Estimating the global radiative impact of the sea ice-albedo feedback in the Arctic

A simple method for estimating the global radiative forcing caused by the sea ice-albedo feedback in the Arctic is presented. It is based on observations of cloud cover, sea ice concentration, and top-of-atmosphere broadband albedo. The method does not rely on any sort of climate model, making the assumptions and approximations clearly visible and understandable and allowing them to be easily changed. Results show that the globally and annually averaged radiative forcing caused by the observed loss of sea ice in the Arctic between 1979 and 2007 is approximately 0.1 W m(-2); a complete removal of Arctic sea ice results in a forcing of about 0.7 W m(-2), while a more realistic ice-free summer scenario (no ice for 1 month and decreased ice at all other times of the year) results in a forcing of about 0.3 W m(-2), similar to present-day anthropogenic forcing caused by halocarbons. The potential for changes in cloud cover as a result of the changes in sea ice makes the evaluation of the actual forcing that may be realized quite uncertain since such changes could overwhelm the forcing caused by the sea ice loss itself, if the cloudiness increases in the summertime.