Study Finds Ethanol Worse for Climate than Gasoline

By Lisa Raffensperger

The Earth Trends News - February 10, 2008

Original URL

Ethanol's climate benefits, already assailed by many environmentalists, have become even more troubled in the past week. A study published online in Science magazine last Thursday indicates that, over a 30 year span, ethanol from corn nearly doubles the greenhouse gas emissions of the equivalent amount of gasoline, while ethanol produced from switchgrass increases emissions by 50 percent.

Because biofuel feedstocks absorb carbon as they grow, their combustion produces no net CO₂ in the atmosphere. But processing the plants into fuel is an energy-intensive process, which is largely powered by fossil fuels. Still, until now it has been generally accepted that corn ethanol does have greenhouse gas savings over gasoline, albeit small.

However, previous calculations have failed to account for land use change caused by burgeoning ethanol production, in part because it was especially difficult to measure. The study released last week, using widely respected agricultural modeling software, is the first to include carbon emissions caused by land use change in its calculation. Taking these emissions into account, the environmental profile of biofuels changes drastically.

World Ethanol Production, 1975-2005

Source: EarthTrends, 2007 using data from Earth Policy Institute, 2006.

Direct and indirect emissions of expanding croplands

The land on which biofuel feedstocks like corn and switchgrass are grown must come from somewhere. The two possible options, the paper's authors say, are to plow up forests or grasslands to make new cropland or to divert existing cropland to biofuels. In the former scenario, emissions are created directly by the decomposition or burning of plant material and the turning over of soil. Emissions are also created in the latter scenario, though indirectly. Fewer acres of food crops triggers higher prices, and in turn, farmers around the world respond by clearing forests and grassland to plant these valuable crops. This correlation was confirmed in a recent study, which found that higher soybean prices accelerate deforestation in the Amazon rainforest.

Though more efficient farming techniques or crop processing could also produce better biofuel yields, the authors point out that increasing cropland remains the most inexpensive and quick response to growing grain demand. However, emissions caused by the conversion of an acre of forest into cropland for biofuels are much greater than the annual emissions that an acre of biofuels will save over gasoline. In the study authors calculate that it would take 167 years of corn ethanol production on converted land to "pay back" the emissions debt of land use change.

A change of course for biofuels

The study's findings certainly shouldn't be taken to mean that all biofuels are environmentally destructive. Cellulosic ethanol that makes use of waste biomass, such as agricultural residues or wood chips, doesn't demand expanding cropland. Similarly, feedstocks like switchgrass can be grown on abandoned agricultural land or land not suited to food production.

Land use changes simply must be accounted for in evaluating the environmental impact of current and future biofuels. While the technology of ethanol production is rapidly developing, promising greater efficiency in the future, the magnitude of damage done by clearing land will still outweigh new technologies for years to come. The biofuels industry in the U.S. will need a change of course, toward cellulosic and waste-capturing technologies, but most pointedly, away from expanding cropland to produce fuels.

Top photo by Jami Dwyer via Flickr

Read more... Sphere: Related Content