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Abstract

What can we learn from the waning Arctic sea ice? About the Arctic climate system, our impacts on it, about the Earth system as a whole? This presentation explores these questions from a variety of angles, bringing together models and observations, the millimetre scale of sea-ice crystals and large scale global impacts, climate-model projections of future Arctic sea ice and our own inability to preserve the Arctic summer sea-ice cover. The ongoing loss of Arctic sea ice is among the most pronounced consequences of global warming that we have observed so far. Because of the very high signal-to-noise ratio of the satellite record over the past 40 years, the observed sea-ice retreat can be interpreted as a highly sensitive proxy for our ability to understand the climate system, to model its change, to assess its future evolution, and to draw the necessary consequences from these insights. This is the more the case as many of the governing processes are surprisingly linear, which in principle allows one to greatly simplify the complexity of the presented analyses for example of Arctic amplification, climate sensitivity, Arctic clouds, and the response of radiative fluxes.