In both polar regions, there is strong evidence of the ongoing impacts of climate change on terrestrial and freshwater species, communities and ecosystems (very high confidence). Recent studies project that such changes will continue (high confidence), with implications for biological resources and globally important feedbacks to climate (medium confidence).
Strong evidence exists of changes in species’ ranges and abundances and in the position of some tree lines in the Arctic (high confidence). An increase in greenness and biological productivity has occurred in parts of the Arctic (high confidence). Surface albedo is projected to decrease and the exchange of greenhouse gases between polar landscapes and the atmosphere will change (very high confidence). Although recent models predict that a small net accumulation of carbon will occur in Arctic tundra during the present century (low confidence), higher methane emissions responding to the thawing of permafrost and an overall increase in wetlands will enhance radiative forcing (medium confidence). [15.4.1, 15.4.2, 15.4.6].
In both polar regions, components of the terrestrial cryosphere and hydrology are increasingly being affected by climate change (very high confidence). These changes will have cascading effects on key regional bio-physical systems and cause global climatic feedbacks, and in the north will affect socio-economic systems (high confidence).
Freshwater and ice flows into polar oceans have a direct impact on sea level and (in conjunction with the melt of sea ice) are important in maintaining the thermohaline circulation. In the Arctic, there has been increased Eurasian river discharge to the Arctic Ocean, and continued declines in the ice volume of Arctic and sub-Arctic glaciers and the Greenland ice sheet (very high confidence). Some parts of the Antarctic ice sheet are also losing significant volume (very high confidence). Changes to cryospheric processes are also modifying seasonal runoff and routings (very high confidence). These combined effects will impact freshwater, riparian and near-shore marine systems (high confidence) around the Arctic, and on sub-Antarctic islands. In the Arctic, economic benefits, such as enhanced hydropower potential, may accrue, but some livelihoods are likely to be adversely affected (high confidence). Adaptation will be required to maintain freshwater transportation networks with the loss of ice cover (high confidence). [15.4.1, 15.4.6, 15.7.1].
Continued changes in sea-ice extent, warming and acidification of the polar oceans are likely to further impact the biomass and community composition of marine biota as well as Arctic human activities (high confidence).
Although earlier claims of a substantial mid-20th century reduction of Antarctic sea-ice extent are now questioned, a recently reported decline in krill abundance is due to regional reductions in Antarctic sea-ice extent; any further decline will adversely impact their predators and ecosystems (high confidence). Acidification of polar waters is predicted to have adverse effects on calcified organisms and consequential effects on species that rely upon them (high confidence). The impact of climate change on Arctic fisheries will be regionally specific; some beneficial and some detrimental. The reduction of Arctic sea ice has led to improved marine access, increased coastal wave action, changes in coastal ecology/biological production and adverse effects on ice-dependent marine wildlife, and continued loss of Arctic sea ice will have human costs and benefits (high confidence). [15.2.1, 15.2.2, 15.4.3].
Already Arctic human communities are adapting to climate change, but both external and internal stressors challenge their adaptive capabilities (high confidence). Benefits associated with climate change will be regionally specific and widely variable at different locations (medium confidence).
Impacts on food accessibility and availability, and personal safety are leading to changes in resource and wildlife management and in livelihoods of individuals (e.g., hunting, travelling) (high confidence). The resilience shown historically by Arctic indigenous peoples is now being severely tested (high confidence). Warming and thawing of permafrost will bring detrimental impacts on community infrastructure (very high confidence). Substantial investments will be needed to adapt or relocate physical structures and communities (high confidence). The benefits of a less severe climate are dependant on local conditions, but include reduced heating costs, increasing agricultural and forestry opportunities, more navigable northern sea routes, and marine access to resources (medium confidence). [15.4.5, 15.5, 15.7]