hurricanes

A recent article in PNAS by Santer et al. (Proc. Natl. Acad. Sci. U.S.A. 106, 10.1073/pnas.0901736106, 2009) utilized 22 climate models to demonstrate that changes in water vapor (the most powerful natural greenhouse gas) distribution over the oceans is consistent with patterns caused specifically by anthropogenic forcing of climate. As water vapor is the fuel that powers hurricanes, they show a link between anthropogenic forcing and the recent increases in hurricane intensity. Of course, their real result is a demonstration that the Earth's recent warming patterns are human-caused. For a more detailed look at the intensification of hurricanes, check out http://www.toddalbert.com/comps/hurricanes/

In order for tropical storms to strengthen into hurricanes, they need two main ingredients -- warm water and moderate upper-level winds. Satellite imagery provide excellent measures of sea surface temperatures, indicating how the region of hurricane formation in the North Atlantic, Caribbean, and Gulf of Mexico are at ideal temperatures for storm formation.

Of course, the Atlantic isn't the only region susceptible to tropical cyclones (we just don't call them "hurricanes" elsewhere). The map below shows additional warm areas of water, ideal for the formation of these storms. Too close to the equator, though, the storms won't form because of the weak Coriolis effect there.

Note the unusually cool water along the equator in the eastern Pacific, off the coast of South America. This cold water allows penguins to thrive in the Galapagos Islands and also controls global climate in many ways. When this water warms, we call it an El Niño event.