A US farmer displays an ear of corn and a beaker of 200-proof ethanol.
Hailed until only months ago as a silver bullet in the fight against global warming, biofuels are now accused of snatching food out of the mouths of the poor.
Billions have been poured into developing sugar- and grain-based ethanol and biodiesel to help wean rich economies from their addiction to carbon-belching fossil fuels, the overwhelming source of man-made global warming.
Heading the rush are the United States, Brazil and Canada, which are eagerly transforming corn, wheat, soy beans and sugar cane into cleaner-burning fuel, and the European Union (EU) is to launch its own ambitious program.
But as soaring prices for staples bring more of the planet's most vulnerable people face-to-face with starvation, the image of biofuels has suddenly changed from climate saviour to a horribly misguided experiment.
The head of the International Monetary Fund (IMF) recently said biofuels "posed a real moral problem" and called for a moratorium on using food crops to power cars, trucks and buses.
The vital problem of global warming "has to be balanced with the fact that there are people who are going to starve to death," said Dominique Strauss-Kahn.
"Producing biofuels is a crime against humanity," the UN's former special rapporteur for the right to food, Jean Ziegler of Switzerland, has said.
And on May 22, his replacement, Olivier De Schutter, said new investments and subsidies favoring the production of biofuels should be frozen in an effort to curb food price rises.
Biofuels may still be in their infancy but they are growing rapidly, with annual production leaping by double-digit percentages.
US targets for reducing US carbon emissions require American producers to supply at least 136 billion liters of renewable fuel by 2020.
De Schutter described the target and a European Union goal of having biofuels meet ten percent of transport energy demands by 2020 as "unrealistic."
"By abandoning them (the targets), we would send a strong signal to the markets that the price of food crops will not infinitely rise, thus discouraging speculation on commodity futures," he said.
"I have therefore proposed a freeze on all new investments and subsidies favoring the production of fuel by growing crops on arable and non-degraded lands, when such lands are suitable for the production of food crops."
In 2007, 20 percent of grain - 81 million tons - produced in the United States was used to make ethanol, according to US think tank the Earth Policy Institute, which predicts that the percentage will jump to nearly a quarter this year. "We are looking at a five-fold increase in renewable fuel," said Bush's top climate change advisor, Jim Connaughton.
But more than half of that legislatively-mandated production would come from "second-generation" biofuels made from non-food sources such as switchgrass and wood byproducts, he said.
EU and Brazilian officials have contested the link between biofuels and the world food crisis.
"This is highly exaggerated," Sergio Serra, Brazil's ambassador for climate change, told AFP.
"There is no real relation of cause and effect between the expansion of the production of biofuels and the raising of food prices. At least it is not happening in Brazil."
Defenders of biofuels say food shortfalls have multiple causes, including a growing appetite for meat among the burgeoning middle class in China and India.
On average, it takes more than four kilograms of grain to produce 1kg of pork, and 2kg of grain to yield 1kg of beef.
Climate change may well be a contributing factor.
Some scientists fear rising temperatures and shifting rainfall patterns may be worsening water scarcity in key agriculture areas such as Australia's wheat belt, and rice-growing deltas may be hit by saline intrusion from rising seas.
In addition, the surging cost of oil has had an indirect impact on many poor people, adding to the pinch caused by rising food prices.