| Summary: | The Last Glacial Maximum (LGM) Laurentide Ice Sheet covered most of the North American continent poleward of 40 degrees N, with the exception of Alaska that remained relatively warm, dry, and largely ice free. Experiments with a global atmospheric circulation model are in broad agreement with proxies: the Alaskan summer temperatures are comparable to the preindustrial, and the annual precipitation is reduced by 30-50%. The warm conditions are attributed to a lowering of the local planetary albedodue to a decreased cloudiness in response to the cold LGM sea surface temperatures (SSTs) and a stationary anticyclone forced by the ice sheetthat allows more shortwave radiation to reach the surface. Stationary waves are shown to counteract the shortwave cloud feedback by converging less heat over the target region. The LGM SST field also yields an equatorward shifted Pacific stormtrack, which results in drier conditions in Alaska and abundant precipitation at the southern margin of the Laurentide Ice Sheet.
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