An increasing body of research is directed toward understanding how tropical cyclone activity responds to climate change. On the other hand, there is very little understanding about how changing tropical cyclone activity might have feedbacks on climate itself. Here I argue that tropical cyclones are an integral part of the climate system owing to their control of the thermohaline circulation of the oceans.

It has been known for almost a century that the long-term behavior of the deep overturning circulation of the ocean is controlled by downward mixing of warm, tropical surface waters. This conclusion is strongly supported by contemporary modeling studies. Many physical oceanographers believe that the mixing is caused by tidally generated internal waves breaking in the thermocline, but calculations of the heat flux into the ocean necessary to re-warm the cold wakes of tropical cyclones strongly suggest that these storms are the principal mixing agents responsible for driving the thermohaline circulation. I will present the results of a very simple coupled climate model in which the vertical mixing is assumed to be caused by global tropical cyclone activity, while the latter is itself regarded as a function of tropical climate. When coupled with two or three other important climate feedbacks, this model is capable of explaining several climate enigmas, including the excessive high latitude warmth of the early Eocene and abrupt climate changes.