BEIJING - China has been working to reduce the risk of decreasing grain harvests caused by global warming in coming decades.

Estimates placed the losses suffered by 2030 at between 5 percent and 10 percent if climate change continues, Chinese Academy of Agricultural Sciences Deputy Dean Tang Huajun said.

The threats climate change generates include shrinkages of arable land, water shortages and extreme weather, Tang said.

The country plans to boost annual grain output to 550 million tons by 2020, a 50 million ton increase over 2007.

"But the output of the country's three main foods - rice, wheat and corn - may suffer a 37 percent decline in the second half of this century if the government fails to take effective measures to address climate change's impact," Tang said.

He based his prediction on a study of climate change's impact on the country's grain production over the past 20 years.

Drought poses the direst threat to grain harvests. It caused average annual losses of about 15 to 25 million tons, or 4 to 8 percent of the country's annual output, from 1995 until 2005, Tang said, citing government figures.

Other weather-related natural disasters, such as floods, hailstorms and typhoons, have also taken tolls, he added.

Experts have said current monitoring suggests global warming will lead to changes in the locations in which these three staples are planted.

Yang Peng, a researcher with the academy, said rising temperatures have already caused the planting area for winter wheat, which is more vulnerable to extreme weather, to shift up to 200 kilometers northward.

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The rice planting area has significantly increased in the northeastern provinces of Liaoning, Jilin and Heilongjiang, he said.

"More guidelines, such as those about selecting seeds according to the consequences of climate change, will benefit farmers," he said.

A research project, looking at root and tuber crops as means to ensure adequate food supplies, is under way.

The government in February signed an agreement with the International Potato Center, a Peru-based research institute, to open a major research center in Beijing.

"Part of the center's mission is to develop varieties that grow quickly and can adapt to regions throughout China," Xie Kaiyun, a leading potato scientist at the International Potato Center's Beijing office, said.

The State Council, or Cabinet, announced earlier this year that it will provide subsidies to farmers who grow high-yield seed potatoes.

"The room for increasing the production of root and tuber crops, especially potatoes, has much more potential than planting the three main crops," he said.

Potatoes' advantages include low requirements for water and land quality, and attributes that suit a country facing severe water shortages and shrinking arable land.

"The yield of improved varieties (of potato) in Yulin city, Shaanxi province, reached 75 tons a hectare," Xie said.

"It is believed an average yield of 30 tons a hectare nationwide will not be difficult."