CHICAGO — Biofuels could lose their green sheen if they are grown at the expense of tropical forests. Demand for the liquid fuels could lead to severe deforestation, researchers warn, which would release far more carbon into the atmosphere than that saved by switching to the greener fuels.
“The bottom line is that crop-based biofuels are going to increase greenhouse gas emissions if they continue to be produced the way they are today,” says Holly Gibbs, a research fellow at StanfordUniversity, who presented a new assessment of land use and biofuel production February 14 at the annual meeting of the American Association for the Advancement of Science.
Increased demand for biofuel crops such as corn, soybean, cassava and palm oil has ripple effects, Gibbs says. Most industrialized countries aiming to replace fossil fuels with biofuels don’t have the agricultural land to grow these fuels. And many of the most promising plants, such as sugarcane and palm oil, are better suited to the tropics anyway. The primary source of new cropland to grow these plants is cleared and burned tropical forest, Gibbs says.
Around 340 billion metric tons of carbon are stored in tropical forests and savannahs, which are typically burned when cleared for agricultural use. The greenhouse gas emissions released when that land is cleared far outweighs any savings from not using fossil fuels, according to several studies.
“It’s like weatherizing your house and deliberately keeping your windows open — it’s just not a smart policy,” says Peter Frumhoff of the Union of Concerned Scientists, who also spoke at the meeting.
Using detailed satellite images, Gibbs tracked changes in land use in the tropics through time. She examined snapshots from 1980, 1990 and 2000 of several parcels of land that were covered with either mature intact forest, disrupted forest, shrubs, plantations or water. In the 1980s about half of the land converted to agriculture came from cleared forests; by the 1990s it was more than 70 percent. Overall, from 1980 to 2000, 80 percent of new cropland came from clearing forests, Gibbs says.
By assessing the amount of carbon released from deforestation and the amount saved by using biofuels rather than fossil fuels, Gibbs and her colleagues calculated the net gain or loss of emissions under different crop and land-use regimes. Crunching the numbers revealed that even high-yield biofuel crops such as sugar cane and palm oil would reduce emissions an average of 2.5 tons of carbon per hectare per year. That doesn’t touch the amount of carbon intact forests would keep out of the atmosphere, Gibbs says. The billions of tons stored in tropical forests is the equivalent of 40 years’ worth of global fossil fuel emissions, she says.
Michael Coe, a scientist at WoodsHoleResearchCenter in Falmouth, Mass., says that advancing corn-based ethanol use in the United States is viable and has benefits. But the benefits can’t be confused with a net positive balance in greenhouse gas emissions.
“Under the best scenarios we can’t find a way that it makes greenhouse gas sense to burn ethanol in the U.S. that’s made from corn if it is grown in the tropics,” Coe says. “The amount of carbon released is much greater than the debt saved.”
Gibbs is certain that biofuels fit into the energy equations of the future. But “no single biofuel is going to be able to fulfill our energy needs. We need a diversified portfolio,” she says. Policy and market incentives are needed to use already degraded land for crops, an endeavor that is currently high cost, low profit, she says. The way things are going now, “we’re burning the rainforest in our gas tanks.”