Polar Regions

Abstract

This chapter assesses the state of physical, biological and social knowledge concerning the Arctic and Antarctic ocean and cryosphere, how they are affected by climate change, and how they will evolve in future.Concurrently, it assesses the local, regional and global consequences and impacts of individual and interacting polar system changes, and it assesses response options to reduce risk and build resilience in the polar regions.Key findings are:(1979-2018).While the drivers of historical decadal variability are known with medium confidence, there is currently limited evidence and low agreement concerning causes of the strong recent decrease (2016)(2017)(2018), and low confidence in the ability of current-generation climate models to reproduce and explain the observations.{3.2.1.1}Shipping activity during the Arctic summer increased over the past two decades in regions for which there is information, concurrent with reductions in sea ice extent (high confidence).Transit times across the Northern Sea Route have shortened due to lighter ice conditions, and while long-term, pan-Arctic datasets are incomplete, the distance travelled by ships in Arctic Canada nearly tripled during 1990-2015 (high confidence).Greater levels of Arctic ship-based transportation and tourism have socioeconomic and political implications for global trade, northern nations, and economies linked to traditional shipping corridors; they will also exacerbate region specific risks for marine ecosystems and coastal communities if further action to develop and adequately implement regulations does not keep pace with increased shipping (high confidence).{3.2.1.1;3.2.4.2; 3.2.4.3; 3.4.3.3.2;3.5.2 .7}Permafrost temperatures have increased to record high levels (very high confidence), but there is medium evidence and low agreement that this warming is currently causing northern permafrost regions to release additional methane and carbon dioxide.During 2007-2016, continuous-zone permafrost temperatures in the Arctic and Antarctic increased by 0.39 0.15C and 0.37 0.10C respectively.Arctic and boreal permafrost region soils contain 1460-1600 Gt organic carbon (medium confidence).Changes in permafrost influence global climate through emissions of carbon dioxide and methane released from the microbial breakdown of organic carbon, or the release of trapped methane.{3.4.1; 3.4.3}Climate-related changes to Arctic hydrology, wildfire and abrupt thaw are occurring (high confidence), with impacts on vegetation and water and food security.Snow and lake ice cover has declined, with June snow extent decreasing 13.4 5.4% per decade (1967-2018) (high confidence).Runoff into the Arctic Ocean increased for Eurasian and North American rivers by 3.3 1.6% and 2.0 1.8% respectively (1976-2017; medium confidence).Area burned and frequency of fires (including extreme fires) are unprecedented over the last 10,000 years (high confidence).There has been an overall greening of the tundra biome, but also browning in some regions of tundra and boreal forest, and changes in the abundance and distribution of animals including reindeer and salmon (high confidence).Together, these impact access to (and food availability within) herding, hunting, fishing, forage and gathering areas, affecting the livelihood, health and cultural identity of residents including Indigenous peoples (high confidence).{3.4.1; 3.4.3;3.5.2}Limited knowledge, financial resources, human capital and organisational capacity are constraining adaptation in many human sectors in the Arctic (high confidence).Harvesters of renewable resources are adjusting timing of activities to changes in seasonality and less safe ice travel conditions.Municipalities the mass of glaciers.Important differences in the trajectories of loss emerge from 2050 onwards, depending on mitigation measures taken (high confidence).For stabilised global warming of 1.5C, an approximately 1% chance of a given September being sea ice free at the end of century is projected; for stabilised warming at a 2C increase, this rises to 10-35% (high confidence).The potential for reduced (further 5-10%) but stabilised Arctic autumn and spring snow extent by mid-century for Representative Concentration Pathway (RCP)2.6 contrasts with continued loss under RCP8.5 (a further 15-25% reduction to end of century) (high confidence).Projected mass reductions for polar glaciers between 2015 and 2100 range from 16 7% for RCP2.6 to 33 11% for RCP8.5 (medium confidence).{3.2.2; 3.3.2;3.4.2,Cross-Chapter Box 6 in Chapter 2}Both polar oceans will be increasingly affected by CO2 uptake, causing conditions corrosive for calcium carbonate shell-producing organisms (high confidence), with associated impacts on marine organisms and ecosystems (medium confidence).It is very likely that both the Southern Ocean and the Arctic Ocean will experience year-round conditions of surface water undersaturation for mineral forms of calcium carbonate by 2100 under RCP8.5;under RCP2.6 the extent of undersaturated waters are reduced markedly.Imperfect representation of local processes and sea ice interaction in global climate models limit the ability to project the response of specific polar areas and the precise timing of undersaturation at seasonal scales.Differences in sensitivity and the scope for adaptation to projected levels of ocean acidification exist across a broad range of marine species groups.{3.2.1; 3.2.2.3; 3.2.3}Future climate-induced changes in the polar oceans, sea ice, snow and permafrost will drive habitat and biome shifts, with associated changes in the ranges and abundance of ecologically important species (medium confidence).Projected shifts will include further habitat contraction and changes in abundance for polar species, including marine mammals, birds, fish, and Antarctic krill (medium confidence).Projected range expansion of subarctic marine species will increase pressure for high-Arctic species (medium confidence), with regionally variable impacts.Continued loss of Arctic multi-year sea ice will affect ice-related and pelagic primary production (high confidence), with impacts for whole ice-associated, seafloor and open ocean ecosystems.On Arctic land, projections indicate a loss of globally unique biodiversity as some high Arctic species will be outcompeted by more temperate species and very limited refugia exist (medium confidence).Woody shrubs and trees are projected to expand, covering 24-52% of the current tundra region by 2050.{3.2.2.1; 3.2.3;3.2.3.1;Box 3.4; 3.4.2;3.4.3}The projected effects of climate-induced stressors on polar marine ecosystems present risks for commercial and subsistence fisheries with implications for regional economies, cultures and the global supply of fish, shellfish, and Antarctic krill (high confidence).Future impacts for linked human systems depend on the level of mitigation and especially the responsiveness of precautionary management approaches (medium confidence).Polar regions support several of the world's largest commercial fisheries.Specific impacts on the stocks and economic value in both regions will depend on future climate change and on the strategies employed to manage the effects on stocks and ecosystems (medium confidence).Under high emission scenarios current management strategies of some high-value stocks may not sustain current catch levels in the future (low confidence); this exemplifies the limits to the ability of existing natural resource management frameworks to address ecosystem change.Adaptive management that combines annual measures and within-season provisions informed by assessments of future ecosystem trends reduces the risks of negative climate change impacts on polar fisheries (medium confidence).{3.2.4; 3.5.2;3.5.

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