| Summary: | The rapid shrinkage of Arctic sea ice is viewed as one of the most dramatic and most well-documented consequences of present climate change. The disappearance of sea ice during summer will have fundamental consequences for the en-vironment and economy of the Arctic. It will also affect weather and climate in lower latitudes, and possibly world-wide through various feedback processes. Observing and modelling programs are in place to understand and predict these changes in the Arctic; including recent efforts at the University of Alberta. The difficulty of understanding and predicting changing Arctic sea-ice cover, in light of global air-temperature increases, becomes obvious when comparing sea-ice trends in the Southern Ocean around Antarctica. The public discussion often ignores the fact that Antarctic sea ice is increasing, both in winter and summer (Fig. 1), while air temperatures are decreasing over most parts of the continent (Thompson and Solomon, 2002). Thus a thorough understanding of the fundamentally different climate sys-tems of the Arctic and Antarctic is required. Here, I summarize some investigations to better un-derstand the nature and role of Antarctic sea ice, performed with the RV Polarstern while I was still with the Alfred
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