Sensitivity studies evaluate the greatest impact that Arctic and Antarctic sea-ice anomalies could have on the global atmospheric
circulation with 15-year seasonal cycle simulations of the NCAR Community Climate Model version 2 (CCM2). In separate sensitivity experiments, all Arctic sea ice or Antarctic sea ice were removed and replaced by open water at -1.9 degrees C. The results of the simulations were compared against each other and to a standard
15-year seasonal cycle run with boundary conditions set for the present climate. Arctic sea ice is different from Antarctic sea ice in these simulations in that the Northern Hemisphere (NH) sea ice has less seasonal variability, less maximum seasonal extent and is typically closer to the pole than Southern Hemisphere (SH) sea
ice. Surface thermal forcing resulting from the Arctic sea ice removal tends to be larger in the zonal mean and less in zonal wavenumbers 1 and 2 than that resulting from Antarctic sea ice removal. Statistically significant response in both hemispheres result from the Arctic sea ice removal as well as from the Antarctic sea ice removal. The responses include a global redistribution of atmospheric mass. The anomalies resulting from Arctic sea ice
removal are more significant in the SH during austral autumn (NH spring) about the time of maximum climatological NH sea ice extent. The local response in the NH responses is largest during winter. A parallel response results from the Antarctic sea ice removal.
Maximum NH response to SH sea ice removal occurs during August to November, about the time of maximum climatological sea ice extent in the SH. The maximum local response occurs during winter in the SH.
Cross-hemispheric responses appear to be more dramatic in the case
of SH sea ice removal, suggesting that changes in Antarctic sea ice may have a larger global atmospheric impact than changes in Arctic
sea ice. The forcing of local surface pressure anomalies by the Antarctic sea ice removal is largely confined to zonal wavenumbers 1-3. Both zonal wavenumbers 1 and 2 of the surface pressure anomaly contribute to a modified East Asian monsoon circulation noted in an earlier study. The filtered pressure anomaly field shows increased pressure over southern China near 20 degrees N and decreased pressure to the north near 40 degrees N. Thus, the contribution of wavenumbers 1 and 2 of the pressure anomaly help produce a highly localized
change in monsoon precipitation in response to the Antarctic sea ice removal.