The Immediacy of Arctic Change

As we examine the world after the Paris Agreement, lessons from recent environmental trends and modelling of the impacts on the Arctic cryosphere under different greenhouse gas (GHG) concentration show, with increasing confidence, that stabilizing global temperatures near 2° C will slow but not halt large changes in the Arctic in the foreseeable future (decades). Substantial changes in the Arctic environment and feedbacks into the global system are inevitable before mid-century, even under the most optimistic greenhouse gas reduction scenarios, and are emission dependent in the second half of the century. Sea ice has undergone a regime shift from multi-year to first-year sea ice, and summer sea ice is very likely to be esentially gone within the next few decades. The Arctic cryosphere has the potential to affect ecosystems and humans outside the Arctic through sea level rise, a growing evidence of influence on weather, GHG release, and climate feedbacks to ocean and atmospheric circulation. Recent extreme winter temperatures in 2016 and lack of winter sea ice cover in winter 2017, both suggest new and rapid shifts in the Arctic. There is evidence for two-way interactions between the Arctic and midlatitudes. Although thermodynamic forcing of weather systems by rising Arctic temperatures and loss of sea ice is increasing, dynamic linkages are confounded by the large chaotic nature of the jet stream, and thus potential midlatitude impacts are nonlinear. Linkages appear to be regional (eastern Asia and eastern North America) and episodic. Extreme warming of the Arctic in winter 2016 and fall 2016 had a strong trajectories from midlatitudes.