Subtropic warming could mean bigger deserts

Earth's atmosphere is warming faster over the subtropics than anywhere else, which could mean bigger deserts and more drought from Africa to Australia to the Middle East, researchers said on Thursday.

Photo: Subtropic warming could mean bigger deserts

Subtropic warming could mean bigger deserts

The fast-heating area girdles the globe at about 30 degrees north and south latitude, crossing the southern United States, southern China and north Africa in the Northern Hemisphere, and southern Australia, South Africa and southern South America in the Southern Hemisphere.

Based on 25 years of satellite data, researchers at the University of Washington also determined that the jet streams -- a pattern of westerly winds that help drive weather in both hemispheres -- have shifted about 70 miles toward their respective poles.

This is important because the jet streams mark the northern and southern boundaries of the tropic climate zones, said John Wallace, an atmospheric scientist and co-author of a research paper in this week's Science journal. The jet streams' shift toward the poles means the zones are expanding, reports Reuters.

The researchers think the overall effect of the tropical expansion could be similar to that of El Nino, a phenomenon in which warm water in the west Pacific moves eastward toward the Americas.

El Nino can cause warmer, drier summers, so tropical expansion might have contributed to the unusually dry conditions seen in the subtropical American Southwest and Mediterranean Europe in recent years.

It's still unclear whether the jet stream migration and tropical expansion were triggered by natural climate variation or human-caused global warming, the researchers said.

"One can certainly think of various mechanisms of how global warming-related changes in the atmosphere could induce the changes we see," Reichler said. "But it's very speculative at this point."

Another possibility, the researchers say, is that the depletion of Earth's ozone layer from pollutant such as refrigerated gases is mimicking patterns created by global warming and heating up the troposphere that way, informs FOX News.