Editing IPCC:AR6/WGII/Cross-Chapter-Paper-6 (section)

=== CCP6.2.2 Terrestrial and Freshwater Ecosystems ===

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Since the publication of AR5 ( [[#IPCC--2014|IPCC, 2014]] ) and SROCC ( [[#IPCC--2019|IPCC, 2019]] ) and their findings (Table CCP6.2), more studies confirm rapid changes in Arctic terrestrial and freshwater systems including increased permafrost thaw, changes to tundra hydrology and vegetation (overall greening of the tundra, regional browning of tundra and boreal forests), coastal and riverbank erosion ( ''high confidence'' ) ( [[#Canadell--2021|Canadell et al., 2021]] ; [[#Mustonen--2021|Mustonen and]] [[#Shadrin--2021|Shadrin, 2021]] ), reduced duration of snow cover and river and lake ice, increased rain-on-snow events, and reduced land-ice extent and thickness ( [[#Bieniek--2018|Bieniek et al., 2018]] ; [[#Brown--2018|Brown et al., 2018]] ). Climate change continues to alter vegetation and attendant biodiversity, with divergent regional trends across the Arctic due to disparities in local conditions and changes in growing seasons ( [[#Zhu--2016|Zhu et al., 2016]] ; [[#Taylor--2020|Taylor et al., 2020]] ). Warming facilitates woody vegetation growth in northeastern Siberia, western Alaska, and northern Quebec ( [[#Song--2018|Song et al., 2018]] ; [[#García%20Criado--2020|García Criado et al., 2020]] ), as well as a northward expansion of shrub vegetation and sub-Arctic and boreal species ( [[#Davidson--2020|Davidson et al., 2020]] ).

Further evidence shows that warming and changes to the Arctic hydrologic cycle increase the risk of wildfire ( ''medium confidence'' ) ( [[#Mustonen--2021|Mustonen and]] [[#Shadrin--2021|Shadrin, 2021]] ). Both the frequency of and the area burned by wildfires during recent years are unprecedented compared with the last 10,000 years ( ''high confidence'' ) ( [[#Meredith--2019|Meredith et al., 2019]] ; [[#Irannezhad--2020|Irannezhad et al., 2020]] ). Fire risk levels are projected to increase across most tundra and boreal regions, and interactions between climate and shifting vegetation ( [[#Song--2018|Song et al., 2018]] ) will influence future fire intensity and frequency ( ''medium confidence'' ) ( [[#Curtis--2018|Curtis et al., 2018]] ).

For all warming scenarios, declines in snow cover in the Arctic by 2050 (Table CCP6.1) may accelerate vascular plant, moss and lichen extinction rates (32% for Arctic–alpine and 12% for boreal species), especially after the tipping point of 20–30% decrease in snow cover duration is passed ( [[#Niittynen--2018|Niittynen et al., 2018]] ). Even though the overall regional water cycle will intensify, including increased precipitation, evapotranspiration and river discharge to the Arctic Ocean (Table CCP6.1), snow and permafrost decline may lead to further soil drying ( ''medium confidence'' ) ( [[#Meredith--2019|Meredith et al., 2019]] ). Glacial ice melt poses a risk to ecosystems and people through remobilisation of sequestered hazardous waste and transported pollutants (Table CCP6.3) ( [[#Wang--2019|Wang et al., 2019]] ).

In the Antarctic, there is further ''high agreement'' since the publication of SROCC that melt and ice-free areas are causing increases in the rates of colonisation and utilisation of coastal environments by terrestrial biota and land-based colonies of seals and birds ( [[#Gutt--2021|Gutt et al., 2021]] ), although colonisation rates remain variable ( [[#Ruiz-Fernandez--2017|Ruiz-Fernandez et al., 2017]] ; [[#Bokhorst--2021|Bokhorst et al., 2021]] ). Soil temperatures along the Antarctic Peninsula are now sufficient for germination of non-native plants; invasions by non-endemic species are expected to increase with rising temperatures ( ''high confidence'' ) ( [[#Bokhorst--2021|Bokhorst et al., 2021]] ), posing a risk to endemic polar species ( ''medium confidence'' ) ( [[#Chown--2019|Chown and Brooks, 2019]] ; [[#Gutt--2021|Gutt et al., 2021]] ).

Vegetation responses to warming are contingent on water availability and local temperature ( ''medium confidence'' ) ( [[#Guglielmin--2014|Guglielmin et al., 2014]] ; [[#Royles--2015|Royles and Griffiths, 2015]] ; [[#Amesbury--2017|Amesbury et al., 2017]] ; [[#Cannone--2017|Cannone et al., 2017]] ; [[#Charman--2018|Charman et al., 2018]] ; [[#Robinson--2018|Robinson et al., 2018]] ; [[#Stelling--2018|Stelling et al., 2018]] ), which vary greatly around Antarctica (Figure CCP6.1) ( [[#Turner--2020a|Turner et al., 2020a]] ). Antarctic terrestrial ecosystem responses to changes in water availability are not homogeneous ( [[#Ball--2015|Ball and Levy, 2015]] ; [[#Sadowsky--2016|Sadowsky et al., 2016]] ; [[#Fuentes-Lillo--2017|Fuentes-Lillo et al., 2017]] ; [[#Gooseff--2017|Gooseff et al., 2017]] ; [[#Schroeter--2017|Schroeter et al., 2017]] ; [[#Lee--2018|Lee et al., 2018]] ). West Antarctica is showing evidence of greening in the dominant cryptogrammic vegetation, with greater growth in mosses ( ''high confidence'' ) ( [[#Casanova-Katny--2016|Casanova-Katny et al., 2016]] ; [[#Amesbury--2017|Amesbury et al., 2017]] ; [[#Shortlidge--2017|Shortlidge et al., 2017]] ; [[#Charman--2018|Charman et al., 2018]] ; [[#Prather--2019|Prather et al., 2019]] ). Peatland ecosystems may increase on the west Antarctic Peninsula with future warming ( ''low confidence'' ) ( [[#Yu--2016|Yu et al., 2016]] ; [[#Loisel--2017|Loisel et al., 2017]] ). In contrast, some parts of East Antarctica and the subantarctic islands to the north have been experiencing a drying climate, with declining health of mosses and other vegetation ( ''high confidence'' ) ( [[#Bergstrom--2015|Bergstrom et al., 2015]] ; [[#Bramley-Alves--2015|Bramley-Alves et al., 2015]] ; [[#Robinson--2018|Robinson et al., 2018]] ; [[#Bergstrom--2021|Bergstrom et al., 2021]] ).

Antarctica encountered its first reported heatwave in 2020 (Table CCP6.1). Such abrupt heating can cause wide-ranging effects on biota, from flash-flooding damage and dislodgement of plants to excess melt waters supplying moisture to arid Antarctic ecosystems. This suggests that increased melt may reverse the drying trend if plant communities remain connected to melt streams and there is sufficient precipitation ( ''high agreement, limited evidence'' ) ( [[#Bergstrom--2021|Bergstrom et al., 2021]] ).

Warming of the Antarctic Peninsula has resulted in increased soil microbial abundance and biomass. However, this trend is not as great in southern colder locations ( ''medium confidence'' ) (e.g., [[#Kim--2018|Kim et al., 2018]] ; [[#Newsham--2019|Newsham et al., 2019]] ), as the microbial community structure is affected by vegetation cover and water availability ( ''high confidence'' ) ( [[#Dennis--2019|Dennis et al., 2019]] ; [[#Newsham--2019|Newsham et al., 2019]] ).

Antarctic terrestrial invertebrate communities on the West Antarctic Peninsula may be controlled more by vegetation and water availability than by air temperature ( ''medium confidence'' ) ( [[#Bokhorst--2016|Bokhorst and Convey, 2016]] ; [[#Knox--2016|Knox et al., 2016]] ; [[#Andriuzzi--2018|Andriuzzi et al., 2018]] ; [[#Prather--2019|Prather et al., 2019]] ; [[#Newsham--2020|Newsham et al., 2020]] ). Evidence from laboratory studies, field programmes and sedimentary records indicate that Antarctic freshwater ecosystems may become more productive under climate warming scenarios ( ''medium confidence'' ) (e.g., [[#Schiaffino--2011|Schiaffino et al., 2011]] ; [[#Borghini--2016|Borghini et al., 2016]] ; [[#Píšková--2019|Píšková et al., 2019]] ; [[#Čejka--2020|Čejka et al., 2020]] ).

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