The rush to grow biofuel crops -- widely embraced as part of the solution to global warming -- is actually increasing greenhouse gas emissions rather than reducing them, according to two studies published Thursday in the journal Science.
One analysis found that clearing forests and grasslands to grow the crops releases vast amounts of carbon into the air -- far more than the carbon spared from the atmosphere by burning biofuels instead of gasoline.
"We're rushing into biofuels, and we need to be very careful," said Jason Hill, an economist and ecologist at the University of Minnesota who co-authored the study. "It's a little frightening to think that something this well intentioned might be very damaging."
Even converting existing farmland from food to biofuel crops increases greenhouse gas emissions as food production is shifted to other parts of the world, resulting in the destruction of more forests and grasslands to make way for farmland, the second study found.
The analysis calculated that a U.S. cornfield devoted to producing ethanol would have to be farmed for 167 years before it would begin to achieve a net reduction in emissions.
"Any biofuel that uses productive land is going to create more greenhouse gas emissions than it saves," said Timothy Searchinger, a researcher at the Woodrow Wilson School of Public and International Affairs at Princeton University and the study's lead author.
The studies prompted 10 prominent ecologists and environmental biologists to write to President Bush and congressional leaders Thursday, urging new policy "that ensures biofuels are not produced on productive forests, grassland or cropland."
Since 2000, annual U.S. production of corn-based ethanol has jumped from 1.6 billion gallons to 6.5 billion gallons -- supplying about 5% of the nation's fuel for transportation, according to the Renewable Fuels Assn., an industry lobbying group.
Federal legislation passed last year calls for production of ethanol to more than double over the next decade. In California, Gov. Arnold Schwarzenegger's proposal to reduce greenhouse gas emissions relies heavily on biofuels.
Food crops such as corn, palm oil, sugar cane and soybeans have so far been the main source of biofuels because they are already grown in abundance and are relatively easy to convert.
The fuels are environmentally attractive because, unlike fossil fuels, they are theoretically carbon-neutral. Carbon is released when the fuel is burned, but a similar amount is absorbed from the atmosphere as the crops grow.
Calculating the actual increase or decrease in carbon emissions has been difficult because myriad factors are involved, such as the energy used to produce the fuels and the varying amounts of carbon released through cultivation.
The biggest source of emissions, by far, comes from land-use changes associated with biofuels, the new studies showed.
Hill's analysis looked at the amount of carbon in forests and grasslands that is released into the air when soil is overturned and existing vegetation rots or is burned away.
The study found that clearing an Indonesian peatland rain forest to make way for a biofuel plantation -- a conversion that is occurring rapidly to satisfy Europe's rising demand for biodiesel -- releases so much carbon that a net reduction in emissions would not begin for 423 years.
Cutting down a tropical rain forest in Brazil to grow soybeans for biodiesel increases emissions for 319 years, the researchers found.
Dedicating existing fields to production of crops for biofuel has the same effect -- indirectly.
Searchinger's study focused on the global ripple effect of changing the use of farmland. U.S. farmers have been replacing soybean fields with cornfields to meet the rising demand for ethanol, lowering the world supply of soybeans and driving up their price.
As a result, farmers in Brazil are clearing rain forest to plant soybeans, he said.
His model estimated that devoting 12.8 million hectares of cornfields in the U.S. for ethanol production would bring 10.8 million hectares of additional land into cultivation throughout the world, including 2.8 million hectares in Brazil and 2.3 million hectares in China and India -- much of it former forests and grasslands.
Kenneth Cassman, a professor of agronomy at the University of Nebraska, said the emissions from land-use changes could be countered in part by higher crop productivity. "If you could increase corn yields, you could reduce land pressure," he said.
In a prepared statement, the Biotechnology Industry Organization said that over the last decade biotechnology has helped U.S. farmers increase yields by 30%.
"With agricultural biotechnology farmers can continue to increase yields of crops to meet the demands for both food and fuel," it said.
Several scientists said the biofuel industry needs to focus on potential sources such as municipal trash, crop waste and prairie grasses.
The government is also promoting those sources, but there are technological hurdles, and the powerful agricultural lobby has put its weight behind food-based biofuels to boost crop prices for farmers.
"We need better biofuels before more biofuels," said Alex Farrell, a professor of energy and resources at UC Berkeley who was not involved in the study.