BIOFUELS INCREASE, RATHER THAN DECREASE, HEAT-TRAPPING CARBON DIOXIDE EMISSIONS

Contrary to popular belief, the heat-trapping carbon dioxide gas emitted when biofuels are burned is not fully balanced by the CO2 uptake that occurs as the plants grow

A new study from University of Michigan researchers challenges the widely held assumption that bio-fuels such as ethanol and bio-diesel are inherently carbon neutral.

Contrary to popular belief, the heat-trapping carbon dioxide gas emitted when bio-fuels are burned is not fully balanced by the CO2 uptake that occurs as the plants grow, according to a study by research professor John DeCicco and co-authors at the U-M Energy Institute.

The study, based on U.S. Department of Agriculture crop-production data, shows that during the period when U.S. bio-fuel production rapidly ramped up, the increased carbon dioxide uptake by the crops was only enough to offset 37 percent of the CO2 emissions due to bio-fuel combustion.

The researchers conclude that rising bio-fuel use has been associated with a net increase -- rather than a net decrease, as many have claimed -- in the carbon dioxide emissions that cause global warming. The findings are scheduled to be published online Aug. 25 in the journal Climatic Change.

"This is the first study to carefully examine the carbon on farmland when bio-fuels are grown, instead of just making assumptions about it," DeCicco said. "When you look at what's actually happening on the land, you find that not enough carbon is being removed from the atmosphere to balance what's coming out of the tailpipe."

The use of bio-fuels to displace petroleum has expanded over the last decade in response to policies, such as the U.S. Renewable Fuel Standard, that promote their use for transportation. Consumption of liquid bio-fuels -- mainly corn ethanol and bio-diesel -- has grown in the United States from 4.2 billion gallons in 2005 to 14.6 billion gallons in 2013.

The environmental justification rests on the assumption that bio-fuels, as renewable alternatives to fossil fuels, are inherently carbon neutral because the carbon dioxide released when they are burned was derived from CO2 that the growing corn or soybean plants pulled from the atmosphere through photosynthesis.

That assumption is embedded in the carbon footprint models used to justify and administer policies such as the federal RFS and the California Low-Carbon Fuel Standard. The models, which are based on a technique called life-cycle analysis, have often found that crop-based bio-fuels offer at least modest net greenhouse gas reductions relative to petroleum fuels.

Instead of modeling the emissions, DeCicco and his colleagues analyzed real-world data on crop production, bio-fuel production, fossil fuel production and vehicle emissions -- without presuming that that bio-fuels are carbon neutral. Their empirical work reached a striking conclusion.

"When it comes to the emissions that cause global warming, it turns out that bio-fuels are worse than gasoline," DeCicco said. "So the underpinnings of policies used to promote bio-fuels for reasons of climate have now been proven to be scientifically incorrect.

"Policymakers should reconsider their support for bio-fuels. This issue has been debated for many years. What's new here is that hard data, straight from America's croplands, now confirm the worst fears about the harm that bio-fuels do to the planet."