According to the International Rice Research Institute (IRRI) more than half the world's 6.6 billion people depend on rice for nourishment.

"Parts of the world will become drier and apparently that's already happening, and some parts will become even wetter," said Moroccan crop physiologist Rachid Serraj.

"But most importantly it's going to shift the rainfall distribution. It's going to become more unpredictable, and that is the problem for rice cultivation," he said.

Chinese scientist Peng Shaobing wraps his paddy fields with tarp and blasts them with cold air from air conditioners.

His colleague Indian plant geneticist Kumar Singh grows 2,000 rice varieties inside giant metal cabinets, the seedlings sprouting above styrofoam trays soaked with varying degrees of brine to simulate the seawaters that threaten to engulf rice-growing areas over the next century.

The three IRRI scientists are entrusted with ensuring that the half of mankind who depend on rice will not go hungry as rising temperatures and ocean levels threaten one of the world's most important crops.

The Intergovernmental Panel on Climate Change projects the globe will warm by 0.2 degrees Celsius every 10 years, far higher than the 0.6-degree Celsius rise in the past century, with serious consequences for food production.

IRRI, based in this university town south of the Philippine capital and a vital part of the "Green Revolution" that dramatically raised cereal yields in the 1970s, has gathered top experts to work on "new frontier projects" to meet the threat.

This is apart from more conventional research to further boost yields, make the plants more resistant to pests and disease, and make the grain more palatable.

Rice yields would fall by 10 percent for each one-degree rise in the minimum temperature at night, time spent by the plant for growth processes, said crop physiologist Peng, a pioneer researcher in this field.

Between 1978 and 2003 minimum mean nighttime temperatures rose by 1.5 degrees Celsius, suggesting a 15 percent production decline over 28 years, Peng told AFP.

Higher nighttime temperatures shorten the growing time for rice. "The yield is reduced because the plant doesn't have enough time to grow," Peng said. "Higher night temperatures also leads to poorer grain quality."

Drought and salinity are already a major problems. Twenty-three million hectares (57 million acres), or 18 percent of the world's rice farms are considered "drought-prone", Serraj said.

A dry spell in hot spots such as eastern India can push up to 15 million rain-fed rice farmers into poverty in a single year, he said. Even in China, demand for water from industry and elsewhere is putting pressure on high-yield irrigated rice grown there, he added.

The two countries account for nearly half the world's rice growing areas.

Next to drought, the influx of saltwater not only in coastal but also inland farms through careless irrigation practices is the number-two problem, said Singh.

Some 6.3 percent of the world's soil surface is already considered saline, and global warming or not, the problem affects most of the rice fields of South Asia and Southeast Asia, he told AFP.

Global warming is projected to cause sea levels to rise by between 10 and 85 centimetres (four and 34 inches) over the next century, which would threaten key rice-growing areas in Vietnam, Indonesia, Bangladesh, and India among others.

For the IRRI scientists, the challenge is to produce new breeds and innovate crop management techniques to help farmers meet the triple threat of drought, higher temperatures, and soil salinity, along with the new pests and diseases that will crop up as rice is grown in radically new environments.

Peng said high-yield varieties developed by IRRI seem to have higher tolerance for warmer nighttime temperatures. His experiments seek to determine their yields in simulated cooler night temperatures.

Breeding improved varieties, a process that begins at IRRI and other laboratories and involves crossing the desirable genes of the 110,000 varieties at the IRRI gene bank here, ends with their dispersal to the farmer end-users.

The process used to take about 15 years, but Singh said it can now be done as fast as six years.

It now takes between 3,000 and 5,000 litres (780 and 1300 US gallons) of water to produce one kilogram (2.2 pounds) of rice, but IRRI is trying to breed maize qualities into rice so farmers could also grow them on a dry field.

So which side is winning the race so far, climate change or the scientists? The research is being hampered by a funding crunch that has hit IRRI.

"At this stage, I think it is equal, but if we're not going to increase our support, we're going to lose the battle," Peng said.

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