Rapidly warming climate is likely to seriously alter crop yields in the tropics and subtropics by the end of this century and, without adaptation, will leave half the world's population facing serious food shortages, according to a study to be published on Friday in Science Magazine.

The population of this equatorial belt is among the poorest on Earth and is growing faster than anywhere else, the study said.

"The stresses on global food production from temperature alone are going to be huge, and that doesn't take into account water supplies stressed by the higher temperatures," David Battisti, lead author of the study, said.

Battisti, also a professor at the University of Washington, collaborated with Rosamond Naylor, director of Stanford University's Program on Food Security and the Environment, to examine the impact of climate change on the world's food security.

By combining direct observations with data from 23 global climate models that contributed to a Nobel prize-winning research in 2007, Battisti and Naylor determined that there is greater than a 90 percent probability that by 2100 the lowest growing-season temperatures in the tropics and subtropics will be higher than any temperatures recorded there to date.

In the tropics, the higher temperatures can be expected to cut yields of the primary food crops, maize and rice, by 20 to 40 percent, the researchers said.

The serious climate issues will not be limited to the tropics, the scientists conclude. As an example, they cite record temperatures that struck Western Europe in June, July and August of 2003. The summer-long heat wave in France and Italy cut wheat yields and fodder production by one-third.

"When all the signs point in the same direction, and in this case it's a bad direction, you pretty much know what's going to happen," Battisti said.

"You can let it happen and painfully adapt, or you can plan for it," he said. "You also could mitigate it and not let it happen in the first place, but we're not doing a very good job of that."

Currently three billion people live in the tropics and subtropics, and the number is expected to nearly double by the end of the century.

The area -- from about 35 degrees north latitude to 35 degrees south latitude -- stretches from the southern United States to northern Argentina and southern Brazil, from northern India and southern China to southern Australia and all of Africa.

(Xinhua News Agency January 9, 2009)