Editing IPCC:AR6/WGII/Cross-Chapter-Paper-1 (section)

== CCP1.3 Adaptation and Solutions ==

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Terrestrial, freshwater and coastal marine ecosystems are impacted by the 3 billion people that currently live in in biodiversity hotspots (Gutiérrez et al., 2021). At the same time, biodiversity in hotspots supports the livelihoods of the local communities. The suite of adaptation options for biodiversity are as applicable inside as outside hotspots (Table CCP1.2). Many of these hotspots are now faced with widespread fragmentation and habitat degradation ( ''high confidence'' ) (Table SMCCP1.1).

Because projected changes in biodiversity increase disproportionately with warming, climate change mitigation is the primary action to conserve biodiversity within hotspots. If global warming is kept within the 1.5°C limit of the Paris Agreement, just ~4% of endemic species in biodiversity hotspots would be threatened with extinction from climate change. However, at the current commitments there is projected to be ~3°C warming by 2100 and ~20% and ~32% for terrestrial and marine species, respectively, fall into the category of very high extinction risk (Figure CCP1.6; [[#Manes--2021|Manes et al., 2021]] ).

Although mitigation can sharply reduce extinction risk associated with climate change ( ''high confidence'' ), it cannot reduce all of the risk, nor the risk associated with other drivers that can have a compound effect with climate change. Thus, in addition to mitigation, the literature consistently calls for reducing current non-climate impacts (e.g., habitat conversion, over-exploitation, hunting, fishing, wildfire, pollution, human-introduced invasive species) in order to increase biodiversity resilience to climate change ( ''very high confidence'' ) (Table CCP1.2; e.g., [[#Mantyka-Pringle--2015|Mantyka-Pringle et al., 2015]] ; [[#Warren--2018a|Warren et al., 2018a]] ; [[#Costello--2021|Costello, 2021]] ). The main strategies to increase resilience rely on the combination of well-planned protected areas, restoration of degraded areas and the sustainable use of biodiversity ( ''high confidence'' ) ( [[#IPCC--2019a|IPCC, 2019a]] ; [[#Pörtner--2021|Pörtner et al., 2021]] ) . On land, creating corridors for species is key for facilitating species movements ( ''high confidence'' ) ( [[#McGuire--2016|McGuire et al., 2016]] ; [[#Heikkinen--2020|Heikkinen et al., 2020]] ; [[#Pörtner--2021|Pörtner et al., 2021]] ). Habitat protection has numerous co-benefits, including potential climate mitigation through carbon storage and sequestration, in addition to climatic regulation ( [[#Alkama--2016|Alkama and Cescatti, 2016]] ; [[#Mackey--2020|Mackey et al., 2020]] ) and pandemic prevention ( [[#Allen--2017|Allen et al., 2017]] ; [[#Dobson--2020|Dobson et al., 2020]] , Cross-Chapter Box COVID-19 in Chapter 7).

Active relocation of endangered species to areas where they may be safer from predation and human impacts, as already practised for a few charismatic fauna, is expensive and fraught with complex regulations and concerns over impacts on native species ( [[#Brodie--2021|Brodie et al., 2021]] ). Therefore, managed relocation of species threatened by climate change is questionable for most species.

Healthier marine ecosystems are more resilient to additional stressors, such as storms and climate change ( ''high confidence'' ) ( [[#Isbell--2015|Isbell et al., 2015]] ; [[#Duffy--2016|Duffy et al., 2016]] ; [[#Roberts--2017|Roberts et al., 2017]] ; [[#Bates--2019|Bates et al., 2019]] ; [[#Mariani--2020|Mariani et al., 2020]] ; [[#Costello--2021|Costello, 2021]] ; [[#Donovan--2021|Donovan et al., 2021]] ). Extinction risk is lower when populations are larger and more genetically diverse, individuals are larger and older, and seabed habitats (e.g., coral, kelp, seagrass) are flourishing, as occurs in marine reserves ( ''high confidence'' ) ( [[#Costello--2014|Costello, 2014]] ; [[#Roberts--2017|Roberts et al., 2017]] ; [[#Bates--2019|Bates et al., 2019]] ; [[#Costello--2021|Costello, 2021]] ). Similarly, global fish biomass may be less affected by climate change if biodiversity is greater ( [[#Duffy--2016|Duffy et al., 2016]] ). Thus, a network of reserves representative of global biodiversity, helps attenuate the effects of climate change ( ''medium confidence'' ), for example, by having more abundant fish and top predator populations ( [[#Roberts--2017|Roberts et al., 2017]] ; [[#Beyer--2018|Beyer et al., 2018]] ; [[#Carter--2020|Carter et al., 2020]] ; [[#Sala--2021|Sala et al., 2021]] ). However, the impacts of marine heatwaves on corals across marine reserves illustrates that enhanced resilience is not enough to protect against extreme and future climate change conditions ( ''high confidence'' ) ( [[#Bruno--2018|Bruno et al., 2018]] ; [[#Hughes--2018a|Hughes et al., 2018a]] ; [[#Kleypas--2021|Kleypas et al., 2021]] ).

Mangroves occupy the interface of terrestrial, freshwater and marine environments, dominate in eight hotspots (Table CCP1.1) and are connected to or integral habitats within one-third of all terrestrial and freshwater, and two-thirds of marine, hotspots (Figures CCP1.1; CCP1.2). A global analysis of sediment cores from mangroves indicated that mangroves can accrete sediment at levels of sea level rise projected under low emission scenarios, but may decline at their seaward edge under high emission scenarios ( [[#Saintilan--2020|Saintilan et al., 2020]] , Chapter 3.4.2, Cross-Chapter Box Sea-level rise). However, even if this seaward erosion occurs, the expansion of mangroves inland due to sea level rise will increase carbon sequestration, because they capture carbon from seawater and freshwater runoff, in addition to photosynthesis, into their underlying sediments. If coastal management permits the expansion of mangroves inland with rising sea level, this will increase carbon sequestration because mangroves capture and preserve more carbon in their sediments than other terrestrial and marine forests and biomes ( ''high confidence'' ) (Table CCP1.2; [[#Alongi--2020|Alongi, 2020]] ; [[#Goldstein--2020|Goldstein et al., 2020]] ; [[#Lovelock--2020|Lovelock and Reef, 2020]] ; [[#Saintilan--2020|Saintilan et al., 2020]] ).

On land, fragmentation and habitat degradation are particularly pervasive, imposing hard limits to adaptation of terrestrial and freshwater ecosystems ( [[#Ibisch--2016|Ibisch et al., 2016]] ; [[#Lenoir--2020|Lenoir et al., 2020]] ; [[#Mechler--2020|Mechler et al., 2020]] ). Thus, the protection of existing natural habitats coupled with the restoration of the surrounding non-protected habitat can increase the effectiveness of adaptation strategies in terrestrial and freshwater hotspots ( ''very high confidence'' ) (Table CCP1.2; [[#IPCC--2019a|IPCC, 2019a]] ; [[#Jung--2021|Jung et al., 2021]] ). Additionally, strategic allocation of new protected areas within gaps across elevational and climatic gradients could enhance biodiversity conservation across hotspots. This would align with Target 3 of the Convention on Biological Diversity’s post-2020 draft Global Biodiversity Framework, and could include underrepresented climate and elevation spaces as well as potential climate refugia currently not under protection ( [[#Pörtner--2021|Pörtner et al., 2021]] ). In terrestrial ecosystems, restoration initiatives can help sustain biodiversity, improve resilience in a changing climate, and avoid maladaptation by selecting appropriate native species to be planted (Cross-Chapter Box Bioeconomy in Chapter 5; ( [[#Gann--2019|Gann et al., 2019]] ). In freshwater ecosystems, conservation needs catchment level management of human activities ( [[#Saunders--2002|Saunders et al., 2002]] ; [[#Dudgeon--2006|Dudgeon et al., 2006]] ), especially as 37% of the terrestrial biodiversity hotspots overlap with freshwater (Figure CCP1.2) and 23% border marine hotspots ( [[#Olson--2002|Olson and Dinerstein, 2002]] ).

Protecting biodiversity hotspots is a pragmatic way to conserve biodiversity that is representative of a substantive fraction of genetic and species diversity on Earth ( [[#Mittermeier--2011|Mittermeier et al., 2011]] ) while achieving co-benefits ( [[#Bonan--2016|Bonan, 2016]] ; [[#Sala--2021|Sala et al., 2021]] ). Protecting hotspots also helps protect important ecosystem services. In a global ranking of areas that combine biodiversity conservation while maximising carbon retention and water quality regulation, for example, the terrestrial and freshwater hotspots assessed here ranked high (41st and 34th on average, respectively, on a scale of 100) ( [[#Jung--2021|Jung et al., 2021]] ). The solutions needed to reverse biodiversity decline are well known and articulated in numerous international agreements and goals, such as the Convention of Biological Diversity the United Nations’ Sustainable Development Goals, the Nationally Determined Contributions under the Paris Agreement, the International Union for Nature Conservation’s Bonn Restoration Challenge and the Ramsar Convention on Wetland Conservation. Thus, expanding and enhancing protection of a worldwide network of fully protected areas and protection and restoration of non-protected areas representative of the biodiversity hotspots, including marine, freshwater and terrestrial environments, is a highly recommended adaptation strategy to increase resilience of biodiversity to climate change ( [[#Brito-Morales--2018|Brito-Morales et al., 2018]] ). However, adaptation strategies alone cannot protect biodiversity from climate impacts without complementary and concomitant reduction of greenhouse gas emissions.

'''Table CCP1.2 |''' Examples of adaptation actions that benefit the conservation of biodiversity and climate change mitigation.

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

! '''Terrestrial'''

! '''Freshwater'''

! '''Marine'''

|-
| rowspan="2"| '''Protect biodiversity hotspots'''

| Protect native forests, bush and grasslands

| Stop pollution and sedimentation into streams, rivers, ponds and lakes

| Ban seabed trawling and dredging

|-
| colspan="3"| Control introduction and spread of invasive species and pests

|-
| rowspan="2"| '''Increase connectivity'''

| colspan="2"| Use riverbank and hedgerow corridors to connect protected native habitats

| Already connected

|-
| colspan="3"| Reduce habitat and species loss outside protected areas to add species dispersal (corridors)

|-
| '''Outside biodiversity hotspots'''

| colspan="2"| Environmentally sustainable agriculture, tourism and other land and freshwater uses

| Environmentally sustainable aquaculture, fisheries and tourism

|-
| rowspan="2"| '''Restoration and recovery'''

| Actively rehabilitate old mines, quarries and industrial lands

| Stabilise riverbanks Remove weirs and artificial barriers to fish migration

| rowspan="2"| Ban removal of marine life and habitat and fishing in selected areas to allow passive recovery of habitats, natural population structure, and food webs

|-
| colspan="2"| Reintroduce extirpated native species

|-
| '''Reduce erosion, soil loss and flooding'''

| colspan="3"| Preserve, reduce degradation and restore habitats to enable uplands to absorb rainfall and reduce flash floods

Protect sand-dune systems from erosion due to human and farm animal trampling

Set aside land for salt marshes and mangroves to buffer against river and seawater flooding

Link estuarine and upriver protected areas to provide more wildlife habitat and absorb storm surges and floods

|-
| '''Urban development'''

| Concentrate development to more cost efficiently manage transport and waste management infrastructure

| Limit upland development where it may affect freshwater quality

| Avoid construction in areas at risk of sea level rise and associated storm surges

|-
| '''Greenhouse gas mitigation'''

| Prevent deforestation

Reforestation (especially mangroves)

Revegetation

Fewer farm mammals

Minimise release of greenhouse gases from soils

| Expand wetlands to capture and deposit carbon in soils

| Limit seabed disturbance by trawling and dredging that releases CO 2 and CH 4

Eliminate fishery subsidies and remove tax breaks on fuel for fishing boats

|-
| rowspan="2"| '''Carbon sequestration and preservation'''

| colspan="3"| Allow plants and other organisms to flourish and capture CO 2 from the air and water, and sequester it in biomass, soils and sediments

|-
| Manage forestry to maximise ''in situ'' food web biomass

| colspan="2"| Manage fisheries to maximise ''in situ'' food web biomass

|-
| '''Social'''

| colspan="3"| Communicate information on the benefits of adaptation measures to the public

|-
| '''Political and economic'''

| colspan="3"| Provide leadership and governance of mitigation and adaptation measures, including through regulations and economic incentives that guide the transition to a low carbon emissions economy

|-
| rowspan="2"| '''Scientific'''

| colspan="3"| Address data gaps and make monitoring data and its meaning rapidly available to society so that the public and policy makers are informed of trends in biodiversity and related factors, including climate variables, extreme weather related events, threatened and invasive species, natural habitats, and their relationships

|-
| colspan="3"| Conduct research to improve understanding of cause-effect relationships regarding environmental factors and biodiversity trends, including in nature conservation, forestry, agriculture, fisheries and food production sectors, and improve projections of consequences of management action and inaction

|}

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=== Box CCP1.1 | Climate change and terrestrial biodiversity hotspots on small islands ===

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Despite covering approximately 2% of the Earth’s land area, islands harbour more than 20% of extant terrestrial species ( [[#Wetzel--2013|Wetzel et al., 2013]] ). Islands have disproportionately higher rates of endemism and threat when compared to continents, with 80% of historical extinctions (since 1500 CE) having occurred on islands ( ''high confidence'' ) ( [[#Taylor--2016|Taylor and Kumar, 2016]] ; [[#Spatz--2017|Spatz et al., 2017]] ; [[#Dueñas--2021|Dueñas et al., 2021]] ). Current climate change projections suggest that insular species are particularly sensitive and, even at mild warming levels, substantial losses are expected ( ''high confidence'' ) ( [[#Pouteau--2016|Pouteau and Birnbaum, 2016]] ; [[#Taylor--2016|Taylor and Kumar, 2016]] ; [[#Dawson--2017|Dawson et al., 2017]] ; [[#Manes--2021|Manes et al., 2021]] ). Given islands’ characteristic high endemicity, current high threat levels and the fact that islands host almost half of all species currently considered to be at risk of extinction, especially at higher warming levels ( ''high confidence'' ) ( [[#Taylor--2016|Taylor and Kumar, 2016]] ; [[#Spatz--2017|Spatz et al., 2017]] ), further losses could contribute disproportionately to global biodiversity decline ( ''medium evidence, high agreement'' ) ( [[#Harter--2015|Harter et al., 2015]] ; [[#Pouteau--2016|Pouteau and Birnbaum, 2016]] ; [[#Manes--2021|Manes et al., 2021]] ).

The high vulnerability of terrestrial biodiversity on islands to global change can be explained by a number of limitations, characteristic of both islands and insular species. Older, isolated islands tend to have fewer species and lower functional redundancy but a higher proportion of endemism ( [[#Pouteau--2016|Pouteau and Birnbaum, 2016]] ; [[#Médail--2017|Médail, 2017]] ). Many of these islands contain species with inherently high sensitivity to environmental change (narrow habitat ranges, small population sizes, low genetic diversity and poor adaptive, dispersal and defensive capabilities) ( [[#Harter--2015|Harter et al., 2015]] ). Unlike continental environments, insular species often have limited opportunities for autonomous adaptation from not having enough geographic space to shift their ranges to track suitable climatic conditions ( ''high confidence'' ) ( [[#Fortini--2015|Fortini et al., 2015]] ; [[#Manes--2021|Manes et al., 2021]] ). Local extinction risks are amplified by even small losses of habitat due to global change including human-induced disturbances, extreme events, sea level rise (Chapter 15; Cross-Chapter Box SLR in Chapter 3) and invasive species.

However, some insular species have shown resilience to climate change. Intact island forests, for example, have shown rapid recovery rates after tropical cyclones, despite high levels of initial damage, especially in the Caribbean ( ''medium confidence'' ) ( [[#Luke--2016|Luke et al., 2016]] ; [[#Richardson--2018|Richardson et al., 2018]] ). Additionally, many Mediterranean islands are ‘disturbance adapted’, with continued persistence of some single-island endemic plants, despite exposure to multiple threats ( [[#Vogiatzakis--2016|Vogiatzakis et al., 2016]] ). This continued persistence has been attributed, at least partially, to climate refugia, oceanic buffering and high habitat heterogeneity within topographically complex mountainous regions ( [[#Pouteau--2016|Pouteau and Birnbaum, 2016]] ; [[#Médail--2017|Médail, 2017]] , Chapter 15, Table 15.1). However, this climate resilience will not be sustained under climate change, especially when coupled with habitat degradation ( ''high confidence'' ) ( [[#Wiens--2016|Wiens, 2016]] ).

Adaptation strategies depend on the ability to project future impacts from climate change, but this is hampered by lack of fine-scale climate data, especially for developing small island nations. There is a paucity of robust impacts-based modelling output for terrestrial biodiversity from these islands due to the wide, chronic unavailability of Regional Climate Model (RCM) data premised on the most recent suite of scenarios (RCPs and especially SSPs) ''(medium evidence'' , ''high agreement'' ) (Gutiérrez et al., 2021, Ch.15.8; [[#Pörtner--2021|Pörtner et al., 2021]] ; [[#WMO--2021|WMO, 2021]] ). Additionally, realistic assessments of changing climate on such small ecosystems require further RCM downscaling and verification to sub-island resolutions of &lt;5 km. Furthermore, widely used statistically (bias-corrected) downscaled data at sub-5 km resolutions, such as WorldClim are often unsuitable due to limited spatial and temporal resolutions of observation station data from small islands ( [[#Maharaj--2013|Maharaj and New, 2013]] ; Gutiérrez et al., 2021) and higher errors associated with statistical downscaling and locations with complex topography and coastlines ( [[#Fick--2017|Fick and Hijmans, 2017]] ; [[#Lanzante--2018|Lanzante et al., 2018]] ). Widespread unavailability of such data constrains accurate simulations of climatic variation within the small-scale mountainous and coastal regions of islands, associated with climate refugia and high habitat heterogeneity ( ''high confidence'' ) ( [[#Balzan--2018|Balzan et al., 2018]] ). This is a key element contributing to the continued delay in development of robust adaptation strategies towards not only biodiversity conservation but other important cross-sectoral issues ( ''medium confidence'' ) ( [[#Robinson--2020b|Robinson, 2020b]] ).

Due to islands’ limited size and isolation, conventional conservation measures focused on expanding protected areas, dispersal corridors and buffer zones are of limited effectiveness on islands ( ''high confidence'' ) ( [[#Vogiatzakis--2016|Vogiatzakis et al., 2016]] ). Instead, multifaceted, locally driven holistic climate-smart strategies across mosaics of human-impacted, often heavily degraded and fragmented, landscapes are required. These should ideally be long-term, flexible and sustainable solutions that incorporate social and biocultural knowledge as well as economic co-benefits to island communities in order to ‘buy time’ ( [[#Betzold--2015|Betzold, 2015]] ; [[#Robinson--2020a|Robinson, 2020a]] ). Examples include ecosystem-based approaches such as ridge-to-reef management ( [[#Struebig--2015|Struebig et al., 2015]] ; [[#Ferreira--2019|Ferreira et al., 2019]] , Figure CCP1.1 5.4), which incorporates conservation partnerships among lands inside and outside protected areas to increase connectivity and reduce land use impacts, while building on the interconnections among terrestrial, freshwater, coastal and marine ecosystems. Such strategies require raising awareness of biodiversity values among local communities, and cross-sectoral planning and policy at both island, regional and trans-boundary scales. These lend to private–public partnerships, increasing the potential of solutions reaching beyond protected areas boundaries and affecting socio-political change ( ''high confidence'' ) ( [[#Scobie--2016|Scobie, 2016]] ).

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Box CCP1.1

Limited terrain, natural, economic and data resources across small developing nation islands mean that unconstrained habitat destruction and degradation cannot be sustained, as this harms both people and the biodiversity upon which they depend. This limitation of resources compromises climate adaptation, which is often further complicated by varying governance and states of economic development ( [[#Petzold--2019|Petzold and Magnan, 2019]] ). With changing climate conditions, there is an increased urgency to re-think how progress can be measured, and to create opportunities building on synergies between disaster risk reduction, food security and social justice, so that islands can most benefit from their natural resources and biodiversity in a sustained manner (Box 15.2; [[IPCC:Wg2:Chapter:Chapter-15#15.3.4.4|Section 15.3.4.4]] ).

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