Effects of Pollution on Surface Cloud Radiative Forcing in the Arctic

Four  years of observations from Barrow, Alaska, are used to show that the cloud radiative impact on the surface is a net warming effect between October and May and a net cooling in summer. During episodes of high surface haze aerosol concentrations and cloudy skies, both the net warming and net cooling are amplified, ranging from +12.2 Wm-2 in February to -11.8 Wm-2 in August. In liquid clouds, approximately 50%–70% of this change is caused by changes in cloud particle effective radius, with the remainder being caused by unknown atmospheric feedbacks that increase cloud water path. While the yearly averaged warming and cooling effects nearly cancel, the timing of the forcing may be a relevant control of the amplitude and timing of sea ice melt.