The troubling projections were established in 15 years of field studies at the IRRI complex in Los Banos town south of Manila, in conditions that approximate the way about 40 percent of the world's total rice supplies is produced.

An IRRI report released this week concluded there was "strong evidence of a reduction in rice yields caused by rising temperatures consistent with trends in global warming."

The study, by a nine-member US-China research team led by IRRI crop physiologist Peng Shaobing, found that the effects of global warming at night were more pernicious than in daytime.

The mean minimum night time temperature during the dry season at the IRRI fields has risen since 1979 by 1.13 degrees Celsius, or triple the 0.35 percent rise in maximum daytime temperature, IRRI said in a statement.

"The news is that high night-time minimum temperatures clearly and strongly suppressed rice yields in the seasons in which they occurred, while high daytime temperatures had no measurable effect," it said.

"Yields fell by 10 percent for every one-degree Celsius increase in mean night-time minimum temperature.

"Because the increase in night temperature was three-fold greater than the increase in daytime temperature, rice yields declined by 15 percent for every one-degree Celsius increase in daily mean temperature -- double the seven percent decline that emerged from theoretical models."

IRRI said experts predict that temperatures would rise globally by between 1.5 and 4.5 degrees Celsius in the coming century, or three to nine times more than in the past 100 years.

"IRRI's climate records are consistent with warming trends found elsewhere in the Philippines and globally," it said.

"Global warming thus threatens to erase the hard-won productivity gains that have kept the rice harvest in step with population growth."

IRRI said the cereal is the staple food of more than half of humanity -- mainly in Asia where 90 percent of the crop is grown and consumed.

"Harvest shortfalls induced by global warming would likely be more widespread and persistent. Left unchecked, they could undermine global food security and political stability," it added.

Scientists define global warming as an increase in the average temperature of the earth's surface, which occurs following an increase in greenhouse gases produced by both natural occurrences as well as human economic activity.

However there is a long-running dispute on whether efforts by the international community to slow the contribution of human activity to the warming process, through accords such as the Kyoto Protocol, would make a difference.

IRRI is one of 15 centers funded through the Consultative Group on International Agricultural Research, an association of public and private donor agencies.

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