Arctic Ice and Cloud Feedbacks in CMIP5 Models

Over the twentieth century, the observed warming in the Arctic was almost twice that of the entire globe. This dramatic warming is directly related to the decrease in sea ice cover and thickness. Arctic ice acts as an insulator that keeps the ocean from warming the overlying atmosphere. Sea ice melt is driven by the ice-albedo feedback and also by changes in the downwelling longwave radiation from water vapor and clouds. This study aimed to assess predictions of changes in Arctic sea ice cover in selected CMIP5 simulations, and to determine the main drivers behind those changes. Surface air temperature, water vapor content, cloud fraction and downwelling longwave radiation were studied using CMIP5 simulations with the CCSM4, HADGEM2-CC and MIROC5 models, for RCP8.5. As radiative forcing increased from 2006 to 2100, surface air temperature and water vapor content also increased. Cloud fraction increased over the sea ice and decreased over high latitude land. The increased water vapor and cloudiness over the Arctic Ocean strongly affected the downwelling longwave radiation at the surface, which also increased over time. Our analysis shows that the models produce a longwave feedback that is strongly contributing to sea ice melt.