Description and Validation of the Mit Version of the Giss 2 - D Model

A significant number of long-term climate change simulations are to be carried out in the Integrated Framework of the MIT Joint Program on the Science and Policy of Global Change. Since Global Circulation Models (GCMs) require an enormous amount of computer time, the two-dimensional statistical-dynamic model developed by Stone and Yao has been chosen to be used for the initial stage of the Joint Program. At MIT, the model has been modified to make it more suitable for the purposes of the Joint Program, including developing a new scheme for a surface flux calculation. A number of simulations with the modified version of the model have been performed in which a few schemes for cloud and ocean heat transport calculation have been tested. Comparisons of the results of the present climate simulations with observational data show that the model reasonably reproduces main features of zonally averaged atmospheric circulation. A climate sensitivity produced by the model coupled with a mixed layer ocean model in response to the doubling of the atmospheric CO 2 concentration lies in the range of the results obtained with GCMs. The results of the simulations with a gradual increase of the greenhouse gas concentrations in the atmosphere, in which diffusion of heat into the deep ocean was taken into account, are also similar to those obtained in the analogous simulations with GCMs. As a whole, presented results demonstrate that the modified version of the two-dimensional model can be successfully used for climate change predictions in the Integrated Framework of the Joint Program.