Almost all biofuels used today cause more greenhouse-gas emissions than conventional fuels if the full emissions costs of producing these...

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Almost all biofuels used today cause more greenhouse-gas emissions than conventional fuels if the full emissions costs of producing these “green” fuels are taken into account, two studies published Thursday have concluded.

The benefits of biofuels have come under increasing attack in recent months, as scientists took a closer look at the global environmental cost of their production.

These plant-based fuels were originally billed as better than fossil fuels because the carbon released when they were burned was balanced by the carbon absorbed when the plants grew. But that equation proved overly simplistic because the process of turning plants into fuels causes its own emissions — for refining and transport, for example.

These studies, published in the prestigious journal Science, for the first time take a detailed, comprehensive look at the emissions effects of the huge amount of natural land that is being converted to cropland globally to support biofuels development.

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The destruction of natural ecosystems — whether rain forest in the tropics or grasslands in South America — not only releases greenhouse gases into the atmosphere when they are burned and plowed, but also deprives the planet of natural sponges to absorb carbon emissions. Cropland also absorbs far less carbon than the rain forests or even scrubland that it replaces.

Together the two studies offer sweeping conclusions: It does not matter if it is rain forest or scrubland that is cleared, the greenhouse-gas contribution is significant. More important, they discovered that, globally, the production of almost all biofuels resulted — directly or indirectly, intentionally or not — in new lands being cleared for food or fuel.

“When you take this into account, most of the biofuel that people are using or planning to use would probably increase greenhouse gases substantially,” said Timothy Searchinger, lead author of one of the studies and a researcher in environment and economics at Princeton University.

Searchinger’s team determined that corn-based ethanol almost doubles greenhouse-gas output over 30 years when the land-use changes to grow corn are considered. Cellulosic ethanol made in the U.S. from switchgrass, a fuel that has been singled out by President Bush as a way to reduce the country’s dependence on oil, produces 50 percent more emissions than gasoline does, the study said.

The clearing of grassland releases 93 times the amount of greenhouse gas that would be saved by the fuel made annually on that land, said Joseph Fargione, lead author of the second paper, and a scientist at the Nature Conservancy. “So for the next 93 years you’re making climate change worse, just at the time when we need to be bringing down carbon emissions.”

Searchinger said the only possible exception he could see for now was sugar cane grown in Brazil, which takes relatively little energy to grow and is readily refined into fuel. He added that governments should focus on developing biofuels that did not require cropping, such as those from agricultural waste products. “This land-use problem is not just a secondary effect — it was often just a footnote in prior papers,” Searchinger said. “It is major.”

Industry groups, like the Renewable Fuels Association, immediately attacked the new studies as “simplistic.”

“Biofuels like ethanol are the only tool readily available that can begin to address the challenges of energy security and environmental protection,” said Bob Dineen, the group’s director, in a statement issued after the Science reports’ release.

In the wake of the new studies, a group of 10 of the United States’ most eminent ecologists and environmental biologists on Thursday sent a letter to President Bush and the speaker of the House, Nancy Pelosi, urging a reform of biofuels policies.

The U.S. recently enacted legislation boosting biofuel production to 36 billion gallons in 2022 from 7.5 billion gallons in 2012. The European Union requires 10 percent of transportation to use biofuels by 2020.

The European Union and a number of European countries have recently tried to address the land-use issue with proposals stipulating that imported biofuels cannot come from land that was previously rain forest.

Fargione said that the dedication of so much cropland in the United States to growing corn for bioethanol had caused indirect land-use changes far away — for instance, by increasing pressure on Brazil to meet soybean demand. “Brazilian farmers are planting more of the world’s soybeans — and they’re deforesting the Amazon to do it,” Fargione said.

There should be more focus on producing biofuels from municipal waste and from land that can’t be used for food crops, said Alex Ferrell, an energy and resource professor at the University of California, Berkeley. Soil and plants are essential stores of carbon, containing more than the atmosphere, he said.

Ferrell, who wasn’t involved in the two studies, said the economic model used in Searchinger’s study will have a “profound” impact on the biofuel debate because it questions the rationale of governments who see biofuels as a way to limit global warming.

Information from Bloomberg News is included in this report.

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