The high-latitude ice/snow-albedo feedback is a principal element in many pateoclimate theories and global warming scenarios. The strength of this feedback is determined by the ice/snow effects on the top-of-atmosphere (TOA) albedo, which is also strongly affected by clouds. Using currently available satellite observations, we estimate the radiative effectiveness (RE) of ice and snow with regards to the TOA albedo, which we define as the change in the TOA albedo corresponding to changes of 0% to 100% in the ice or snow cover. The REs of the northern hemisphere (NH) sea ice, land snow, and southern hemisphere (SH) sea ice are found to be 0.22, 0.23 and 0.16, respectively. This means that, for an incident solar flux of about 400 W m(-2) reaching the TOA it? the polar latitudes in summer, local reduction in ice/snow concentrations from 100% to 0% will result in a decrease in reflected short wave radiation of approximately 80 W m(-2). These changes in the TOA albedo are significant, yet smaller than the associated changes in the surface albedo. Comparison of the TOA albedo values with available surface albedo observations helps to identify the role of clouds in the RE of ice/snow. The analysis is based on the whole time-space domain where the sect ice and land snow appear, and reveals a remarkable similarity in the ice and snow RE in the areas with high sea-ice and land-snow cover variability, despite the varying nature of the surface cover, seasonality, and locations. These estimates provide a useful constraint to test current climate models.
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