The campaign against climate change could be set back by the global food crisis, as foreign populations turn against measures to use foodstuffs as substitutes for fossil fuels.

With prices for rice, wheat, and corn soaring, food-related unrest has broken out in places such as Haiti, Indonesia, and Afghanistan. Several countries have blocked the export of grain. There is even talk that governments could fall if they cannot bring food costs down.

One factor being blamed for the price hikes is the use of government subsidies to promote the use of corn for ethanol production. An estimated 30% of America's corn crop now goes to fuel, not food.

"I don't think anybody knows precisely how much ethanol contributes to the run-up in food prices, but the contribution is clearly substantial," a professor of applied economics and law at the University of Minnesota, C. Ford Runge, said. A study by a Washington think tank, the International Food Policy Research Institute, indicated that between a quarter and a third of the recent hike in commodities prices is attributable to biofuels.

Last year, Mr. Runge and a colleague, Benjamin Senauer, wrote an article in Foreign Affairs, "How Biofuels Could Starve the Poor."

"We were criticized for being alarmist at the time," Mr. Runge said. "I think our views, looking back a year, were probably too conservative."

Ethanol was initially promoted as a vehicle for America to cut back on foreign oil. In recent years, biofuels have also been touted as a way to fight climate change, but the food crisis does not augur well for ethanol's prospects.

"It takes around 400 pounds of corn to make 25 gallons of ethanol," Mr. Senauer, also an applied economics professor at Minnesota, said. "It's not going to be a very good diet but that's roughly enough to keep an adult person alive for a year."

Mr. Senauer said climate change advocates, such as Vice President Gore, need to distance themselves from ethanol to avoid tarnishing the effort against global warming. "Crop-based biofuels are not part of the solution. They, in fact, add to the problem. Whether Al Gore has caught up with that, somebody ought to ask him," the professor said. "There are lots of solutions, real solutions to climate change. We need to get to those."

Mr. Gore was not available for an interview yesterday on the food crisis, according to his spokeswoman. A spokesman for Mr. Gore's public campaign to address climate change, the Alliance for Climate Protection, declined to comment for this article.

However, the scientist who shared the Nobel Peace Prize with Mr. Gore, Rajendra Pachauri of the United Nations's Intergovernmental Panel of Climate Change, has warned that climate campaigners are unwise to promote biofuels in a way that risks food supplies. "We should be very, very careful about coming up with biofuel solutions that have major impact on production of food grains and may have an implication for overall food security," Mr. Pachauri told reporters last month, according to Reuters. "Questions do arise about what is being done in North America, for instance, to convert corn into sugar then into biofuels, into ethanol."

In an interview last year, Mr. Gore expressed his support for corn-based ethanol, but endorsed moving to what he called a "third generation" of so-called cellulosic ethanol production, which is still in laboratory research. "It doesn't compete with food crops, so it doesn't put pressure on food prices," the former vice president told Popular Mechanics magazine.

A Harvard professor of environmental studies who has advised Mr. Gore, Michael McElroy, warned in a November-December 2006 article in Harvard Magazine that "the production of ethanol from either corn or sugar cane presents a new dilemma: whether the feedstock should be devoted to food or fuel. With increasing use of corn and sugar cane for fuel, a rise in related food prices would seem inevitable." The article, "The Ethanol Illusion" went so far as to praise Senator McCain for summing up the corn-ethanol energy initiative launched in the United States in 2003 as "highway robbery perpetrated on the American public by Congress."

In Britain, some hunger-relief and environmental groups have turned sharply against biofuels. "Setting mandatory targets for biofuels before we are aware of their full impact is madness," Philip Bloomer of Oxfam told the BBC.

Biofuel advocates say they are being made a bogeyman for a food crisis that has much more to do with record oil prices, surging demand in the developing world, and unusual weather patterns. "The people who seek to solely blame ethanol for the food crisis and the rising price of food that we see across the globe are taking a terribly simplistic look at this very complex issue," Matthew Hartwig of the Renewable Fuels Association said.

Mr. Hartwig said oil companies and food manufacturers are behind the attempt to undercut ethanol. "There is a concerted misinformation campaign being put out there by those people who are threatened by ethanol's growing prominence in the marketplace," he said.

The most obvious impact the food crisis has had in America, aside from higher prices, is the imposition of rationing at some warehouse stores to deal with a spike in demand for large quantities of rice, oil, and flour. The CEO of Costco Wholesale Corp., James Sinegal, is blaming press hype for the buying limits, which were first reported Monday in The New York Sun.

"If it hadn't been picked up and become so prominent in the news, I doubt that we would have had the problems that we're having in trying to limit it at this point," Mr. Sinegal told Fox News Thursday. "I mean, I can't believe the amount of attention that is being paid to this."

The Sun's article, which came as food riots were reported abroad, circulated quickly on the Internet, was republished in newspapers as far away as India, and prompted local and network television stories.

Speaking in Kansas City, Mo., yesterday, the federal agriculture secretary, Edward Schafer, blamed emotion for the spurt of rice buying at warehouse stores. "We don't see any evidence of the lack of availability of rice. There are no supply issues," he told reporters, according to Reuters.