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

==== 2.5.2.8 Risk to Peatland Systems ====

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The overall effect of climate change on the extent of northern peatlands is still debated ( ''limited evidence'' , ''low agreement'' ). It is expected that climate change will drive the expansion of high-latitude peatlands poleward of their present distribution due to warming, permafrost degradation and glacier retreat, which could provide new land and conditions favourable for peat development ( ''limited evidence'' , ''medium agreement'' ) ( [[#Zhang--2017b|Zhang et al., 2017b]] ), as seen during the last de-glacial warming ( ''robust evidence'' , ''high agreement'' ) ( [[#MacDonald--2006|MacDonald et al., 2006]] ; [[#Jones--2010|Jones and Yu, 2010]] ; [[#Ratcliffe--2018|Ratcliffe et al., 2018]] ). Peatland area loss (shrinking) near the southern limit of their current distribution or in areas where the climate becomes unsuitable is also expected ( ''medium evidence'' , ''medium agreement'' ) ( [[#2.3|Section 2.3.4.3.2]] ) ( [[#Finkelstein--2011|Finkelstein and Cowling, 2011]] Gallego-Sala and Prentice, 2013; [[#Schneider--2016|Schneider et al., 2016]] ; [[#Müller--2020|Müller and Joos, 2020]] ) ( [[#Müller--2021|Müller and Joos, 2021]] ), but they could persist if moisture is maintained via their capacity to self-regulate. In western Canada, a study suggests that peatlands may persist until 2100, even though the climate will be less suitable ( [[#Schneider--2016|Schneider et al., 2016]] ). Simulations suggest that climate change-driven increases in temperature and atmospheric CO 2 could drive reductions in the northern peatland area up to 18% (SSP1–2.6), 41% (SSP2–4.5) and 61% (SSP5–8.5) by 2300 ( [[#Müller--2020|Müller and Joos, 2020]] ). This is in contrast with the findings of northern peatland persistence and expansion under RCP2.6 and RCP6.0 scenarios in 1861–2099 by another modelling study ( [[#Qiu--2020|Qiu et al., 2020]] ). In the Tropics, the only available study suggests peatland area will increase until 2300, mainly due to increases in precipitation and the CO 2 fertilisation effect ( [[#Müller--2020|Müller and Joos, 2020]] ; [[#Müller--2021|Müller and Joos, 2021]] ).

The combination of changes in climate and land use represents a substantial risk to peatland carbon stocks, but full assessment is impeded because peatlands are yet to be included in ESMs ( ''limited evidence'' , ''high agreement'' ) ( [[#Loisel--2021|Loisel et al., 2021]] ). It is expected that the carbon balance of peatlands globally will switch from sink to source in the near future (2020–2100), mainly because tropical peatland emissions, together with those from climate change-driven permafrost thaw, will likely surpass the carbon gain expected from climate change-driven enhanced plant productivity in northern high latitudes ( [[#Gallego-Sala--2018|Gallego-Sala et al., 2018]] ; [[#Chaudhary--2020|Chaudhary et al., 2020]] ; [[#Turetsky--2020|Turetsky et al., 2020]] ; [[#Loisel--2021|Loisel et al., 2021]] ) which are mainly caused by groundwater drawdown ( ''robust evidence'' , ''medium agreement'' ) ( [[#Hirano--2014|Hirano et al., 2014]] ; [[#Brouns--2015|Brouns et al., 2015]] ; [[#Cobb--2017|Cobb et al., 2017]] ; [[#Itoh--2017|Itoh et al., 2017]] ; [[#Evans--2021|Evans et al., 2021]] ) ''.'' The overall northern peatland carbon sink has been simulated to persist for at least 300 years under RCP2.6, but not under RCP8.5 ( [[#Qiu--2020|Qiu et al., 2020]] ).

Increases in the extent, severity and duration of fires are expected in all peatland regions in the future due to temperature increases ( [[IPCC:Wg2:Chapter:Chapter-4#4.3.1|Section 4.3.1.1]] ), changes in precipitation patterns ( [[IPCC:Wg2:Chapter:Chapter-4#4.3.1|Section 4.3.1.2]] ) and increases in ignition sources (e.g., lightning) ( [[IPCC:Wg2:Chapter:Chapter-5#5.4.3.2|Section 5.4.3.2]] ), with associated rapid carbon losses to the atmosphere ( ''medium evidence'' , ''high agreement'' ) ( [[#Dadap--2019|Dadap et al., 2019]] ; [[#Chen--2021a|Chen et al., 2021a]] ; [[#Nelson--2021|Nelson et al., 2021]] ). For example, drought has been linked to fires in Southeast Asian peatlands ( [[#Field--2009|Field et al., 2009]] ) and there are predicted decreases in mean summer precipitation (10–30%) for high and low RCPs, particularly over the Indonesian region, by the mid and late 21st century ( [[IPCC:Wg2:Chapter:Chapter-12#12.4|Section 12.4.2.2]] ) ( [[#Tangang--2020|Tangang et al., 2020]] ; [[#Taufik--2020|Taufik et al., 2020]] ). During wet years, the fire probability in Indonesian peatlands also significantly increases (by 15–40%) when temperatures in July to October surpass 0.5°C anomalies compared to the 1995–2015 baseline ( [[#Fernandes--2017|Fernandes et al., 2017]] ). Overall, current evidence suggests that peat carbon losses via fire have the potential to be equal to, or greater than, losses due to human peatland drainage and disturbance ( ''limited evidence'' , ''high agreement'' ) ( [[#Turetsky--2015|Turetsky et al., 2015]] ).

Regarding permafrost peatlands, studies differ, with some projecting a net loss and others a net gain of carbon ( ''medium evidence'' , ''low agreement'' ) ( [[#Estop-Aragonés--2018|Estop-Aragonés et al., 2018]] ; [[#Hugelius--2020|Hugelius et al., 2020]] ; [[#Loisel--2021|Loisel et al., 2021]] ; [[#Väliranta--2021|Väliranta et al., 2021]] ). In some permafrost peatlands, prolonged and warmer growing seasons due to climate change ( [[#2.3|Section 2.3.4.3.1]] ), along with increases in nitrogen deposition since 1850 ( [[#Lamarque--2013|Lamarque et al., 2013]] ), are promoting plant primary productivity. Other studies indicate that increased nitrogen-mediated sequestration could be exceeded by increased decomposition due to climate change-driven warming and fire ( ''medium evidence'' , ''low agreement'' ) ( [[#Natali--2012|Natali et al., 2012]] ; [[#Vonk--2015|Vonk et al., 2015]] ; [[#Keuper--2017|Keuper et al., 2017]] ; [[#Burd--2018|Burd et al., 2018]] ; [[#Estop-Aragonés--2018|Estop-Aragonés et al., 2018]] ; [[#Gallego-Sala--2018|Gallego-Sala et al., 2018]] ; [[#Serikova--2018|Serikova et al., 2018]] ; [[#Wild--2019|Wild et al., 2019]] ; [[#Chaudhary--2020|Chaudhary et al., 2020]] ; [[#Hugelius--2020|Hugelius et al., 2020]] ).

Any climate change- or human-driven degradation of peatlands will also entail losses in water storage ( ''limited evidence'' , ''high agreement'' ) ( [[#Wooster--2012|Wooster et al., 2012]] ; [[#Hirano--2015|Hirano et al., 2015]] ; [[#Cole--2019|Cole et al., 2019]] ; [[#Taufik--2019|Taufik et al., 2019]] ) and biodiversity ( [[#Harrison--2013|Harrison, 2013]] ; [[#Lampela--2017|Lampela et al., 2017]] ; [[#Renou-Wilson--2019|Renou-Wilson et al., 2019]] ). The environmental archive contained in peat that preserves records of vegetation, hydrology, climate change, pollution and/or human disturbances is also being lost as peatlands degrade ( [[#Kasischke--2006|Kasischke and Turetsky, 2006]] ; [[#MacDonald--2006|MacDonald et al., 2006]] ; [[#Turunen--2008|Turunen, 2008]] ; [[#Field--2009|Field et al., 2009]] ; [[#Flannigan--2009|Flannigan et al., 2009]] ; [[#Jones--2010|Jones and Yu, 2010]] ; [[#Kasischke--2010|Kasischke et al., 2010]] ; [[#Peterson--2010|Peterson et al., 2010]] ; [[#Finkelstein--2011|Finkelstein and Cowling, 2011]] ; [[#Rooney--2012|Rooney et al., 2012]] ; [[#Gallego-Sala--2013|Gallego-Sala and Colin Prentice, 2013]] ; [[#Lamarque--2013|Lamarque et al., 2013]] ; [[#Hirano--2014|Hirano et al., 2014]] ; [[#Brouns--2015|Brouns et al., 2015]] ; [[#Turetsky--2015|Turetsky et al., 2015]] ; [[#Miettinen--2016|Miettinen et al., 2016]] ; [[#Schneider--2016|Schneider et al., 2016]] ; [[#Cobb--2017|Cobb et al., 2017]] ; [[#Fernandes--2017|Fernandes et al., 2017]] ; [[#Itoh--2017|Itoh et al., 2017]] ; [[#Gallego-Sala--2018|Gallego-Sala et al., 2018]] ; [[#Greiser--2018|Greiser and Joosten, 2018]] ; [[#Ratcliffe--2018|Ratcliffe et al., 2018]] ; [[#Dadap--2019|Dadap et al., 2019]] ; [[#Leifeld--2019|Leifeld et al., 2019]] ; [[#Chaudhary--2020|Chaudhary et al., 2020]] ; [[#Hoyt--2020|Hoyt et al., 2020]] ; [[#Müller--2020|Müller and Joos, 2020]] ; [[#Qiu--2020|Qiu et al., 2020]] ; [[#Tangang--2020|Tangang et al., 2020]] ; [[#Taufik--2020|Taufik et al., 2020]] ; [[#Turetsky--2020|Turetsky et al., 2020]] ; [[#Chen--2021a|Chen et al., 2021a]] ; [[#Evans--2021|Evans et al., 2021]] ; [[#Loisel--2021|Loisel et al., 2021]] ; [[#Nelson--2021|Nelson et al., 2021]] ; [[#Qiu--2021|Qiu et al., 2021]] ).

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