| Summary: | As global climate changes are becoming increasingly evident, increasing air temperatures, melting glaciers, rising sea levels, and decreasing biodiversity is observed at increasing rates worldwide. The Arctic sea ice cover has has become a key indicator of the ongoing global climate change through its substantial decline in both extent and thickness. In this study we show how the observed regression of the Northern Hemisphere sea ice is distributed over different regions of the Arctic Ocean and adjacent seas. We further provide an evaluation of to what extent the regions are re ecting changes during summer or winter seasons, exemplified by the months of September and March. We also relate the changes to observed atmospheric and oceanographic conditions. Data from passive microwave satellite measurements are used to investigate regional and seasonal time series of ice extent. All regions except one show a decreasing trend throughout the data record. It is found that six of twelve regions has seen an accelerated decline during the last decade. This is either caused by an increasingly smaller summer minimum, or by a prolongation of the regional summer season. It is further found that summer melting is initiated by atmospheric heat in the areas where the recession of ice extent most prominent. The process of freezing during winter is found to be particularly sensitive to the oceanic temperatures in the regions receiving currents of warm Atlantic Water. M-MF
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