Chart from: http://www.drought.gov/portal/server.pt/gateway/PTARGS_0_2_693_208_0_43/http%3B/drought.unl.edu/dm/monitor.html 

California's governor, Arnold Schwarzenegger, warned on Thursday that his state "is headed toward one of the worst water crises in its history".

Now new research suggests that the three-year drought in the Golden State may be a consequence of the expanding tropics, which are gradually growing as human emissions of greenhouse gases warm the planet.

Climate scientists have documented a slow progression of low-latitude weather systems towards the poles, and this has been matched by rising temperatures in many temperate regions. Deciding whether this broadening of the tropical belt is linked to the greenhouse effect has been difficult, however.

Part of the reason, explains Thomas Reichler of the University of Utah, is that there are many ways of defining the tropics. Geographically, the tropical belt is contained between the Tropics of Cancer and Capricorn. It is also the region on either side of the equator where temperatures tend to be hot and humid all year.

Continued at: http://www.newscientist.com/article/dn16516-drought-warning-as-the-tropics-expand.html?DCMP=OTC-rss&nsref=online-news