The Response of the Polar Regions to Increased CO2 in a Global Climate Model with Elastic–Viscous–Plastic Sea Ice

Abstract

A global atmosphere?ocean?sea ice general circulation model (GCM) is used in simulations of climate with present-day atmospheric CO2 concentrations, and with CO2 increasing to double the present-day values. The Parallel Climate Model includes the National Center for Atmospheric Research (NCAR) atmospheric GCM, the Los Alamos National Laboratory ocean GCM, and the Naval Postgraduate School dynamic?thermodynamic sea ice model. The ocean and sea ice grids are at substantially higher resolution than has been previously used in global climate models. The model is implemented on distributed, parallel computer architectures to make computation on the high-resolution grids feasible. The sea ice dynamics uses an elastic?viscous?plastic ice rheology with an explicit solution of the ice stress tensor, which has not previously been used in a coupled, global climate model. The simulations of sea ice and the polar climate in the present-day experiment are compared with observed ice and climate data. The ice cover is too extensive in both hemispheres, leading to a large area of lower-than-observed surface temperatures. The Arctic exhibits a persistent high pressure system that drives the ice motion anticyclonically around the central Arctic. The ice thickness is greatest near the Chukchi Peninsula. Ice is exported through the Fram Strait, though the Canadian Archipelago, and inward through the Bering Strait. The modeled Antarctic sea ice moves at a faster speed than the observational data suggest. Many of the results and biases of the model are similar to those of the NCAR Climate System Model, which has the same atmospheric model component. The response of the model to the increase in CO2 shows a significant thinning of the Arctic sea ice by 0.5 m but only a 10% decrease in ice area. Ice concentrations are reduced within the ice pack, while the ice edges are relatively unchanged. The Antarctic sea ice exhibits much less change in area and little change in thickness, in agreement with the reduced warming in the entire Southern Hemisphere.