We have investigated the sensitivity of the intensity of convective activity and atmospheric radiative cooling to radiatively thick upper-tropospheric clouds using a new version of the Colorado State University General Circulation Model. The model includes a bulk cloud microphysics scheme to predict the formation of cloud water, cloud ice, rain, and snow. The cloud optical properties are interactive and dependent upon the cloud water and cloud ice paths. We find that the formation of a persistent upper tropospheric cloud ice shield leads to decreased atmospheric radiative cooling and increased static stability. Convective activity is then strongly suppressed. In this way, upper-tropospheric clouds act as regulators of the global hydrologic cycle, and provide a negative feedback between atmospheric radiative cooling and convective activity. ¿ American Geophysical Union 1994