The tropics are expanding. That's the latest word from researchers who say the earth's tropical belt has expanded a couple hundred miles over the past 25 years. It's something climatologists have predicted due to global warming and it means areas like the U.S. Southwest could see even drier conditions than normal

The tropics make up about one-quarter of the globe and are generally considered hot, steamy, and damp, but you can also find areas of brutal desert. Climate change experts define the region using long-term models and what's happening in the atmosphere.

The newest study, published Sunday in the new scientific journal Nature Geoscience, shows that by using the weather definition, the tropics are expanding toward Earth's Poles more than predicted.

Independent teams using four different meteorological measurements found that the tropical atmospheric belt has grown by anywhere from 2 to 4.8 degrees latitude since 1979. That translates to a total north and south expansion of 140 to 330 miles.

One key determination of the tropical belt is called the Hadley circulation—prevailing rivers of wind that move vertically as well as horizontally, carrying moisture to rainy areas while drying out arid regions on the edges of the tropics. That wind is circulating over a larger area than it was a couple decades ago.

But that's not the only type of change meteorologists have found that shows an expansion of the tropics. They've seen more tropical conditions by measuring the amount of ozone in the atmosphere, the depth of the lower atmosphere, and the level of dryness in the atmosphere at the edges of the tropics.

Climate scientists have long predicted a growing tropical belt toward the end of the 21st century because of global warming.