Lindsay Renwick, the mayor of this dusty southern Australian town, remembers the constant whir of the rice mill. ''It was our little heartbeat out there, tickety-tick-tickety,'' he said, imitating the giant fans that dried the rice, ''and now it has stopped.''

The Deniliquin mill, the largest rice mill in the Southern Hemisphere, once processed enough grain to satisfy the daily needs of 20 million people. But six long years of drought have taken their toll, reducing Australia's rice crop by 98 percent and leading to the mothballing of the mill last December.

Ten thousand miles, or 16,000 kilometers, separate the mill's hushed rows of oversized silos and sheds - beige, gray and now empty - from the riotous streets of Port-au-Prince, Haiti, but a widening global crisis unites them.

The collapse of Australia's rice production is one of several factors contributing to a doubling of rice prices in the past three months - increases that have led the world's largest exporters to severely restrict exports and spurred panicked hoarding in Hong Kong and the Philippines. The higher prices also set off violent protests in countries including Haiti, Egypt, Cameroon, Ivory Coast, Mauritania, Ethiopia, Uzbekistan, Yemen, the Philippines, Thailand, Indonesia and Italy.

Drought affects every agricultural industry based here, not just rice - from sheepherding, the other mainstay in this dusty land, to the cultivation of wine grapes, the fastest growing crop here often at the expense of rice.
And not just this region is concerned. The chief executive of the National Farmers' Federation in Australia, Ben Fargher, says, ''Climate change is potentially the biggest risk to Australian agriculture.''

But it is the drought's effect on rice that has produced the greatest impact on the rest of the world, so far. It is one of the factors contributing to skyrocketing prices, and many scientists believe it is among the earliest signs that the warming of the planet is starting to affect food production.

While a link between short-term changes in weather and long-term climate change is not certain, the unusually severe drought is consistent with what climatologists predict will be a problem of increasing frequency.

It has already spurred significant changes in Australia's agricultural heartland. Some farmers are abandoning rice, which requires large amounts of water, to plant less water-intensive crops like wheat or, especially here in southeastern Australia, wine grapes. Other rice farmers have sold their fields or their water rights, usually to grape growers.

Scientists and economists worry that the reallocation of scarce water resources - away from rice and other grains and toward more lucrative crops and livestock - threatens poor countries that import rice as a dietary staple.

The global agricultural crisis is threatening to become a political one, pitting the United States and other developed countries against the developing world over the need for affordable food versus the need for renewable energy. Many poorer nations worry that subsidies from rich countries to support biofuels, which turn crops like corn into fuel, are pushing up the price of staples.

The World Bank and the United Nations Educational, Scientific and Cultural Organization both called on major agricultural countries to overhaul policies to avoid a social explosion from rising food prices.

With rice, which is not used in biofuel, the problem is availability. Even in normal times, little of the world's rice is actually exported - more than 90 percent is consumed in the countries where it is grown. The last quarter century has seen rice consumption growing faster than production, with global reserves plunging by half since 2000. Current economic uncertainty has led producers to hoard rice, and speculators and investors even see it as a lucrative, or at least safe, investment, like gold.

All these factors have made countries that buy rice on the global market vulnerable to terrible price swings.

Senegal and Haiti each import four-fifths of their rice. And both have faced mounting unrest as prices have increased. The police suppressed violent demonstrations in Dakar, the Senegalese capital, on March 30, and unrest has spread to other rice-dependent nations in West Africa, notably Ivory Coast. The Haitian president, René Préval, after a week of riots, on Saturday announced subsidies for rice buyers.

But scientists expect the problem to worsen in the decades ahead.
The Intergovernmental Panel on Climate Change, set up by the United Nations, predicted last year that even slight warming would decrease agricultural output in tropical and subtropical countries.

Moderate warming could benefit crop and pasture yields in countries far from the Equator, like Canada and Russia. In fact, the net effect of moderate warming likely would be higher total food production around the world in the next several decades.

But the scientists said the effect would be uneven, and enormous quantities of food would need to be shipped from areas farther from the Equator to feed the populations of often less affluent countries closer to the Equator.

The panel predicted that even greater warming, which might happen by late in this century if few or no limits are placed on greenhouse gas emissions, would hurt total food output and cripple crops in many countries.

Paul Lamine N'Dong, an elder in Joal, Senegal, worries that hot weather and failing rains have already crippled his village's crop of millet, a coarse grain that is eaten locally and traded for rice.

Sitting on a concrete dais reserved for elders, N'Dong said on a recent morning, ''The price rises very quickly, which means we really have to go and look for money.''

''It is live or die,'' he said. For farmers in a richer nation like Australia, the effects of the current drought are already significant.

Rice farmers who do not give up and sell their land or water rights are experimenting with rice varieties or growing techniques that require less water - Australia now has some of the world's highest rice yields per megaliter of water.

Still, Australia's total rice-producing capacity has declined by about a third because many farmers have permanently sold water rights, mostly for grape production. And output last year was far lower because of a severe lack of water: rice farmers received just one-eighth of the water they are usually promised by the government.

The accidental beneficiaries of these conditions have been the farmers who grow wine grapes in the same river basin where the Deniliquin mill stands silent.
Even with the recent doubling of rice prices, to around $1,000 a metric ton for the high grades produced by Australia, it is still more profitable to grow wine grapes.

All told, wine grapes produce a pre-tax profit of close to $2,000 an acre, or $800 per hectare, while rice produces a pre-tax profit of about $240 an acre, or $96 a hectare. Ranchers like Peter Milliken, who has a 37,500-acre sheep farm near Hay, Australia, are trying to reduce the water they use. Milliken is installing a buried 9-mile, or 14.5-kilometer, pipe to replace an irrigation canal that lost up to 90 percent of its water to evaporation - and he's planning for the day when he doesn't irrigate at all.

Sheep farmers have already worked out cooperative arrangements to send flocks to whatever fields have recently received rain, sometimes herding or trucking them long distances. Keeping an eye on a flock, Frank Cox, a drover, said recently, ''We had to move the sheep because they were dying of starvation, and truck them down here.'' The changes here are making rice harder to find.

For instance, SunRice, the Australian rice trading and marketing giant owned by the country's rice growers, began preparing to mothball the Deniliquin mill five months ago, when it noticed that Australian farmers were planting almost no rice. To make sure that it could continue supplying the domestic market as well as export markets in Papua New Guinea, South Pacific island nations, Taiwan and the Middle East, SunRice went into international markets and stepped up rice purchases from other countries, said Gary Helou, the company's chief executive.

The SunRice purchases became one of the many factors that are now making it harder for longtime rice importers elsewhere to find supplies. Researchers are looking for solutions to global rice shortages - for example, rice that blooms earlier in the day, when it is cooler, to counter global warming. Rice plants that happen to bloom on hot days are less likely to produce grains of rice, a difficulty that is already starting to emerge in inland areas of China and other Asian countries as temperatures begin to climb.

The flexibility of farmers in Australia has persuaded some climate experts that, particularly in developed countries, the effects of climate change may be mitigated, if not completely avoided. ''I'm not as pessimistic as most people,'' said Will Steffen, the director of the Fenner School of Environment and Society at Australian National University. ''Farmers are learning how to do things differently.'' Meanwhile, changes like the use of water to grow wine grapes instead of rice carry their own costs, which the developing world is discovering.
''Rice is a staple food,'' said Graeme Haley, the general manager of the town of Deniliquin. ''Chardonnay is not.''

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