Tuesday, October 25, 2016

Do Biofuels Produce Less Carbon Emissions than Petroleum Fuels?

Carbon balance effects of U.S. biofuel production and use (John M. DeCicco, Danielle Yuqiao Liu, Joonghyeok Heo, Rashmi Krishnan, Angelika Kurthen, Louise Wang, Climatic Change, Aug. 25, 2016)

Also discussed here: Biofuels increase, rather than decrease, heat-trapping carbon dioxide emissions (ScienceDaily, Aug.25, 2016)

And here: Controversial study claims biofuels aren’t carbon neutral, says it’s much worse than gasoline (ZNE Science, Aug. 26, 2016)

Today we review research into the belief assumed by government policy to justify agricultural subsidies that biofuels (mostly from corn and soy beans) which currently amounts to 14.6 B gallons/year (or 6% of emissions) offset carbon emissions using petroleum products. This belief is based on the supposition that emissions from biofuels balance carbon emissions by absorbing CO2 from the atmosphere during photosynthesis from the new crops. Results indicate that this additional carbon uptake is only 37% of the emissions from biofuels. The conclusion reached is that the rising use of biofuels (which has tripled over the last 10 years) has resulted in net increase rather than a net decrease in carbon emissions.


Key Quotes:

“Production and consumption of biofuels, meaning biomass-based liquids such as biodiesel and ethanol, has grown steadily in the United States, from 4.2 billion gallons … in 2005 to 14.6 billion gallons .. in 2013”

“In 2013, biofuels accounted for 5.8 % of motor fuel energy end-use and 5.6 % of tailpipe CO2 emissions, up from a 1.4 % share in 2005.”

 “While U.S. biofuel use rose … over this period, additional carbon uptake on cropland was enough to offset only 37 % of the biofuel-related biogenic CO2 emissions. This result falsifies the assumption of a full offset made by LCA and other GHG accounting methods that assume biofuel carbon neutrality

 “Once estimates from the literature for process emissions and displacement effects including land-use change are considered, the conclusion is that U.S. biofuel use to date is associated with a net increase rather than a net decrease in CO2 emissions.”

 “Carbon uptake is dominated by corn, which has the largest planted area and a higher yield than other crops. The carbon harvest from corn alone rose by 25 TgC/yr over the analysis period due to a 17 % increase in planted area and a 7 % increase in yield. The corn-soy rotation is the most extensive U.S. farming practice and soybeans are second to corn basis in planted area. However, soybean yields average less than one-third those of corn by volume and only about 25 % those of corn on a carbon basis.”

 “errors arise when bioenergy is treated as carbon neutral in national and subnational policies, which do not impose globally coherent accounting that tracks all carbon stock changes”

“the conclusion is that rising U.S. biofuel use has been associated with a net increase rather than a net decrease in CO2 emissions. This finding contrasts with those of LCA studies which indicate that even crop-based biofuels such as corn ethanol and soy biodiesel offer modest net GHG reductions.”

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