010|Gething et al., 2010]] ; [[#Lindgren--2012|Lindgren et al., 2012]] ; [[#Mordecai--2013|Mordecai et al., 2013]] ; [[#Liu-Helmersson--2014|Liu-Helmersson et al., 2014]] ; [[#Bhatt--2015|Bhatt et al., 2015]] ; [[#Morin--2015|Morin et al., 2015]] ; [[#Ryan--2015|Ryan et al., 2015]] ; [[#Wesolowski--2015|Wesolowski et al., 2015]] ; [[#Stanaway--2016|Stanaway et al., 2016]] ; [[#Yamana--2016|Yamana et al., 2016]] ; [[#Mordecai--2017|Mordecai et al., 2017]] ; [[#Tesla--2018|Tesla et al., 2018]] ; [[#Ryan--2019|Ryan et al., 2019]] ; [[#Shah--2019|Shah et al., 2019]] ; [[#Iwamura--2020|Iwamura et al., 2020]] ; [[#Mordecai--2020|Mordecai et al., 2020]] ; [[#Colón-González--2021|Colón-González et al., 2021]] ; [[#Ryan--2021|Ryan et al., 2021]] ).Thus, risk reduction is more effective when links between climate change, ecosystem change, health and adaptation are considered concurrently (Sections 2.4, 3.5.3, 7.2, 7.3, 4.3.3, 6.2.2.3, Table SM2.1).

'''Table Cross-Chapter Box ILLNESS.1 |''' Observed climate change impacts on cholera, dengue and malaria incidence. (1) Cholera: endemicity based on ( [[#Ali--2015|Ali et al., 2015]] ). Changes (2003–2018) in suitability for coastal ''Vibrio cholerae'' estimated from model observations driven by sea-surface temperature (SST) and chlorophyll ''a'' (CHL) concentration ( [[#Escobar--2015|Escobar et al., 2015]] ; [[#Watts--2019|Watts et al., 2019]] ); vulnerabilities based on Sigudu et al. (2015) [[#Agtini--2005|Agtini et al. (2005)]] and [[#Sack--2003|Sack et al. (2003)]] . (2) Dengue: endemicity based on [[#Guzman--2015|Guzman and Harris (2015)]] . (3) Malaria: endemicity based on [[#Phillips--2017|Phillips et al. (2017)]] and the WHO Global Malaria Programme. Impacts of climate change on diseases and their vectors are most evident at the margins of current distributions. However, it is difficult to implicate climate change in areas with extensive existing transmission and vector/pathogen abundance, and it is particularly difficult to distinguish from concurrent directional trends in disease control, changes in land use, water access, socioeconomic and public health conditions. As a result, while many studies indicate increasing climate suitability of some areas for cholera, and changes in disease incidence for dengue and malaria, the degree to which these changes can be attributed to climate change remains challenging. Uncertainty statements for malaria and dengue reflect the degree to which observed trends in disease incidence can be related to observed climate change in the given region. For cholera, confidence statements reflect the degree to which observed trends in disease or pathogen incidence and coastal area suitability for outbreaks can be linked to observed climate change drivers in the given region. Acronyms: ONI (Oceanic Niño Index), Tmin (minimum temperature), SPI (Standardised Precipitation Index), LST (land surface temperature). Full references for this table can be found in Table SM2.6.

{| class="wikitable"
|-
!
! '''Cholera'''

! '''Dengue'''

! '''Malaria'''

|-
| colspan="4"| ''Africa''

|-
| Endemicity

| Endemic

| Endemic in sub-Saharan Africa but not South Africa

| Endemic

|-
| Climate drivers

| Disease incidence: northeast Africa, Central Africa and Madagascar: rainfall ( ''medium confidence'' )

Southeast Africa: rainfall, LST, SST, Plankton ( ''medium confidence'' )

eastern South Africa: SST, CHL

( ''low confidence'' due to ''limited evidence'' )

West Africa: rainfall (floods), LST, SST ( ''medium confidence'' )

|
| West Africa: temperature ( ''medium confidence'' )

East Africa: temperature ( ''medium confidence'' )

|-
| Direction of Change

| Area of coastline suitable for outbreak: northandwest Africa: increase ( ''low confidence'' )

Central and East Africa: no change ( ''low confidence'' )

South Africa: decrease ( ''low confidence'' )

| Potentially expanding

( ''low confidence'' )

Dengue and ''A. aegypti'' present but underdetected in climatically suitable areas

| East Africa: upward shift and increase in malaria and ''Anopheles'' spp. in highland areas ( ''medium confidence'' )

Widespread decreases due to malaria control ( ''medium confidence'' ) and warming climate ( ''low confidence'' )

|-
| Vulnerabilities

| Eastern South Africa: women of all ages more affected than men by outbreaks

|
|-
| colspan="4"| ''Asia''

|-
| Endemicity

| Endemic

| Endemic in South Asia, Southeast Asia and East Asia

| Endemic in South Asia, Southeast Asia, partially endemic in East Asia

|-
| Climate drivers

| Disease incidence: East Asia: SST, CHL, SLR ( ''medium confidence'' )

South Asia: SST, CHL, LST, rainfall (floods) ( ''high confidence'' )

| South Asia: rainfall, temperature, Humidity ''(medium confidence)''

Southeast Asia: rainfall, temperature ( ''medium confidence)''

East Asia: rainfall, temperature, Typhoons ( ''low confidence'' )

| South Asia: rainfall, temperature ( ''medium confidence'' )

Southeast Asia: rainfall, temperature ( ''medium confidence'' )

|-
| Direction of Change

| Area of coastline suitable for outbreak: increase ( ''low confidence'' )

| Southeast Asia: increase ( ''low confidence'' )

South Asia: increase ( ''medium confidence'' )

East Asia: increase ( ''low confidence'' )

| South Asia: increase ( ''medium confidence'' )

|-
| Vulnerabilities

| Southeast Asia: infants (&lt;9 years) with highest incidences of cholera

South Asia: older children and young adults (aged 16–20 years) more frequently reported with cholera than non-cholera diarrhoea

|
|-
| colspan="4"| ''Australasia''

|-
| Endemicity

| Not endemic

| Partially endemic in northern Australia

| Not endemic

|-
| Climate drivers

| No evidence for disease incidence

| Rainfall, temperature ( ''low confidence'' )

|
|-
| Direction of Change

| Area of coastline suitable for outbreak: no change ( ''low confidence'' )

| Increase in sporadic outbreaks due to climate change ( ''low confidence'' )

| No change

|-
| colspan="4"| ''Central America''

|-
| Endemicity

| Not endemic

| Endemic

| Partially endemic

|-
| Climate drivers

| No evidence for disease incidence

| ONI, SST, Tmin, temperature, rainfall, drought ( ''low confidence'' )

|
|-
| Direction of Change

| Areas of coastline suitable for outbreak: decrease ( ''low confidence)''

| Increasing due to climate ( ''low confidence'' )

Upward expansion of ''A. aegypti'' ( ''low confidence'' )

| Overall decrease not linked to climate change. Focal increases due to human activities.

|-
| colspan="4"| ''South America''

|-
| Endemicity

| Epidemic

| Endemic in all regions except southern South America

| Endemic

|-
| Climate drivers

| Abundance of coastal ''V. cholerae'' : northwestern South America:

SST, Plankton ( ''low confidence'' )

| Temperature, precipitation, drought

| Northern South America: temperature ( ''low confidence'' )

northern and southeastern South America: Tmax, Tmin, humidity ( ''low confidence'' )

|-
| Direction of Change

| Area of coastline suitable for outbreak: no change ( ''low confidence'' )

| Increasing due to urbanisation and decreased vector control programmes, not strongly linked to climate

| Higher elevation regions: Increase ( ''low confidence'' )

|-
| colspan="4"| ''Europe''

|-
| Endemicity

| Not endemic

| Southern Europe: focal outbreaks

| Not endemic

|-
| Climate drivers

| No evidence for disease incidence

Abundance of coastal ''V. cholerae'' : northern Europe: SST, Plankton ( ''medium confidence'' )

|
|-
| Direction of Change

| Area of coastline suitable for outbreak: increase ( ''low confidence'' )

| Mediterranean regions of southern Europe: outbreaks ( ''low confidence'' )

| No change

|-
| colspan="4"| ''North America''

|-
| Endemicity

| Not endemic

| Partially endemic in southern North America

| Not endemic

|-
| Climate drivers

| No evidence for disease incidence

Abundance of coastal V. cholerae: eastern North America: SST ( ''low confidence'' due to ''limited evidence'' )

| Winter Tmin ( ''low confidence'' )

|
|-
| Direction of Change

| Area of coastline suitable for outbreak: increase ( ''low confidence'' )

| Declining

| No change

|-
| colspan="4"| ''Small Islands''

|-
| Endemicity

| Epidemic

| Endemic on many small islands in the Tropics

| Endemic on many small islands in the Tropics

|-
| Climate drivers

| Disease incidence: Caribbean: SST, LST, rainfall ( ''low'' to ''medium confidence'' )

| Caribbean: SPI, Tmin ( ''low confidence'' )

|
|-
| Direction of Change

| Area of coastline suitable for outbreak: Caribbean and Pacific small islands: Decrease ( ''low confidence'' )

| Increasing ( ''low confidence'' )

| Decrease in Caribbean not linked to climate

|}

'''Observed and projected changes'''
In aquatic systems, at least 30 human pathogens with water infection routes (freshwater and marine) are affected by climate change ( [[IPCC:Wg2:Chapter:Chapter-3#3.5.3|Section 3.5.3]] , Table SM3.G) ( [[#Nichols--2018|Nichols et al., 2018]] ) . Warming, acidification, hypoxia, SLR and increases in extreme weather and climate events (e.g., MHWs, storm surges, flooding and drought), which are projected to intensify in the 21st century ( ''high confidence'' ) ( [[#IPCC--2021b|IPCC, 2021b]] ), are driving species’ geographic range shifts and global rearrangements in the location and extent of areas with suitable conditions for many harmful pathogens, including viruses, bacteria, algae, protozoa and helminths ( ''high confidence'' ) (Sections 2.3, 2.4.2.7, 3.5.5.3) ( [[#Trtanj--2016|Trtanj et al., 2016]] ; [[#Ebi--2017|Ebi et al., 2017]] ; [[#Manning--2017|Manning and Nobles, 2017]] ; [[#Pecl--2017|Pecl et al., 2017]] ; [[#Mantzouki--2018|Mantzouki et al., 2018]] ; [[#Nichols--2018|Nichols et al., 2018]] ; [[#Bindoff--2019|Bindoff et al., 2019]] ; [[#IPCC--2019b|IPCC, 2019b]] ; [[#Kubickova--2019|Kubickova et al., 2019]] ; [[#Watts--2019|Watts et al., 2019]] ; [[#Watts--2020|Watts et al., 2020]] ; [[#Watts--2021|Watts et al., 2021]] ).

The incidence of cholera and ''Vibrio'' -related disease outbreaks have been shown to originate primarily in coastal regions, and then spread inland via human transportation. Our understanding of the impacts of climate-change drivers on the dynamics of ''Vibrio'' pathogens and related infections has been strengthened through improved observations from long-term monitoring programmes ( [[#Vezzulli--2016|Vezzulli et al., 2016]] ) and statistical modelling supported by large-scale and high-resolution satellite observations ( ''high confidence'' ) (( [[#Baker-Austin--2013|Baker-Austin et al., 2013]] ; [[#Escobar--2015|Escobar et al., 2015]] ; [[#Jutla--2015|Jutla et al., 2015]] ; [[#Martinez--2017|Martinez et al., 2017]] ; [[#Semenza--2017|Semenza et al., 2017]] ; [[#Racault--2019|Racault et al., 2019]] ; [[#Campbell--2020|Campbell et al., 2020]] ).

The poleward expansion of the distribution of ''Vibrio'' spp. has increased the risk of vibriosis outbreaks from multiple species in northern latitudes. Specifically, the coastal area suitable for ''Vibrio'' infections in the past 5 years has increased by 50.6% compared with a 1980s baseline at latitudes of 40°N–70°N; in the Baltic region, the highest-risk season has been extended by 6.5 weeks over the same periods ( [[#Watts--2021|Watts et al., 2021]] ). Already, studies have noted greater numbers of ''Vibrio'' -related human infections and, most notably, disease outbreaks linked to extreme weather events such as heat waves in temperate regions such as Northern Europe ( [[#Baker-Austin--2013|Baker-Austin et al., 2013]] ; [[#Baker-Austin--2017|Baker-Austin et al., 2017]] ; [[#Baker-Austin--2018|Baker-Austin et al., 2018]] ) ( ''high confidence'' ). By the end of the 21st century, under RCP6.0, the number of months of risk of ''Vibrio'' illness is projected to increase in Chesapeake Bay by 10.4 ± 2.4%, with largest increases during May and September, which are the months of strong recreational and occupational use, compared to a 1985–2000 baseline ( [[#Jacobs--2015|Jacobs et al., 2015]] ; [[#Davis--2019a|Davis et al., 2019a]] ). In the Gulf of Alaska, the coastal area suitable for ''Vibrio'' spp. is projected to increase on average by 58 ± 17.2% in summer under RCP6.0 by the 2090s, compared to a 1971–2000 baseline ( ''low to medium confidence'' ) ( [[#Jacobs--2015|Jacobs et al., 2015]] ).

<div id="_idContainer059" class="Box_Header-continued"></div>

Cross-Chapter Box ILLNESS

The coastal area suitable for ''V. cholerae'' (the causative agent for cholera) has increased by 9.9% globally compared to a 2000s baseline ( [[#Escobar--2015|Escobar et al., 2015]] ; [[#Watts--2019|Watts et al., 2019]] ). However, in the case of ''V. cholerae'' and cholera disease incidence, climate change is more difficult to implicate because outbreaks require independent drivers to coincide (i.e., introduction of pathogenic strains of ''V. cholerae'' in the waters via mobility of human-infected populations) and observed trends are difficult to separate from concurrent directional trends in disease control, sanitation and water access, socioeconomic and public health conditions.

On land, increased global connectivity and mobility, unsustainable exploitation of wild areas and species and land conversion (agricultural expansion, intensification of farming, deforestation and infrastructure development), together with climate change-driven range shifts of species and human migration (Cross-Chapter Box MOVING PLATE in Chapter 5), have modified the interfaces between people and natural systems ( [[#IPBES--2018a|IPBES, 2018a]] ). Climate-driven increase in temperature, the frequency and intensity of extreme events as well as changes in precipitation and relative humidity have provided opportunities for rearrangements of disease geography and seasonality, and emergence into new areas ( ''high confidence'' ) ( [[#2.4.2.7|Section 2.4.2.7]] ). In particular, malaria has expanded into higher elevations in recent decades and, although attributing this to climate change remains challenging ( [[#Hay--2002|Hay et al., 2002]] ; [[#Pascual--2006|Pascual et al., 2006]] ; [[#Alonso--2011|Alonso et al., 2011]] ; [[#Campbell--2019c|Campbell et al., 2019c]] ), evidence that the elevational distribution of malaria has tracked warmer temperatures is compelling for some regions ( [[#Siraj--2014|Siraj et al., 2014]] ). Models based on both empirical relationships between temperature and the ''Anopheles'' mosquito and ''Plasmodium'' parasite traits that drive transmission ( [[#Mordecai--2013|Mordecai et al., 2013]] ; [[#Yamana--2013|Yamana and Eltahir, 2013]] ; [[#Johnson--2015|Johnson et al., 2015]] ) and existing mosquito distributions ( [[#Peterson--2009|Peterson, 2009]] ) predict that warming will increase the risk of malaria in highland East Africa and Southern Africa, while decreasing the risk in some lowland areas of Africa, as temperatures exceed the thermal optimum and upper thermal limit for transmission ( [[#Peterson--2009|Peterson, 2009]] ; [[#Yamana--2013|Yamana and Eltahir, 2013]] ; [[#Ryan--2015|Ryan et al., 2015]] ; [[#Watts--2021|Watts et al., 2021]] ).

In contrast to malaria, dengue has expanded globally since 1990, particularly in Latin America and the Caribbean, South Asia and sub-Saharan Africa ( [[#Stanaway--2016|Stanaway et al., 2016]] ). While urbanisation, changes in vector control and human mobility play roles in this expansion ( [[#Gubler--2002|Gubler, 2002]] ; [[#Åström--2012|Åström et al., 2012]] ; [[#Wesolowski--2015|Wesolowski et al., 2015]] ), the physiological suitability of temperatures for dengue transmission is also expected to have increased as climates have warmed ( [[#Colón-González--2013|Colón-González et al., 2013]] ; [[#Liu-Helmersson--2014|Liu-Helmersson et al., 2014]] ; [[#Mordecai--2017|Mordecai et al., 2017]] ; [[#Rocklöv--2019|Rocklöv and Tozan, 2019]] ). Models predict that dengue transmission risk will expand across many tropical, subtropical and seasonal temperate environments with future warming ( [[#Åström--2012|Åström et al., 2012]] ; [[#Colón-González--2013|Colón-González et al., 2013]] ; [[#Ryan--2019|Ryan et al., 2019]] ; [[#Iwamura--2020|Iwamura et al., 2020]] ; [[#Watts--2021|Watts et al., 2021]] )).

'''Adaptation options'''
During the 21st century, public health adaptation measures (Figure Cross-Chapter Box ILLNESS.2) have been put in place in attempts to control or eradicate a variety of infectious diseases by improving surveillance and early detection systems; constraining pathogen, vector, and/or reservoir host distributions and abundances; reducing the likelihood of transmission to humans; and improving treatment and vaccination programmes and strategies ( ''robust evidence'' , ''high agreement'' ) ( [[#Chinain--2014|Chinain et al., 2014]] ; [[#Adrian--2016|Adrian et al., 2016]] ; [[#Friedman--2017|Friedman et al., 2017]] ; [[#Konrad--2017|Konrad et al., 2017]] ; [[#Semenza--2017|Semenza et al., 2017]] ; [[#Borbor-Córdova--2018|Borbor-Córdova et al., 2018]] ; [[#Rocklöv--2020|Rocklöv and Dubrow, 2020]] ). In addition, the effective management and treatment of domestic and waste-water effluent, through better infrastructure and preservation of aquatic systems acting as natural water purifiers, have been key to securing the integrity of the surrounding water bodies, such as groundwater, reservoirs and lakes, and agricultural watersheds as well as protecting public health ( ''high confidence'' ) ( [[#Okeyo--2018|Okeyo et al., 2018]] ; [[#Guerrero-Latorre--2020|Guerrero-Latorre et al., 2020]] ; [[#Kitajima--2020|Kitajima et al., 2020]] ; [[#Sunkari--2021|Sunkari et al., 2021]] ). The preservation and restoration of natural ecosystems, with their associated higher levels of biodiversity, have been reported as significant buffers against epidemics and large-scale pathogen transmission ( ''medium confidence'' ) ( [[#Johnson--2010|Johnson and Thieltges, 2010]] ; [[#Ostfeld--2017|Ostfeld and Keesing, 2017]] ; [[#Keesing--2021|Keesing and Ostfeld, 2021]] ). Furthermore, the timely allocation of financial resources and sufficient political will in support of a ‘One Health’ scientific research approach, recognising the health of humans, animals and ecosystems as interconnected ( [[#Rubin--2014|Rubin et al., 2014]] ; [[#Whitmee--2015|Whitmee et al., 2015]] ; [[#Zinsstag--2018|Zinsstag et al., 2018]] ), holds potential for improving surveillance and prevention strategies that may help to reduce the risks of further spread and new emergence of pathogens and vectors ( ''medium confidence'' ) ( [[#Destoumieux-Garzón--2018|Destoumieux-Garzón et al., 2018]] ; [[#Hockings--2020|Hockings et al., 2020]] ; [[#Volpato--2020|Volpato et al., 2020]] ; [[#Hopkins--2021|Hopkins et al., 2021]] ; [[#Pörtner--2021|Pörtner et al., 2021]] ).

[[File:68b022be607d6a88f2a3699aef68fdb3 IPCC_AR6_WGII_Figure_2_Cross-Chapter-Box-Illness-1.png]]

'''Figure Cross-Chapter Box ILLNESS.1 |''' '''Adaptation measures to reduce risks of climate change impact on water- and vector-borne diseases.''' Impacts are identified at three levels: (1) on pathogen, host/vector distributions and abundance; (2) on pathogen-host transmission cycle occurrence and efficiency; and (3) on the likelihood of transmission to humans. Adaptation typology is based on ( [[#Biagini--2014|Biagini et al., 2014]] ; [[#Pecl--2019|Pecl et al., 2019]] ). For each type of adaptation, examples are provided with their level of evidence and agreement.

Cross-Chapter Box ILLNESS

Cross-Chapter Box ILLNESS

Cross-Chapter Box ILLNESS

<div id="2.6.5" class="h2-container"></div>

<span id="adaptation-in-practice-case-studies-and-lessons-learned"></span>
=== 2.6.5 Adaptation in Practice: Case Studies and Lessons Learned ===

<div id="h2-20-siblings" class="h2-siblings"></div>

Adaptation plans for biodiversity and EbA have been adopted in many places and on different scales, but it is difficult to get a systematic overview of adaptation in practice. We have therefore reviewed a series of contrasting case studies to illustrate some of the key issues. There is a pressing need for more thorough monitoring and evaluation of adaptation to assess effectiveness. Climate change adaptation is conceptually difficult to measure, but it is possible to test which techniques work in reducing vulnerability and to monitor their deployment ( [[#Morecroft--2019|Morecroft et al., 2019]] ).

Adaptation can take place on a range of scales, with specific projects nested within overarching national strategies. Small-scale projects can be adaptation-focused, but on the larger scale, adaptation is often integrated with wider objectives. Within an urban or peri-urban context, the benefits of natural and semi-natural areas for health and well-being help to justify support for EbA. Economic well-being is also an important factor in many cases whether, as in Durban, South Africa ( [[#2.6.5.7|Section 2.6.5.7]] ), it provides new job opportunities or, as in the Andes ( [[#2.6.5.4|Section 2.6.5.4]] ), it supports long-established agricultural practices. Action on the ground often depends on factors on a range of scales, for example, a local plan, a national strategy and international funding. In Durban, partnerships between local communities, local authorities and the academic community were essential, together with an international context. Nevertheless, there are examples of communities using traditional or local knowledge (LK) to adapt to changing circumstances, with little or no external input, ( [[#2.6.5.4|Section 2.6.5.4]] ); Their scope for adaptation is, however, often limited by factors beyond their direct control.

Specific interventions to protect species from climate change, such as the case of African penguins in South Africa ( [[#2.6.5|Section 2.6.5.5]] ) and threatened plant species in the Tasmanian Wilderness World Heritage Area ( [[#2.6.5.8|Section 2.6.5.8]] ), are rare. However, in countries where nature reserves are actively managed or where ecosystem restoration projects are progressing, local practitioners may use their knowledge to adapt to weather conditions and their associated effects (e.g., fire and water shortages). This is good practice, but it may not be sufficient to address the likely future changes in climate ( [[#Duffield--2021|Duffield et al., 2021]] ). Training and resources to support conservation practitioners are becoming available. Examples include the Climate Change Adaptation Manual in England, UK ( [[#2.6.5.2|Section 2.6.5.2]] ), and The Alliance for Freshwater Life ( https://allianceforfreshwaterlife.org ) which provides expertise for the sustainable management of freshwater biodiversity ( [[#Darwall--2018|Darwall et al., 2018]] ).

Adaptation is widely recognised as important for national conservation policies and is being considered in a variety of countries ( [[#2.6.5.2|Section 2.6.5.2]] , 2.6.5.3). Adaptation in this strategic context includes decisions about the selection and objectives for protected areas, for example, identifying places which can act as refugia. It can also mean recognising where protected areas remain important but will support a changing range of species and ecosystems. This is important for directing resources effectively and ensuring that the management of the sites remains appropriate. There are, however, often major uncertainties, and the extent to which there will be a need for more radical measures will depend on the success of reducing GHG emissions globally. A global rise of 1.5°C–2°C would require relatively incremental adjustments to conservation management in many parts of the world, but a 3°C–4°C rise would require radical, transformational changes to preserve many species and maintain ecosystem services ( [[#Morecroft--2012|Morecroft et al., 2012]] ).

Whilst adaptation strategies for conservation are relatively common, at least on an outline level, their implementation is slow in most places. This may partly reflect a lack of resources for conservation in many parts of the world; however, another barrier is that people often value protected sites in their present form. Actions which might jeopardise this are inevitably a last resort. Initiatives to engage wider communities in discussions are likely to be essential in gaining support for such changing approaches.

EbA and adaptation for biodiversity are intrinsically linked and the largest-scale interventions for adaptation in ecosystems have tended to bring together both elements. For example, adaptation to reduce the risk of flooding by habitat creation and using natural processes ( [[#2.6.5.2|Section 2.6.5.2]] , Cross-Chapter Box SLR in Chapter 3), such as re-naturalising straightened river systems or creating wetlands for water storage, offers the potential to meet multiple objectives and has increased the overall funding available for ecosystem restoration.

<div id="2.6.5.1" class="h3-container"></div>

<span id="case-study-assisted-colonisationmanaged-relocation-in-practice"></span>
==== 2.6.5.1 Case Study: Assisted Colonisation/Managed Relocation in Practice ====

<div id="h3-49-siblings" class="h3-siblings"></div>

Scale: Global

Issue: Helping species move in order to track shifting climate space

Managed relocation (assisted migration and colonisation) is the movement of species, populations or genotypes to places outside the areas of their historical distribution ( [[#Hoegh-Guldberg--2008|Hoegh-Guldberg et al., 2008]] ), and it may be an option where they are not able to disperse and colonise naturally. It requires careful consideration of scientific, ethical, economic and legal issues between the object of relocation and the receiving ecosystem ( [[#Hoegh-Guldberg--2008|Hoegh-Guldberg et al., 2008]] ; [[#Richardson--2009|Richardson et al., 2009]] ; [[#Schwartz--2012|Schwartz et al., 2012]] ).

Individual cases show that assisted migration can be successful. Anich and Ward (2017) extended the geographic breeding range of a rare bird, Kirtland’s warbler, ''Setophaga kirtlandii'' , by 225 km by using song playbacks to attract migrating individuals. Wadgymar (2015) successfully transplanted an annual legume, ''Chamaecrista fasciculata'' , to sites beyond its current poleward range limit, while Liu (2012) found that all but one of 20 orchid species survived when transplanted to higher elevations than their current range limits. After introducing two British butterfly species to sites ∼ 65 and ∼ 35 km beyond their poleward range margins, Willis (2009) observed that both of these populations grew, expanded their ranges and survived for at least the 8 year span of the study.

Butterflies have been favoured subjects for assisted migration in response to regional climate warming, since they are easy to move and their range dynamics have been extensively studied. The Chequered Skipper, ''Carterocephalus palaemon'' , became locally extinct in England in the 1970s, in an area not close to either the species’ poleward or equatorial range limits. Nonetheless, Maes (2019) considers climate a crucial parameter for reintroduction, using SDMs for both choosing the source population in Belgium and introduction site.

The success of assisted migration for conservation purposes has been variable. [[#Bellis--2019|Bellis et al. (2019)]] identified 56 successes and 33 failures among 107 translocations of insects undertaken explicitly for conservation purposes. They concluded that failure was most strongly associated with the low numbers of individuals being released. Another potential source of failure is local adaptation: there is ''good evidence'' that adaptive differences among potential source populations can be important. For example, the transplants of ''Chamaecrista fasciculata'' were more successful when sourced from the most poleward existing sites, while individuals from more equatorial habitats performed poorly even when artificially warmed ( [[#Wadgymar--2015|Wadgymar et al., 2015]] ).

<div id="2.6.5.2" class="h3-container"></div>

<span id="case-study-adaptation-for-conservation-and-natural-flood-management-in-england-uk"></span>
==== 2.6.5.2 Case Study: Adaptation for Conservation and Natural Flood Management in England, UK ====

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Scale: National

Issue: National approach to adaptation in the natural environment

Threats to biodiversity from climate change in England include range retractions of cold-adapted species and the effects of more frequent extreme weather events such as drought. These threats are exacerbated by land use and management, for example, fragmenting habitats, draining land and straightening rivers. There are also risks to people, which are exacerbated by environmental factors, including flooding and over-heating in urban areas. The National Adaptation Programme provides a broad policy framework for England and includes a chapter on the natural environment. There are also adaptation plans produced by public bodies such as Natural England and the UK Environment Agency, with a wide range of responsibilities including flood defence. The principles of adaptation to climate change are well established in the UK conservation community and resources are available. Natural England has published a Climate Change Adaptation Manual jointly with the Royal Society for the Protection of Birds (a major conservation NGO) ( [[#Natural%20England%20and%20RSPB--2020|Natural England and RSPB, 2020]] ) and a spatial mapping tool for vulnerability to climate change ( [[#Taylor--2014|Taylor et al., 2014]] ).

Duffield et al. (2021) found that awareness of the need for adaptation was common amongst nature reserve managers and that they were implementing actions that might build resilience to climate change, such as restoring ecosystem processes and reducing habitat fragmentation. There was recognition that it will be necessary to change the management objectives of protected sites to adjust to changing circumstances, but little implementation of such changes. The main example of managing change was at the coast where the SLR is causing transitions from terrestrial and freshwater systems to coastal and marine ones.

A range of EbA approaches are starting to contribute to adaptation in England, but the best-developed is Natural Flood Management (NFM): restoring natural processes and natural habitats to reduce flood risk ( [[#Wingfield--2019|Wingfield et al., 2019]] ). Over the last decade, a series of NFM projects have been established in local areas. The Environment Agency collated the evidence base for NFM ( [[#Burgess-Gamble--2021|Burgess-Gamble et al., 2021]] ) and was able to draw on 65 case studies ( [[#Ngai--2017|Ngai et al., 2017]] ) covering the management of rivers and floodplains, woodlands, runoff, and coasts and estuaries.

NFM includes a broad range of techniques, some of which deliver real benefits for biodiversity and allow natural ecological processes to become re-established. Others, such as creating ‘woody debris dams’—barriers artificially constructed from tree trunks and branches in watercourses to slow the flow of water— have fewer benefits, although they may be good for some species. [[#Dadson--2017|Dadson et al. (2017)]] concluded that ‘the hazard associated with small floods in small catchments may be significantly reduced’ by NFM techniques. However, they noted that the most extreme flood events may overwhelm any risk management measures, and failed to find clear evidence of NFM reducing flood risk downstream in large catchments.

Challenges in deploying large-scale NFM remain, which partly reflects the length of time necessary to demonstrate the effectiveness of pilot studies and build confidence; building stakeholder support is important ( [[#Huq--2017|Huq et al., 2017]] ). There are now a number of examples of where collaborative initiatives between local communities, landowners and government agencies have been successful in establishing effective NFM schemes ( [[#Short--2019|Short et al., 2019]] ).

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<span id="case-study-protected-area-planning-in-response-to-climate-change-in-thailand"></span>
==== 2.6.5.3 Case Study: Protected Area Planning in Response to Climate Change in Thailand ====

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Scale: National

Issue: Protected area network planning

Many countries in the Association of Southeast Asian Nations (ASEAN) are expanding protected area networks to meet the Aichi Target 11 of at least 17% of terrestrial area protected, and it is important to take the effects of climate change into account. Existing protected areas in Thailand cover approximately 21% of the land area and it is one of the few tropical countries that has achieved the Aichi Target 11. Most protected areas in Thailand were established on an ad hoc basis to protect remaining forest cover and, as a result, they do not represent diverse habitats and their associated species ( [[#Chutipong--2014|Chutipong et al., 2014]] ; [[#Tantipisanuh--2016|Tantipisanuh, 2016]] ) so they may not be resilient to the interacting impacts of future land use and climate change ( [[#Klorvuttimontara--2011|Klorvuttimontara et al., 2011]] ; [[#Trisurat--2018|Trisurat, 2018]] ).

Recent research conducted in northern Thailand indicated that the existing protected areas (31% of the regional area) cannot secure the viability of many medium-sized and large mammals. The climate space of most species will shift substantially, bringing a risk of extinction. Results, based on a spatial distribution model and network flow, determined there was a need for expansion areas of 5,200 km 2 in size, or 3% of the region, to substantially minimise the high level of risk and increase the average coping capacity of the protection of suitable habitats from 82%—the current plan—to 90%. These results were adopted by Thailand’s Department of National Parks, Wildlife and Plant Conservation, and included in the National Wildlife Administration and Conservation Plan for 2021–2031.

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<span id="case-study-effects-of-climate-change-on-tropical-high-andean-social-ecological-systems"></span>
==== 2.6.5.4 Case Study: Effects of Climate Change on Tropical High Andean Social Ecological Systems ====

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Scale: Regional

Issue: Complex ramifications of glacial retreat on vegetation, animals, herders and urban populations

Accelerated warming is shrinking tropical glaciers at rates unseen since the middle of the Little Ice Age ( [[#Rabatel--2013|Rabatel et al., 2013]] ; [[#Zemp--2015|Zemp et al., 2015]] ). Climate-driven upwards migration of species, associated with warming and glacier retreat, has modified species distribution and richness and community composition along the Andes altitudinal gradient ( [[#Seimon--2017|Seimon et al., 2017]] ; [[#Carilla--2018|Carilla et al., 2018]] ; [[#Zimmer--2018|Zimmer et al., 2018]] ; [[#Moret--2019|Moret et al., 2019]] ). Climate-driven glacier retreat alters hydrological regimes, directly impacting Andean pastoralists ( [[#López-i-Gelats--2016|López-i-Gelats et al., 2016]] ; [[#Postigo--2020|Postigo, 2020]] ; [[#Thompson--2021|Thompson et al., 2021]] ) and the provision of water to lowland regions ( [[#Vuille--2018|Vuille et al., 2018]] ; [[#Hock--2019|Hock et al., 2019]] ; [[#Orlove--2019|Orlove et al., 2019]] ; [[#Rasul--2019|Rasul and Molden, 2019]] ). The drying of wetlands has modified alpine plant communities, which are relevant for storing carbon, regulating water and providing food for local livestock; this has led to negative impacts on herders’ livelihoods ( [[#Dangles--2017|Dangles et al., 2017]] ; [[#Polk--2017|Polk et al., 2017]] ; [[#Postigo--2020|Postigo, 2020]] ) and affecting the wild vicuña and the domesticated alpaca and llama. The wool from Vicuña ( ''Vicugna vicugna'' ) and alpaca ( ''V. pacos'' ) is an important source of income for indigenous communities and the llama ( ''Lama glama'' ) is their main source of meat. Vicuña are adjusting their feeding behaviour and spatial distribution as vegetation migrates upwards ( [[#Reider--2020|Reider and Schmidt, 2020]] ), causing them to roam outside protected areas and become vulnerable to illegal poaching.

Andean herders have responded to the drying of grasslands by increasing livestock mobility, accessing new grazing areas through kinship and leases, creating and expanding wetlands through building long irrigation canals (several kilometres in length), limiting the allocation of wetlands to new households and sometimes cultivating grasses ( [[#Postigo--2013|Postigo, 2013]] ; [[#López-i-Gelats--2015|López-i-Gelats et al., 2015]] ; [[#Postigo--2020|Postigo, 2020]] ). These adaptive responses to regional climate change are enabled by deeply embedded indigenous institutions that have traditionally governed Andean pastoralists, but they have become severely compromised by national socioeconomic pressures ( [[#Valdivia--2010|Valdivia et al., 2010]] ; [[#Postigo--2019|Postigo, 2019]] ; [[#Postigo--2020|Postigo, 2020]] ). For instance, the quality of water and local pastoralists’ access to it and control of it have declined, due to new mining concessions granted in the headwaters of Andean watersheds ( [[#Bebbington--2009|Bebbington and Bury, 2009]] ) and the diversion of water to areas of lowland coastal desert for agricultural irrigation ( [[#Mark--2017|Mark et al., 2017]] ).

Glacier mass and runoff in the Tropics are projected to diminish by &gt;70% and &gt;10%, respectively, by 2100, under mean of RCP2.6, 4.5 and 8.5 ( [[#Huss--2018|Huss and Hock, 2018]] ; [[#Hock--2019|Hock et al., 2019]] ). In Peru, montane ice-field meltwater provides 80% of the water resources for the arid coast where half the population lives ( [[#Thompson--2021|Thompson et al., 2021]] ). Increasing variability of precipitation has compromised rain-fed agriculture and power generation, particularly in the dry season, exacerbating pressures for new sources of water ( [[#Bradley--2006|Bradley et al., 2006]] ; [[#Bury--2013|Bury et al., 2013]] ; [[#Buytaert--2017|Buytaert et al., 2017]] ). There is therefore a risk of increasing conflicts between adaptation to climate change to benefit human and natural communities in the high Andes and maintaining water provisioning for lowland agricultural and urban areas.

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<span id="case-study-helping-african-penguins-adapt-to-climate-change"></span>
==== 2.6.5.5 Case Study: Helping African Penguins Adapt to Climate Change ====

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Scale: Regional/local

Issue: Adaptation for a threatened species

The African penguin, ''Spheniscus demersus'' , is the only resident penguin species on mainland Africa. It breeds in a handful of colonies in South Africa and Namibia. In 2017, the penguins of Cape Town’s Boulders Beach colony attracted almost one million visitors, providing 885 jobs and USD 18.9 M in revenue ( [[#Van%20Zyl--2018|Van Zyl and Kinghorn, 2018]] ). Ninety-six percent of the population of this species has been lost since 1900, with a 77% decline in the last two decades ( [[#Sherley--2018|Sherley et al., 2018]] ). By 2019, only 17,700 pairs remained ( [[#Sherley--2020|Sherley et al., 2020]] ). The species is listed as endangered on the IUCN Red List ( [[#Birdlife%20International--2018|Birdlife International, 2018]] ) and if this trajectory persists, the African penguin will become functionally extinct in the near future ( [[#Sherley--2018|Sherley et al., 2018]] ).

Historically, hunting and the collection of eggs and guano were the main threats, but three aspects of climate change now predominate. Firstly, an eastward shift of several hundred kilometres in the distributions of their main prey species, anchovies and sardines, has reduced food availability ( [[#Roy--2007|Roy et al., 2007]] ; [[#Crawford--2011|Crawford et al., 2011]] ). While adult penguins typically forage up to 400 km from their colonies, they are restricted to a ~20-km radius from their colonies during breeding months ( [[#Ludynia--2012|Ludynia et al., 2012]] ; [[#Pichegru--2012|Pichegru et al., 2012]] ). The resulting food shortage at this critical time is compounded by competition with commercial fisheries and environmental fluctuations ( [[#Crawford--2011|Crawford et al., 2011]] ; [[#Pichegru--2012|Pichegru et al., 2012]] ; [[#Sherley--2018|Sherley et al., 2018]] ). This has impacted adults’ survival and their ability to raise high-quality offspring ( [[#Crawford--2006|Crawford et al., 2006]] ; [[#Crawford--2011|Crawford et al., 2011]] ; [[#Sherley--2013|Sherley et al., 2013]] ; [[#Sherley--2014|Sherley et al., 2014]] ).

The increasing frequency and intensity of heat waves recorded in recent decades presents a second threat ( [[#van%20Wilgen--2016|van Wilgen and Wannenburgh, 2016]] ; [[#Van%20Wilgen--2016|Van Wilgen et al., 2016]] ; [[#Mbokodo--2020|Mbokodo et al., 2020]] ). Nests were historically built in insulated guano burrows, but are now frequently sited on open ground ( [[#Kemper--2007|Kemper et al., 2007]] ; [[#Pichegru--2012|Pichegru et al., 2012]] ; [[#Sherley--2012|Sherley et al., 2012]] ). High temperatures frequently expose the birds to severe heat stress, causing adults to abandon their nests and resulting in the mortality of eggs and chicks ( [[#Frost--1976|Frost et al., 1976]] ; [[#Shannon--1999|Shannon and Crawford, 1999]] ; [[#Pichegru--2012|Pichegru et al., 2012]] ). Intensifying storm surges and greater wave heights can cause nest flooding ( [[#Randall--1986|Randall et al., 1986]] ; [[#de%20Villiers--2002|de Villiers, 2002]] ).

The African penguin’s survival in the wild is dependent on the success of adaptation action. Increasing access to food resources is a management priority ( [[#Birdlife%20International--2018|Birdlife International, 2018]] ). One approach is to reduce fishing pressure immediately around breeding colonies. An experiment excluding fishing around colonies since 2008 has demonstrated positive effects ( [[#Pichegru--2010|Pichegru et al., 2010]] ; [[#Pichegru--2012|Pichegru et al., 2012]] ; [[#Sherley--2015|Sherley et al., 2015]] ; [[#Sherley--2018|Sherley et al., 2018]] ; [[#Campbell--2019b|Campbell et al., 2019b]] ). A second approach is to establish breeding colonies closer to their prey. An ongoing translocation initiative aims to entice birds eastwards, to recolonise an extinct breeding colony and potentially establish a new one ( [[#Schwitzer--2013|Schwitzer et al., 2013]] ; [[#Sherley--2014|Sherley et al., 2014]] ; [[#Birdlife%20International--2018|Birdlife International, 2018]] ). Penguin ‘look-alikes’ or decoys, constructed from rubber and concrete, have been placed at the site of the extinct colony, and, along with call play-backs, these give the illusion of an established penguin colony ( [[#Morris--2018|Morris and Hagen, 2018]] ). This approach has not yet proven successful.

To promote on-site adaptation to heat extremes and flooding, initiatives are underway to provide cooler nesting sites that also provide storm protection and are sufficiently above the high-water level ( [[#Birdlife%20International--2018|Birdlife International, 2018]] ; [[#Saving%20Animals%20From%20Extinction--2018|Saving Animals From Extinction, 2018]] ). Artificial nest boxes of various designs and constructed from a range of materials have been explored, in combination with the use of natural vegetation. Some designs have proven successful, increasing breeding success ( [[#Kemper--2007|Kemper et al., 2007]] ; [[#Sherley--2012|Sherley et al., 2012]] ), but the same designs have had less success at other locations ( [[#Pichegru--2013|Pichegru, 2013]] ; [[#Lei--2014|Lei et al., 2014]] ).

Hand-rearing and releasing African penguin chicks, including from eggs, has long proven valuable because moulting parents, being shore-bound, are unable to feed late-hatching chicks. Since 2006, over 7,000 orphaned chicks have been released into the wild as part of the Chick Bolstering Project, with a success rate of 77% ( [[#Schwitzer--2013|Schwitzer et al., 2013]] ; [[#Sherley--2014|Sherley et al., 2014]] ; [[#Klusener--2018|Klusener et al., 2018]] ; [[#SANCCOB--2018|SANCCOB, 2018]] ). A new project at Boulders Beach aims to use real-time weather station data, within-nest temperatures and known thresholds of penguin heat stress as triggers for implementing a Heat Wave Response Plan. Drawing on well-established chick-rearing facilities and a large body of expertise, this includes removing heat-stressed eggs and birds, hand-rearing and/or rehabilitation and release. It is hoped that such birds can be released at the proposed new colony site.

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<span id="case-study-conserving-climate-change-refugia-for-the-joshua-tree-in-joshua-tree-national-park-ca-usa"></span>
==== 2.6.5.6 Case Study: Conserving Climate Change Refugia for the Joshua Tree in Joshua Tree National Park, CA, USA ====

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Scale: Local

Issue: Possible extirpation of a plant species from a national park

Joshua Tree National Park conserves 3200 km 2 of the Mojave and Sonoran Desert ecosystems. The climate of the national park is arid, with an average summer temperature of 27.3°C ± 0.7°C and average annual precipitation of 170 ± 80 mm yr -1 in the period 1971–2000 ( [[#Gonzalez--2018|Gonzalez et al., 2018]] ). From 1895 to 2017, the average annual temperature increased at a significant (P &lt; 0.0001) rate of 1.5°C ± 0.1°C per century and the average annual precipitation decreased at a significant (P = 0.0174) rate of -32 ± 12% per century ( [[#Gonzalez--2018|Gonzalez et al., 2018]] ). Anthropogenic climate change accounts for half the magnitude of a 2000–2020 drought in the southwestern USA, the most severe since the 1500s ( [[#Williams--2020|Williams et al., 2020]] ).

The national park was established to protect ecosystems and cultural features unique to the region, particularly the Joshua tree ( ''Yucca brevifolia'' ), a tall, tree-like yucca that provides habitat for birds and other small animals and holds cultural significance. The national park protects the southernmost populations of the Joshua tree. Palaeo-biological data from packrat ( ''Neotoma'' spp.) middens and fossilised dung of the extinct Shasta ground sloth ( ''Nothrotheriops shastensis'' ) show that Joshua trees grew 13,000–22,000 years ago across a wider range, extending as far as 300 km south into what is now México ( [[#Holmgren--2010|Holmgren et al., 2010]] ; [[#Cole--2011|Cole et al., 2011]] ). A major retraction of this range began ~11,700 years ago, coinciding with warming of approximately 4°C, caused by Milankovitch cycles, which marked the end of the Pleistocene and the beginning of the Holocene ( [[#Cole--2011|Cole et al., 2011]] ), suggesting a sensitivity of Joshua trees of 300 km of latitude per 4°C.

Under an emissions scenario that could increase park temperatures by &gt;4°C by 2100, the suitable climate for the Joshua tree could shift northwards and the species become extirpated from the park ( [[#Sweet--2019|Sweet et al., 2019]] ). Plant mortality would increase from drought stress and wildfires, which have been rare or absent in the Mojave, but which invasive grasses have fuelled and may continue to fuel ( [[#Brooks--2006|Brooks and Matchett, 2006]] ; [[#DeFalco--2010|DeFalco et al., 2010]] ; [[#Abatzoglou--2011|Abatzoglou and Kolden, 2011]] ; [[#Hegeman--2014|Hegeman et al., 2014]] ).

The national park had been trying to conserve the species wherever in the park it was found. The future risk of extirpation prompted adaptation of conservation efforts to focus on protecting potential refugia, where suitable conditions may persist for the species into the future ( [[#Barrows--2020|Barrows et al., 2020]] ). The national park used spatial analyses of suitable climate to identify potential refugia under all emissions scenarios, except for the highest ( [[#Barrows--2012|Barrows and Murphy-Mariscal, 2012]] ; [[#Sweet--2019|Sweet et al., 2019]] ). The park prioritises the refugia for removal of invasive grasses and fire control ( [[#Barrows--2020|Barrows et al., 2020]] ) and works to restore refugia that have burned in fires, using native plants, including nursery-grown Joshua tree seedlings. The park and its partners are monitoring plant species composition and abundance in the refugia for early warnings of any changes ( [[#Barrows--2014|Barrows et al., 2014]] ).

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<span id="case-study-ecosystem-based-adaptation-in-durban-south-africa"></span>
==== 2.6.5.7 Case Study: Ecosystem Based Adaptation in Durban, South Africa ====

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Scale: Local

Issue: EbA in a city and surrounding area

Durban was an early pioneer of EbA in a city context, establishing a Municipal Climate Protection Programme (MCPP) in 2004 ( [[#Roberts--2012|Roberts et al., 2012]] ). The city, situated in a global biodiversity hotspot (World Bank, 2016), has a rapidly growing population (approximately 3.5 million) and is highly fragmented ( [[#Roberts--2013|Roberts et al., 2013]] ). High levels of development, particularly in peri-urban areas, have encroached into natural habitats (World Bank, 2016). Degradation of the natural resource base in this way has direct economic and financial costs, is threatening Durban’s long-term sustainability and is exacerbated by climate change (World Bank, 2016; [[#eThekwini%20Municipality--2020|eThekwini Municipality, 2020]] ). The impacts of climate change are anticipated to increase unless appropriate mitigation and adaptation interventions are prioritised ( [[#eThekwini%20Municipality--2020|eThekwini Municipality, 2020]] ). High rates of poverty, unemployment and health problems have pushed Durban to explore a climate change adaptation work stream within its MCPP ( [[#Roberts--2013|Roberts et al., 2013]] ; [[#Roberts--2020b|Roberts et al., 2020b]] ).

A single approach to adaptation is likely to be insufficient ( [[#Archer--2014|Archer et al., 2014]] ), and community-based adaptation should be integrated as part of a package of tools applied at the city level. Durban’s climate change adaptation work stream is composed of three separate components: municipal adaptation (adaptation activities linked to the key functions of local government), community-based adaptation (CbA, focused on improving the adaptive capacity of local communities), and a series of urban management interventions (addressing specific challenges such as the urban heat island, increased storm-water runoff, water conservation and SLR) ( [[#Roberts--2013|Roberts et al., 2013]] ).

Lessons learnt from Durban’s experience include the importance of meaningful partnerships, long-term financial commitments ( [[#Douwes--2015|Douwes et al., 2015]] ) and significant political and administrative will ( [[#Roberts--2012|Roberts et al., 2012]] ; [[#Roberts--2020b|Roberts et al., 2020b]] ). Securing these requires strong leadership ( [[#Douwes--2015|Douwes et al., 2015]] ), including from local champions ( [[#Archer--2014|Archer et al., 2014]] ), even when EbA is considered cost-effective ( [[#Roberts--2012|Roberts et al., 2012]] ). Projects for the restoration of natural habitats are seen as an ideal tool, as they combine mitigation outcomes with an increased adaptation capacity, not only reducing the vulnerability of ecosystems and communities ( [[#Douwes--2016|Douwes et al., 2016]] ) but creating economic opportunities. These include direct job creation ( [[#Diederichs--2016|Diederichs and Roberts, 2016]] ; [[#Douwes--2016|Douwes and Buthelezi, 2016]] ) with various spin-offs such as better education for schoolchildren ( [[#Douwes--2015|Douwes et al., 2015]] ). Indirect benefits, including better water quality and reduced flooding, are generated as a result of improved ecosystem service delivery ( [[#Douwes--2016|Douwes and Buthelezi, 2016]] ). In areas that are already developed, opportunities for green-roof infrastructure can yield reductions in roof storm-water runoff (by approx.. 60 ml/m 2 /min during a rainfall event), slow the release of water over time and reduce temperatures on roof surfaces ( [[#Roberts--2012|Roberts et al., 2012]] ).

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<span id="case-study-protecting-gondwanan-refugia-against-fire-in-tasmania-australia"></span>
==== 2.6.5.8 Case Study: Protecting Gondwanan Refugia against Fire in Tasmania, Australia ====

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Scale: Local

Issue: Protection of rare endemic species

The Tasmanian Wilderness World Heritage Area (TWWHA) has a high concentration of ‘palaeo-endemic’ plant species which are restricted to living in cool, wet climates and fire-free environments, but recent wildfires have burnt substantial stands that are unlikely to recover ( [[#Harris--2018b|Harris et al., 2018b]] ; [[#Bowman--2021a|Bowman et al., 2021a]] ). The fires led to government inquiries and a fire-fighting review, which have suggested changes to management as climate change will make such fires more likely in the future ( [[#AFAC--2016|AFAC, 2016]] ; [[#Press--2016|Press, 2016]] ; [[#AFAC--2019|AFAC, 2019]] ).

Most of the TWWHA is managed as a wilderness zone and is currently carried out in a manner that allows natural processes to predominate. The exclusion of fire from stands of fire-sensitive trees such as the pencil pine, ''Athrotaxis cupressoides'' , is part of this management strategy, possible in the past due to the moisture differential and lower flammability of these areas. However, in recent years, the threat posed by extensive and repeated wildfires and increasing awareness that fire risk is likely to increase ( [[#Fox-Hughes--2014|Fox-Hughes et al., 2014]] ; [[#Love--2017|Love et al., 2017]] ; [[#Love--2019|Love et al., 2019]] ) have meant that more direct management intervention has been implemented. There has been a realisation that a ‘hands off’ approach to managing the threat will not be sufficient to protect the palaeo-endemics. Not only is fire-fighting difficult in this remote wilderness area, but limited resources mean that fire managers must prioritise where fires will be fought when many fires are threatening towns and lives across the state simultaneously.

After the wildfires in 2016 caused extensive damage ( [[#Bowman--2021a|Bowman et al., 2021a]] ), significant efforts and resources were spent trying to protect the remaining stands of pencil pine during the 2019 fires, using new approaches including the strategic application of long-term fire retardant and the installation of kilometres of sprinkler lines ( [[#AFAC--2019|AFAC, 2019]] ). These approaches are thought to have been effective at halting the fire and protecting high-value vegetation in some situations. Impact reports are currently being finalised to quantify the extent of fire-sensitive vegetation communities that have been affected. However, there is concern that these interventions may have adverse effects on the values of the TWWHA if applied widely, so while research is ongoing, these will only be applied in strategic areas (e.g., fire retardant is not being applied to some areas).

The TWWHA Management Plan (2016) emphasises Aboriginal fire management as an important value of the area, along with Aboriginal knowledge of plants, animals, marine resources and minerals (ochre and rock sources), and the connection with the area as a living and dynamic landscape. Fire management planning aims to protect important sites from fire and ensure that management does not impact Aboriginal cultural values ( [[#DPIPWE--2016|DPIPWE, 2016]] ). Increasingly, there is an acknowledgment that the cessation of traditional fire use has led to changes in vegetation and there are calls to incorporate Aboriginal burning knowledge into the fire management of the TWWHA.

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<span id="case-study-bhojtal-lake-bhopal-india"></span>
==== 2.6.5.9 Case Study: Bhojtal Lake, Bhopal, India ====

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Scale: Local

Issue: Protection of water resources and biodiversity

The city of Bhopal, the capital of Madhya Pradesh state in central India, is dependent for its water supply on Bhojtal, a large man-made lake bordering the city ( [[#Everard--2020|Everard et al., 2020]] ). Bhojtal is also an important conservation site, with its wetlands protected under the Ramsar convention and diverse flora and fauna ( [[#WWF--2006|WWF, 2006]] ). It also provides a wide range of other benefits to people, including tourism, recreation, navigation and subsistence and commercial fisheries, supporting the livelihoods of many families ( [[#Verma--2001|Verma, 2001]] ).

Climate change in Bhopal may pose ecological and socioeconomic stresses due to changes in rainfall and weather patterns ( [[#Ministry%20of%20Environment--2019|Ministry of Environment et al., 2019]] ), and exacerbated by a series of problems such as waste-water discharge, illegal digging of bore wells and unsustainable water extraction/exploitation ( [[#Everard--2020|Everard et al., 2020]] ). Ecosystem service provision at Bhojtal was assessed using the Rapid Assessment of Wetland Ecosystem Services (RAWES) approach, including an analysis of the lake’s water quality. Information on the geology, hydrology and catchment ecology of the lake was collected and a baseline biodiversity assessment was conducted.

The Lake Bhopal Conservation and Management Project ( [[#JICA--2007|JICA, 2007]] ) was developed with the following actions:

# Desilting and dredging; deepening and widening of spill channel; prevention of pollution (sewage scheme); management of shoreline and fringe area; improvement and management of water quality
# Soil and water conservation measures using vegetative and engineering structures, particularly at upper ridges of watersheds; construction of small check dams or percolation tanks for recharge purposes in areas marked for ‘drainage line recharge measures’
# Afforestation initiatives

Implementation of these measures with the help of local communities improved the lake’s health. NbS are more resilient adaptation measures towards climate change. Restoration not only reduced water stress but also provides multiple societal benefits in the urban area ( [[#Kabisch--2016|Kabisch et al., 2016]] ).

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<span id="case-study-addressing-the-vulnerability-of-peat-swamp-forests-in-southeast-asia"></span>
==== 2.6.5.10 Case Study: Addressing the Vulnerability of Peat Swamp Forests in Southeast Asia ====

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Scale: Regional

Issue: Protecting peatland biodiversity, carbon and ecosystem services from climate change and land degradation

Peatlands in SEA have undergone extensive logging, drainage and land use conversion that have caused habitat loss for endemic species, i.e., the orangutan ( ''Pongo'' spp.) ( [[#Gregory--2012|Gregory et al., 2012]] ; [[#Struebig--2015|Struebig et al., 2015]] ). Prolonged droughts associated with El Niño ( [[IPCC:Wg2:Chapter:Chapter-4#4.4.3|Section 4.4.3.2]] ) compound the effects of drainage, leading to large recurrent fires ( [[#Langner--2009|Langner and Siegert, 2009]] ; [[#Gaveau--2014|Gaveau et al., 2014]] ; [[#Putra--2019|Putra et al., 2019]] ). Under RCP8.5, it is projected that by the end of this century, the annual rainfall over SEA will decrease significantly (by 30%), and the number of consecutive dry days will increase significantly (by 60%) over Indonesia and Malaysia (Supari et al., 2020). Peat degradation and losses to fire result in high GHG emissions ( [[#Miettinen--2016|Miettinen et al., 2016]] ) as well as haze pollution which is a trans-boundary problem in the region ( [[#Heil--2007|Heil et al., 2007]] ).

Improving the resilience of SEA peatlands to fire and climate change through restoration is extremely difficult and presents many challenges. The Indonesian government has tasked the Badan Restorasi Gambut (Peatland Restoration Agency) to restore peatlands ( [[#Darusman--2021|Darusman et al., 2021]] ; [[#Giesen--2021|Giesen, 2021]] ). Other local initiatives exist, such as fire management programmes and restoration projects ( [[#Puspitaloka--2020|Puspitaloka et al., 2020]] ). Since 2016, the government of Indonesia has re-wetted ~380,000 hectares of degraded peatlands, mainly by blocking canals and flooding, but less than 2000 hectares have been successfully restored to sustaining native plant species common to peat swamp forests ( [[#Giesen--2021|Giesen, 2021]] ). Replanting native trees has had relatively little success ( [[#Lampela--2017|Lampela et al., 2017]] ) because such trees have low tolerance to prolonged inundation and no fire adaptation strategies ( [[#Page--2009|Page et al., 2009]] ; [[#Roucoux--2013|Roucoux et al., 2013]] ; [[#Dohong--2018|Dohong et al., 2018]] ; [[#Cole--2019|Cole et al., 2019]] ; [[#Luom--2020|Luom, 2020]] ; [[#Giesen--2021|Giesen, 2021]] ).

The barriers to successful management are complex, and include the disparity in time frames between ecological restoration and political/socioeconomic needs ( [[#Harrison--2020|Harrison et al., 2020]] ) and an over-focus on fire-fighting rather than fire prevention ( [[#Mishra--2021a|Mishra et al., 2021a]] ). Early protection of peat forests has been highlighted as a more effective management strategy than restoration, not only on islands in SEA but also in areas like Papua New Guinea, which may be targeted for the expansion of estate crop plantations ( [[#Neuzil--1997|Neuzil et al., 1997]] ; [[#Dennis--1999|Dennis, 1999]] ; [[#Anshari--2001|Anshari et al., 2001]] ; [[#Anshari--2004|Anshari et al., 2004]] ; [[#Hooijer--2006|Hooijer et al., 2006]] ; [[#Heil--2007|Heil et al., 2007]] ; [[#Page--2009|Page et al., 2009]] ; [[#Page--2011|Page et al., 2011]] ; [[#Posa--2011|Posa et al., 2011]] ; [[#Miettinen--2012|Miettinen et al., 2012]] ; [[#Wetlands%20International--2012|Wetlands International, 2012]] ; [[#Biagioni--2015|Biagioni et al., 2015]] ; [[#Miettinen--2016|Miettinen et al., 2016]] ; [[#Rieley--2016|Rieley and Page, 2016]] ; [[#Adila--2017|Adila et al., 2017]] ; [[#Cole--2019|Cole et al., 2019]] ; [[#Vetrita--2019|Vetrita and Cochrane, 2019]] ; [[#Harrison--2020|Harrison et al., 2020]] ; [[#Hoyt--2020|Hoyt et al., 2020]] ; [[#Ruwaimana--2020|Ruwaimana et al., 2020]] ; [[#Ward--2020|Ward et al., 2020]] ; [[#Cole--2021|Cole et al., 2021]] ).

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=== 2.6.6 Limits to Adaptation Actions by People ===

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The evidence summarised above (Sections 2.6.2–2.6.4) shows that by restoring ecosystems it is possible to increase their resilience to climate change, including the resilience of the populations of species they support and of human communities. However, changes to healthy ecosystems and biodiversity are already happening as described in this chapter ( ''robust evidence'' , ''high agreement'' ) and further changes are inevitable even in scenarios of low GHG emissions ( ''robust evidence'' , ''high agreement'' ). Planning to manage the consequences of inevitable changes and prioritise investments in conservation actions where they have the best chance of succeeding (e.g., [[#2.6.5.6|Section 2.6.5.6]] ) will be an increasingly necessary component of adaptation ( ''robust evidence'' , ''high agreement'' ) (Table 2.6).

It is possible to help species survive by active interventions such as translocation, but, as described above ( [[#2.6.5.1|Section 2.6.5.1]] ), this is not straightforward, is not suitable for all species and is resource-intensive. Modifying local microclimate or hydrological conditions can work for some species (Sections 2.6.2, 2.6.5.5), but is likely to be less effective at higher levels of climate change. It will also be less successful for larger species and more mobile ones. The microclimate of a tree is much more closely coupled with wider atmospheric conditions than that of a small plant or animal in the boundary layer, and mobile species like birds and large mammals range over large areas rather than being confined to discrete locations where conditions can be manipulated.

There is potential for using evolutionary changes to enhance the adaptive capacity for target species, as is being done on the Great Barrier Reef where symbionts and corals that have survived recent intense heat-induced bleaching events are being translocated into areas that have had large die-off. However, known limitations to genetic adaptations preclude species-level adaptations to climates beyond their ecological and evolutionary history (Sections 2.2.4.6; 2.6.1). All of these interventionist approaches are constrained by requiring significant financial resources and expertise. They also require a high level of understanding of individual species autecology, which can take years to acquire, even when resources are available. ''Ex situ'' conservation (e.g., seed banks) may be the only option to conserve some species, especially as levels of warming increase, but this will not be feasible for all species.

While the science of restoration has generated many successes, some habitats are very difficult to restore, making certain decisions effectively irreversible. For example, ''Acacia nilotica'' was introduced into Indonesia in the 1850s for gum arabic, with planting expanded for fire breaks in the 1960s. This tree became invasive and has already replaced &gt;50% of the savanna habitat in the Baluran National Park, with complete replacement expected in the near future. This shift from savanna to acacia forest is causing large declines in native species, including the charismatic wild banteng, ''Bos javanicus'' , and the wild dog (dhole, ''Cuon alpinus'' ) ( [[#Caesariantika--2011|Caesariantika et al., 2011]] ; [[#Padmanaba--2017|Padmanaba et al., 2017]] ; [[#Zahra--2020|Zahra et al., 2020]] ). Multiple approaches to controlling the spread of this acacia have been ineffective, highlighting the difficulty of reversing the decision to plant this tree ( [[#Zahra--2020|Zahra et al., 2020]] ). Another example is the difficulties in restoring the tropical peat forests of SEA ( [[#2.6.5.10|Section 2.6.5.10]] ).

EbA, when implemented well, can reduce risks to people but there are limits. For example, an extreme flood event may exceed the capacity of natural catchments to hold water or slow its flow ( [[#Dadson--2017|Dadson et al., 2017]] ), and urban shade trees and green spaces can make a few degrees difference to temperatures experienced by people but this may not be enough in the hottest conditions.

In general, adaptation measures can substantially reduce the adverse impacts of 1°C–2°C of global temperature rise, but beyond this losses will increase ( [[#IPCC--2018b|IPCC, 2018b]] ), including species extinctions and changes like major biome shifts which cannot be reversed on human time scales. Some adaptation measures will also become less effective at higher temperatures. Whilst adaptation is essential to reduce risks, it cannot be regarded as a substitute for effective climate change mitigation ( ''robust evidence'' , ''high agreement'' ).

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=== 2.6.7 Climate Resilient Development ===

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CRD is the subject of Chapter 18. This section briefly assesses some of the fundamental issues for CRD relating to ecosystems. An overview of the importance of specific ecosystem services for CRD is presented in Box 18.7 in Chapter 18. A large body of evidence has demonstrated the extent to which human life, well-being and economies are dependent on healthy ecosystems and also the range of threats that these are faced with ( ''high confidence'' ) ( [[#IPBES--2019|IPBES, 2019]] ; [[#Dasgupta--2021|Dasgupta, 2021]] ; [[#Pörtner--2021|Pörtner et al., 2021]] ). An analysis of 64 studies found a strong positive synergy among eight critical regulating services of healthy ecosystems, including climate regulation, water provisioning, pest and disease control and adjacent-crop pollination ( [[#Lee--2016|Lee and Lautenbach, 2016]] ). The health of ecosystems is, in turn, reliant upon the maintenance of natural levels of species’ richness and functional diversity ( ''high confidence'' ) ( [[#Lavorel--2020|Lavorel et al., 2020]] ) (see [[#2.5.4|Section 2.5.4]] ). A meta-analysis of 74 studies documented that the mechanism for increased ecosystem stability is increased asynchrony among species, which itself is a product of greater species diversity ( [[#Xu--2021b|Xu et al., 2021b]] ). Responding to these threats requires the protection and restoration of natural and semi-natural ecosystems, together with sustainable management of other areas.

The CBD set the Aichi 2020 Target at 17% of each country to be protected for biodiversity. Analyses suggest that 30% or even 50% of land and sea needs to be protected or restored to confer adequate protection for species and ecosystem services ( ''high confidence'' ) ( [[#Dinerstein--2019|Dinerstein et al., 2019]] ; [[#Woodley--2019|Woodley et al., 2019]] ; [[#Brooks--2020|Brooks et al., 2020]] ; [[#Hannah--2020|Hannah et al., 2020]] ; [[#Zhao--2020|Zhao et al., 2020]] ; [[#Sala--2021|Sala et al., 2021]] ). [[#Hannah--2020|Hannah et al. (2020)]] estimated that limiting warming to 2°C and protecting 30% of high-biodiversity regions (in Africa, Asia and Latin America) reduced the risk of species’ extinctions by half ( ''medium confidence'' ). The placement of protected areas is as important as the total area ( [[#Pimm--2018|Pimm et al., 2018]] ), and the quality of the protection (strictness and enforcement) is as important as the official land designation ( [[#Shah--2021|Shah et al., 2021]] ). Pimm et al. (2018) found that many small protected areas are successful because they are in areas of very high biodiversity containing species with small range sizes, while many large regions identified as wild are often of low biodiversity value even though they may have a high mitigation value (e.g., the high Arctic tundra). A global meta-analysis of 89 restoration projects found that biodiversity increased by 44% and ecosystem services by 25% after restoration but values remained lower than in intact reference systems ( [[#Rey%20Benayas--2009|Rey Benayas et al., 2009]] ).

There is also increasing evidence, reported in this chapter, that the loss and degradation of natural and semi-natural habitats exacerbates the impacts of climate change and climatic extreme events on biodiversity and ecosystem services ( ''high confidence'' ) (e.g., in ( [[#Ogden--2013|Ogden et al., 2013]] ; [[#Eigenbrod--2015|Eigenbrod et al., 2015]] ; [[#Struebig--2015|Struebig et al., 2015]] ; [[#Stevens--2016|Stevens et al., 2016]] ; [[#Oliver--2017|Oliver et al., 2017]] ; [[#McAlpine--2018|McAlpine et al., 2018]] ; [[#Taffarello--2018|Taffarello et al., 2018]] ; [[#Lehikoinen--2019|Lehikoinen et al., 2019]] ; [[#Birk--2020|Birk et al., 2020]] ; [[#Chapman--2020|Chapman et al., 2020]] ; [[#Agol--2021|Agol et al., 2021]] ; [[#Khaniya--2021|Khaniya et al., 2021]] ; [[#Lara--2021|Lara et al., 2021]] ; [[#Lehikoinen--2021|Lehikoinen et al., 2021]] ). Considering these two sets of evidence together, it is clear that climate change adaptation and ecosystem degradation both need to be addressed if either is to be tackled successfully ( ''robust evidence'' , ''high agreement'' ) as a number of recent publications concluded ( [[#Haddad--2015|Haddad et al., 2015]] ; [[#Hannah--2020|Hannah et al., 2020]] ; [[#Arneth--2021|Arneth et al., 2021]] ; [[#Pörtner--2021|Pörtner et al., 2021]] ). Taking this combined body of evidence, the assessment is that the protection and restoration of natural and semi-natural ecosystems are key adaptation measures ( ''robust evidence'' , ''high agreement'' ) ( [[#2.5.4|Section 2.5.4]] ).

Large-scale protection and restoration of ecosystems can also make a significant contribution to climate change mitigation ( [[#Dinerstein--2020|Dinerstein et al., 2020]] ; [[#Roberts--2020a|Roberts et al., 2020a]] ; [[#Soto-Navarro--2020|Soto-Navarro et al., 2020]] ). Globally, there is a 38% overlap between areas of high carbon storage and high intact biodiversity (mainly in the peatland tropical forests of Asia, the western Amazon and the high Arctic), but only 12% of this is protected ( ''high confidence'' ) (see also sections 2.4.4.4.1, 2.4.4.4.3, 2.5.3.4) ( [[#Soto-Navarro--2020|Soto-Navarro et al., 2020]] ). Peatlands are particularly important carbon stores but are threatened by human disturbance, LULCC ( [[#Leifeld--2019|Leifeld et al., 2019]] ) and fire (sections 2.4.3.8, 2.5.2.8) ( [[#Turetsky--2015|Turetsky et al., 2015]] ). Restoration of peatlands is not only an efficient climate solution in terms of emissions of GHGs ( [[#Nugent--2019|Nugent et al., 2019]] ), it may also increase ecosystem resilience ( [[#Glenk--2021|Glenk et al., 2021]] ). Global restoration efforts are ongoing to target degraded temperate peatlands in the Americas and Europe ( [[#Chimner--2017|Chimner et al., 2017]] ) in recognition of their importance for climate change mitigation ( [[#Paustian--2016|Paustian et al., 2016]] ; [[#Bossio--2020|Bossio et al., 2020]] ; [[#Humpenöder--2020|Humpenöder et al., 2020]] ; [[#Drever--2021|Drever et al., 2021]] ; [[#Tanneberger--2021|Tanneberger et al., 2021]] ). It has been estimated that the global GHG-saving potential of peatland restoration is similar to the most optimistic sequestration potential from all agricultural soils ( [[#Leifeld--2018|Leifeld and Menichetti, 2018]] ). However, the pressure on peatlands from human activity remains high in many parts of the world ( [[#Humpenöder--2020|Humpenöder et al., 2020]] ; [[#Tanneberger--2021|Tanneberger et al., 2021]] ). Currently, the rapid destruction of tropical peatlands overshadows any current restoration efforts in temperate peatlands or any potential carbon gain from natural high-latitude peatlands ( [[#Roucoux--2017|Roucoux et al., 2017]] ; [[#Wijedasa--2017|Wijedasa et al., 2017]] ; [[#Leifeld--2019|Leifeld et al., 2019]] ) (Sections 2.4.3.8, 2.4.4.4.2, 2.4.4.4.4, 2.5.2.8, 2.5.3.4).

Recent studies have highlighted the importance of ensuring that ecosystem protection is not implemented in a way which disadvantages those who live in or depend on the most intact ecosystems ( [[#Mehrabi--2018|Mehrabi et al., 2018]] ; [[#Schleicher--2019|Schleicher et al., 2019]] ) or risk food security. The actual area of land to be protected and the balance between sustainable use and protection will need careful planning and targeting to where it can have the most benefit ( [[#Pimm--2018|Pimm et al., 2018]] ). It will also be important to ensure that protection measures are effective in preventing damage ( [[#Shah--2021|Shah et al., 2021]] ).

At a local level, EbA can often provide a wide range of additional benefits for sustainable development in both rural and urban areas ( [[#Wilbanks--2003|Wilbanks, 2003]] ; [[#Nelson--2007|Nelson et al., 2007]] ; [[#Cohen-Shacham--2016|Cohen-Shacham et al., 2016]] ; [[#Hobbie--2020|Hobbie and Grimm, 2020]] ; [[#Martín--2020|Martín et al., 2020]] ). A number of the case studies above, such as in Durban and at Bhojtal Lake, illustrate this (section 2.6.5). A key element of CRD is ensuring that actions taken to mitigate climate change do not compromise adaptation, biodiversity and human needs. This depends on choosing appropriate actions for different locations (Box 2.2, Cross-Chapter Box NATURAL in this chapter). A particularly notable case of this is the creation of woodland described in Box 2.2: re-afforestation of previously forested areas can provide multiple benefits ( [[#Lee--2018|Lee et al., 2018]] ; [[#Lee--2020|Lee et al., 2020]] ) including those for climate change mitigation, adaptation and biodiversity. However, planting trees where they would not naturally grow can create multiple problems including the loss of native biodiversity and the disruption of hydrology (Box 2.2). It is also the case that protection of existing natural forest ecosystems is the highest priority for reducing GHG emissions ( [[#Moomaw--2019|Moomaw et al., 2019]] ) and restoration may not always be practical (see [[#2.6.5.10|Section 2.6.5.10]] ). (Sections 2.4.3.6, 2.4.3.7, 2.4.4.3, 2.4.4.4, 2.5.2.6, 2.5.2.7, 2.5.3.3, Box 2.2, Cross-Chapter Box NATURAL in this chapter)

In some cases, actions supported by international donors and presented as addressing climate change adaptation and mitigation in the natural environment can have damaging consequences for people and nature as well as failing to deliver adaptation and mitigation. One example of this was presented by [[#Work--2019|Work et al. (2019)]] , who reviewed three climate change mitigation and adaptation projects in Cambodia: an irrigation project, a protected-area forest management project and a reforestation project. In each case, they found evidence of the rights of local communities being violated, maladaptation and the destruction of biodiverse habitats. They concluded that the potential for maladaptation and adverse social and environmental impacts had been ignored by international donors and the national authorities, and that there was a need for much stricter accountability mechanisms. [[#Moyo--2021|Moyo et al. (2021)]] , using case studies from South Africa, documented greater success of ecosystem restoration projects when they embraced broader SDGs, particularly enhancement of people’s livelihoods. Better assessment of the impacts of adaptation and mitigation measures on people and ecosystems, before they are implemented, will be increasingly necessary to avoid unintended and damaging consequences as their deployment is scaled up ( [[#Larsen--2014|Larsen, 2014]] ; [[#Enríquez-de-Salamanca--2017|Enríquez-de-Salamanca et al., 2017]] ; [[#Pour--2017|Pour et al., 2017]] ). This applies to ostensibly nature-based approaches as well as more engineering-based ones.

Another aspect of the benefits to people from ecosystems that needs to be taken into account in CRD is increasingly strong evidence of the benefits of natural environments for human health and well-being beyond the provision of basic necessities such as food and water ( [[#Bratman--2019|Bratman et al., 2019]] ; [[#Marselle--2021|Marselle et al., 2021]] ). Meta-analyses of 162 studies involving 51,738 people documented that individuals with high levels of contact with nature throughout their lives felt significantly happier, healthier and more satisfied with their lives, and engaged in more pro-nature behaviours than those with little or no contact with nature ( ''high confidence'' ) ( [[#Capaldi--2014|Capaldi et al., 2014]] ; [[#Mackay--2019|Mackay and Schmitt, 2019]] ; [[#Pritchard--2020|Pritchard et al., 2020]] ; [[#Whitburn--2020|Whitburn et al., 2020]] ) ''.'' Meta-analyses of manipulative human trials across 65 studies documented a significant increase in positive feelings and attitudes and a decline in negative feelings after experimental treatments involving nature ( ''medium confidence'' ) ( [[#Bowler--2010b|Bowler et al., 2010b]] ; [[#McMahan--2015|McMahan and Estes, 2015]] ; [[#Soga--2017|Soga et al., 2017]] ). In the context of CRD improving ''the extent to which humans see themselves as part of the natural world'' '''''—''''' known as human-nature connectedness (HNC) '''''—''''' increasing access to natural areas, particularly within urban areas, can provide additional health, cultural and recreation benefits of NbS as well as increasing public engagement and support ( ''robust evidence'' , ''high agreement'' ) ( [[#Wilbanks--2003|Wilbanks, 2003]] ; [[#Nelson--2007|Nelson et al., 2007]] ; [[#Bowler--2010b|Bowler et al., 2010b]] ; [[#Capaldi--2014|Capaldi et al., 2014]] ; [[#McMahan--2015|McMahan and Estes, 2015]] ; [[#Cohen-Shacham--2016|Cohen-Shacham et al., 2016]] ; [[#Soga--2017|Soga et al., 2017]] ; [[#Mackay--2019|Mackay and Schmitt, 2019]] ; [[#Work--2019|Work et al., 2019]] ; [[#Hobbie--2020|Hobbie and Grimm, 2020]] ; [[#Pritchard--2020|Pritchard et al., 2020]] ; [[#Whitburn--2020|Whitburn et al., 2020]] ).

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'''Cross-Chapter Box NATURAL | Nature-Based Solutions for Climate Change Mitigation and Adaptation'''
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Authors: Camille Parmesan (France/USA/UK, Chapter 2), Gusti Anshari (Indonesia, Chapter 2, CCP7), Polly Buotte (USA, Chapter 4), Donovan Campbell (Jamaica, Chapter 15), Edwin Castellanos (Guatemala, Chapter 12), Annette Cowie (Australia, WGIII Chapter 12), Marta Rivera Ferre (Spain, Chapter 8), Patrick Gonzalez (USA, Chapter 2, CCP3), Elena López Gunn (Spain, Chapter 4), Rebecca Harris (Australia, Chapter 2, CCP3), Jeff Hicke (USA, Chapter 14), Rachel Bezner Kerr (USA/Canada, Chapter 5), Rodel Lasco (Philippines, Chapter 5), Robert Lempert (USA, Chapter 1), Brendan Mackey (Australia, Chapter 11), Paulina Martinetto (Argentina, Chapter 3), Robert Matthews (UK, WGIII, Chapter 3), Timon McPhearson (USA, Chapter 6), Mike Morecroft (UK, Chapter 2, CCP5), Aditi Mukherji (India, Chapter 4), Gert-Jan Nabuurs (the Netherlands, WGIII Chapter 7), Henry Neufeldt (Denmark/Germany, Chapter 5), Roque Pedace (Argentina, WGIII Chapter 3), Julio Postigo (USA/Peru, Chapter 12), Jeff Price (UK, Chapter 2, CCP1), Juan Pulhin (Philippines, Chapter 10), Joeri Rogelj (UK/Belgium, WGI Chapter 5), Daniela Schmidt (UK/Germany, Chapter 13), Dave Schoeman (Australia, Chapter 3), Pramod Kumar Singh (India, Chapter 18), Pete Smith (UK, WGIII Chapter 12), Nicola Stevens (South Africa, Chapter 2, CCP3), Stavana E. Strutz (USA, Chapter 2), Raman Sukumar (India, Chapter 1), Gautam Hirak Talukdar (India, Chapter 2, CCP1), Maria Cristina Tirado (USA/Spain, Chapter 7), Christopher Trisos (South Africa, Chapter 9)

'''''Nature-based solutions provide adaptation and mitigation benefits for climate change as well as contributing to other sustainable development goals (''''' '''high confidence''' '''''). Effective nature-based climate change mitigation stems from inclusive decision-making and adaptive management pathways that deliver climate-resilient systems serving multiple sustainable development goals. Robust decision-making adjusts management pathways as systems are impacted by ongoing climate change. Poorly conceived and poorly designed nature-based mitigation efforts have the potential for multiple negative impacts, including competing for land and water with other sectors, reducing human well-being and failing to provide mitigation that is sustainable in the long term (''''' '''high confidence''' ''''').'''''

The concept of Nature-based Solutions (NbS) is broad and under debate, but has become prominent in both the scientific literature and policy since AR5, and includes earlier concepts like EbA. The key point is that these are actions benefitting both people and biodiversity ( [[#IUCN--2020|IUCN, 2020]] ) (WGII Glossary). In the context of climate change, NbS provide adaptation and mitigation benefits in ways that support wild species and habitats, often contributing to other sustainable development goals ( ''robust evidence'' , ''high agreement'' ) ( [[#Griscom--2017|Griscom et al., 2017]] ; [[#Keesstra--2018|Keesstra et al., 2018]] ; [[#Hoegh-Guldberg--2019|Hoegh-Guldberg et al., 2019]] ; [[#IPCC--2019a|IPCC, 2019a]] ; [[#Lewis--2019|Lewis et al., 2019]] ; [[#Lavorel--2020|Lavorel et al., 2020]] ; [[#Malhi--2020|Malhi et al., 2020]] ; [[#Seddon--2020b|Seddon et al., 2020b]] ) (AR6 WGIII Chapter 12; Sections 2.2, 2.5.4, 2.6.3, 2.6.5, 2.6.7). Well-designed and implemented NbS mitigation schemes can increase carbon uptake or reduce GHG emissions at the same time as protecting or restoring biodiversity and incorporating elements of food provisioning ( [[#Mehrabi--2018|Mehrabi et al., 2018]] ). A variety of measures can be part of NbS, ranging from the protection of natural terrestrial, freshwater and marine ecosystems to the restoration of degraded ones (this Cross-Chapter Box; [[IPCC:Wg2:Chapter:Chapter-13#13.3|Section 13.3]] ) and more sustainable management of naturally regenerating ecosystems used for food, fibre and energy production (Figure Cross-Chapter Box NATURAL.1, [[IPCC:Wg2:Chapter:Chapter-5|Chapter 5]] in this report, Cross-Working Group Box BIOECONOMY in Chapter 5). Agro-ecological practices mitigate and adapt to climate change and can promote native biodiversity ( ''high confidence'' ) ( [[#Sinclair--2019|Sinclair et al., 2019]] ; [[#Snapp--2021|Snapp et al., 2021]] ).

'''The Role of Restoration in Nature-Based Solutions'''
Where natural ecosystems have been degraded or destroyed, re-establishing them and restoring natural processes can be a key action for adaptation and mitigation, and the science of restoration is well established ( [[#de%20los%20Santos--2019|de los]] [[#Santos--2019|Santos et al., 2019]] ; [[#Duarte--2020|Duarte et al., 2020]] ) ( [[IPCC:Wg2:Chapter:Chapter-13#13.4.1|Section 13.4.1]] ). Such restoration activities need to adapt to ongoing climate change risks for the landscape and oceans and the species composition of biological communities. Indeed, the impacts of climate change may overwhelm attempts at restoration/conservation of previous or existing ecosystems, particularly when the ecosystem is already near its tipping point, as is the case with tropical coral reefs ( [[#Bates--2019|Bates et al., 2019]] ; [[#Bruno--2019|Bruno et al., 2019]] ).

Land (e.g., forests) and oceans (e.g., fisheries) managed for products using sustainable practices (whether applied by individuals, states or Indigenous Peoples) can also be carbon- and biodiversity-rich, and thus considered effective NbS ( [[#Paneque-Gálvez--2018|Paneque-Gálvez et al., 2018]] ; [[#Soto-Navarro--2020|Soto-Navarro et al., 2020]] ). Indigenous Peoples and private forest owners manage, use or occupy at least one-quarter of the global land area, over one-third of which overlaps with protected areas, thus combining both protection and production ( [[#Jepsen--2015|Jepsen et al., 2015]] ; [[#Garnett--2018|Garnett et al., 2018]] ; [[#IPBES--2019|IPBES, 2019]] ; [[#Santopuoli--2019|Santopuoli et al., 2019]] ).

The protection/restoration of natural systems including reducing non-climate stressors, and the sustainable management of semi-natural areas emerge as necessary actions for adaptation to minimise extinctions of species, the reaching of tipping points that cause regime shifts in natural system and the loss of whole ecosystems and their associated benefits for humans ( [[#Scheffer--2001|Scheffer et al., 2001]] ; [[#Folke--2005|Folke et al., 2005]] ; [[#Luther--2020|Luther et al., 2020]] ) (Chapters 2 and 3 in this report; AR6 WGIII Chapter 7). Such measures are critical for the conservation of biodiversity and the provision of ecosystem goods and services in the face of projected climate change ( [[#Duarte--2020|Duarte et al., 2020]] ). Supporting local livelihoods and providing benefits to indigenous local communities and millions of private landowners, together with their active engagement in decision-making, are critical to ensuring support for NbS and their successful delivery ( ''high confidence'' ) ( [[IPCC:Wg2:Chapter:Chapter-5|Chapter 5]] in this report; Figure Cross-Chapter Box NATURAL.1)( [[#Ceddia--2015|Ceddia et al., 2015]] ; [[#Blackman--2017|Blackman et al., 2017]] ; [[#Nabuurs--2017|Nabuurs et al., 2017]] ; [[#Smith--2019a|Smith et al., 2019a]] ; [[#Smith--2019b|Smith et al., 2019b]] ; [[#Jones--2020a|Jones et al., 2020a]] ; [[#McElwee--2020|McElwee et al., 2020]] ; [[#Cao--2021|Cao et al., 2021]] ).

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Cross-Chapter Box NATURAL

'''Forests'''
Intact natural forest ecosystems are major stores of carbon and support large numbers of species that cannot survive in degraded habitats ( ''very high confidence'' ). Extensive areas of natural forest ecosystems remain in tropical, boreal and (to a lesser extent) temperate biome regions, but in many regions they are managed (sustainably and unsustainably) or have been degraded or cleared. Deforestation and land degradation continue to be a source of global GHG emissions ( ''very high confidence'' ) ( [[#Friedlingstein--2019|Friedlingstein et al., 2019]] ). Protection of existing natural forests and sustainable management of semi-natural forests that continue to provide goods and services are highly effective NbS ( [[#Bauhus--2009|Bauhus et al., 2009]] ) ( ''high confidence'' ) ''.''

Natural forests and sustainably managed biodiverse forests play important roles in climate change mitigation and adaptation while providing many other ecosystem goods and services ( ''very high confidence'' ) ( [[#Bradshaw--2015|Bradshaw and Warkentin, 2015]] ; [[#Favero--2020|Favero et al., 2020]] ; [[#Mackey--2020|Mackey et al., 2020]] ). Contributions of natural forests to climate change mitigation are estimated at a median of 5–7 GtCO 2 yr -1 ( [[#Roe--2019|Roe et al., 2019]] ). Forests influence the water cycle on a local, regional and global scale ( [[#Creed--2018|Creed and van Noordwijk, 2018]] ), reducing surface runoff, increasing infiltration to groundwater and improving water quality ( [[#Bruijnzeel--2004|Bruijnzeel, 2004]] ; [[#Zhou--2015a|Zhou et al., 2015a]] ; [[#Ellison--2017|Ellison et al., 2017]] ; [[#Alvarez-Garreton--2019|Alvarez-Garreton et al., 2019]] ). Recent evidence shows that downwind precipitation is also influenced by evapotranspiration from forests ( [[#Keys--2016|Keys et al., 2016]] ; [[#Ellison--2017|Ellison et al., 2017]] ). Protecting existing natural forests and sustainably managing production forests in a holistic manner can optimise the provision of the many functions forests fulfil for owners, conservation, mitigation and for society as a whole ( [[#Bauhus--2009|Bauhus et al., 2009]] ; [[#Nabuurs--2013|Nabuurs et al., 2013]] ).

Reforestation of previously forested land can help to protect and recover biodiversity and is one of the most practical and cost-effective ways of sequestering and storing carbon ( ''high confidence'' ) ( [[#Nabuurs--2017|Nabuurs et al., 2017]] ; [[#Hoegh-Guldberg--2018|Hoegh-Guldberg et al., 2018]] ; [[#Paneque-Gálvez--2018|Paneque-Gálvez et al., 2018]] ; [[#Smith--2018|Smith et al., 2018]] ; [[#Cook-Patton--2020|Cook-Patton et al., 2020]] ; [[#Cowie--2021|Cowie et al., 2021]] ; [[#Drever--2021|Drever et al., 2021]] ). This can be achieved through planting or by allowing natural colonisation by tree and shrub species. The most effective method to deploy depends upon local circumstances (e.g., the presence of remnant forest cover) or socio-cultural and management objectives. Reforestation with climate-resilient native or geographically-near species restores biodiversity at the same time as sequestering large amounts of carbon ( [[#Lewis--2019|Lewis et al., 2019]] ; [[#Rozendaal--2019|Rozendaal et al., 2019]] ). It can also restore hydrological processes, thereby improving water supply and quality ( [[#Ellison--2017|Ellison et al., 2017]] ) and reducing the risk of soil erosion and floods ( ''high confidence'' ) ( [[#Locatelli--2015|Locatelli et al., 2015]] ).

Climate change may mean that, in any given location, different species will be able to survive and become dominant and restoring the former composition of forests may not be possible (Sections 2.4, 2.5). Severe disturbances such as insect/pathogen outbreaks, wildfires and droughts, which are an increasing risk, can cause widespread tree mortality resulting in sequestered forest carbon being returned to the atmosphere ( [[#Anderegg--2020|Anderegg et al., 2020]] ; [[#Senf--2021|Senf and Seidl, 2021]] ), suggesting that we need to adapt (Sections 2.4, 2.5, 13.3 14.4.1, Box 14.1). Adaptation measures, such as increasing the diversity of forest stands through ecological restoration rather than monoculture plantations can help to reduce these risks ( ''high confidence'' ). When plantations are established without effective landscape planning and meaningful engagement including free prior and informed consent, they can present risks to biodiversity and the rights, well-being and livelihoods of indigenous and local communities as well as being less climate-resilient than natural forests ( ''very high confidence'' ) ( [[IPCC:Wg2:Chapter:Chapter-5#5.6|Section 5.6]] ) ( [[#Corbera--2017|Corbera et al., 2017]] ; [[#Mori--2021|Mori et al., 2021]] ).

Afforesting areas such as savannas and temperate peatlands, which would not naturally be forested, damages biodiversity and increases vulnerability to climate change ( ''high confidence'' ), so cannot be considered a nature-based solution and can even exacerbate GHG emissions (Sections 2.4.3.5, 2.5.2.5, Box 2.2 in this chapter). Remote sensing-based assessments of the suitability of land for planting trees can overestimate potential, due to their failure to adequately distinguish between degraded forest and naturally open areas ( [[#Bastin--2019|Bastin et al., 2019]] ; [[#Veldman--2019|Veldman et al., 2019]] ; [[#Bastin--2020|Bastin et al., 2020]] ; [[#Sullivan--2020|Sullivan et al., 2020]] ).

<div id="_idContainer066" class="Box_Header-continued"></div>

Cross-Chapter Box NATURAL

'''Peatlands'''
Peatlands are naturally high-carbon ecosystems, which have built up over millennia. Draining, cutting and burning peat lead to oxidation and the release of CO 2 ( ''very high confidence'' ). Re-wetting by blocking drainage and preventing cutting and burning can reverse this process on temperate peatlands ( ''medium confidence'' ) but takes many years ( [[#Bonn--2016|Bonn et al., 2016]] ). Trees are naturally found on many tropical peatlands and restoration can involve removing non-native species like the oil palm and re-establishing natural forest. However, peatland tropical forest is difficult to fully restore, and native pond-fish, vital as a local food, often do not return. Protecting intact peat forests, rather than attempting to restore cleared forest, is by far the more effective pathway, in terms of cost, CO 2 mitigation and the protection of food sources ( [[#Kreft--2007|Kreft and Jetz, 2007]] ). Naturally treeless temperate and boreal peatlands have, in some cases, been drained to enable trees to be planted, which then leads to CO 2 emissions, and restoration requires the removal of trees as well as re-blocking drainage ( ''high confidence'' ) (Sections 2.4.3.8, 2.5.2.8, 2.6.5.10).

'''Blue Carbon'''
Blue carbon ecosystems (mangroves, saltmarshes and seagrass meadows; see Glossary Appendix II) often have high local rates of carbon accumulation and sequestration ( [[IPCC:Wg2:Chapter:Chapter-3#3.5.5.5|Section 3.5.5.5]] ) ( [[#Macreadie--2019|Macreadie et al., 2019]] ). However, quantification of their overall mitigation value is difficult due to the variable production of CH 4 and N 2 O ( [[#Adams--2012|Adams et al., 2012]] ; [[#Rosentreter--2018|Rosentreter et al., 2018]] ; [[#MacLean--2019b|MacLean et al., 2019b]] ), uncertainties regarding the provenance of the carbon accumulated ( [[#Macreadie--2019|Macreadie et al., 2019]] ) and the release of CO 2 by biogenic carbonate formation in seagrass ecosystems ( [[#Saderne--2019|Saderne et al., 2019]] ). Therefore, blue carbon strategies, referring to climate change mitigation and adaptation actions based on the conservation and restoration of blue carbon ecosystems, can be effective NbS, with evidence of the recovery of carbon stocks following restoration, although their global or regional carbon sequestration potential and net mitigation potential may be limited ( ''medium confidence'' ) (Sections 3.6.3.1.6, 13.4.3) (section 5.6.2.2.2 in ( [[#Canadell--2021|Canadell et al., 2021]] )) ( [[#Duarte--2020|Duarte et al., 2020]] ).

They can also significantly attenuate wave energy, raise the seafloor (thereby counteracting the effects of SLR) and buffer storm surges and erosion from flooding ( ''high confidence'' ) (Sections 13.2.2, 13.10.2). Additionally, they provide a suite of cultural (e.g., tourism and the livelihoods and well-being of native and local communities), provision (e.g., mangrove wood, edible fish and shellfish) and regulation (e.g., nutrient cycling) services ( ''high confidence'' ) ( [[IPCC:Wg2:Chapter:Chapter-3#3.5.5.5|Section 3.5.5.5]] ). These services have motivated the implementation of management and conservation strategies of these ecosystems (Sections 3.6.3.1.6, 13.4.2). Blue carbon strategies are relatively new, with many of them experimental and small-scale; there is therefore only ''limited evidence'' of their long-term effectiveness. There is also limited information on the potential emission of other GHGs from restored blue carbon ecosystems, although reconnecting hydrological flow in mangroves and restoring saltmarshes are effective interventions to reduce CH 4 and CO 2 ( ''limited evidence'' , ''medium agreement'' ) ( [[#Kroeger--2017|Kroeger et al., 2017]] ; [[#Al-Haj--2020|Al-Haj and Fulweiler, 2020]] ).

'''Urban Nature-Based Solutions'''
NbS can be a key part of urban climate adaptation efforts. Direct human adaptation benefits may stem from the cooling effects of urban forests and green spaces (parks and green roofs), from coastal wetlands and mangroves reducing storm surges and flooding and from sustainable drainage systems designed to reduce surface flooding as a result of extreme rainfall as well as the general benefits to human health and well-being ( ''high confidence'' ) (Sections 2.2, 2.6, Chapter 6) ( [[#Kowarik--2011|Kowarik, 2011]] ; [[#Frantzeskaki--2019|Frantzeskaki et al., 2019]] ; [[#Keeler--2019|Keeler et al., 2019]] ). Not all green schemes are considered ‘Nature-Based Solutions’ if they do not benefit biodiversity, but carefully designed urban greening can be effective NbS. Careful planning also helps limit negative equity consequences such as benefitting wealthy neighbourhoods more than poor neighbourhoods ( [[#Geneletti--2016|Geneletti et al., 2016]] ; [[#Pasimeni--2019|Pasimeni et al., 2019]] ; [[#Grafakos--2020|Grafakos et al., 2020]] ). Effective planning should also consider what is appropriate for the climate and conditions of each city. For example, some trees emit volatiles (e.g., isoprene) which, in the presence of certain atmospheric pollutants, can increase surface ozone which can, in turn, cause human respiratory problems ( [[#Kreft--2007|Kreft and Jetz, 2007]] ). Wetland restoration close to human settlements needs to be paired with mosquito control to prevent negative impacts on human health and well-being ( [[#Stewart-Sinclair--2020|Stewart-Sinclair et al., 2020]] ), but it has been shown to provide better filtration and toxicity reduction with a lower environmental impact than other forms of waste-water treatment ( [[#Vymazal--2021|Vymazal et al., 2021]] ), including ‘green roofs’ and ‘green walls’ ( [[IPCC:Wg2:Chapter:Chapter-6|Chapter 6]] in this report) ( [[#Addo-Bankas--2021|Addo-Bankas et al., 2021]] ).

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Cross-Chapter Box NATURAL

'''Agro-Ecological Farming'''
AF is a holistic approach that incorporates ecological and socioeconomic principles, many of which have been shown to have a positive impact on biodiversity and on the resilience of human and natural systems to climate change (chapter 5, this report). It strives to enhance biodiversity, soil health and synergies between agro-ecosystem components, reduces reliance on synthetic inputs (e.g., pesticides), builds on IKLK and fosters social equity (e.g., supporting fair, local markets) ( [[#HLPE--2019|HLPE, 2019]] ; [[#Wezel--2020|Wezel et al., 2020]] ). AF practices include inter-cropping; the mobility of livestock grazing across landscapes; organic agriculture; and the integration of livestock, fish and cropping, cover crops and agro-forestry (Sections 5.14, FAQ 12.5, FAQ 13.5).

Agro-forestry, cover crops and other practices that increase vegetation cover and enhance soil organic matter, carefully managed and varying by agro-ecosystem, mitigate climate change ( ''high confidence'' ) ( [[#Zomer--2016|Zomer et al., 2016]] ; [[#Aryal--2019|Aryal et al., 2019]] ; [[#Nadège--2019|Nadège et al., 2019]] ). Global meta-analyses demonstrate agro-forestry as storing 20–33% more soil carbon than conventional agriculture ( [[#De%20Stefano--2018|De Stefano and Jacobson, 2018]] ; [[#Shi--2018|Shi et al., 2018]] ) and reducing the spread of fire (Sections 5.6, 13.5.2, 7.4.3, Box 7.7). Minimising synthetic inputs such as nitrogen-based fertilizers reduces emissions ( [[#Gerber--2016|Gerber et al., 2016]] ). Cover crops can reduce N 2 O emissions and increase soil organic carbon ( [[#Abdalla--2019|Abdalla et al., 2019]] ). Conservation farming (no-till with residue retention and crop rotation) increases soil organic carbon, particularly in arid regions ( [[#Sun--2020|Sun et al., 2020]] ). Silvo-pastoral systems (pastures with trees) and other practices that increase vegetation cover and enhance soil organic matter increase sequestered carbon in vegetation and soils ( [[#Zomer--2016|Zomer et al., 2016]] ; [[#Aryal--2019|Aryal et al., 2019]] ; [[#Nadège--2019|Nadège et al., 2019]] ; [[#Ryan--2019|Ryan, 2019]] ). Agro-ecologically improved management of land for crops and grazing has significant mitigation potential, estimated at 2.8–4.1 GtCO 2 -eq yr -1 ( [[#Smith--2020|Smith et al., 2020]] ) (Sections 5.10, 5.14, Box 5.10, Cross Working-Group Box BIOECONOMY in Chapter 5; WGIII 7.4.3, Box 7.7).

AF enhances adaptation to climate change, including resilience to extreme events. Building organic matter improves the water-holding capacity of soils and buffers against drought; increased perenniality and high levels of ground cover reduce soil erosion during storms; agro-forestry shelters livestock and crops during heat waves; landscape complexity and agro-biodiversity increase resilience to disease and pests and stabilise livestock production; and restoration of oyster reefs provides thermal refugia and storm surge protection ( [[#Henry--2018|Henry et al., 2018]] ; [[#Kremen--2018|Kremen and Merenlender, 2018]] ; [[#Kuyah--2019|Kuyah et al., 2019]] ; [[#Gilby--2020|Gilby et al., 2020]] ; [[#Niether--2020|Niether et al., 2020]] ; [[#Richard--2020|Richard et al., 2020]] ; [[#Howie--2021|Howie and Bishop, 2021]] ; [[#Snapp--2021|Snapp et al., 2021]] ). Livestock mobility enables adjustment to increased climatic variability while maintaining the productivity of pastoral systems ( [[#Turner--2019|Turner and Schlecht, 2019]] ; [[#Scoones--2020|Scoones, 2020]] ). The adoption of agro-ecology principles and practices will therefore be highly beneficial to maintaining healthy, productive food systems under climate change ( ''high confidence'' ) (Sections 5.4.4, 13.5.2, FAQ 12.4).

AF practices such as hedgerows and poly-cultures maintain habitat and connectivity for biodiversity, thus aiding the ability of wild species to respond to climate change via range shifts, and support ecosystem functioning under climate stress compared to conventional agriculture ( ''high confidence'' ) ( [[IPCC:Wg2:Chapter:Chapter-5#5.4.4.4|Section 5.4.4.4]] ) ( [[#Buechley--2015|Buechley et al., 2015]] ; [[#Kremen--2018|Kremen and Merenlender, 2018]] ; [[#Albrecht--2020|Albrecht et al., 2020]] ). Increasing farm biodiversity benefits pollination, pest control, nutrient cycling, water regulation and soil fertility ( [[#Beillouin--2019|Beillouin et al., 2019]] ; [[#Tamburini--2020|Tamburini et al., 2020]] ; [[#Snapp--2021|Snapp et al., 2021]] ). Biodiverse agro-forestry systems increase ecosystem services and biodiversity benefits compared to simple agro-forestry and conventional agriculture ( ''high confidence'' ), with up to 45% more biodiversity and 65% more ecosystem services compared to conventional production of timber and crops and profits from livestock in the Atlantic Forest in Brazil ( [[#Santos--2019|Santos et al., 2019]] ), including benefits for birds and local tree species ( [[#Braga--2019|Braga et al., 2019]] ) and meaning there are fewer invasive exotic plants species ( [[#de%20Almeida%20Campos%20Cordeiro--2018|de Almeida Campos Cordeiro et al., 2018]] ). AF includes the conservation of semi-natural woodlands, which can conserve bird predators of insect pests ( [[#Gonthier--2019|Gonthier et al., 2019]] ). The richness and abundance of insect species, including essential pollinators, are increased by organic farming (Sections 5.10, 12.6) ( [[#Kennedy--2013|Kennedy et al., 2013]] ; [[#Haggar--2015|Haggar et al., 2015]] ; [[#Lichtenberg--2017|Lichtenberg et al., 2017]] ).

AF significantly improves food security and nutrition by increasing access to healthy, diverse diets and raising incomes for food producers, due to the increased biodiversity of crops, animals and landscapes ( ''high confidence'' ) ( [[#Garibaldi--2016|Garibaldi et al., 2016]] ; [[#D’Annolfo--2017|D’Annolfo et al., 2017]] ; [[#Isbell--2017|Isbell et al., 2017]] ; [[#Dainese--2019|Dainese et al., 2019]] ; [[#Kerr--2021|Kerr et al., 2021]] ). Livestock mobility improves the site-specific matching of animals’ needs with food availability ( [[#Damonte--2019|Damonte et al., 2019]] ; [[#Mijiddorj--2020|Mijiddorj et al., 2020]] ; [[#Postigo--2021|Postigo, 2021]] ), and can generate a form of re-wilding that restores lost ecosystem functioning ( [[#Gordon--2021|Gordon et al., 2021]] ). Conservation of crop wild relatives ''in situ'' supports the genetic diversity of crops for a range of future climate scenarios ( [[#Redden--2015|Redden et al., 2015]] ).

System-level agro-ecological transitions require policy support for experimentation and exchange of knowledge by farmers, community-based participatory methodologies and market and policy measures, for example, public procurement, local and regional market support, regulation or payments for environmental services ( [[#Mier%20y%20Terán%20Giménez%20Cacho--2018|Mier y Terán Giménez Cacho et al., 2018]] ; [[#HLPE--2019|HLPE, 2019]] ; [[#Snapp--2021|Snapp et al., 2021]] ). Scientific consensus about the food security and environmental implications of agro-ecological transitions on a global scale is lacking. Yields of agro-forestry and organic farming can be lower than high-input agricultural systems but, conversely, AF can boost productivity and profit, varying according to the time frame and the socioeconomic, political or ecosystem context ( ''medium confidence'' ) ( [[IPCC:Wg2:Chapter:Chapter-5#5.1|Section 5.1]] 4) ( [[#Muller--2017|Muller et al., 2017]] ; [[#Barbieri--2019|Barbieri et al., 2019]] ; [[#Smith--2019b|Smith et al., 2019b]] ; [[#Smith--2020|Smith et al., 2020]] ). Such contrasting results and the limited investment in agro-ecological research to date mean it is paramount to assess the global and regional impacts of agro-ecological transitions on food production, ecosystems and economies in the context of climate change adaptation ( [[IPCC:Wg2:Chapter:Chapter-5#5.1|Section 5.1]] 4) ( [[#DeLonge--2016|DeLonge et al., 2016]] ; [[#Muller--2017|Muller et al., 2017]] ; [[#Barbieri--2019|Barbieri et al., 2019]] ).

[[File:9b527bc0e7657ae134249fb5a63588f3 IPCC_AR6_WGII_Figure_2_Cross-Chapter-Box-NATURAL_1.png]]

'''Figure Cross-Chapter Box NATURAL.1 |''' '''Decision-making framework to co-maximise adaptation and mitigation benefits from natural systems.''' Decision-making pathways are designed to add robustness in the face of uncertainties in future climate change and its impacts. Emphasis is on keeping open as many options as possible, for as long as possible, with periodic re-evaluation to aid in choosing pathways forward, even as systems are being impacted by ongoing climate change.

<div id="_idContainer068" class="Box_Header-continued"></div>

Cross-Chapter Box NATURAL

'''Conclusions'''
NbS provide adaptation and mitigation benefits for climate change as well as contributing to achieving other sustainable development goals ( ''high confidence'' ). NbS avoid further emissions and promote CO 2 removal, by using approaches that yield long-lasting mitigation benefits and avoid negative outcomes for other sustainable development goals. Poorly conceived and poorly designed mitigation efforts have the potential for multiple negative impacts: (1) cascading negative effects on long-term mitigation by promoting short-term sequestration over existing long-term accumulated carbon stocks; (2) being detrimental for biodiversity, undermining conservation adaptation; and (3) eroding other ecosystem services important for human health and well-being ( ''high confidence'' ). Conversely, well-designed and implemented mitigation efforts have the potential to provide co-benefits in terms of climate change adaptation as well as providing multiple goods and services, including the conservation of biodiversity, clean and abundant water resources, flood mitigation, sustainable livelihoods, food and fibre security and human health and well-being ( ''high confidence'' ). A key aspect of such ‘smart’ climate mitigation is the implementation of inclusive and adaptive management pathways ( [[IPCC:Wg2:Chapter:Chapter-1#1.4.2|Section 1.4.2]] ). These entail acceptance of the uncertainty inherent in projections of future climate change, especially at the regional or local level, and using decision-making processes that keep open as many options as possible for as long as possible, with periodic re-evaluation to aid in choosing pathways forward, even as systems are being impacted by ongoing climate change (Figure Cross-Chapter Box NATURAL.1; Cross-Chapter Box DEEP in Chapter 17; [[IPCC:Wg2:Chapter:Chapter-1#1.4.2|Section 1.4.2]] ).

<div id="_idContainer070" class="Box_Header-continued"></div>

Cross-Chapter Box NATURAL

'''Table Cross-Chapter Box NATURAL.1 |''' Assessment of benefits and trade-offs between mitigation and strategies for both biodiversity and human adaptation to future climate change. Best practices highlight approaches that lead to maximal positive synergy between mitigation and adaptation; worst practices are those most likely to lead to negative trade-offs for adaptation. Many best practices have additional societal benefits beyond adaptation, such as food provisioning, recreation and improved water quality. Mitigation Potential (Mit. Pot.) and Restoration Potential (Rest. Pot.) are considered.

{| class="wikitable"
|-
! '''System'''

! '''Mit. Pot.'''

! '''Rest. Pot.'''

! '''Best practices and adaptation benefits'''

! '''Worst practices and negative adaptation trade-offs'''

! '''Additional societal benefits'''

! '''References'''

|-
| colspan="7"| Forests

|-
| '''''Boreal forests'''''

| medium

| medium

| Maintain or restore species and structural diversity, reduce fire risk, spatially separate wood production and sustainably intensify management in some regions

| Very large-scale clear cuts, aiming for one or few tree species, although boreal is characterised by few tree species and a natural fire risk

| Providing goods and services, jobs and improved air quality and hydrology

| ( [[#Drever--2021|Drever et al., 2021]] )

|-
| '''''Temperate forests'''''

| very high

| high

| Maintain or restore natural species and structural diversity, leading to more biodiverse and resilient systems

| Planting large-scale non-native monocultures which would lead to loss of biodiversity and poor climate change resilience

| Providing goods and services, jobs and improved hydrology and biodiversity

| Sections 2.4.3; 2.5; Box 2.2 ; ( [[#Nabuurs--2017|Nabuurs et al., 2017]] ; [[#Roe--2019|Roe et al., 2019]] ; [[#Favero--2020|Favero et al., 2020]] )

|-
| '''''Tropical wet forests'''''

| high

| moderate

| Maintain or restore natural species and structural diversity, high biodiversity, more resilient to climate change

| Planting non-native monocultures, loss of biodiversity, poor climate change resilience, soil erosion

| Indigenous foods, medicines and other forest products, including sustainable selective logging

| [[#2.4.3|Section 2.4.3]] ( [[#Edwards--2014|Edwards et al., 2014]] )

|-
| '''''Tropical dry forests'''''

| high

| moderate

| Integrated landscape management

| Planting non-native monocultures, loss of biodiversity, poor climate change resilience, soil erosion

|
| ( [[#Foli--2018|Foli et al., 2018]] )

|-
| '''''Tropical peatland forests'''''

| very high

| low

| Integrated landscape management

| Cutting native rainforest and planting palm oil for biodiesel results in very high carbon emissions from exposed peat soils

| Forest pond fish are a major food for local communities

| [[#2.4.3|Section 2.4.3]] ; 2.5; ( [[#Smith--2019b|Smith et al., 2019b]] )

|-
| colspan="6"| Blue carbon

| AR6 WGI 5.6.2.2.2

( [[#Canadell--2021|Canadell et al., 2021]] )

|-
| '''''Mangroves'''''

| moderate

| high

| Conservation, restoration of hydrological flows, re-vegetation with native plants, livelihood diversification, landscape planning for landward and upstream migration

| Potential NH 4 emissions

| Improved fisheries and biodiversity, coastal protection against SLR and storm surges, recreation and cultural benefits

| Sections 3.4.2.5; 3.5.5.5; 3.6.3.1; ( [[#Macreadie--2019|Macreadie et al., 2019]] ; [[#Duarte--2020|Duarte et al., 2020]] ; [[#Sasmito--2020|Sasmito et al., 2020]] )

|-
| '''''Saltmarshes'''''

| moderate

| high

| Conservation, reduction of nutrient loads, restoration of hydrological flows and sediment delivery, re-vegetation with native plants, landscape planning for landward and upstream migration

| Potential NH 4 emissions

| Improved fisheries and biodiversity, protection against SLR and storm surges, recreational and cultural benefits

| Sections 3.4.2.5; 3.5.5.5; 3.6.3.1; ( [[#Macreadie--2019|Macreadie et al., 2019]] ; [[#Duarte--2020|Duarte et al., 2020]] )

|-
| '''''Seagrasses'''''

| moderate

| high

| Conservation, restoration, improve water quality and reduce local stressors (reduction of industrial sewage, anchoring and trawling regulation)

| Potential NH 4 emissions

| Improved fisheries and biodiversity, protection from shoreline erosion, recreational benefits

| [[IPCC:Wg2:Chapter:Chapter-3#3.4.2.5|Section 3.4.2.5]] ; 3.5.5.5; 3.6.3.1; ( [[#de%20los%20Santos--2019|de los]] [[#Santos--2019|Santos et al., 2019]] ; [[#Macreadie--2019|Macreadie et al., 2019]] ; [[#Duarte--2020|Duarte et al., 2020]] )

|-
| colspan="7"| Urban ecosystems

|-
| '''''Urban forests'''''

| moderate to high*

| moderate

| Integrated landscape management. Species richness (including exotics) can be high.

| Monoculture of an exotic tree lowers resilience and reduces biodiversity

| Recreation and aesthetics, stormwater absorption benefits, heat mitigation, air quality improvements

| Chapter 6, this report

|-
| '''''Urban wetlands'''''

| moderate*

| moderate

| Integrated landscape management

|
| Recreation and aesthetics, stormwater absorption, heat mitigation, coastal flood protection

| Chapter 6, this report

|-
| '''''Urban grasslands'''''

| moderate*

| moderate

| Integrated landscape management

| fertilised commercial grass monocultures often require irrigation and are less resilient to droughts than native, mixed grasses and forbs

| Recreation and aesthetics, stormwater absorption, heat mitigation

| Chapter 6, this report

|-
| colspan="7"| Open grasslands and savanna

|-
| '''''Boreal and temperate peatlands'''''

| high

| moderate

| Block drainage channels, raise water levels to their natural condition, remove planted trees, re-vegetation of bare peat, no fires, increased biodiversity resilience, reduced flood risk

| Inappropriate hydrological restoration, e.g., flood surface depth greater than natural depth leading to methane emissions

| Improved water quality in some conditions

| Sections 2.4.3; 2.5;( [[#Bonn--2016|Bonn et al., 2016]] ; [[#Nugent--2019|Nugent, 2019]] ; [[#Taillardat--2020|Taillardat et al., 2020]] )

|-
| '''''Tropical savannas and grasslands (including rangelands)'''''

| moderate

| high

| Control of feral herbivores, reintroduce indigenous burning, reintroduce native herbivores and controlled grazing, strategic design of water holes, community-based natural resource management, grass reseeding, clearing of invasive and encroaching woody plants

| Afforestation,over-grazing/stocking, no burning, inappropriate placement and design of watering points. All lead to loss of biodiversity and resilience, soil erosion and water insecurity.

| Improved grazing potential for livestock and dairy production, sustainable wildlife harvests, increased water security, income from eco-tourism, medicinal plants, fuel wood, enhanced food security

| Sections 2.4.3; 2.5; Box 2.1; ( [[#Stafford--2017|Stafford et al., 2017]] ; [[#Moura--2019|Moura et al., 2019]] ; [[#Shackelford--2021|Shackelford et al., 2021]] ; [[#Stringer--2021|Stringer et al., 2021]] ; [[#Wilsey--2021|Wilsey, 2021]] )

|-
| '''''Temperate grasslands and rangelands'''''

| moderate to high

| moderate to high

| Integrated landscape management, sustainable grazing, community-based natural resource management, native grassland species are more resistant to drought than introduced species

| Monocultures (especially of introduced species), over-fertilising with chemical or organic amendments, failure to manage human–wildlife clashes, failure to distribute income equitably, inadequate enabling policy to facilitate integrated landscape management

| Sustainable harvest of wildlife, livestock and dairy production, wild fruits, medicinal plants, construction material, fuel wood, income from ecotourism

| Sections 2.4.3; 2.5, Box 2.1; ( [[#Farai--2017|Farai, 2017]] ; [[#Baker--2018|Baker et al., 2018]] ; [[#Homewood--2020|Homewood et al., 2020]] ; [[#Wilsey--2021|Wilsey, 2021]] )

|-
| '''''AF and aquaculture'''''

| high

| high (context-specific)

| Biodiverse systems on the landscape scale, participatory adaptation to context, short value chains, farmer incentives, biodiversity synergies, reduced climate risk

| Poorly chosen species, practices and amendments can lead to low yields. Simplified agro-forestry systems and industrial-scale organic agriculture lack a holistic system-wide approach. Over-fertilising with organic amendments.

| Food security, human health, livelihoods, socio-cultural benefits, e.g., culturally appropriate foods

| Sections 5.4, 5.10, 5.12, 5.14 ; ( [[#Coulibaly--2017|Coulibaly et al., 2017]] ; [[#HLPE--2019|HLPE, 2019]] ; [[#Quandt--2019|Quandt et al., 2019]] ; [[#Sinclair--2019|Sinclair et al., 2019]] ; [[#Smith--2019b|Smith et al., 2019b]] ; [[#Muchane--2020|Muchane et al., 2020]] ; [[#Reppin--2020|Reppin et al., 2020]] )

|}

Cross-Chapter Box NATURAL

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=== FAQ 2.5 | How can we reduce the risks of climate change to people by protecting and managing nature better? ===

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''Damage to our natural environment can increase the risks that climate change poses to people. Protecting and restoring nature can be a way to adapt to climate change, with benefits for both humans and biodiversity. Examples include reducing flood risk by restoring catchments and coastal habitats, the cooling effects of natural vegetation and shade from trees and reducing the risk of extreme wildfires by better management of natural fires.''

Protecting and restoring natural environments, such as forests and wetlands, can reduce the risks that climate change poses to people as well as supporting biodiversity, storing carbon and providing many other benefits for human health and well-being. Climate change is bringing an increasing number of threats to people, including flooding, droughts, wildfire, heat waves and rising sea levels. These threats can, however, be reduced or aggravated, depending on how land, sea and freshwater are managed or protected. There is now clear evidence that ‘Nature-based Solutions’ (NbS) can reduce the risks that climate change presents to people. ‘Ecosystem-based Adaptation’ (EbA) is a part of NbS and includes:

* ''Natural flood management:'' As warm air holds more water and, in some places, because of changing seasonal rainfall patterns, we are seeing more heavy downpours in many parts of the world. This can create serious flooding problems, with loss of life, homes and livelihoods. The risk of flooding is higher where natural vegetation has been removed, wetlands drained or channels straightened. In these circumstances, water flows quicker and the risk of flood defences being breached is increased. Restoring the natural hydrology of upstream catchments by restoring vegetation, creating wetlands and re-naturalising watercourse channels and reinstating connections with the floodplain can reduce this risk. In a natural catchment with trees or other vegetation, water flows slowly overland and much of it soaks into the soil. When the water reaches a watercourse, it moves slowly down the channel, both because of the longer distance it travels when the channel bends and because vegetation and fallen trees slow the flow. Wetlands, ponds and lakes can also hold water back and slowly release it into river systems.
* ''Restoring natural coastal defences:'' Rising sea levels as a result of climate change mean that coasts are eroding at a fast rate and storm surges are more likely to cause damaging coastal flooding. Natural coastal vegetation, such as saltmarshes and mangrove swamps can, in the right places, stabilise the shoreline and act as a buffer, absorbing the force of waves. On a natural coast, the shoreline will move inland and as the sea level rises, the coastal vegetation will gradually move inland with it. This contrasts with hard coastal defences such as sea walls and banks, which can be overwhelmed and fail. In many places, however, coastal habitats have been cleared and where there are hard sea defences behind the coastal zone, the vegetation disappears as the coast erodes rather than moving inland. This is often referred to as ‘coastal squeeze’ as the vegetation is squeezed between the sea and the sea wall. Restoring coastal habitats and removing hard sea defences, can help reduce the risks of catastrophic flooding.
* ''Providing local cooling:'' Climate change is bringing higher temperatures globally, which can result in heat waves that affect people’s health, comfort and agriculture. In cities, this can be a particular problem for health as temperatures are typically higher than in the countryside. Trees give shade, which people, in both rural and urban areas, have long used to provide cool places for themselves, for growing crops such as coffee and for livestock. Planting trees in the right place can be a valuable, low-cost natural-based solution to reduce the effects of increasing heat, including reducing water temperatures in streams and rivers which can help to maintain fisheries. Trees and other vegetation also have a cooling effect as a result of water being lost from their leaves through evaporation and transpiration (i.e., the loss of water through pores in the leaves, known as stomata). Natural areas, parks, gardens in urban areas can help reduce air temperatures by up to a few degrees.
* ''Restoring natural fire regimes:'' Some natural ecosystems are adapted to burning, such as savannas and some temperate and boreal forests. Where fire has been suppressed or non-native species of trees are planted in more open habitats, there is a risk that potential fuel accumulates, which can result in larger and hotter fires. Solutions can include restoring natural fire regimes and removing non-native species to decrease the vulnerability of people and ecosystems to the exacerbated fire risk that climate change is bringing due to higher temperatures and, in some places, changing rainfall patterns.

NbS, including protecting and restoring mangroves, forests and peatlands, also play an important part in reducing greenhouse gas emissions and taking carbon dioxide out of the atmosphere. They can also help people in a wide range of other ways, including through providing food, materials and opportunities for recreation. There is increasing evidence that spending time in natural surroundings is good for physical and mental health.

[[File:c1ea74c36c2df6de789d1008b368a15c IPCC_AR6_WGII_Figure_2_FAQ_2.5.1.png]]

'''Figure FAQ2.5.1 |''' '''Different NbS strategies that contribute to climate resilient development'''

If NbS are to be effective, it is important that the right adaptation actions are carried out in the right place and that local communities play an active part in making decisions about their local environment. When they are not part of the process, conflicts can emerge and benefits can be lost.

While NbS help us to adapt to climate change and reduce the amount of greenhouse gases in the atmosphere, it is important to note that there are limits to what they can do. To provide a safe environment for both people and nature, it will be essential to radically reduce greenhouse gas emissions, especially those from fossil-fuel burning in the near future.

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=== 2.6.8 Feasibility of Adaptation Options ===

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The [[#IPCC--2018a|IPCC (2018a)]] defined feasibility as ‘the degree to which climate goals and response options are considered possible and/or desirable’ ( [[#IPCC--2018b|IPCC, 2018b]] ) and set out an approach to assessing the feasibility of pathways to limit the global temperature rise to 1.5°C. [[#Singh--2020|Singh et al. (2020)]] developed this approach for adaptation, recognising six different dimensions of feasibility: economic, technological, institutional, socio-cultural, environmental/ecological and geophysical (Table 2.9). Feasibility is considered more fully in other chapters of this report, including Cross-Chapter Box FEASIB in Chapter 18. Adaptation for biodiversity conservation and EbA encompasses a large range of approaches and techniques (Sections 2.6.2, 2.6.3) and will vary in different contexts globally, as illustrated by the range of case studies ( [[#2.6.5|Section 2.6.5]] ). It is important to take into account specific regional and local circumstances as well as the type of adaptation action envisaged before making a feasibility assessment. It is also important to note that what is a feasible adaptation response at one point in time may change with the level of warming experienced—some techniques will be become less effective at higher levels of warming. With global temperature rises of &lt;2°C, in many cases, it will be realistic to build resilience and maintain species and ecosystems ''in situ'' , but, at higher levels of warming, this will become increasingly difficult; managing inevitable change, including the consequences of loss and damage, will be important ( [[#Prober--2019|Prober et al., 2019]] ). Similarly, to be effective at higher levels of warming may require the adaptation of the EbA approaches themselves ( [[#Calliari--2019|Calliari et al., 2019]] ; [[#Martín--2021|Martín et al., 2021]] ; [[#Ossola--2021|Ossola and Lin, 2021]] ). We have therefore not attempted a global-scale assessment of the feasibility of adaptation options, but rather present some key cross-cutting considerations in assessing feasibility for adaptation of and through ecosystems.

Many of the necessary techniques for climate change adaptation for biodiversity and EbA have been demonstrated and shown to provide a wide range of additional benefits. This does, however, depend on deploying the right techniques in the right place (Box 2.2) as well as engaging local communities (see [[#2.6.6|Section 2.6.6]] ). There is also a challenge where there is high demand for land for other purposes, especially for agriculture and urban development. Table 2.8 summarises the main feasibility considerations, drawing on previous sections. An assessment of constraints on EbA by Nalau et al. (2018) addressed similar issues.

'''Table 2.8 |''' Considerations in assessing the feasibility of ecosystem restoration for climate change adaptation, according to [[#Singh--2020|Singh et al. (2020)]]

{| class="wikitable"
|-
! '''Feasibility''' '''characteristics'''

! '''Feasibility indicators'''

! '''Factors relevant to ecosystem restoration'''

|-
| rowspan="4"| ''Economic''

| Micro-economic viability

| rowspan="4"| Costs are highly variable, depending on techniques and whether land purchase is required. Costs will depend on local rates for labour and materials.

Economic benefits to local communities where employment is created and where loss from extreme events are avoided ( [[#2.6.4|Section 2.6.4]] ; [[#De%20Groot--2013|De Groot et al., 2013]] ).

|-
| Macro-economic viability

|-
| Socioeconomic vulnerability reduction potential

|-
| Employment and productivity enhancement potential

|-
| rowspan="2"| ''Technological''

| Technical resource availability

| rowspan="2"| Techniques are available for restoration of most ecosystems (Sections 2.6.2; 2.6.3), although this can be very difficult to achieve in some circumstances and take a long time, e.g., the restoration of peat swamp forests ( [[#2.6.5.10|Section 2.6.5.10]] ).

Successful implementation may also require skills which are in short supply and training may be required.

|-
| Risks mitigation potential (stranded assets, unforeseen impacts)

|-
| rowspan="4"| ''Institutional''

| Political acceptability

| rowspan="4"| This will vary according to local factors. It should, however, be noted that EbA and adaptation for conservation have been implemented in a wide range of different countries (see the case studies in [[#2.6.5|Section 2.6.5]] ). In many cases, the EbA can meet multiple policy objectives but falls between different decision-makers’ responsibilities.

|-
| Legal, regulatory feasibility

|-
| Institutional capacity and administrative feasibility

|-
| Transparency and accountability potential

|-
| rowspan="5"| ''Socio-cultural''

| Social co-benefits (health, education)

| rowspan="5"| Multiple benefits to local communities are possible, but full engagement and/or leadership of the affected members of these communities has been shown to be critical. IKLK can provide important insights ( [[#2.6.6|Section 2.6.6]] ).

|-
| Socio-cultural acceptability

|-
| Social and regional inclusiveness

|-
| Benefits for gender equity

|-
| Inter-generational equity

|-
| rowspan="2"| ''Environmental/ecological''

| Ecological capacity

| rowspan="2"| It is important to assess the benefits for ecosystems in relation to other potential options. In particular, for some EbA approaches, it may be possible to achieve a range of different outcomes for biodiversity.

|-
| Adaptive capacity/potential

|-
| rowspan="3"| ''Geophysical''

| Physical feasibility

| rowspan="3"| Appropriate measures need to be designed to take account of local geophysical conditions, e.g., catchment characteristics, which define where some habitats can occur. This is also critical for ensuring the effectiveness of EbA in reducing natural hazards.

|-
| LUC enhancement potential

|-
| Hazard risk reduction potential

|}

A key element of economic feasibility is the cost of adaptation options. Costs of adaptation vary greatly depending on the actions taken, the location, the methods used, the need for ongoing maintenance and whether land purchase is necessary. At its simplest, adaptation may be a matter of taking account of actual or potential climate change impacts in the course of conservation planning and have little or no additional cost. For example, if a species of conservation concern colonises or starts to use a new area as a result of climate change, like migrant waterfowl shifting the locations where they overwinter ( [[#Pavón-Jordán--2020|Pavón-Jordán et al., 2020]] ), protection or habitat management may be redirected there. At the other extreme, large-scale restoration can incur significant costs, for example, between 1993 and 2015, the EU-LIFE nature programme invested 167.6 million Euro in 80 projects, which aim to restore over 913 km 2 of peatland habitats in Western European countries ( [[#Andersen--2017|Andersen et al., 2017]] ). This is equivalent to &lt;2% of the remaining peatland area, much of which has been affected to at least some extent by human pressures, and restoring the total affected area will cost considerably more.

[[#De%20Groot--2013|De Groot et al. (2013)]] analysed 94 restoration projects globally and found costs varied by several orders of magnitude, but in terrestrial and freshwater ecosystems mostly in the range of USD 100–10,000 per hectare. They did, however, estimate that the majority of these projects provided net benefits and should be considered as high-yield investments. Some methods can be much cheaper than others, even in the same type of ecosystems in the same country; the estimated cost of restoring forest cover in Brazil varied between a mean of USD 49 using natural regeneration compared to a mean of USD 2041 per hectare using planting ( [[#Brancalion--2019|Brancalion et al., 2019]] ). When assessing costs, it is also important to take into account the benefits delivered by different options, both in economic terms and regarding other wider benefits.

The ‘technological’ dimension of feasibility in the context of ecosystems can be regarded as the range of techniques available and the capacity to implement them. As described in Sections 2.6.2 and 2.6.3 above, a wide range of techniques have been developed and are starting to be implemented. There is good evidence to support adaptation for biodiversity and EbA in general terms and, in many cases, adaptation draws on techniques for habitat creation and restoration which have been developed to meet other objectives. However, feasibility needs to be assessed alongside the likely effectiveness: a feasible but ineffective scheme is of no value and the evaluation of success for specific interventions remains poorly developed ( [[#Morecroft--2019|Morecroft et al., 2019]] ). It is therefore often important to proceed with the use of pilot studies, good monitoring and the evaluation of outcomes to build confidence before greater deployment of approaches. A linked technical area is the availability of specialist skills and knowledge to implement adaptation; this can vary considerably according to the type of adaptation measure.

Institutional dimensions are dealt with more fully in other chapters, but in the specific context of the natural environment it is notable that EbA is relevant to a wide range of organisations and policy objectives, in addition to environmental departments, NGOs and agencies which traditionally deliver conservation. Upscaling implementation is likely to be dependent on this wider range of interests. There can, however, be problems, in that appropriate geographies for decision-making about ecosystems (e.g., a catchment) may not directly map onto governance arrangements.

Socio-cultural factors are important for adaptation of the natural environment. Reviewing the constraints of EbA, Nalau et al. (2018) found that risk perceptions and cultural preferences for particular types of management approaches were frequently identified in studies.

In the IPCC feasibility assessment framework, one integral dimension is ‘environmental/ecological’. In this respect, adaptation by and for ecosystems should perform well, and this may be a reason to prefer EbA to other approaches when there is an alternative. It should, however, be noted that sometimes apparently environmentally positive approaches such as forest creation can be done in ways which are damaging ( [[#2.6.7|Section 2.6.7]] and Box 2.2) and the impacts need to be critically assessed for local circumstances.

Geophysical dimensions are important for ecosystems as they have typically shaped which ecosystems can occur where, and feasibility will depend on implementing adaptation options in places where they are appropriate. Palaeo-ecological studies can help inform potential options ( [[#Wingard--2017|Wingard et al., 2017]] )

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'''Box 2.2 | Risks of Maladaptive Mitigation'''
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To hold global temperature rise to well below 2°C and pursue efforts to limit it to 1.5°C as required by the Paris Agreement requires major changes in land use and management. There are many opportunities for NbS, which can provide climate change mitigation and adaptation in ways that protect and restore biodiversity and provide a wide range of benefits to people (Cross-Chapter Box NATURAL in this chapter). There are also new technologies and approaches to develop the bioeconomy in ways which will provide many benefits (Cross-Working Group Box BIOECONOMY in Chapter 5). Nevertheless, renewable energy is a large and essential element of climate change mitigation and there are adverse impacts on biodiversity associated with some types of renewable energy, including wind and solar technologies ( [[#Rehbein--2020|Rehbein et al., 2020]] ). However, one of the most serious conflicts emerging is that between land-based approaches to mitigation and the protection of biodiversity, particularly as a result of afforestation strategies and potentially large areas devoted to bioenergy, including bioenergy with carbon capture and storage (BECCS). It is important to recognise the impacts of climate change mitigation at the same time as assessing the direct impacts of climate change, and ensure that adaptation and mitigation are joined up.

BECCS is an integral part of all widely accepted pathways to keeping global temperature rise to 1.5°C ( [[#IPCC--2018b|IPCC, 2018b]] ). This requires large areas of land, which can be in conflict with the need to produce food and protect biodiversity ( [[#Smith--2018|Smith et al., 2018]] ). One study examined the combined impacts of climate change and LULCC for bioenergy, and found that severe impacts on species were likely if bioenergy was a major component of strategies for climate change mitigation ( [[#Hof--2018|Hof et al., 2018]] ). A study on the potential impacts of bioenergy production and climate change on European birds found that one scenario for land conversion for bioenergy to meet a 2°C target would have less impact on species range loss than a global temperature increase of 4°C, but noted that if bioenergy were the only mitigation option it would 'very likely result in the negative effects of bioenergy outweighing the positive effects' ( [[#Meller--2015|Meller et al., 2015]] ). To avoid the worst impacts of BECCS, it will need to be carefully targeted according to context and local conditions, and other mitigation strategies prioritised so that its use can be minimised ( [[#IPCC--2019a|IPCC, 2019a]] ; [[#Ohashi--2019|Ohashi et al., 2019]] ).

Reforestation of previously forested areas can bring multiple benefits, but planting trees in places where they do not naturally grow can have serious environmental impacts, including potentially exacerbating the effects of climate change. Savannas are amongst the ecosystems at risk from afforestation programmes. Savannas are grass-dominated, high-diversity ecosystems with endemic species adapted to high-light environments, herbivory and fire ( [[#Staver--2011|Staver et al., 2011]] ; [[#Murphy--2016|Murphy et al., 2016]] ). Interactions between climate change, elevated CO 2 and the disruption of natural disturbance regimes have led to the widespread encroachment of woody plants ( [[#Stevens--2016|Stevens et al., 2016]] ), causing a fundamental shift in ecosystem structure and function with loss of grass and reduced fire frequency ( [[#Archibald--2009|Archibald et al., 2009]] ) and stream flow ( [[#Honda--2016|Honda and Durigan, 2016]] ) (Sections 2.4.3.5, 2.5.2.5, Box 2.1, 2.5.4, TAble 2.5, Figure 2.11). Afforestation exacerbates this degradation ( [[#Bremer--2010|Bremer and Farley, 2010]] ; [[#Veldman--2015|Veldman et al., 2015]] ; [[#Abreu--2017|Abreu et al., 2017]] ). Global-scale analyses aimed at identifying degraded forest areas suitable for reforestation ( [[#Veldman--2019|Veldman et al., 2019]] ) cannot reliably separate naturally grassy ecosystems with sparse tree cover from degraded forests, so local information is essential to ensure tree planting is targeted where it can benefit most and avoid harm. Figure Box 2.2.1 indicates where these issues are most likely to arise.

[[File:aacd2bdfbf1968820cea7b7d587c76f6 IPCC_AR6_WGII_Figure_2_Box_2_2_1.png]]

'''Figure Box 2.2.1 |''' '''Regions where savannas are at potential risk from afforestation.''' Based on ( [[#Veldman--2015|Veldman et al., 2015]] )

A similar issue can occur in naturally treeless peatlands which can be afforested if they are drained, but this leads to the loss of distinctive peatland species and communities as well as high GHG emissions ( [[#Wilson--2014|Wilson et al., 2014]] ). The mitigation benefits of growing timber are reduced or become negative in these conditions due to the CO 2 emissions from the oxidation of the drained peat—they can become a net carbon source rather than a carbon sink ( [[#Simola--2012|Simola et al., 2012]] ; [[#Crump--2017|Crump, 2017]] ; [[#Goldstein--2020|Goldstein et al., 2020]] ) ''.'' (Sections 2.4.3.8, 2.5.2.8)

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=== FAQ 2.6 | Can tree planting tackle climate change? ===

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''Restoring and preventing further loss of native forests is essential for combatting climate change. Planting trees in historically unforested areas (grasslands, shrublands, savannas and some peatlands) can reduce biodiversity and increase the risks of damage from climate change. It is therefore essential to target tree planting to the appropriate locations and use appropriate species. Restoring and protecting forests reduces human vulnerability to climate change, reduces air pollution, stores carbon and builds the resilience of natural systems.''

Like all living plants, trees remove carbon dioxide from the atmosphere through the process of photosynthesis. In trees, this carbon uptake is relatively long-term, since much of it is stored in the trees’ woody stems and roots. Therefore, tree planting can be a valuable contribution to reducing climate change. Besides capturing carbon, planting trees can reduce some negative impacts of climate change by providing shade and cooling. It can also help prevent erosion and reduce flood risk by slowing water flow and improving ground water storage. Restoring forest in degraded areas supports biodiversity and can provide benefits to people, ranging from timber to food and recreation.

There are some areas where replacing lost trees is useful. These include forest that has been recently cut down and where reforestation is usually practical. However, it is very important to correctly identify areas of forest that are degraded or have definitely been deforested. Reforesting places, especially where existing native forest patches occur, brings benefits both in sucking up carbon from the atmosphere and helping us to adapt to climate change. Plantations of a non-native species, although offering some economic benefits, do not usually provide the same range of positive impacts, generally have lower biodiversity, reduced carbon uptake and storage, and are less resilient to climate change.

Reforestation options include the natural regeneration of the forest, assisted restoration, enrichment planting, native-tree plantations, commercial plantations and directed tree planting in agro-forestry systems and urban areas. Reforestation with native species usually contributes to a wide range of sustainability goals, including biodiversity recovery, improved water filtration and groundwater recharge. It can reduce the risks of soil erosion and floods. In cities, planting trees can support climate change adaptation by reducing the heat of the area, and promote a wide range of social benefits such as providing shade and benefitting outdoor recreation. Urban trees can also lower energy costs by reducing the demand for conventional sources of cooling like air-conditioning, especially during peak-demand periods. It is therefore important to recognise that there are a wide range of different planting and forest management strategies. The choice will depend on the objectives and the location.

'''Not everywhere''' is suitable for tree planting. It is particularly problematic in native non-forested ecosystems. These natural ecosystems are not deforested and degraded but are instead naturally occurring non-forested ecosystems. These areas vary from open grasslands to densely wooded savannas and shrublands. Here, restoring the natural ecosystems instead of afforesting them will better contribute to increasing carbon storage and increasing the area’s resilience to climate change and other environmental changes. It is important to remember that, just because a tree can grow somewhere, it does not mean that it should. These systems are very important in their own right, storing carbon in soils, supporting rich biodiversity and providing people with important ecosystem services such as grasslands for animal grazing. Planting trees in these areas destroys the ecosystem and threatens the biodiversity which is adapted to these environments. They can also impact on ecosystem services such as forage for livestock, on which many people rely.

Many of these open areas also occur in low-rainfall areas. Planting trees there uses a lot of water and can cause reductions in stream flow and groundwater. Many of these locations also burn regularly, and planting trees threatens the establishing trees but can also increase the intensity of the fires from that of a grass-fuelled fire to that of a wood-fuelled fire. Swapping grassy ecosystems for forests may contribute to warming, as forests absorb more incoming radiation (warmth) than grasslands. Aside from the negative impacts to adaptation, it is also questionable just how much carbon can be sequestered in these landscapes as planting trees in grassy ecosystems can reduce carbon gains. Furthermore, a high below-ground carbon store prevents carbon loss to fire in these fire-prone environments.

Another example is peatlands. Peat stores an incredible amount of carbon; maintaining and restoring peatlands is therefore important to reduce atmospheric carbon. However, the restoration actions depend on what type of peatland it is and where it is located. Many temperate and boreal peatlands are naturally treeless. Here, planting trees is often only possible following drainage, but draining and planting (especially of non-native species) destroys native biodiversity and releases GHGs. Many peatlands, especially in the Tropics, are naturally forested, and restoring them requires re-wetting and restoring the natural tree cover (see Figure FAQ2.2.1) which will increase carbon storage.

There are actions we can perform instead of planting trees in non-forested ecosystems, and these include:

* Address the causes of deforestation, forest degradation and widespread ecosystem loss
* Reduce carbon emissions from fossil fuels
* Focus on ecosystem restoration over tree planting. For example, in restoring tropical grassy ecosystems, we can look at actions that cut down trees, enhance grass regrowth and restore natural fire regimes. We then have a much better chance of both enhancing carbon capture and reducing some of the harmful effects of climate change.

In between the two extremes of where planting trees is highly suitable and areas where it is not, it is important to remember that the context matters and that decisions to (re)forest should look beyond simply the act of planting trees. We can consider '''what the ecological, social and economic goals are of tree planting''' . It is then important to verify the local context and decide '''what restoration action will be most effective''' . It is also more efficient and effective to conserve existing forests before worrying about reforesting.

[[File:c5db988068a9cc52222c375bc2e9765d IPCC_AR6_WGII_Figure_2_FAQ_2.6.1.png]]

'''Figure FAQ2.6.1 |''' '''Some places are more appropriate for tree planting than others and caution needs to be applied when planting in different biomes, with some biomes being more suitable than others.''' This figure highlights some basic biome-specific guidelines when planting in natural and semi-natural vegetation.

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