Arctic cloud and sea ice feedbacks from satellite observations and a global climate model*

Over the next century, the Arctic Ocean is projected to become seasonally sea ice-free. Assessing feedbacks between clouds and sea ice as the Arctic loses sea ice cover is important because of clouds’ radiative impacts on the Arctic surface. Here, present and future Arctic cloud-sea ice relationships are assessed using spaceborne lidar observations and a fully-coupled global climate model that incorporates a lidar simulator. Using a novel surface mask that restricts the analysis to where sea ice concentration varies, we isolate the influence of sea ice cover on Arctic Ocean clouds during summer and fall. Summer cloud structure and fraction are nearly identical over sea ice and over open water, but more clouds are observed over open water than over sea ice in the fall. With future sea ice loss, modeled summer cloud fraction, vertical structure, and optical depth barely change, while the boundary layer deepens and clouds become more opaque over open water during fall. There is little evidence for a summer cloud-sea ice feedback but strong evidence for a positive cloud-sea ice feedback that emerges during non-summer months as the Arctic warms and sea ice disappears.