Clearing Land for Biofuels Makes Global Warming Worse

Mason Inman
for National Geographic News
February 7, 2008
Growing crops to make biofuels may accelerate global warming, not slow down its effects, a new study says.

When farmers clear native ecosystems such as forests or grasslands to grow crops, this gives off substantial amounts of carbon dioxide, the primary greenhouse gas that fuels climate change.

Biofuels such as ethanol from corn and biodiesel from palm oil typically start out with a "carbon debt."

Before these biofuels could reduce individual carbon dioxide emissions, they would first have to pay off this debt, which would take decades or centuries.

"I was surprised that with so many of the crops, it takes so long before you break even [on carbon emissions]," said study co-author David Tilman of the University of Minnesota in St. Paul. The university and the nonprofit group the Nature Conservancy conducted the study.

"I don't think we can afford to make biofuels if we have to wait 50 years for any benefit," he added.

Many scientists believe the planet is at a crucial juncture, and that carbon dioxide emissions must be reduced sharply over the next 50 years to avoid the catastrophic consequences of climate change.

But there are some kinds of biofuels that could be helpful, such as those made from grasses or algae, as they avoid the debt problem, Tilman said.

The study will be published online tomorrow in the journal Science.

Carbon Dioxide Release

Biofuels release roughly as much carbon dioxide when burnt as regular gasoline or diesel. But since biofuel crops also soak up carbon dioxide as they grow, they were thought to reduce overall emissions as compared with fossil fuels.

However, few earlier studies into biofuel viability factored in carbon released at the start, when land is converted to grow crops.

When grasslands are cleared, the soils also lose much of the carbon they've stored over the years, Tilman said.

And when rain forests with floors of peat—a thick layer of partly decomposed plants—are razed for crops, the peat rots and releases tons of carbon dioxide emissions over decades, the study found.

Sugarcane ethanol had the smallest "carbon debt," which takes about 17 years to pay off, Tilman said. Corn ethanol's debt would takes 93 years to pay off.

When tropical rain forests are cleared for growing palm, the crop's biodiesel carries an 86-year debt. Even worse, when peatland rain forests are cleared for the crop, they rack up a 423-year carbon debt.

Tropical Clearing

This clearing of rain forests for biofuel is happening in Brazil, Indonesia, and Malaysia, and will probably start happening in the [Democratic Republic of the] Congo," Tilman said. "Economics favors production of these biofuels, since they're cheaper than petroleum"—even though they may be worse for Earth's climate, he added.

(Related news: "Ethanol Production Could Be Eco-Disaster, Brazil's Critics Say" [February 8, 2007].)

Roel Hammerschlag, of the Stockholm Environment Institute U.S. in Somerville, Massachusetts, also expects increased use of biofuels will drive land clearing in those countries.

"A large fraction of the land appropriate for biofuels lies in developing nations who can and should benefit from the new markets," Hammerschlag said.

"I do hope that these articles will launch a bigger debate [on biofuels]," he added.

Sue Page of the University of Leicester in England is an expert on tropical peatland forests.

"There is no way to avoid the problems [of growing crops for biofuels in tropical regions]," she said.

The only way to prevent massive carbon dioxide emissions is not putting plantations on peat soils in the first place, Page said.

The maximum lifespan for oil-palm cultivation on lowland tropical peat is less than a hundred years, because the land tends to get too compact and floods, Page said.

"The carbon debt incurred in developing the peatland for biofuel production can never be repaid," she said.

Cropland Explosion

With foods crops increasingly being turned into fuels, the world will need more cropland to feed everyone, according to another study also being published in Science this week. That study focused on the effects of the explosion of corn for biofuel in the United States.

(See biofuel breakthroughs photos.)

For every 5 acres (2 hectares) devoted to corn to make ethanol, the world would need more than 4 more acres (1.6 more hectares) of cropland for food. So increased use of biofuels may drive farmers to convert more native ecosystems into cropland, damaging the environment in the process, the study authors argue.

(Related news: "Ethanol Not So Green After All?" [July 11, 2006].)

Other kinds of biofuels could still be climate-friendly, since they wouldn't cause carbon dioxide emissions from land use changes, Tilman said. These include biofuels made from switchgrass and prairie grasses, waste materials from forests, and algae grown in vats. "These all work in the lab, on a small scale," Tilman said.

"We'll see which of these work on a large scale. We're still in the learning phase."

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