AS EMERGING POWERHOUSES like China seek new sources of energy to keep their cars and industries running, an ever larger portion of the world’s crops - cassava and corn, sugar and palm oil - is being diverted for biofuels.

With food prices rising sharply , many experts are calling on countries to scale back their headlong rush into green fuel development, arguing that the combination of ambitious biofuel targets and mediocre harvests of some crucial crops is contributing to high prices, hunger and political instability.

The United Nations Food and Agriculture Organization reported that its index of food prices was the highest in its more than 20 years of existence. Prices rose 15 percent from October to January alone, possibly “throwing an additional 44 million people in low- and middle-income countries into poverty,” the World Bank said.

Soaring food prices have caused riots or contributed to political turmoil in a host of poor countries in recent months, including Algeria, Egypt and Bangladesh, where palm oil, a common biofuel ingredient, provides crucial nutrition to a desperately poor populace.

During the second half of 2010, the price of corn rose steeply - 73 percent in the United States - an increase that the United Nations World Food Program attributed in part to the greater use of American corn for bioethanol.

“The fact that cassava is being used for biofuel in China, rapeseed is being used in Europe, and sugar cane elsewhere is definitely creating a shift in demand curves,” said Timothy D. Searchinger, a research scholar at Princeton University in New Jersey. “Biofuels are contributing to higher prices and tighter markets.”

In the United States, Congress has mandated that biofuel use must reach 36 billion gallons annually by 2022. The European transportation fuel must come from renewable sources by 2020. China, India, Indonesia and Thailand have adopted biofuel targets as well.

To be sure, many factors help drive up the price of food, including bad weather and high oil prices.

“The problem is complex, so it is hard to come up with sweeping statements like biofuels are good or bad,” said Olivier Dubois, a bioenergy expert at the Food and Agriculture Organization in Rome. “But what is certain is that biofuels are playing a role.”

Mr. Dubois and other food experts suggest that nations should revise their policies so that fuel mandates can be suspended when food stocks get low or prices become too high.

“The policy really has to be food first,” said Hans Timmer, director of the Development Prospects Group of the World Bank. “The problems occur when you set targets for biofuels irrespective of the prices of other commodities.”

When China a decade ago set out to make bioethanol from corn, the plan caused shortages and a rise in food prices. In 2007 the government banned the use of grains to make biofuel. Chinese scientists then perfected the process of making fuel from cassava.

“They’re moving very aggressively in this new direction; cassava seems to be the go-to crop,” said Greg Harris, an analyst with Commodore Research and Consultancy in New York.

Although a part of diets in Africa, cassava is not central to Asian diets. The Chinese reasoned that making fuel with cassava would not affect food prices, at least at home.

More distant impacts are likely, however. Because cassava chips have been used as animal feed, new demand from the biofuels industry might affect the cost of meat.

In countries where China is paying generously for cassava, farmers may be tempted to grow the crop instead of vegetables or rice. And if China turned to Africa as a source, one of that continent’s staple food crops could be in jeopardy, although exporting cassava could also become a business opportunity.

“This is becoming a more valuable cash crop,” Mr. Harris said. “The farmland is limited, so the more that is devoted to fuel, the less is devoted to food.”

The Chinese demand for cassava could also dent biofuel production in poorer Asian nations: in the Philippines and Cambodia, developers were forced to suspend the construction of cassava bioethanol plants because the tuber had become too expensive.

Biofuels development in wealthier nations has proved to have a powerful effect on crops. Nearly 40 percent of the corn grown in the United States goes to make fuel. The prices of corn on the Chicago Mercantile Exchange rose 73 percent from June to December 2010.

Such price rises also have distant ripple effects, food security experts say. The price of corn in Rwanda rose 19 percent last year.

“For Americans it may mean a few extra cents for a box of cereal,” said Marie Brill, senior policy analyst at ActionAid, an international development group. “But that kind of increase puts corn out of the range of impoverished people.”

Higher prices also mean that groups like the World Food Program can buy less food to feed the world’s hungry.

European biofuels developers are buying large tracts of what they call “marginal land” in Africa with the aim of cultivating biofuel crops, particularly the woody bush known as jatropha. Advocates say that promoting jatropha for biofuels production has little impact on food supplies. But some of that land is used by poor people for subsistence farming or for gathering food like wild nuts.

“We have to move away from the thinking that producing an energy crop doesn’t compete with food,” said Mr. Dubois of the Food and Agriculture Organization. “It almost inevitably does.”


By ELISABETH ROSENTHAL

Using food crops like cassava to satisfy China’s needs for biofuel may lead to higher food prices and cause global hunger to increase. (AGNES DHERBEYS FOR THE NEW YORK TIMES)

The European Union, the U.S. and some Asian nations are mandating targets for biofuel. Cassava in Thailand. (AGNES DHERBEYS FOR THE NEW YORK TIMES)