Monday, December 8, 2014

Flawed studies underpin low-carbon fuel policies

Nearly all of the studies used to promote biofuels as climate-friendly alternatives to petroleum fuels are flawed and need to be redone. This conclusion is just one of the findings of my advanced review paper, "The Liquid Carbon Challenge: Evolving Views on Transportation Fuels and Climate," recently published online by Wiley Interdisciplinary Reviews: Energy and Environment. The unhappy assessment is based on an in-depth review of the literature published on the topic over the past two decades.

Once the erroneous carbon accounting methods are corrected, the results will show that policies used to promote biofuels -- such as the U.S. Renewable Fuel Standard (RFS) and California's Low-Carbon Fuel Standard (LCFS) -- actually worsen the buildup of CO2 in the atmosphere rather than reducing emissions as promised. 

A major problem with existing studies is that they fail to correctly account for the CO2 absorbed from the atmosphere when corn, soybeans, sugarcane and other biomass feedstocks are grown to produce biofuels. 

Does this field absorb more carbon dioxide when its soybeans
are used to make biodiesel rather than, say, tofu? 
Almost all of the farm fields used to grow the crops harvested for producing biofuels were already being used to grow crops for other reasons. Using the land for fuel rather than food does not significantly increase the amount of CO2 being removed from the atmosphere and therefore provides no climate mitigation benefit.

As emphasized by the paper's other key finding, the real challenge is to remove CO2 from the atmosphere at faster rates and larger scales than is done by established agricultural and forestry activities. Focusing on raising the rate of net carbon uptake rather than on producing biofuels will lead to climate policies that are effective rather than counterproductive when it comes to balancing out CO2 emissions from the use of gasoline and other liquid fuels.

The "Liquid Carbon Challenge" paper examines the four main approaches that have been used to evaluate the carbon dioxide impacts of liquid transportation fuels, both petroleum-based fuels and biofuels. It takes a critical look at carbon footprinting, a popular form of lifecycle analysis developed to evaluate the total emissions of CO2 and other greenhouse gases associated with the production and use of a product.

Numerous fuel-related carbon footprint studies have been published over the past two decades, but there is widespread disagreement over the results.

Even so, these methods were advocated by environmental groups and subsequently mandated by Congress as part of the 2007 federal energy bill's provisions to promote biofuels through the RFS. Shortly thereafter, parallel efforts in California led to that state's adoption of the LCFS based on a carbon footprinting model.

Unfortunately, such carbon footprint comparisons fail to properly reflect the dynamics of the terrestrial carbon cycle, miscounting CO2 uptake during plant growth. CO2 uptake occurs on all productive lands, whether or not the land is harvested for biofuel. This accounting error helps explain why the results of such studies have remained in dispute for so long, with especially sharp disagreements over comparisons of biofuels, such as ethanol and biodiesel, to conventional fuels such as gasoline and diesel from petroleum.

Editor's note: this post is adapted from a University of Michigan News Service story headlined "A closer look at the flawed studies behind policies used to promote 'low-carbon' biofuels" that appeared following the publication of the final print version of the "Liquid Carbon Challenge" paper in Volume 4 of WIREs Energy & Environment. 

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