Farmers in South Asia may reap only half of today's wheat harvest in 40 years' time as global temperatures rise and rain falls in different places, according to a study on climate change and agriculture.

Climate change may cut corn, wheat and rice yields across developing countries by 2050, boosting prices and causing hunger, according to a study by the Washington-based International Food Policy Research Institute, or IFPRI, financed by the Asian Development Bank and the World Bank.

The United Nations' Food and Agriculture Organization has said it's "cautiously optimistic" food output can rise 70 percent to feed an increased world population in 2050. The agency expects nine-tenths of the growth to come from higher yields and more intensive farming.

"Developing countries are likely to be hardest hit by climate change and will suffer bigger declines in crop yields," Gerald Nelson, lead author of the study and an IFPRI research fellow, said on a Sept. 29 conference call.

In South Asia, average yields in 2050 will drop about 50 percent from 2000 levels for wheat because of climate change and fall 17 percent and 6 percent, respectively, for rice and corn, according to the study.

Across developing countries, yields for irrigated wheat would slide between 28 percent and 34 percent, depending on the climate-change forecast used. In developed countries, the expected decline would be limited to 4.9 percent to 5.7 percent.

Food Prices

Rising food costs would be worsened by lower yields caused by climate change, with wheat, corn and rice prices more than doubling from 2000 levels, the researchers said.

World wheat prices may rise as high as $334 a metric ton in 2050 from $113 in 2000, compared with a gain to $158 a ton without any climate-change effect, the study shows.

"Even without climate change, food prices will rise," Nelson said. "Climate change makes this problem worse."

Rice prices might jump to $421 a ton from $190, compared with an increase to $307 a ton without climate change. Global corn prices may increase to as much as $240 a ton from $95 in 2000, compared to $155 a ton with an unchanged climate.

IFPRI predicted future production using a crop-simulation model called DSSAT and two climate-change scenarios, by the U.S. National Center for Atmospheric Research and the Commonwealth Scientific and Industrial Research Organization.

Rain-Fed Wheat

Rain-fed wheat would do better in developed countries as growing conditions improve in Canada, China and northern Russia, according to Nelson. The report forecast a yield increase of between 2.4 percent and 3.1 percent.

"China actually turns out to be rather well off under climate change," Nelson said. Some crops that are barely at their "comfort level" in the country "do better" as temperatures rise, he said.

For irrigated rice, yields might decline between 14 percent and 19 percent in developing countries, the study shows.

Irrigated-corn yields in developing countries would fall between 2 percent and 2.8 percent because of a changing climate, while yields in developed countries would drop between 1.2 percent and 8.7 percent, depending on the scenario used.

The figures exclude so-called CO2 fertilization, whereby higher carbon dioxide levels in the atmosphere might boost plant growth. Including the effect, which is disputed by scientists, the study forecast smaller declines or increases in developing- country yields.

Underfed Children

Globally, climate change means 25 million more children would be underfed in 2050 compared with a world with no shift, according to the study.

"Agriculture and human well-being will be negatively affected by climate change," the study said. "Crop yields will decline, production will be affected, crop and meat prices will increase and consumption of cereals will fall, leading to reduced calorie intake and increased child malnutrition."

Agricultural investments by developing countries would have to rise between $7.1 billion and $7.3 billion a year to counteract the effects of climate change on nutrition, according to the IFPRI study.

Expanding rural roads would require an annual $2.67 billion of extra spending, mostly in sub-Saharan Africa, according to the study. Improvement of irrigation efficiency needs $2.16 billion a year, mostly in South and East Asia, it shows.