Effect of retreating sea ice on Arctic cloud cover in simulated recent global warming

Abstract

This study investigates the effect of sea ice reduction on Arctic cloud cover in historical simulations with the coupled Atmosphere-Ocean general circulation model MIROC5. Arctic sea ice has been shown to exhibit substantial reductions under simulated global warming conditions since the 1970s, particularly in September. This simulated reduction is consistent with satellite observation results. However, Arctic cloud cover increases significantly during October, leading to extensive reductions in sea ice because of the enhanced heat and moisture fluxes from the underlying ocean. Sensitivity experiments with the atmospheric model MIROC5 clearly show that sea ice reduction causes increased cloud cover. Increased cloud cover occurs primarily in the lower troposphere; however, clouds in the thin surface layers directly above the ocean decrease despite the increased moisture flux because the surface air temperature rises in these thin layers, causing the relative humidity to decrease. As cloud cover increases, the cloud radiative effect cause an increase in the surface downward longwave radiation (DLR) by approximately 40–60 % compared with changes in clear-sky surface DLR in fall. These results suggest that an increase in Arctic cloud cover as a result of reduced sea ice coverage may further melt the sea ice and enhance the feedback processes of Arctic warming.