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

== CCP6.1 The Global Importance of Climate Change in Polar Regions ==

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Polar regions (Figure CCP6.1) are considered flagship areas for climate change, since some of the most extreme climate change impacts that are projected to occur by 2050 elsewhere in the world have already been observed in the Arctic and Antarctic and have resulted in transformative and unprecedented change. Polar regions are not only home to cultural keystone species such as polar bears (Arctic) and penguins (Antarctic) but they also play fundamental roles in regulating the global climate system and in the provision of ecosystem services for the global community and for Arctic Indigenous Peoples and local communities in the region.

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[[File:096ff0bf0d1b48c5a3363752e7497863 IPCC_AR6_WGII_Figure_CCP6_001.png]]

'''Figure CCP6.1 |''' '''Polar regions include the Arctic, Antarctica, Iceland, Greenland, Faroe Islands and some sub-Arctic areas (e''' '''.''' '''g., Bering Sea and Aleutian Islands as well as the Fennoscandian and Siberian boreal areas), and all sub-Antarctic areas.''' This CCP augments the geographical boundaries for the Arctic ( [[#Meredith--2019|Meredith et al., 2019]] ) to also include the sub-Arctic boundary (as defined by the Arctic Biodiversity Assessment), northern boreal areas, parts of the Siberian taiga and southern Labrador. The Antarctic region is delineated along the sub-Antarctic Front ( [[#Orsi--1995|Orsi et al., 1995]] ). Geographic boundaries of the polar regions and important sub-regional locations are displayed, including five marine sectors as defined in the Marine Ecosystem Assessment for the Southern Ocean (MEASO), for example, Grant et al., (2021).

These changes are causing a suite of direct and cascading risks for all polar ecosystems with larger effects to date in the Arctic than the Antarctic ( ''high confidence'' ), due to larger and regionally more consistent physical changes (Figure CCP6.2, Table CCP6.1; Chapter 3) ( [[#Meredith--2019|Meredith et al., 2019]] ; [[#Ranasinghe--2021|Ranasinghe et al., 2021]] ). In the Arctic, these changes affect every sector of society, impacting its 4,000,000 inhabitants, including 400,000 Indigenous People. The Antarctic has no permanent human settlements; however, many nations conduct field research, operate seasonal and permanent stations and have an interest in the management of the region ( [[#Hughes--2018|Hughes et al., 2018]] ; [[#Grant--2021|Grant et al., 2021]] ). During summer, when Antarctic science, tourism and fishery activities are greatest, 4400 people live there, whereas only 1100 people live there over winter ( [[#Meredith--2019|Meredith et al., 2019]] ). Although adaptation is occurring in polar regions, it is uneven and sporadic and does not meet the risks posed by future climate change. Indigenous knowledge-based solutions, inclusive ecosystem-based policies and integrated technologies demonstrate the potential to effectively address climate change impacts across scales and sectors, yet implementation barriers remain (CCP6.4.1).

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[[File:8a53df49424426aa01f7c1137c0e7b15 IPCC_AR6_WGII_Figure_CCP6_002.png]]

'''Figure CCP6.2 |''' '''Observed and projected climate changes across the Arctic (A, C–H) and Antarctic (B, I–N).''' Boundary lines in each plot are based on the polar regions defined in Figure CCP6.1. All data shown here are extracted from the IPCC WGI Interactive Atlas ( [[#Gutiérrez--2021|Gutiérrez et al., 2021]] ; [[#Iturbide--2021|Iturbide et al., 2021]] ); data set details can be found in the Atlas ( https://interactive-atlas.ipcc.ch/ ). Arctic (A) and Antarctic (B) are observed temperature trends (°C per decade) over land for the period 1980–2015, derived from ERA5 adjusted data set. Projected changes from an ensemble of CMIP6 projections: annual mean temperature over land is depicted for 2°C (C, I) and 4°C (F, L). Global warming levels (GWL) in the Arctic and Antarctic, respectively; annual mean sea surface temperature is depicted for 2°C (D, J) and 4°C (G, M) GWL in the Arctic and Antarctic respectively; annual sea ice (%) is depicted for 2°C (E, K) and 4°C (H, N) GWL in the Arctic and Antarctic, respectively.

This Cross Chapter Paper (CCP) assesses the impacts, risks and adaptation implications resulting from the physical and chemical changes in the polar regions that were detailed in the Intergovernmental Panel on Climate Change (IPCC) Working Group I (WGI) contribution to the IPCC 6th Assessment Report (AR6) ( [[#IPCC--2021|IPCC, 2021]] ). Several key WGI AR6 findings have important implications for natural and human systems in polar regions. Warming and wetting have persisted as key climatic impact drivers in polar regions ( ''very high confidence'' ) and will ''very likely'' [[#footnote-000|2]] continue to 2100 ( [[#Fox-Kemper--2021|Fox-Kemper et al., 2021]] ; [[#Gulev--2021|Gulev et al., 2021]] ) with cascading climate effects regarding heatwaves, fire, weather, floods and heavy precipitation, river runoff, snowfall, glaciers and ice sheets (IS), permafrost, lake, river and sea ice, relative sea level and coastal flooding and erosion ( [[#Gutiérrez--2021|Gutiérrez et al., 2021]] ; [[#Ranasinghe--2021|Ranasinghe et al., 2021]] ) (Table CCP6.1). They represent major climate hazards in all key risks for polar regions (Table CCP6.5). Key points of departure for this CCP also include IPCC 5th Assessment Report (AR5) ( [[#IPCC--2014|IPCC, 2014]] ) and the Polar Regions chapter in the Special Report on the Ocean and Cryosphere in a Changing Climate (SROCC) ( [[#Meredith--2019|Meredith et al., 2019]] ). SROCC assessed physical, biological and social systems concerning the Arctic and Antarctic Oceans and cryosphere, and how they are affected by current and future climate change. This CCP assesses the rapidly increasing evidence that has been published since AR5 and SROCC, and advances previous IPCC assessments. First, results from the Coupled Model Intercomparison Projects (CMIP6) are an important advance since SROCC, which improve the certainty and resolution of projections of the main climate impact drivers and the risks they have for polar systems ( [[#Fox-Kemper--2021|Fox-Kemper et al., 2021]] ; [[#Ranasinghe--2021|Ranasinghe et al., 2021]] ). Second, building from the framework outlined in SROCC ( [[#Crate--2019|Crate et al., 2019]] ), scientific, Indigenous knowledge (IK) and local knowledge (LK) systems are included in this assessment. Importantly, Indigenous authors led the assessment of the impacts, adaptation and governance of climate change for Indigenous Peoples, which is an important advance since AR5 and represents an important step towards Indigenous self-determination in international assessment processes ( [[#Ford--2012|Ford et al., 2012]] ; [[#Ford--2016|Ford et al., 2016]] ; [[#Hill--2020|Hill et al., 2020]] ).

Herein, observed impacts and future risks (CCP6.2), key risks and adaptation (CCP6.3) and climate resilient development pathways (CCP6.4) in the polar regions are assessed. The CCP describes how the implications of climate change impacts in the Arctic and Antarctic extend beyond their boundaries, in terms of transregional coupled ecological systems (CCP6.2.1, CCP6.2.2), global nutritional security (CCP6.2.3), global trade and shipping (CCP6.2.4) and cultural value (CCP6.2.5, CCP6.2.6). Given the synthetic and policy-facing mandate of CCPs and with SROCC as a key point of departure, this CCP is not intended to cover the full breadth of issues for polar regions but rather it highlights select key policy-relevant topics by synthesising and adding value to the relevant material from AR6 sectoral and regional chapters.

'''Table CCP6.1 |''' Climatic impact drivers in the Arctic and Antarctic derived from WGI-AR6 chapters (indicated as WGI-9 ( [[#Fox-Kemper--2021|Fox-Kemper et al., 2021]] ) and WGI-12 ( [[#Ranasinghe--2021|Ranasinghe et al., 2021]] )) and [[#Meredith--2019|Meredith et al. (2019)]] (indicated as SROCC-3). Supplementary Material (SMCCP6.1) contains supplemental data for these drivers of projected changes (2021–2040, 2041–2060, 2081–2100) derived from the WGI-AR6 Interactive Atlas (indicated as Atlas) ( [[#Gutiérrez--2021|Gutiérrez et al., 2021]] ) ( https://interactive-atlas.ipcc.ch ).

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

! '''Region'''

! '''Observed changes'''

! '''Projected changes'''

|-
| colspan="4"| '''''Marine and sea ice'''''

|-
| ''Sea level (relative)''

| Arctic

| No consistent trend (increase in northwest America, decrease in northeast America, stable in Greenland and Arctic Russia) (WG1-12)

| Rise in all polar regions (except areas of substantial land uplift in northeast Canada, the west coast of Greenland) ( ''high confidence'' );

Increase of extreme sea levels in Russian Arctic and northwest America ( ''high confidence'' ) Greenland/Iceland and northeast America (given glacial isostatic adjustment) ( ''medium confidence,'' WG1-12)

|-
|
| Antarctic

|
| Rise in all polar regions (except areas of substantial land uplift in west Antarctica) ( ''high confidence'' , WG1-12)

|-
| ''Sea surface temperature''

| Arctic

| Increase of ~0.5°C per decade during 1982–2017 in ice-free regions in summer ( ''high confidence'' , SROCC-3)

| Further increases ( ''high confidence'' , WG1-12)

|-
|
| Antarctic

| Warmed in northern areas of Southern Ocean but cooled in its southernmost regions since the 1980s ( ''high confidence'' , SROCC-3)

| Circumpolar increases ( ''high confidence'' , WG1-12)

|-
| ''Sea ice cover''

| Arctic

| Loss (particularly of multi-year sea ice) accelerated since 2001 ( ''very likely'' , WG1-9)

| Will become sea ice free (&lt; 1 × 10 6 km 2 ) during summer before 2050, irrespective of global warming level ( ''likely'' , WG1-9)

|-
|
| Antarctic

| No significant circumpolar trend from 1979–2018 ( ''very high confidence'' ), but decrease off the Antarctic Peninsula ( ''high confidence'' ) and increases and decreases in other regions ( ''medium confidence'' , WG1-9)

| Circumpolar decrease ( ''low confidence'' due to limited understanding of driving processes, WG1-9)

|-
| ''Ocean surface pH''

| Both poles

| Decrease since 1980 at rates of 0.003–0.026 pH units per decade in open polar zones ( ''very likely'' , WG1-12)

| Further acidification by 0.1–0.6 pH by 2100 (Atlas), characterised by year-round conditions corrosive for aragonite minerals by 2100 ( ''very likely'' , SROCC-3)

|-
| colspan="4"| '''''Terrestrial, freshwater and ice'''''

|-
| Atmospheric temperature

| Arctic

| Increase of means higher than twice global mean, most pronounced in cold season ( ''high confidence'' , WG1-12)

| Further increase (Table SMCCP6.1)

|-
|
| Antarctic

| Warmed from 1957 to 2016 at 0.2–0.3°C per decade in west Antarctica ( ''very likely'' ); no consistent change in east Antarctica ( ''limited evidence'' , WG1-12)

| Region: future warming across continent ( ''high confidence'' , WG1-12)

|-
| Extreme heat events

| Arctic

| Increase since 1979 (WG1-12)

| Polar amplification will drive further increases ( ''high confidence'' , WG1-12)

|-
|
| Antarctic

| Heatwave across Antarctica (2020) (WG1-12, ( [[#Robinson--2020|Robinson et al., 2020]] ).

| Further increase, with &gt;50 additional days above freezing by 2100 (under RCP8.5, vs. 2014) over the Antarctic Peninsula but smaller changes over mainland Antarctica ( ''medium confidence,'' WG1-12)

|-
| ''Fire weather (FW)''

| Arctic

| Over four decades, fire season lengthened and number of fires increased in North America (WG1-12)

| FW index increases and more frequent fires in tundra regions ( ''high confidence'' , WG1-12)

|-
| Precipitation

| Arctic

| Increase, highest during the cold season ( ''likely'' , Atlas)

|
|-
|
| Antarctic

| Increasing trend over the 20th century, while large interannual variability masks any existing trend since the end of 1970 ( ''medium confidence'' , Atlas)

|
|-
| ''Floods''

| Arctic

| Increasing river runoff, increasing heavy precipitation ( ''high confidence'' , WG1-12)

| Further increases in all variables ( ''high confidence'' , WG1-12)

|-
| ''Snowfall''

| Arctic

| Recent overall declines in snow extent and seasonal duration ( ''high confidence'' , WG1-12)

| Higher % of precipitation as rain (fall and spring) ( ''high confidence'' , WG1-12)

|-
|
| Antarctic

| Increases in the 20th century ( ''medium confidence'' , WG1-12)

| Further increases (over land) ( ''likely'' , WG1-12)

|-
| ''Glaciers and IS''

| Arctic

| Losses in glacier mass since 2000 ( ''high confidence'' , WG1-12); losses in Greenland IS mass since 1980 at increasing rates ( ''high confidence'' , WG1-9)

| Further mass loss until 2100 under all warming scenarios ( ''virtually certain'' , WG1-9 and -12)

|-
|
| Antarctic

| Losses in glacier mass since 2000 ( ''high confidence'' , WG1-12); losses in Antarctic IS mass since 1992 (in west Antarctica but also parts of east Antarctica since 2000) ( ''high confidence'' , WG1-9)

| Further mass loss until 2100 under all warming scenarios ( ''likely'' , WG1-9 and -12)

|-
| ''Permafrost''

| Arctic

| Rising permafrost temperatures over past three to four decades ( ''high confidence'' , WG1-9); decreases in permafrost active layer thickness ( ''very high confidence'' ) ( [[#Biskaborn--2019|Biskaborn et al., 2019]] ). Submarine permafrost warming ( ''medium confidence'' , WG1-9)

| Increases in temperature and active layer thickness (WG1-9); near-surface terrestrial permafrost extent will reduce under all scenarios by 2100 ( ''virtually certain'' , WG1-9)

|-
|
| Antarctic

| Rising permafrost temperatures over past three to four decades ( ''high confidence'' , WG1-9)

|
|-
| ''Lake, river ice''

| Arctic

| Declines in seasonal lake ice cover thickness and duration over most Arctic lakes; declines in cold-season river ice extent ( ''high confidence,'' WG1-12)

| Many lakes will lose &gt;1 month lake ice cover by 2050 ( ''medium confidence'' ), Reductions in average Northern Hemisphere seasonal river ice duration of 6.10 days per 1°C GWL (WG1-12)

|-
| ''Coastal floods/erosion''

| Arctic

| Increase ( ''medium confidence'' , WG1-12)

| Further increase ( ''high agreement-limited evidence,'' WG1-12)

|-
|
| Antarctic

| (Lack of studies, WG1-12)

|
|}

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