Zheng Guoguang, head of the State Meteorological Administration, said the impact of global warming means that China will likely need an extra 10 million hectares (247 million acres) of farmland by 2030.

The year 2030 is a key date because that is when the nation's population is expected to peak at 1.5 billion people, up from just over 1.3 billion today, requiring an extra 100 million tons of food to feed them.

"Global warming may cause the grain harvest to fall by five to 10 percent, that is by 30-50 million tons, by 2030," the China Daily quoted Zheng as saying.

"Warmer weather will shorten the growth period of some grains and their seeds won't have enough time to ripen."

Farmland has been shrinking rapidly in recent years due to China's historic urbanisation process, and Zheng's estimate of an extra 10 million hectares is nearly double what is available today.

The government has said farmland must not fall below 12 million hectares by 2010, but the China Daily said that target was already approaching.

Zheng, speaking at an agricultural forum in northern China, said global warming would also see insects become a worsening problem.

He further warned that even a slight increase in temperature would lead to ground water evaporating faster, hurting grain harvests.

Chinese authorities have issued a series of reports and studies in recent months outlining the grim impact global warming will have on the country.

Last month environmental authorities said climate change was shrinking wetlands at the source of China's two greatest rivers -- the Yangtze and the Yellow -- which had reduced water flows.

Other studies found that massive glaciers in northwestern China's Xinjiang region and in the Himalayas had been shrinking rapidly.

This would have dire consequences for much of Asia as many of the region's rivers begin in those regions.

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