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ABSTRACT
Present-day control and 1%yr^sup -1^ increasing carbon dioxide runs have been made using two versions of the Community Climate System Model, version 3.5. One uses the standard versions of the ocean and sea ice components where the horizontal resolution is 1° and the effects of mesoscale eddies are parameterized, and the second uses a resolution of 1/ 108 where the eddies are resolved. This is the first time the parameterization has been tested in a climate change run compared to an eddy-resolving run. The comparison is made not straightforward by the fact that the two control run climates are not the same, especially in their sea ice distributions. The focus is on the Antarctic Circumpolar Current region, where the effects of eddies are of leading order. The conclusions are that many of the differences in the two carbon dioxide transient forcing runs can be explained by the different control run sea ice distributions around Antarctica, but there are some quantitative differences in the meridional overturning circulation, poleward heat transport, and zonally averaged heat uptake when the eddies are parameterized rather than resolved.
1. Introduction
Nearly all projections of future change made with climate models have used an ocean component that has non-eddy-resolving horizontal resolution of about 18 or coarser. Since the late 1990s, the large majority of these ocean components have used the Gent and McWilliams (1990) parameterization to represent the effects of mesoscale eddies on the mean flow. A question that has frequently been raised is: Does this parameterization give the correct ocean response in climate change scenario runs? Examples are Solovev et al. (2002), Hallberg and Gnanadesikan (2006), and a recent review paper on the Southern Ocean by Marshall and Speer (2012). Marshall and Speer write, ''The emerging link between upwelling and mesoscale eddy fluxes places a large burden on climate models as the relatively small-scale eddy fluxes are computationally difficult to obtain and their parameterizations may not always be faithful, especially in a changing climate.'' In this paper, aspects of this important question are addressed for the first time. We compare results from an idealized future climate scenario using two versions of a climate model that uses different ocean components where the horizontal resolution is non-eddy resolving and eddy resolving.