ISSUES IN ECOLOGY NUMBER SEVENTEEN SPRING 2013 in order for wood harvested for biofuel to have Repa ent of this "carbon debt"can o no net carbon emissions,or net carbon stor once the net GHG emissions from production of he ow the eds that which th e lands pical have stored without being used for biofuels. Indirect Effects grasslands,and grasslands in the U Plant biomass and soils store large amounts of depending on the cropand the type of and carbon,that destroys these carbon creates a "carb cthanol would create a carbon debt that woul CO,into the atmosphere.Converting unfarmed perennial vegetation to ar ime for the carb t assoc CRP land in Michigan to biofuels under five differ. ent scenarios ranged from 29 years for corn- soybean rotations managed without tillage to Box 4.What Is Life Cycle Analysis? Life cycle ar gravepictur of all er nvironmental impact mental Pro components nalysis identifies and quantifies the er rocessin ental 2009.Trends in Plant Science- Adapt from SC Davis e f the gaghebotelTmesedaaaetenueadneconomicadenion ement ct other variables and feed back into the cycle.Such indirect effects are perhaps the CAs are impe they ae ed into legisl ence and Security Act.EPA's RFS2 standard ouse gas emissions'means the ad e gas emissions Code of F ederal Part 80) mportance of these analyses for policy. ton Agency 2006.Life cycle a esa.rp orts, The Ecological Society of America.esahg@esa.ord esa 7© The Ecological Society of America • esahq@esa.org esa 7 ISSUES IN ECOLOGY NUMBER SEVENTEEN SPRING 2013 in order for wood harvested for biofuel to have no net carbon emissions, or net carbon stor￾age, it must be grown and harvested in such a way that the landscape-level carbon captured equals or exceeds that which the forest would have stored without being used for biofuels.7 Indirect Effects Plant biomass and soils store large amounts of carbon, so land conversion that destroys these stores and accelerates the decomposition of carbon creates a “carbon debt” by releasing CO2 into the atmosphere. Converting unfarmed perennial vegetation to annual crops grown for biofuels loses not only much of the carbon currently in the soil but can also lose the future carbon that would have been stored if the land had been left unconverted. Repayment of this “carbon debt” can occur once the net GHG emissions from production and combustion of the biofuels drop below the GHG emissions of the fossil fuel being replaced. Conversion of native lands (tropical rainforest, peatland rainforest, native Brazilian grasslands, and grasslands in the U.S.) was estimated to incur large carbon debts that would take decades to centuries to pay off, depending on the crop and the type of land being converted.8 Conversion of grasslands in the central U.S. to production of corn for ethanol would create a carbon debt that would take 93 years to repay. The estimated payback time for the carbon debt associated with con￾verting Conservation Reserve Program (CRP) land in Michigan to biofuels under five differ￾ent scenarios ranged from 29 years for corn￾soybean rotations managed without tillage to Box 4. What Is Life Cycle Analysis? Life cycle analysis or assessment (LCA) provides a “cradle to grave” picture of all environmental impacts of biofuels and the processes that go into producing them. The U.S. Environ￾mental Protection Agencya describes LCA as a systematic, phased approach with four components: • Goal definition and scoping describes the product, process or activity; establishes the context for the assessment; and identifies the boundaries and environmental effects to be reviewed. • Inventory analysis identifies and quantifies the energy, water, and materials use and environmental releases (e.g., air emis￾sions, solid waste disposal, wastewater discharges). • Impact assessment assesses the potential human and eco￾logical effects of energy, water, and material use and the environmental releases identified in the inventory analysis. • Interpretation evaluates the results of the inventory analysis and impact assessment. An LCA incorporates data on many aspects of the life cycle, including fertilizer use, changes in crops or acreage, and energy used for growing and transporting feedstocks and for processing the biofuel. These data are then used in economic and environ￾mental models to assess net effects on GHG generation (see Figure 3). While an important tool, like any analysis LCA does not guarantee agreement among investigators. One reason for the variation in results is disagreement about what factors should go into an LCA. For example, one criticism of LCAs is that they often leave out various types of information, such as how changes in prices will affect other variables and feed back into the cycle. Such indirect effects are perhaps the most difficult to quantify and thus the most contentious. LCAs are imperfect, but they are incorporated into legislation such as the Energy Independence and Security Act. EPA’s RFS2 standard, for example, uses indirect land use analysis in determining the life cycle GHG emissions of various biofuels sources. As noted in the regula￾tion, “Congress specified that: The term ‘lifecycle greenhouse gas emissions’ means the aggregate quantity of greenhouse gas emissions (including direct emissions and significant indirect emissions such as significant emissions from land use changes), as determined by the Administrator, related to the full fuel lifecycle . . .” (40 Code of Federal Regulations Part 80). There are challenges for both scientists and policymakers when there are no accepted protocols or rules for deciding which components should be included or excluded in LCAs. Calls for standardized approaches for biofuels LCA thus seem particularly pertinent given the importance of these analyses for policy.b Sources: a U.S. Environmental Protection Agency. 2006. Life cycle assessment: principles and practice. EPA/600/R-06/060, USEPA, Cincinnati, OH. b Mitchell, R.B., L.L. Wallace, W. Wilhelm, G. Varvel, and B. Wienhold. 2010. Grasslands, rangelands, and agricultural systems. Biofuels and Sustainability Reports, Ecological Society of America, Washington, D.C. http://esa.org/biofuelsreports/ Figure 3. GHG life cycle analysis of biofuels. Adapted from SC Davis et al. 2009. Trends in Plant Science 14: 140-146. Policy GHG Economic incentive GHG GHG GHG GHG GHG Energy Fertilizers Pesticides Herbicides Seeds Biofuel crop yield Liquid fuel Fuel used Energy Energy Energy GHG GHG Land-use conversion Manufacture/ transport Biofuel cultivation Conversion processing Transport