evidence: J. C. Comiso, A. C. Bliss, R. Gersten, C. L. Parkinson, and T. Markus Background The sea ice cover is one of the key components of the polar climate system. It has been a focus of attention in recent years, largely because of a strong decrease in the Arctic sea ice cover and modeling results that indicate that global warming is amplified in the Arctic on account of ice-albedo feedback. This results from the high reflectivity (albedo) of the sea ice compared to ice-free waters. A satellite-based data record starting in late 1978 shows that indeed rapid changes have been occurring in the Arctic, where the ice coverage has been declining at a substantial rate. In contrast, in the Antarctic the sea ice coverage has been increasing although at a lesser rate than the decreases in the Arctic. Shown below are up-to-date satellite observations of the sea ice covers of both the Arctic and the Antarctic, along with comparisons with the historical satellite record of more than 4 decades.