Arctic amplification

Arctic amplification describes the enhanced warming of the Arctic relative to the global average during periods of global warming. It is a regional response of the coupled atmosphere, ocean, snow and sea-ice system, not a separate source of global warming. The Intergovernmental Panel on Climate Change assessed that Arctic surface air temperature likely increased by more than twice the global average over the two decades preceding its 2019 polar-regions assessment, with loss of snow and sea ice contributing to the amplified warming. The precise ratio depends on the period, region and metric being compared.

Snow and sea ice reflect a substantial share of incoming sunlight. When they retreat, darker ocean or land is exposed and absorbs more solar energy, warming the surface and encouraging further melting. This is the ice–albedo feedback. NOAA explains that this seasonal feedback is one contributor to Arctic amplification. It is not a complete account of the phenomenon: the seasonal pattern of Arctic warming also reflects how energy is exchanged between the ocean, ice and atmosphere.

Research identifies several connected processes in addition to changing surface reflectivity. The Arctic atmosphere often has a strong vertical temperature structure, affecting how added heat is distributed and emitted to space. Water vapour and clouds influence radiation, while ocean heat stored beneath or near the ice can be released to the atmosphere, especially in seasons when ice cover is reduced. Atmospheric and ocean circulation also move energy across the Arctic boundary. Their relative importance differs between seasons and studies. A 2021 analysis of climate-model experiments found that enhanced winter ocean heating associated with sea-ice loss, aided by summer surface-albedo and winter cloud feedbacks, was central in its simulated Arctic amplification; it also cautioned against treating some accompanying atmospheric feedbacks as simple initiating causes.

Amplified Arctic warming accompanies rapid changes in sea ice, snow, permafrost and ecosystems. The IPCC notes that polar-system changes can affect people and climate beyond the region, including through sea-level rise from land-ice loss and the release of greenhouse gases from thawing permafrost. Arctic amplification describes a comparative warming pattern; by itself it does not establish that every local Arctic change is caused by one feedback or predict a particular weather event. Its magnitude and mechanisms are studied using observations, paleoclimate evidence and climate models.