The sensitivity of a global climate model to increased atmospheric CO2 concentrations is presented, assessed, and compared with earlier studies. The ocean is represented by a 50-m slab in which the heat convergence due to oceanic dynamics is prescribed, producing an accurate simulation of sea surface temperatures, sea-ice extents, and associated features in the control simulation. Changes in surface temperature are qualitatively similar to those found in earlier studies using models with similar or lower horizontal resolution, although the global warming is slightly larger. The simulated changes in hydrology agree broadly with those in studies made with higher horizontal resolution and prescribed changes in sea surface temperatures and include a drying over the northern mid-latitude continents. Many of the discrepancies in the responses of different models can be traced to differences in the simulations of present-day climate. The choice of convective parametrization appears to influence the senstivity of the simulated response in the tropics. ¿ American Geophysical Union 1987