Climate Sensitivity to Continental Ice Sheet Size and Configuration

Richard A. Shinn Earth System Science Center, The Pennsylvania State University, University Park, Pennsylvania

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Eric J. Barron Earth System Science Center, The Pennsylvania State University, University Park, Pennsylvania

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Abstract

A version of the NCAR Community Climate Model (CCM) has been used to carry out a study of climate sensitivity to the size and distribution of continental ice sheets by comparing two perpetual season, fixed sea surface temperature (SST), winter simulations of the climate at a glacial maximum. The two simulations differ only in the size and configuration of the continental ice sheet boundary conditions. These conditions represent minimum and maximum ice sheet extent for a glacial maximum as presently constrained by the geologic evidence. All other boundary conditions are as specified by CLIMAP (1981) for winter surface conditions during the Last Glacial Maximum (LGM). The ice sheets specified by CLIMAP (1981), used by many previous researchers to simulate ice age climate conditions, are intermediate in size between the minimum and maximum ice sheets used for the simulations described here. The maximum case simulation resulted in unexpected positive temperature anomalies over the Northern Hemisphere midlatitudes as well as a more baroclinic atmosphere with stronger Northern Hemisphere thermal gradients, jet streams and storm tracks shifted 5° to 10° poleward. A more distinct split jet stream flow is observed over the maximum case Laurentide ice sheet, and jet stream intensity decreases over the maximum case North Pacific while increasing over the maximum case North Atlantic.

Abstract

A version of the NCAR Community Climate Model (CCM) has been used to carry out a study of climate sensitivity to the size and distribution of continental ice sheets by comparing two perpetual season, fixed sea surface temperature (SST), winter simulations of the climate at a glacial maximum. The two simulations differ only in the size and configuration of the continental ice sheet boundary conditions. These conditions represent minimum and maximum ice sheet extent for a glacial maximum as presently constrained by the geologic evidence. All other boundary conditions are as specified by CLIMAP (1981) for winter surface conditions during the Last Glacial Maximum (LGM). The ice sheets specified by CLIMAP (1981), used by many previous researchers to simulate ice age climate conditions, are intermediate in size between the minimum and maximum ice sheets used for the simulations described here. The maximum case simulation resulted in unexpected positive temperature anomalies over the Northern Hemisphere midlatitudes as well as a more baroclinic atmosphere with stronger Northern Hemisphere thermal gradients, jet streams and storm tracks shifted 5° to 10° poleward. A more distinct split jet stream flow is observed over the maximum case Laurentide ice sheet, and jet stream intensity decreases over the maximum case North Pacific while increasing over the maximum case North Atlantic.

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