Changes in heat index associated with CO2-induced global warming

Changes in Heat Index (a combined measure of temperature and humidity) asso ciated with global warming are evaluated based on the output from four exte nded integrations of the GFDL coupled ocean-atmosphere climate model. The f our integrations are: a control with constant levels of atmospheric carbon dioxide (CO2), a second integration in which an estimate of the combined ra diative forcing of greenhouse gases and sulfate aerosols over the period 17 65-2065 is used to force the model, and a third (fourth) integration in whi ch atmospheric CO2 increases at the rate of 1% per year to double (quadrupl e) its initial value, and is held constant thereafter. While the spatial pa tterns of the changes in Heat Index are largely determined by the changes i n surface air temperature, increases in atmospheric moisture can substantia lly amplify the changes in Heat Index over regions which are warm and humid in the Control integration. The regions most prone to this effect include humid regions of the Tropics and summer hemisphere extra-tropics, including the southeastern United States, India, southeast Asia and northern Austral ia.