Indirect Emissions from Biofuels: How Important?

Jerry M. Melillo, John M. Reilly, David W. Kicklighter, Angelo C. Gurgel, Timothy W. Cronin, Sergey Paltsev, Benjamin S. Felzer, Xiaodong Wang, Andrei P. Sokolov, C. Adam Schlosser.

Science 4 December 2009:
Vol. 326. no. 5958, pp. 1397 – 1399

One of the major consequences of using bioenergy (biofuels) is the increase in terrestrial carbon emissions and consequently an increase in net greenhouse gas emissions (GHG). In this paper two biogeochemistry models were used to predict the environmental consequences of the expanded global cellulosic biofuels program over the 21st century through the analysis of emissions released from both direct and indirect land –use used.  Indirect emissions are the emissions produced when the land required for the cultivation of biofuels displaces agriculture production and requires additional land-use change resulting in increased GHGs.

Currently the methods to estimate indirect emissions are undefined so they are ignored. Thus, current methods of calculating the direct and indirect GHG emissions associated with the carbon intensity (CI, also defined as the GHG emissions/MJ energy produced) of biofuels are incomplete.  The models in this paper then are used to predict and estimate future land-use scenarios accounting for both direct and indirect emissions.

In model 1 the conversion of natural areas to meet increased demand for land, is permissible, as long as the conversion is profitable. In model 2 there is a more extensive use of existing managed land. The direct effects (i.e. changes in carbon storage and N2O emissions) are estimated only in areas devoted to biofuels; the indirect effects are defined and quantified as the differences between the total effects and the direct effects. The paper describes each model in detail and explains their estimated long term and short term pros and cons. To summarize the results: model 2, where there is less willingness to convert land, will be more economically favorable than model 1, because “avoiding deforestation will be reflected in lower estimates of indirect emissions and lower carbon penalties.”

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