The Arctic sea ice represents an important energy reservoir for the climate of the northern hemisphere. The shrinking of the polar ice in the past decades decreases the stored energy and raises serious concerns about future climate changes.[1-4] Model calculations of the present authors [5,6] suggest that half of the global warming during the past fifty years is directly related to the retreat of the sea ice, while the cause is not well understood, e.g. the role of surface pollution [7-10]. We have analysed the reported annual melting and freezing data of the northern sea ice in the years 1979 to 2018 [11] to gain some insight. Two features can be deduced from our simple model: (i) recent results [12,13] are confirmed that approximately 60 % of the loss of sea ice stems from energy transport to the arctic region. (ii) We find evidence that the remaining part of the ice retreat originates from an increasing surface absorption of solar radiation, obviously due to the rising surface pollution of the sea ice. While the phenomenon was previously considered by several authors in a qualitative way, our analysis contributes semi-quantitative information on the situation. We estimate that the relevant fall-out of light absorbing aerosols onto the sea ice increased by 17 +/- 5 % during the past fifty years. A deposition of additional 3 +/- 1 % of solar radiation in the melting region results that accounts for the ice retreat. Recalling the important role of the ice loss for the terrestrial climate,[3,5,9] the precipitation of air pollution in the Arctic seems to be an important factor for the global warming.
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