In this paper we present results of an atmospheric general circulation model (GCM) experiment in which Arctic sea ice limits were substantially reduced in all months. March sea ice limits were set equivalent to modern September limits, and all sea ice was removed in September. Sea ice coverage for other months varied between these two extremes. This climate sensitivity experiment makes predictions about mean northern hemisphere atmospheric conditions (including temperature, pressure, wind patterns, and precipitation) consistent with these boundary constraints. The major effects of reduced sea ice limits are observed in winter. They include large regional warming of the circum‐Arctic region, northward migration of the Icelandic low pressure system, and strengthening of the Azores high. Changes in net heating over the North Atlantic Ocean suggest that increases in sea surface temperatures and salinities in this region would also accompany reductions in Arctic sea ice limits. In the wind field, a weakening of the polar easterlies and an intensification of cyclonic circulation over the Norwegian‐Greenland Sea suggest that surface water exchange between the Atlantic and Arctic would increase when sea ice limits are reduced. However, zonally averaged changes in strength of the westerlies or upper level jet stream are minimal. The late Pliocene cooling of the North Atlantic Ocean and North American Arctic margin may have been linked in part to the development of perennial sea ice co
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