NUMERICAL SIMULATION OF ICE-AGE CLIMATE WITH A GLOBAL GENERAL CIRCULATION MODEL.

Abstract

The global distribution of July climate has been simulated with a two-level atmospheric general circulation model using the surface boundary conditions of sea-surface temperature, ice-sheet topography and surface albedo assembled by CLIMAP for 18,000 years before present. These conditions represent an approximate doubling of the ice-covered surface area of the earth, a 1 degree C decrease of the average sea-surface temperature, and an increase of the average surface albedo from 0. 14 to 0. 22. The results are in general agreement with those found from more simplified models and diagnostic calculations, and are verified at least in terms of the surface temperature by the available independent paleoclimatic data. Significant disagreement exists, however with the temperature, pressure and circulation found in a previous study using the NCAR GCM with different ice-age boundary conditions, including in particular somewhat lower tropical sea-surface temperatures. The sensitivity of the simulated ice-age climate to such boundary condition changes needs further research.