The response of tropical cyclone statistics to an increase in CO₂ with fixed sea surface temperatures

Confirming earlier results of Yoshimura and Sugi, a significant fraction of the reduction in globally averaged tropical storm frequency seen in simulations in which both SST and CO₂ are increased can be thought of as the effect of the CO₂ increase with fixed SSTs.

Globally, the model produces a decrease in tropical cyclone frequency of about 10% due to doubling of CO₂ and an additional 10% for a 2-K increase in SST, resulting in roughly a 20% reduction when both effects are present. The relative contribution of the CO₂ effect to the total reduction is larger in the Northern than in the Southern Hemisphere. The average intensity of storms increases in the model with increasing SST, but intensity remains roughly unchanged, or decreases slightly, with the increase in CO₂ alone.