Philippines-based IRRI has tracked a northward shift in rice-growing areas in China, which is home to a fifth of humanity and produces 35 percent of the world's rice.

While economic development, the shift to high-value vegetables and land conversion steered farmers away from rice farming in southern China, "another factor that may have contributed is climate change," IRRI geographer Robert Hijmans wrote in the forthcoming issue of the IRRI journal Rice Today.

Liaoning, Jilin, Nei Mongol and Heilongjiang now account for 11.5 percent of China's rice growing areas, up from 2.7 percent in 1979.

The four northern provinces also saw "relatively strong increases in yield" over the period, he said.

Warming in high latitudes such as northern China, where a 2.5 degree-Celsius rise in minimum temperature in Heilongjiang was monitored over the past 40 years, has been above the global average of 0.03 degrees Celsius rise per year, he said.

While yield declines result from increased minimum temperature in areas near the equator, "in relatively cool areas as Heilongjiang, warming may have contributed to higher yields through a longer growing season and reduced cold stress," Hijmans added.

Meanwhile, free trade, changing diets, and rapid urbanisation could lead to a decline in rice production, one of the world's leading experts on the crop said.

"As prosperous rice-growing countries move toward free trade in agricultural production, they may increasingly find it difficult to sustain producers' interest in rice farming," said Mahabub Hossain, a former IRRI economist.

He said global rice demand growth has slowed as rapid urbanisation and rising per capita income in middle and high-income countries in Asia and Latin America prompt people to diversify their diets, while population control has reduced population growth rates in rice-eating China, Malaysia and Thailand.

However, this may be offset by "increased consumption due to poverty reduction among low-income households" in West Asia, sub-Saharan Africa and South America, where rapid migration to urban areas has led to changes in diets from ones based on maize or root crops to rice-based ones.

Hossain said urbanisation would lead to "economic pressure to reduce the area under rice cultivation to accommodate agricultural diversification in favor of higher-value crops" and as farms are lost to build housing, factories and roads.

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