Climate Change Pushing Tropics Farther, Faster

From an article by Richard A. Lovett for National Geographic News:

Over the past 25 years the tropics have expanded by as much as 300 miles (500 kilometers) north and south—evidence of climate change in action, a new study says.

This not only means that rain-drenched regions near the Equator are growing, experts say, but also that global warming may be pushing deserts poleward in places such as the U.S. Southwest, Mexico, Australia, South Africa, South America, and the Mediterranean.

(See a map of where global warming will hit the hardest.)

"The rate of increase is pretty big," said study lead author Dian Seidel of the National Oceanographic and Atmospheric Administration's (NOAA) Air Resources Laboratory in Silver Spring, Maryland.

"It's several degrees of latitude over the course of 25 years."

Tracking Air Circulation

If it sounds strange to think of the tropics as expanding, that's because geographers and climate scientists view them differently. To mapmakers, the tropics are simply the regions between 23.5 degrees north and south latitude, where at least once a year the sun is directly overhead.

But Seidel and her team based their definition of the tropical belt on air circulation.