Perturbation of the atmospheric temperature distribution caused by an increased content of CO2 is a key problem in climate research. The main concern is the increase in temperatures at the Earth's surface due to an increased greenhouse effect. A general cooling of the stratosphere is predicted to take place when CO2 increases. A direct effect of lower temperatures in the stratosphere is a change in the rates of some of the chemical reactions which control the ozone layer. Anthropogenic release of carbon dioxide may therefore lead to changes in the ozone layer in the future. The present paper shows that estimates of the temperature effect on ozone depend markedly on the level of chlorine in the stratosphere, as the catalytic ozone reduction by nitrogen and chlorine reactions respond differently to changes in temperature.