May 24, 2017

What we’ve learned about hurricanes and climate change since Katrina

Kerry Emanuel
Washington Post

North Atlantic hurricane power [is] strongly correlated with the temperature of the tropical Atlantic during hurricane season, and that both had been increasing rapidly over the previous [40] years or so.

Hurricanes are giant heat engines driven by the thermodynamic disequilibrium between the tropical oceans and atmosphere. This disequilibrium drives a strong flow of heat from the ocean to the atmosphere and is a direct consequence of the greenhouse effect: The tropical atmosphere is so opaque to infrared radiation that the sea surface cannot cool very much by directly radiating heat to space. Instead, it cools mostly by the evaporation of water, the same mechanism by which our sweaty bodies cool on a hot day.

...The theory of the hurricane heat engine places an upper limit on hurricane wind speeds. Called the “potential intensity,” it is directly proportional to this disequilibrium. Virtually every study that has been done, dating  to 1987, shows increasing potential intensity in most places as our climate continues to warm; the average trend is about 10 mph for every degree centigrade of tropical sea surface temperature increase, or roughly 20 mph for each doubling of atmospheric CO2 concentration.