Just when gas prices have finally fallen, here's another reason to cringe at the pump. The ethanol produced on millions of new hectares of corn in the United States in the last 2 years--touted as the green future of oil and gas--will increase deforestation in the Amazon and result in a large increase in carbon emissions to the atmosphere. That's the conclusion from research presented at a symposium this afternoon on biofuels and tropical deforestation. In fact, most new farmland in the tropics is converted from forests that had been rich storehouses of carbon, another scientist reported.
Fossil fuels, of course, contribute to global warming when burned; in contrast, biofuels are made from living plants, which have recently sucked carbon dioxide from the atmosphere. But last year two papers in Science pointed out that biofuels could have a large downside: They may worsen global warming, in large part because of the carbon emissions that come when forests are cut down for new farmland.
Michael Coe of the Woods Hole Research Center in Massachusetts examined the potential impact of the biofuels target set in 2007 by the U.S. Congress. By 2022, the U.S. should annually produce 57 billion liters of corn-based ethanol along with 76 billion liters from other sources. Here's the nexus with the Amazon: When farmers in the U.S. planted more corn and less soy in 2007, Brazilian farmers started planting more soy, an increase of 500,000 hectares. Often, they cut down and burned rainforest to plant more fields.
If the U.S. reaches its target for corn-based ethanol, Coe estimated that Brazilian farmers would plant up to 1 million more hectares of soy. Depending on whether pasture or forests are converted to fields, the amount of carbon emissions released as a result would be 130 to 650 times greater than the emissions saved by burning ethanol rather than fossil fuels. The net amount could be 1.8 to 9.1 petagrams of CO2-equivalent greenhouse gas emissions. "That's a significant amount," he said.
How much of new farmland comes from forests? Holly Gibbs, a postdoc at Stanford University, quantified this for the first time across the tropics by analyzing a random sample of 600 satellite images taken in 1980, 1990, and 2000. The various types of land cover--cropland, pasture, forests, and so forth--in each image had been identified by the U.N. Food and Agriculture Organization. All told, 80% of new fields had been converted from forests. (Most of the rest is shrubland.)
It's not known how much of new farmland is being used for biofuels, but Gibbs estimates it could be anywhere from a third to two-thirds. Unless biofuels are planted in pastures or degraded lands, she said, "we're going to be burning rainforest in our gas tanks."