Two new studies just published in Science examine the life cycle impact of ethanol, particularly the carbon debt acquired by converting native ecosystems to biofuel production:
…The first, by ecologists at Princeton and the Woods Hole Research Center, reviews the environmental consequences of increased biofuel consumption, which had never been examined comprehensively…
The researchers break new ground by exposing a kind of mega-accounting error: Prior studies had never credited the carbon-dioxide emissions that arise when virgin forests, grasslands and the like are cleared to grow biofuel feedstocks. About 2.7 times more carbon is stored in terrestrial soils and plant material than in the atmosphere, and this carbon is released when these areas are cleared (often by burning) and the soil is tilled. Compounding problems is the loss of “carbon sinks” that absorb atmospheric CO2 in the bargain. Previous projections had also ignored the second-order effects of transferring normal farm land to biofuels, which exerts world-wide pressure on land use.
So, incredibly, when the hidden costs of conversion are included, greenhouse-gas emissions from corn ethanol over the next 30 years will be twice as high as from regular gasoline. In the long term, it will take 167 years before the reduction in carbon emissions from using ethanol “pays back” the carbon released by land-use change. As they say, it’s not easy being green.
The second study comes out of the University of Minnesota and the Nature Conservancy and explores what the authors call the “carbon debt” when native ecosystems are converted to biofuel stock. Until the debt is repaid, biofuels from those fields will be greater net emitters than the fossil fuels they replace. The authors find that the debt for corn ethanol in the U.S. is between 48 and 93 years. In Indonesia and Malaysia, which have a 1.5% annual rate of deforestation to produce palm oil for Western European biodiesel, the debt is as high as 423 years. Yep, that’s four centuries. Even Fidel Castro won’t last that long….
The first paper is Land Clearing and the Biofuel Carbon Debt, from the University of Minnesota and The Nature Conservancy. Abstract at Science:
Increasing energy use, climate change, and carbon dioxide (CO2) emissions from fossil fuels make switching to low-carbon fuels a high priority. Biofuels are a potential low-carbon energy source, but whether biofuels offer carbon savings depends on how they are produced. Converting rainforests, peatlands, savannas, or grasslands to produce food-based biofuels in Brazil, Southeast Asia, and the United States creates a ‘biofuel carbon debt’ by releasing 17 to 420 times more CO2 than the annual greenhouse gas (GHG) reductions these biofuels provide by displacing fossil fuels. In contrast, biofuels made from waste biomass or from biomass grown on abandoned agricultural lands planted with perennials incur little or no carbon debt and offer immediate and sustained GHG advantages.
The second paper is Use of U.S. Croplands for Biofuels Increases Greenhouse Gases Through Emissions from Land Use Change. Abstract at Science:
Most prior studies have found that substituting biofuels for gasoline will reduce greenhouse gases because biofuels sequester carbon through the growth of the feedstock. These analyses have failed to count the carbon emissions that occur as farmers worldwide respond to higher prices and convert forest and grassland to new cropland to replace the grain (or cropland) diverted to biofuels. Using a worldwide agricultural model to estimate emissions from land use change, we found that corn-based ethanol, instead of producing a 20% savings, nearly doubles greenhouse emissions over 30 years and increases greenhouse gases for 167 years. Biofuels from switchgrass, if grown on U.S. corn lands, increase emissions by 50%. This result raises concerns about large biofuel mandates and highlights the value of using waste products.
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