Sydney, Jan 12 Global warming will severely damage crop output in tropical regions and deprive half the world of food by the century-end, according to a study.

The population of the equatorial belt will bear the brunt of unprecedented shortages, home to the poorest on earth.

Currently three billion people live in the tropics and subtropics, and their number is expected to nearly double by the end of the century. The area stretches from the southern US to northern Argentina and southern Brazil, from northern India and southern China to southern Australia and all of Africa.

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. But rising temperatures also are likely to play havoc with soil moisture, cutting yields even further.

"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," said David Battisti, University of Washington atmospheric sciences professor, co-author of the study.

He collaborated with Rosamond Naylor, director of Stanford University's Programme 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 Nobel prize-winning research in 2007, Battisti and Naylor determined 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.

They used the data as a filter to view historic instances of severe food insecurity, and concluded such instances are likely to become more commonplace.

Those include severe episodes in France in 2003 and Ukraine in 1972. In the case of Ukraine, a near-record heat wave reduced wheat yields and contributed to disruptions in the global cereal market that lasted two years.

The serious climate issues won't 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, killing an estimated 52,000 people.

The summer-long heat wave in France and Italy cut wheat yields and fodder production by one-third. In France alone, temperatures were nearly 6.5 degrees Fahrenheit above the long-term mean, and the scientists say such temperatures could be normal for France by 2100, said a Washington release.

"This is a compelling reason for us to invest in adaptation, because it is clear that this is the direction we are going in terms of temperature and it will take decades to develop new food crop varieties that can better withstand a warmer climate," Naylor said.