Radical Uncertainty in the Arctic

Twenty years ago the Arctic was more resilient than now as sea ice was three times thicker than today. Heavier and more persistent sea ice provided a buffer against the influence of short-term climate fluctuations. Increases in sea ice/atmospheric interactions now lead to revisiting the concept of abrupt change. The recent decade has seen an increase in Arctic extreme events in climate and ecosystems including events beyond previous records. Radical uncertainty is defined by situations for which historical data provide limited guidance to future outcomes. The type, location, and timing are unknowable. The Arctic has reached such a place due to an increase of multiple process interactions causing new extremes. Recent multi-year environmental extremes, albedo instabilities, and increased sensitivity of sea ice to storms in marginal seas, are overcoming negative radiative feedback that point to the passing of impending climatic and ecosystem thresholds. Current climate models have deficiencies in including multiple storm-sea ice/tundra-ecosystem interactions. Such new extremes include Greenland ice mass loss, sea ice as thin and more mobile, permafrost melt, wildfires, bottom to top ecosystem reorganizations, Asian cold events, and shifts in the stratospheric polar vortex and tropospheric jet stream. Unless CO2 emissions are reduced, further Arctic extremes are expected in the next decades, faster than projected by models, with environmental and societal impacts spreading through the Arctic and beyond.