Mean Kinetic Temperature

It’s part of our culture. Hurricanes became media stars when Dan Rather, a cub reporter from Houston, convinced CBS headquarters in 1961 to add 15 minutes to the (then) 15 minutes of network news featuring — surprise — him, braving the Galveston Seawall while big, bad Hurricane Carla languorously eyed the Texas Coast. While there’s still debate about whether Carla may have actually been more powerful than 2005′s legendary Katrina, it is certainly true that she made Dan a rather big man.

So this year is supposed to be another big one. The planetary surface temperature is warmer than it was back in Carla’s day. Aren’t these two things related?

Hurricanes long since graduated from being singular weather events to becoming climatic signposts.  After all, it seems pretty logical that they should be enhanced by global warming, as the thermal source that they convert to destructive kinetic energy is the heat of the ocean, which should go up with the surface temperature.

Tropical cyclones are a bit more complicated than “warmer ocean in, bigger hurricane out”.  For months on end, the vast majority of the earth’s tropical oceans sport surface temperatures above 80°F, the threshold required for their formation. Given this massive amount of suitable ocean surface, why are there so few hurricanes? And why would warming of a degree or two really change this?

Under global warming, it turns out that the threshold temperature goes up too.  A report published last November in Nature Geoscience found a rise of about 0.5 degrees in that temperature in recent decades paralleling the observed rise in tropical ocean surface temperatures.  Everything else being equal (which never occurs), this would mean no increase in hurricane frequency and intensity.