Editing IPCC:AR6/WGIII/Chapter-7 (section)

=== Box 7.2 | Climate-smart Forestry in Europe ===

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'''Summary'''

European forests have been regarded as prospering and increasing for the last five decades. However, these views also changed recently. Climate change is putting a large pressure on mono species and high stocked areas of Norway spruce in Central Europe ( [[#Hlásny--2021|Hlásny et al. 2021]] ; [[#Senf--2021|Senf and Seidl 2021]] ) with estimates of mortality reaching 200 million m 3 , biodiversity under pressure, the Mediterranean area showing a weak sector and harvesting pressure in the Baltics and north reaching maxima achievable. A European strategy for unlocking the EU’s forests and forest sector potential was needed at the time of developing the LULUCF regulation and was based on the concept of ‘climate-smart forestry’ (CSF) ( [[#Nabuurs--2017|Nabuurs et al. 2017]] ; [[#Verkerk--2020|Verkerk et al. 2020]] ).

'''Background'''

The idea behind CSF is that it considers the whole value chain from forest to wood products and energy, illustrating that a wide range of measures can be applied to provide positive incentives for more firmly integrating climate objectives into the forest and forest sector framework. CSF is more than just storing carbon in forest ecosystems; it builds upon three main objectives; (i) reducing and/or removing GHG emissions; (ii) adapting and building diverse forests for forest resilience to climate change; and (iii) sustainably increasing forest productivity and incomes. These three CSF objectives can be achieved by tailoring policy measures and actions to regional circumstances in member states’ forest sectors.

Box 7.2

'''Case description'''

The 2015 annual mitigation effect of EU-28 forests via contributions to the forest sink, material substitution and energy substitution is estimated at 569 MtCO 2 yr –1 , or 13% of total current EU emissions. With the right set of incentives in place at EU and member states levels, it was found that the EU-28 has the potential to achieve an additional combined mitigation impact through the implementation of CSF of 441 MtCO 2 yr –1 by 2050. Also, with the Green Deal and its biodiversity and forest strategy, more emphasis will be placed on forests, forest management and the provision of renewables. It is the diversity of measures (from strict reserves to more intensively managed systems while adapting the resource) that will determine the success. Only with co-benefits in, for example, nature conservation, soil protection, and provision of renewables, wood for buildings and income, the mitigation and adaptation measures will be successful.

'''Interactions, limitati''' '''ons and lessons'''

Climate-smart forestry is now taking shape across Europe with various research and implementation projects ( [[#Climate%20Smart%20Forest%20and%20Nature%20Management--2021|Climate Smart Forest and Nature Management, 2021]] ). Pilots and projects are being implemented by a variety of forest owners, some with more attention on biodiversity and adaptation, some with more attention on production functions. They establish examples and in longer term the outreach to the 16 million private owners in Europe. However, the right triggers and incentives are often still lacking. For example, adapting the spruce forest areas in Central Europe to climate change requires knowledge about different species, biodiversity and different management options and eventually use in industry. It requires alternative species to be available from the nurseries, as well as improved monitoring to assess the success and steer activities.

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==== 7.4.2.4 Fire Management (Forest and Grassland/Savanna Fires) ====

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'''Activities, co-benefits, risks and implementation opportunities and barriers.''' Fire management objectives include safeguarding life, property, and resources through the prevention, detection, control, restriction, and management of fire for diverse purposes in natural ecosystems (SRCCL, Chapter 6). Controlled burning is an effective economic method of reducing fire danger and stimulating natural regeneration. Co-benefits of fire management include reduced air pollution compared to much larger, uncontrolled fires, prevention of soil erosion and land degradation, biodiversity conservation in rangelands, and improvement of forage quality ( [[#Hurteau--2011|Hurteau and Brooks 2011]] ; [[#Falk--2017|Falk 2017]] ; [[#Hurteau--2019|Hurteau et al. 2019]] ). Fire management is still challenging because it is not only fire suppression at times of fire, but especially proper natural resource management in between fire events. Furthermore, it is challenging because of legal and policy issues, equity and rights concerns, governance, capacity, and research needs ( [[#Wiedinmyer--2010|Wiedinmyer and Hurteau 2010]] ; [[#Goldammer--2016|Goldammer 2016]] ; [[#Russell-Smith--2017|Russell-Smith et al. 2017]] ). It will increasingly be needed under future enhanced climate change.

'''Conclusions from AR5 and IPCC Special Reports (SR1.5, SROCC and SRCCL); mitigation potential, costs, and pathways.''' In the SRCCL, fire management is among the nine options that can deliver medium-to-large benefits across multiple land challenges (climate change mitigation, adaptation, desertification, land degradation, and food security) ( ''high confidence'' ). Total emissions from fires have been on the order of 8.1 GtCO 2 -eq yr –1 in terms of gross biomass loss for the period 1997–2016 (SRCCL, Chapter 2, and Cross-Chapter Box 3 in Chapter 2). Reduction in fire CO 2 emissions was calculated to enhance land carbon sink by 0.48 GtCO 2 -eq yr –1 for the 1960–2009 period ( [[#Arora--2018|Arora and Melton 2018]] ) (SRCCL, Table 6.16).

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===== Developments since AR5 and IPCC Special Reports (SR1.5, SROCC and SRCCL) =====

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'''Savannas.''' Savannas constitute one of the most fire-prone vegetation types on Earth and are a significant source of GHG emissions. Savanna fires contributed 62% (4.92 PgCO 2 -eq yr –1) ) of gross global mean fire emissions between 1997 and 2016. Regrowth from vegetation postfire sequesters the CO 2 released into the atmosphere, but not the CH 4 and N 2 O emissions which contributed an approximate net of 2.1 PgCO 2 -eq yr −1 ( [[#Lipsett-Moore--2018|Lipsett-Moore et al. 2018]] ). Therefore, implementing prescribed burning with low intensity fires, principally in the early dry season, to effectively manage the risk of wildfires occurring in the late dry season is associated with reducing emissions ( [[#Whitehead--2014|Whitehead et al. 2014]] ). Considering this fire management practice, estimates of global opportunities for emissions reductions were estimated at 69.1 MtCO 2 -eq yr −1 in Africa (29 countries, with 20 least developed African countries accounting for 74% of the mitigation potential), 13.3 MtCO 2 -eq yr −1 in South America (six countries), and 6.9 MtCO 2 -eq yr –1 in Australia and Papua New Guinea ( [[#Lipsett-Moore--2018|Lipsett-Moore et al. 2018]] ). In Australia, savanna burning emissions abatement methodologies have been available since 2012, and abatement has exceeded 9.3 MtCO 2 -eq mainly through the management of low intensity early dry season fire. Until September 2021, 78 projects were registered (Australian Government, Clean Energy Regulator, 2021).

'''Forests.''' Fire is also a prevalent forest disturbance ( [[#Falk--2011|Falk et al. 2011]] ; [[#Scott--2014|Scott et al. 2014]] ; [[#Andela--2019|Andela et al. 2019]] ). About 98 Mha of forest were affected by fire in 2015, affecting about 4% of the tropical (dry) forests, 2% of the subtropical forests, and 1% of temperate and boreal forests ( [[#FAO--2020a|FAO 2020a]] ). Between 2001–2018, remote sensing data showed that tree-covered areas correspond to about 29% of the total area burned by wildfires, most in Africa. Prescribed fires are also applied routinely in forests worldwide for fuel reduction and ecological reasons ( [[#Kalies--2016|Kalies and Yocom Kent 2016]] ). Fire resilience is increasingly managed in Southwestern USA forest landscapes, which have experienced droughts and widespread, high-severity wildfires ( [[#Keeley--2019|Keeley et al. 2019]] ). In these forests, fire exclusion management, coupled with a warming climate, has led to increasingly severe wildfires ( [[#Hurteau--2014|Hurteau et al. 2014]] ). However, the impacts of prescribed fires in forests in reducing carbon emissions are still inconclusive. Some positive impacts of prescribed fires are associated with other fuel reduction techniques ( [[#Loudermilk--2017|Loudermilk et al. 2017]] ; [[#Flanagan--2019|Flanagan et al. 2019]] ; [[#Stephens--2020|Stephens et al. 2020]] ), leading to maintaining carbon stocks and reducing carbon emissions in the future where extreme fire weather events are more frequent ( [[#Krofcheck--2018|Krofcheck et al. 2018]] , 2019; [[#Hurteau--2019|Hurteau et al. 2019]] ; [[#Bowman--2020a|Bowman et al. 2020a]] ,b; [[#Goodwin--2020|Goodwin et al. 2020]] ). Land management approaches will certainly need to consider the new climatic conditions (e.g., the proportion of days in fire seasons with the potential for unmanageable fires more than doubling in some regions in northern and eastern boreal forest) ( [[#Wotton--2017|Wotton et al. 2017]] ).

'''Critical assessment and conclusion.''' There is ''low confidence'' that the global technical mitigation potential for grassland and savanna fire management by 2050 is 0.1 (0.09–0.1) GtCO 2 yr –1 , and the economic mitigation potential (&lt;USD100 tCO 2 –1 ) is 0.05 (0.03–0.07) GtCO 2 yr –1 . Savanna fires produce significant emissions globally, but prescribed fires in the early dry season could mitigate emissions in different regions, particularly Africa. Evidence is less clear for fire management of forests, with the contribution of GHG mitigation depending on many factors that affect the carbon balance (e.g., [[#Simmonds--2021|Simmonds et al. 2021]] ). Although prescribed burning is promoted to reduce uncontrolled wildfires in forests, the benefits for the management of carbon stocks are unclear, with different studies reporting varying results especially concerning its long-term effectiveness ( [[#Wotton--2017|Wotton et al. 2017]] ; [[#Bowman--2020b|Bowman et al. 2020b]] ). Under increasing climate change however, an increased attention on fire management will be necessary.

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==== 7.4.2.5 Reduce Degradation and Conversion of Grasslands and Savannas ====

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'''Activities, co-benefits, risks and implementation opportunities and barriers.''' Grasslands cover approximately 40.5% of the terrestrial area (i.e., 52.5 million km 2 ) divided as 13.8% woody savanna and savanna; 12.7% open and closed shrub; 8.3% non-woody grassland; and 5.7% is tundra ( [[#White--2000|White et al. 2000]] ). Sub-Saharan Africa and Asia have the most extensive total area, 14.5 and 8.9 million km 2 , respectively. A review by [[#Conant--2017|Conant et al. (2017)]] reported based on data on grassland area ( [[#FAO--2013|FAO 2013]] ) and grassland soil carbon stocks ( [[#Sombroek--1993|Sombroek et al. 1993]] ) a global estimate of about 343 PgC (in the top 1 m), nearly 50% more than is stored in forests worldwide ( [[#FAO--2007|FAO 2007]] ). Reducing the conversion of grasslands and savannas to croplands prevents soil carbon losses by oxidation, and to a smaller extent, biomass carbon loss due to vegetation clearing (SRCCL, Chapter 6). Restoration of grasslands through enhanced soil carbon sequestration, including (i) management of vegetation, (ii) animal management, and (iii) fire management, was also included in the SRCCL and is covered in [[#7.4.3.1|Section 7.4.3.1]] . Similar to other measures that reduce conversion, conserving carbon stocks in grasslands and savannas can be achieved by controlling conversion drivers (e.g., commercial and subsistence agriculture, see [[#7.3|Section 7.3]] ) and improving policies and management. In addition to mitigation, conserving grasslands provide various socio-economic, biodiversity, water cycle and other environmental benefits ( [[#Claassen--2010|Claassen et al. 2010]] ; [[#Ryals--2015|Ryals et al. 2015]] ; [[#Bengtsson--2019|Bengtsson et al. 2019]] ). Annual operating costs, and opportunity costs of income foregone by undertaking the activities needed for avoiding conversion of grasslands making costs one of the key barriers for implementation ( [[#Lipper--2010|Lipper et al. 2010]] ).

'''Conclusions from AR5 and IPCC Special Reports (SR1.5, SROCC and SRCCL); mitigation potential, costs, and pathways.''' The SRCCL reported a mitigation potential for reduced conversion of grasslands and savannas of 0.03–0.12 GtCO 2 -eq yr –1 ( [[#Griscom--2017|Griscom et al. 2017]] ; [[#IPCC--2019|IPCC 2019]] ) considering the higher loss of soil organic carbon in croplands ( [[#Sanderman--2017|Sanderman et al. 2017]] ). Assuming an average starting soil organic carbon stock of temperate grasslands ( [[#Poeplau--2011|Poeplau et al. 2011]] ), and the mean annual global cropland conversion rates (1961–2003) ( [[#Krause--2017|Krause et al. 2017]] ), the equivalent loss of soil organic carbon over 20 years would be 14 GtCO 2 -eq, for example, 0.7 GtCO 2 yr –1 (SRCCL, Chapter 6). IPCC AR5 and AR4 did not explicitly consider the mitigation potential of avoided conversion of grasslands-savannas but the management of grazing land is accounted for considering plant, animal, and fire management with a mean mitigation potential of 0.11–0.80 tCO 2 -eq ha –1 yr –1 depending on the climate region. This resulted in 0.25 GtCO 2 -eq yr –1 at USD20 tCO 2 –1 to 1.25 GtCO 2 -eq yr –1 at USD100 tCO 2 –1 by 2030.

'''Developments since AR5 and IPCC Special Reports (SR1.5, SROCC and SRCCL).''' Unlike most of the measures covered in [[#7.4|Section 7.4]] , there are currently no global, spatially explicit mitigation potential estimates for reduced grassland conversion to generate technical and economic potentials by region. Literature developments since AR5 and SRCCL are studies that provide mitigation estimates in one or a few countries or regions. Modelling experiments comparing Californian forests and grasslands found that grasslands resulted in a more resilient carbon sink than forests to future climate change ( [[#Dass--2018|Dass et al. 2018]] ). However, previous studies indicated that precipitation is a key controller of the carbon storage in these grasslands, with the grassland became a carbon sink in 2005, when the region received relatively high spring precipitation ( [[#Ma--2007|Ma et al. 2007]] ). In North America, grassland conversion was the source for 77% of all new croplands from 2008–2012 ( [[#Lark--2015|Lark et al. 2015]] ). Avoided conversion of North American grasslands to croplands presents an economic mitigation potential of 0.024 GtCO 2 -eq yr –1 and technical potential of 0.107 GtCO 2 -eq yr –1 ( [[#Fargione--2018|Fargione et al. 2018]] ). This potential is related mainly to root biomass and soils (81% of emissions from soils). Estimates of GHG emissions from any future deforestation in Australian savannas also point to the potential mitigation of around 0.024 GtCO 2 -eq yr –1 ( [[#Bristow--2016|Bristow et al. 2016]] ). The expansion of the Soy Moratorium (SoyM) from the Brazilian Amazon to the Cerrado (Brazilian savannas) would prevent the direct conversion of 3.6 Mha of native vegetation to soybeans by 2050 and avoid the emission of 0.02 GtCO 2 -eq yr –1 ( [[#Soterroni--2019|Soterroni et al. 2019]] ).

'''Critical assessment and conclusion.''' There is ''low confidence'' that the global technical mitigation potential for reduced grassland and savanna conversion by 2050 is 0.2 (0.1–0.4) GtCO 2 yr –1 , and the economic mitigation potential (&lt;USD100 tCO 2 –1 ) is 0.04 GtCO 2 yr –1 . Most of the carbon sequestration potential is in below-ground biomass and soil organic matter. However, estimates of potential are still based on few studies and vary according to the levels of soil carbon, and ecosystem productivity (e.g., in response to rainfall distribution). Conservation of grasslands presents significant benefits for desertification control, especially in arid areas (SRCCL, Chapter 3). Policies supporting avoided conversion can help protect at-risk grasslands, reduce GHG emissions, and produce positive outcomes for biodiversity and landowners ( [[#Ahlering--2016|Ahlering et al. 2016]] ). In comparison to tropical rainforest regions that have been the primary target for mitigation policies associated to natural ecosystems (e.g., REDD+), conversion grasslands and savannas has received less national and international attention, despite growing evidence of concentrated cropland expansion into these areas with impacts of carbon losses.

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==== 7.4.2.6 Reduce Degradation and Conversion of Peatlands Activities, Co-benefits, Risks and Implementation Barriers ====

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Peatlands are carbon-rich wetland ecosystems with organic soil horizons in which soil organic matter concentration exceeds 30% (dry weight) and soil carbon concentrations can exceed 50% ( [[#Page--2016|Page and Baird 2016]] , [[#Boone%20Kauffman--2017|Boone Kauffman et al. 2017]] ). Reducing the conversion of peatlands avoids emissions of above- and below-ground biomass and soil carbon due to vegetation clearing, fires, and peat decomposition from drainage. Similar to deforestation, peatland carbon stocks can be conserved by controlling the drivers of conversion and degradation (e.g., commercial and subsistence agriculture, mining, urban expansion) and improving governance and management. Reducing conversion is urgent because peatland carbon stocks accumulate slowly and persist over millennia; loss of existing stocks cannot be easily reversed over the decadal time scales needed to meet the Paris Agreement ( [[#Goldstein--2020|Goldstein et al. 2020]] ). The main co-benefits of reducing conversion of peatlands include conservation of a unique biodiversity including many critically endangered species, provision of water quality and regulation, and improved public health through decreased fire-caused pollutants ( [[#Griscom--2017|Griscom et al. 2017]] ). Although reducing peatland conversion will reduce land availability for alternative uses including agriculture or other land-based mitigation, drained peatlands constitute a small share of agricultural land globally while contributing significant emissions ( [[#Joosten--2009|Joosten 2009]] ). Mitigation through reduced conversion of peatlands therefore has a high potential of avoided emissions per hectare ( [[#Roe--2019|Roe et al. 2019]] ).

'''Conclusions from AR5 and IPCC Special Reports (SR1.5, SROCC and SRCCL); mitigation potential, costs, and pathways.''' In the SRCCL (Chapters 2 and 6), it was estimated that avoided peat impacts could deliver 0.45–1.22 GtCO 2 -eq yr –1 technical potential by 2030–2050 ( ''medium confidence'' ) ( [[#Hooijer--2010|Hooijer et al. 2010]] ; [[#Griscom--2017|Griscom et al. 2017]] ; [[#Hawken--2017|Hawken 2017]] ). The mitigation potential estimates cover tropical peatlands and include CO 2 , N 2 O and CH 4 emissions. The mitigation potential is derived from quantification of losses of carbon stocks due to land conversion, shifts in GHG fluxes, alterations in net ecosystem productivity, input factors such as fertilisation needs, and biophysical climate impacts (e.g., shifts in albedo, water cycles, etc.). Tropical peatlands account for only about 10% of peatland area and about 20% of peatland carbon stock but about 80% of peatland carbon emissions, primarily from peatland conversion in Indonesia (about 60%) and Malaysia (about 10%) ( [[#Hooijer--2010|Hooijer et al. 2010]] ; [[#Page--2011|Page et al. 2011]] ; [[#Leifeld--2018|Leifeld and Menichetti 2018]] ). While the total mitigation potential of peatland conservation is considered moderate, the per hectare mitigation potential is the highest among land-based mitigation measures ( [[#Roe--2019|Roe et al. 2019]] ).

'''Developments since AR5 and IPCC Special Reports (SR1.5, SROCC and SRCCL).''' Recent studies continue to report high carbon stocks in peatlands and emphasise the vulnerability of peatland carbon after conversion. The carbon stocks of tropical peatlands are among the highest of any forest, 1,211–4,257 tCO 2 -eq ha –1 in the Peruvian Amazon ( [[#Bhomia--2019|Bhomia et al. 2019]] ) and 1,956–14,757 tCO 2 -eq ha –1 in Indonesia ( [[#Novita--2021|Novita et al. 2021]] ). Ninety percent of tropical peatland carbon stocks are vulnerable to emission during conversion and may not be recoverable through restoration; in contrast, boreal and temperate peatlands hold similar carbon stocks (1,439–5,619 tCO 2 -eq ha –1 ) but only 30% of northern carbon stocks are vulnerable to emission during conversion and irrecoverable through restoration ( [[#Goldstein--2020|Goldstein et al. 2020]] ). A recent study shows global mitigation potential of about 0.2 GtCO 2 -eq yr –1 at costs up to USD100 tCO 2 –1 ( [[#Roe--2021|Roe et al. 2021]] ). Another study estimated that 72% of mitigation is achieved through avoided soil carbon impacts, with the remainder through avoided impacts to vegetation ( [[#Bossio--2020|Bossio et al. 2020]] ). Recent model projections show that both peatland protection and peatland restoration ( [[#7.4.2.7|Section 7.4.2.7]] ) are needed to achieve a 2°C mitigation pathway and that peatland protection and restoration policies will have minimal impacts on regional food security ( [[#Leifeld--2019|Leifeld et al. 2019]] , [[#Humpenöder--2020|Humpenöder et al. 2020]] ). Global studies have not accounted for extensive peatlands recently reported in the Congo Basin, estimated to cover 145,500 km 2 and contain 30.6 PgC, as much as 29% of total tropical peat carbon stock ( [[#Dargie--2017|Dargie et al. 2017]] ). These Congo peatlands are relatively intact; continued preservation is needed to prevent major emissions ( [[#Dargie--2019|Dargie et al. 2019]] ). In northern peatlands that are underlain by permafrost roughly 50% of the total peatlands north of 23° latitude, ( [[#Hugelius--2020|Hugelius et al. 2020]] ), climate change (i.e., warming) is the major driver of peatland degradation (e.g., through permafrost thaw) ( [[#Schuur--2015|Schuur et al. 2015]] , [[#Goldstein--2020|Goldstein et al. 2020]] ). However, in non-permafrost boreal and temperate peatlands, reduction of peatland conversion is also a cost-effective mitigation strategy. Peatlands are sensitive to climate change and there is ''low confidence'' about the future peatland sink globally (SRCCL, Chapter 2). Permafrost thaw may shift northern peatlands from a net carbon sink to net source ( [[#Hugelius--2020|Hugelius et al. 2020]] ). Uncertainties in peatland extent and the magnitude of existing carbon stocks, in both northern ( [[#Loisel--2014|Loisel et al. 2014]] ) and tropical ( [[#Dargie--2017|Dargie et al. 2017]] ) latitudes limit understanding of current and future peatland carbon dynamics ( [[#Minasny--2019|Minasny et al. 2019]] ).

'''Critical assessment and conclusion.''' Based on studies to date, there is ''medium confidence'' that peatland conservation has a technical potential of 0.86 (0.43–2.02) GtCO 2 -eq yr –1 of which 0.48 (0.2–0.68) GtCO 2 -eq yr –1 is available at USD100 tCO 2 –1 (Figure 7.11). High per hectare mitigation potential and high rate of co-benefits particularly in tropical countries, support the effectiveness of this mitigation strategy ( [[#Roe--2019|Roe et al. 2019]] ). Feasibility of reducing peatland conversion may depend on countries’ governance, financial capacity and political will.

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==== 7.4.2.7 Peatland Restoration ====

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'''Activities, co-benefits, risks and implementation barriers.''' Peatland restoration involves restoring degraded and damaged peatlands, for example through rewetting and revegetation, which both increases carbon accumulation in vegetation and soils and avoids ongoing CO 2 emissions. Peatlands only account for about 3% of the terrestrial surface, predominantly occurring in boreal ecosystems (78%), with a smaller proportion in tropical regions (13%), but may store about 600 GtC or 21% of the global total soil organic carbon stock of about 3000 Gt ( [[#Page--2011|Page et al. 2011]] ; [[#Leifeld--2018|Leifeld and Menichetti 2018]] ). Peatland restoration delivers co-benefits for biodiversity, as well as regulating water flow and preventing downstream flooding, while still allowing for extensive management such as paludiculture ( [[#Tan--2021|Tan et al. 2021]] ). Rewetting of peatlands also reduces the risk of fire, but may also mobilise salts and contaminants in soils ( [[#van%20Diggelen--2020|van Diggelen et al. 2020]] ) and in severely degraded peatlands, restoration of peatland hydrology and vegetation may not be feasible ( [[#Andersen--2017|Andersen et al. 2017]] ). At a local level, restoration of peatlands drained for agriculture could displace food production and damage local food supply, although impacts to regional and global food security would be minimal ( [[#Humpenöder--2020|Humpenöder et al. 2020]] ). Collaborative and transparent planning processes are needed to reduce conflict between competing land uses ( [[#Tanneberger--2020b|Tanneberger et al. 2020b]] ). Adequate resources for implementing restoration policies are key to engage local communities and maintain livelihoods ( [[#Resosudarmo--2019|Resosudarmo et al. 2019]] ; [[#Ward--2021|Ward et al. 2021]] ).

'''Conclusions from AR5 and IPCC Special Reports (SR1.5, SROCC and SRCCL); mitigation potential, costs, and pathways.''' Large areas (0.51 Mkm 2 ) of global peatlands are degraded of which 0.2 Mkm 2 are tropical peatlands ( [[#Griscom--2017|Griscom et al. 2017]] ; [[#Leifeld--2018|Leifeld and Menichetti 2018]] ). According the SRCCL, peatland restoration could deliver technical mitigation potentials of 0.15 – 0.81GtCO 2 -eq yr –1 by 2030–2050 ( ''low confidence'' ) ( [[#Couwenberg--2010|Couwenberg et al. 2010]] ; [[#Griscom--2017|Griscom et al. 2017]] ) '''(''' Chapters 2 and 6 of the SRCCL), though there could be an increase in methane emissions after restoration ( [[#Jauhiainen--2008|Jauhiainen et al. 2008]] ). The mitigation potential estimates cover global peatlands and include CO 2 , N 2 O and CH 4 emissions. Peatlands are highly sensitive to climate change ( ''high confidence'' ), however there are currently no studies that estimate future climate effects on mitigation potential from peatland restoration.

'''Developments since AR5 and IPCC Special Reports (SR1.5, SROCC and SRCCL).''' The most recent literature and reviews indicate with ''high confidence'' that restoration would decrease CO 2 emissions and with ''medium confidence'' that restoration would decrease net GHG emissions from degraded peatlands ( [[#Wilson--2016|Wilson et al. 2016]] ; [[#Ojanen--2020|Ojanen and Minkkinen 2020]] ; [[#van%20Diggelen--2020|van Diggelen et al. 2020]] ). Although rewetting of drained peatlands increases CH 4 emissions, this effect is often outweighed by decreases in CO 2 and N 2 O emissions but depends very much on local circumstances ( [[#Günther--2020|Günther et al. 2020]] ). Restoration and rewetting of almost all drained peatlands is needed by 2050 to meet 1.5°C–2°C pathways which is unlikely to happen ( [[#Leifeld--2019|Leifeld et al. 2019]] ); immediate rewetting and restoration minimises the warming from cumulative CO 2 emissions ( [[#Nugent--2019|Nugent et al. 2019]] ).

According to recent data, the technical mitigation potential for global peatland restoration is estimated at 0.5–1.3 GtCO 2 -eq yr –1 ( [[#Leifeld--2018|Leifeld and Menichetti 2018]] ; [[#Griscom--2020|Griscom et al. 2020]] ; [[#Bossio--2020|Bossio et al. 2020]] ; [[#Roe--2021|Roe et al. 2021]] ) (Figure 7.11), with 80% of the mitigation potential derived from improvements to soil carbon ( [[#Bossio--2020|Bossio et al. 2020]] ). The regional mitigation potentials of all peatlands outlined in [[#Roe--2021|Roe et al. (2021)]] reflect the country-level estimates from ( [[#Humpenöder--2020|Humpenöder et al. 2020]] ).

Climate mitigation effects of peatland rewetting depend on the climate zone and land use. Recent analysis shows the strongest mitigation gains from rewetting drained temperate and boreal peatlands used for agriculture and drained tropical peatlands ( [[#Ojanen--2020|Ojanen and Minkkinen 2020]] ). However, estimates of emission factors from rewetting drained tropical peatlands remain uncertain ( [[#Wilson--2016|Wilson et al. 2016]] ; [[#Murdiyarso--2019|Murdiyarso et al. 2019]] ). Topsoil removal, in combination with rewetting, may improve restoration success and limit CH 4 emissions during restoration of highly degraded temperate peatlands ( [[#Zak--2018|Zak et al. 2018]] ). In temperate and boreal regions, co-benefits mentioned above are major motivations for peatland restoration ( [[#Chimner--2017|Chimner et al. 2017]] ; [[#Tanneberger--2020a|Tanneberger et al. 2020a]] ).

'''Critical assessment and conclusion.''' Based on studies to date, there is ''medium confidence'' that peatland restoration has a technical potential of 0.79 (0.49–1.3) GtCO 2 -eq yr –1 (median) of which 0.4 (0.2–0.6) GtCO 2 -eq yr –1 is available up to USD100 tCO 2 –1 . The large land area of degraded peatlands suggests that significant emissions reductions could occur through large-scale restoration especially in tropical peatlands. There is ''medium confidence'' in the large carbon stocks of tropical peat forests (1956–14,757 tCO 2 -eq ha –1 ) and large rates of carbon loss associated with land cover change (640–1650 tCO 2 -eq ha –1 ) ( [[#Goldstein--2020|Goldstein et al. 2020]] ; [[#Novita--2021|Novita et al. 2021]] ). However, large-scale implementation of tropical peatland restoration will likely be limited by costs and other demands for these tropical lands.

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==== 7.4.2.8 Reduce Conversion of Coastal Wetlands ====

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'''Activities, co-benefits, risks and implementation barriers.''' Reducing conversion of coastal wetlands, including mangroves, marshes and seagrass ecosystems, avoids emissions from above and below ground biomass and soil carbon through avoided degradation and/or loss. Coastal wetlands occur mainly in estuaries and deltas, areas that are often densely settled, with livelihoods closely linked to coastal ecosystems and resources ( [[#Moser--2012|Moser et al. 2012]] ). The carbon stocks of these highly productive ecosystems are sometimes referred to as ‘blue carbon’. Loss of existing stocks cannot be easily reversed over decadal time scales ( [[#Goldstein--2020|Goldstein et al. 2020]] ). The main drivers of conversion include intensive aquaculture, agriculture, salt ponds, urbanisation and infrastructure development, the extensive use of fertilisers, and extraction of water resources ( [[#Lovelock--2018|Lovelock et al. 2018]] ). Reduced conversion of coastal wetlands has many co-benefits, including biodiversity conservation, fisheries production, soil stabilisation, water flow and water quality regulation, flooding and storm surge prevention, and increased resilience to cyclones ( [[#Windham-Myers--2018|Windham-Myers et al. 2018]] a; [[#UNEP--2020|UNEP 2020]] ). Risks associated with the mitigation potential of coastal wetland conservation include uncertain permanence under future climate scenarios, including the effects of coastal squeeze, where coastal wetland area may be lost if upland area is not available for migration as sea levels rise ( [[#Lovelock--2020|Lovelock and Reef 2020]] ) (AR6 WGII, [[IPCC:Wg3:Chapter:Chapter-3#3.4.2|Section 3.4.2]] .5). Preservation of coastal wetlands also conflicts with other land use in the coastal zone, including aquaculture, agriculture, and human development; economic incentives are needed to prioritise wetland preservation over more profitable short-term land use. Integration of policies and efforts aimed at coastal climate mitigation, adaptation, biodiversity conservation, and fisheries, for example through integrated coastal zone management and marine spatial planning, will bundle climate mitigation with co-benefits and optimise outcomes ( [[#Herr--2017|Herr et al. 2017]] ).

'''Conclusions from AR5 and IPCC Special Reports (SR1.5, SROCC and SRCCL); mitigation potential, costs, and pathways.''' Coastal wetlands contain high, yet variable, organic carbon stocks, leading to a range of estimates of the global mitigation potential of reduced conversion. The SRCCL (Chapter 2) and SROCC (Chapter 5), report a technical mitigation potential of 0.15–5.35 GtCO 2 -eq yr –1 by 2050 ( [[#Pendleton--2012|Pendleton et al. 2012]] ; [[#Lovelock--2017|Lovelock et al. 2017]] ; [[#Howard--2017|Howard et al. 2017]] ; [[#Griscom--2017|Griscom et al. 2017]] ) '''.''' The mitigation potential is derived from quantification of losses of carbon stocks in vegetation and soil due to land conversion, shifts in GHG fluxes associated with land use, and alterations in net ecosystem productivity. The wide range in estimates mostly relate to the scope (all coastal ecosystems vs mangroves only) and different assumptions on decomposition rates. Loss rates of coastal wetlands have been estimated at 0.2–3% yr –1 , depending on the vegetation type and location ( [[#Atwood--2017|Atwood et al. 2017]] ; [[#Howard--2017|Howard et al. 2017]] ).

'''Developments since AR5 and IPCC Special Reports (SR1.5, SROCC and SRCCL).''' Global technical mitigation potential for conservation of coastal wetlands from recent literature have focused on protection of mangroves; estimates range from 0.06–2.25 GtCO 2 -eq yr –1 ( [[#Griscom--2020|Griscom et al. 2020]] ; [[#Bossio--2020|Bossio et al. 2020]] ) with 80% of the mitigation potential derived from improvements to soil carbon ( [[#Bossio--2020|Bossio et al. 2020]] ). Regional potentials ( [[#Roe--2021|Roe et al. 2021]] ) reflect mangrove protection; marsh and seagrass protection were not included due to lack of country-level data on marsh and seagrass distribution and conversion.

Global estimates show mangroves have the largest per hectare carbon stocks (see IPCC AR6 WGII Box 3.4 for estimates of carbon stocks, burial rates and ecosystem extent for coastal wetland ecosystems). Mean ecosystem carbon stock in mangroves is 3131 tCO 2 -eq ha –1 among the largest carbon stocks on Earth. Recent studies emphasise the variability in total ecosystem carbon stocks for each wetland type, based on species and climatic and edaphic conditions ( [[#Kauffman--2020|Kauffman et al. 2020]] ; [[#Bedulli--2020|Bedulli et al. 2020]] ; [[#Ricart--2020|Ricart et al. 2020]] ; Alongi et al. 2020; F. [[#Wang--2021|Wang et al. 2021]] ), and highlight the vulnerability of soil carbon below 1 m depth ( [[#Arifanti--2019|Arifanti et al. 2019]] ). Sea level strongly influences coastal wetland distribution, productivity, and sediment accretion; therefore, sea level rise will impact carbon accumulation and persistence of existing carbon stocks ( [[#Macreadie--2019|Macreadie et al. 2019]] ) (IPCC AR6 WGII Box 3.4).

Recent loss rates of mangroves are 0.16–0.39% yr –1 and are highest in South-East Asia ( [[#Hamilton--2016|Hamilton and Casey 2016]] ; [[#Friess--2019|Friess et al. 2019]] ; [[#Hamilton--2016|Hamilton and Casey 2016]] ). Assuming loss of soil carbon to 1 m depth after deforestation, avoiding mangrove conversion has the technical potential to mitigate approximately 23.5–38.7 MtCO 2 -eq yr –1 ( [[#Ouyang--2020|Ouyang and Lee 2020]] ); note, this potential is additional to reduced conversion of forests ( [[#Griscom--2020|Griscom et al. 2020]] ) ( [[#7.4.2.1|Section 7.4.2.1]] ). Regional estimates show that about 85% of mitigation potential for avoided mangrove conversion is in South-East Asia and Pacific (32 MtCO 2 -eq yr –1 at USD100 tCO 2 –1 ), 10% is in Latin American and the Caribbean (4 MtCO 2 -eq yr –1 ), and approximately 5% in other regions ( [[#Griscom--2020|Griscom et al. 2020]] ; [[#Roe--2021|Roe et al. 2021]] ).

Key uncertainties remain in mapping extent and conversion rates for salt marshes and seagrasses ( [[#McKenzie--2020|McKenzie et al. 2020]] ). Seagrass loss rates were estimated at 1–2% yr –1 ( [[#Dunic--2021|Dunic et al. 2021]] ) with stabilisation in some regions ( [[#de%20los%20Santos--2019|de los]] [[#Santos--2019|Santos et al. 2019]] ) (AR6 WGII, [[IPCC:Wg3:Chapter:Chapter-3#3.4.2|Section 3.4.2]] .5); however, loss occurs non-linearly and depends on site-specific context. Tidal marsh extent and conversion rates remains poorly estimated, outside of the USA, Europe, South Africa, and Australia ( [[#Mcowen--2017|Mcowen et al. 2017]] ; [[#Macreadie--2019|Macreadie et al. 2019]] ).

'''Critical assessment and conclusion.''' There is ''medium confidence'' that coastal wetland protection has a technical potential of 0.8 (0.06–5.4) GtCO 2 -eq yr –1 of which 0.17 (0.06–0.27) GtCO 2 -eq yr –1 is available up to USD100 tCO 2 –1 . There is a ''high certainty'' ( ''robust evidence'' , ''high agreement'' ) that coastal ecosystems have among the largest carbon stocks of any ecosystem. As these ecosystems provide many important services, reduced conversion of coastal wetlands is a valuable mitigation strategy with numerous co-benefits. However, the vulnerability of coastal wetlands to climatic and other anthropogenic stressors may limit the permanence of climate mitigation.

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==== 7.4.2.9 Coastal Wetland Restoration ====

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'''Activities, co-benefits, risks and implementation barriers.''' Coastal wetland restoration involves restoring degraded or damaged coastal wetlands including mangroves, salt marshes, and seagrass ecosystems, leading to sequestration of ‘blue carbon’ in wetland vegetation and soil (SRCCL, Chapter 6; SROCC, Chapter 5). Successful approaches to wetland restoration include: (i) passive restoration, the removal of anthropogenic activities that are causing degradation or preventing recovery; and (ii) active restoration, purposeful manipulations to the environment in order to achieve recovery to a naturally functioning system ( [[#Elliott--2016|Elliott et al. 2016]] ) (IPCC AR6 WGII Chapter 3). Restoration of coastal wetlands delivers many valuable co-benefits, including enhanced water quality, biodiversity, aesthetic values, fisheries production (food security), and protection from rising sea levels and storm impacts ( [[#Barbier--2011|Barbier et al. 2011]] ; [[#Hochard--2019|Hochard et al. 2019]] ; [[#Sun--2020|Sun and Carson 2020]] ; [[#Duarte--2020|Duarte et al. 2020]] ). Of the 0.3 Mkm 2 coastal wetlands globally, 0.11 Mkm 2 of mangroves are considered feasible for restoration ( [[#Griscom--2017|Griscom et al. 2017]] ). Risks associated with coastal wetland restoration include uncertain permanence under future climate scenarios (IPCC AR6 WGII, Box 3.4), partial offsets of mitigation through enhanced methane and nitrous oxide release and carbonate formation, and competition with other land uses, including aquaculture and human settlement and development in the coastal zone (SROCC, Chapter 5). To date, many coastal wetland restoration efforts do not succeed due to failure to address the drivers of degradation (van [[#Katwijk--2016|Katwijk et al. 2016]] ). However, improved frameworks for implementing and assessing coastal wetland restoration are emerging that emphasise the recovery of ecosystem functions ( [[#Zhao--2016|Zhao et al. 2016]] ; [[#Cadier--2020|Cadier et al. 2020]] ). Restoration projects that involve local communities at all stages and consider both biophysical and socio-political context are more likely to succeed ( [[#Brown--2014|Brown et al. 2014]] ; [[#Wylie--2016|Wylie et al. 2016]] ).

'''Conclusions from AR5 and IPCC Special Reports (SR1.5, SROCC and SRCCL); mitigation potential, costs, and pathways.''' The SRCCL reported that mangrove restoration has the technical potential to mitigate 0.07 GtCO 2 yr –1 through rewetting ( [[#Crooks--2011|Crooks et al. 2011]] ) and take up 0.02–0.84 GtCO 2 yr –1 from vegetation biomass and soil enhancement through 2030 ( ''medium confidence'' ) ( [[#Griscom--2017|Griscom et al. 2017]] ). The SROCC concluded that cost-effective coastal blue carbon restoration had a potential of about 0.15–0.18 GtCO 2 -eq yr –1 , a low global potential compared to other ocean-based solutions but with extensive co-benefits and limited adverse side effects ( [[#Gattuso--2018|Gattuso et al. 2018]] ).

'''Developments since AR5 and IPCC Special Reports (SR1.5, SROCC and SRCCL).''' Recent studies emphasise the time frame needed to achieve the full mitigation potential ( [[#Duarte--2020|Duarte et al. 2020]] ; [[#Taillardat--2020|Taillardat et al. 2020]] ). The first project-derived estimate of the net GHG benefit from seagrass restoration found 1.54 tCO 2 -eq (0.42 MgC) ha –1 yr –1 10 years after restoration began ( [[#Oreska--2020|Oreska et al. 2020]] ); comparable to the default emission factor in the Wetlands Supplement ( [[#Kennedy--2014|Kennedy et al. 2014]] ). Recent studies of rehabilitated mangroves also indicate that annual carbon sequestration rates in biomass and soils can return to natural levels within decades of restoration ( [[#Cameron--2019|Cameron et al. 2019]] ; [[#Sidik--2019|Sidik et al. 2019]] ). A meta-analysis shows increasing carbon sequestration rates over the first 15 years of mangrove restoration with rates stabilising at 25.7 ± 7.7 tCO 2 -eq (7.0 ± 2.1 MgC) ha –1 yr –1 through forty years, although success depends on climate, sediment type, and restoration methods ( [[#Sasmito--2019|Sasmito et al. 2019]] ). Overall, 30% of mangrove soil carbon stocks and 50–70% of marsh and seagrass carbon stocks are unlikely to recover within 30 years of restoration, underscoring the importance of preventing conversion of coastal wetlands ( [[#Goldstein--2020|Goldstein et al. 2020]] ) ( [[#7.4.2.8|Section 7.4.2.8]] ).

According to recent data, the technical mitigation potential for global coastal wetland restoration is 0.04–0.84 GtCO 2 -eq yr –1 ( [[#Griscom--2020|Griscom et al. 2020]] ; [[#Bossio--2020|Bossio et al. 2020]] ; [[#Roe--2021|Roe et al. 2021]] ) with 60% of the mitigation potential derived from improvements to soil carbon ( [[#Bossio--2020|Bossio et al. 2020]] ). Regional potentials based on country-level estimates from [[#Griscom--2020|Griscom et al. (2020)]] show the technical and economic (up to USD100 tCO 2 –1 ) potential of mangrove restoration; seagrass and marsh restoration was not included due to lack of country-level data on distribution and conversion (but see [[#McKenzie--2020|McKenzie et al. 2020]] for updates on global seagrass distribution). Although global potential is relatively moderate, mitigation can be quite significant for countries with extensive coastlines (e.g., Indonesia, Brazil) and for small island states where coastal wetlands have been shown to comprise 24–34% of their total national carbon stock ( [[#Donato--2012|Donato et al. 2012]] ). Furthermore, non-climatic co-benefits can strongly motivate coastal wetland restoration worldwide ( [[#UNEP--2021a|UNEP 2021a]] ). Major successes in both active and passive restoration of seagrasses have been documented in North America and Europe ( [[#Lefcheck--2018|Lefcheck et al. 2018]] ; [[#de%20los%20Santos--2019|de los]] [[#Santos--2019|Santos et al. 2019]] ; [[#Orth--2020|Orth et al. 2020]] ); passive restoration may also be feasible for mangroves ( [[#Cameron--2019|Cameron et al. 2019]] ).

There is high site-specific variation in carbon sequestration rates and uncertainties regarding the response to future climate change ( [[#Jennerjahn--2017|Jennerjahn et al. 2017]] ; [[#Nowicki--2017|Nowicki et al. 2017]] ) (IPCC AR6 WGII Box 3.4). Changes in distributions ( [[#Kelleway--2017|Kelleway et al. 2017]] ; [[#Wilson--2019|Wilson and Lotze 2019]] ) ''',''' methane release (Al-Haj and Fulweiler 2020), carbonate formation ( [[#Saderne--2019|Saderne et al. 2019]] ), and ecosystem responses to interactive climate stressors are not well-understood ( [[#Short--2016|Short et al. 2016]] ; Fitzgerald and Hughes 2019; [[#Lovelock--2020|Lovelock and Reef 2020]] ).

'''Critical assessment and conclusion.''' There is ''medium confidence'' that coastal wetland restoration has a technical potential of 0.3 (0.04–0.84) GtCO 2 -eq yr –1 of which 0.1 (0.05–0.2) GtCO 2 -eq yr –1 is available up to USD100 tCO 2 –1 . There is ''high confidence'' that coastal wetlands, especially mangroves, contain large carbon stocks relative to other ecosystems and ''medium confidence'' that restoration will reinstate pre-disturbance carbon sequestration rates. There is ''low confidence'' on the response of coastal wetlands to climate change; however, there is ''high confidence'' that coastal wetland restoration will provide a suite of valuable co-benefits.

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