Energy and greenhouse gas emission effects of corn and cellulosic ethanol with technology improvements and land use changes

Regional variations in the environmental impacts of plant biomass production are significant, and the environmental impacts associated with feedstock supply also contribute substantially to the environmental performance of biobased products. Thus, the regional variations in the environmental performance of biobased products are also significant. This study scrutinizes greenhouse gas (GHG) emissions associated with two biobased products (i.e., ethanol and soybean oil) whose feedstocks (i.e., corn and soybean) are produced in different farming locations. We chose 40 counties in Corn Belt States in the United States as biorefinery locations (i.e., corn dry milling, soybean crushing) and farming sites, and estimated cradle-to-gate GHG emissions of ethanol and of soybean oil, respectively. The estimates are based on 1 kg of each biobased product (i.e., ethanol or soybean oil). The system boundary includes biomass production, the biorefinery, and upstream processes. Effects of direct land use change are included in the greenhouse gas analysis and measured as changes in soil organic carbon level, while the effects of indirect land use change are not considered in the baseline calculations. Those indirect effects however are scrutinized in a sensitivity analysis. GHG emissions of corn-based ethanol range from 1.1 to 2.0 kg of CO2 equivalent per kilogram of ethanol, while GHG emissions of soybean oil are 0.4–2.5 kg of CO2 equivalent per kilogram of soybean oil. Thus, the regional variations due to farming locations are significant (by factors of 2–7). The largest GHG emission sources in ethanol production are N2O emissions from soil during corn cultivation and carbon dioxide from burning the natural gas used in corn dry milling. The second largest GHG emission source groups in the ethanol production system are nitrogen fertilizer (8–12%), carbon sequestration by soil (−15–2%), and electricity used in corn dry milling (7–16%). The largest GHG emission sources in soybean oil production are N2O emissions from soil during soybean cultivation (13–57%) and carbon dioxide from burning the natural gas used in soybean crushing (21–47%). The second largest GHG emission source groups in soybean oil production are carbon sequestration by soil (−29–24%), diesel used in soybean cultivation (4–24%), and electricity used in the soybean crushing process (10–21%). The indirect land use changes increase GHG emissions of ethanol by 7–38%, depending on the fraction of forest converted when newly converted croplands maintain crop cultivation for 100 years. Farming sites with higher biomass yields, lower nitrogen fertilizer application rates, and less tillage are favorable to future biorefinery locations in terms of global warming. For existing biorefineries, farmers are encouraged to apply a site-specific optimal nitrogen fertilizer application rate, to convert to no-tillage practices and also to adopt winter cover practices whenever possible to reduce the GHG emissions of their biobased products. Current practices for estimating the effects of indirect land use changes suffer from large uncertainties. More research and consensus about system boundaries and allocation issues are needed to reduce uncertainties related to the effects of indirect land use changes.

Greenhouse gas release from land use change (the so-called "carbon debt") has been identified as a potentially significant contributor to the environmental profile of biofuels. The time required for biofuels to overcome this carbon debt due to land use change and begin providing cumulative greenhouse gas benefits is referred to as the "payback period" and has been estimated to be 100-1000 years depending on the specific ecosystem involved in the land use change event. Two mechanisms for land use change exist: "direct" land use change, in which the land use change occurs as part of a specific supply chain for a specific biofuel production facility, and "indirect" land use change, in which market forces act to produce land use change in land that is not part of a specific biofuel supply chain, including, for example, hypothetical land use change on another continent. Existing land use change studies did not consider many of the potentially important variables that might affect the greenhouse gas emissions of biofuels. We examine here several variables that have not yet been addressed in land use change studies. Our analysis shows that cropping management is a key factor in estimating greenhouse gas emissions associated with land use change. Sustainable cropping management practices (no-till and no-till plus cover crops) reduce the payback period to 3 years for the grassland conversion case and to 14 years for the forest conversion case. It is significant that no-till and cover crop practices also yield higher soil organic carbon (SOC) levels in corn fields derived from former grasslands or forests than the SOC levels that result if these grasslands or forests are allowed to continue undisturbed. The United States currently does not hold any of its domestic industries responsible for its greenhouse gas emissions. Thus the greenhouse gas standards established for renewable fuels such as corn ethanol in the Energy Independence and Security Act (EISA) of 2007 set a higher standard for that industry than for any other domestic industry. Holding domestic industries responsible for the environmental performance of their own supply chain, over which they may exert some control, is perhaps desirable (direct land use change in this case). However, holding domestic industries responsible for greenhouse gas emissions by their competitors worldwide through market forces (via indirect land use change in this case) is fraught with a host of ethical and pragmatic difficulties. Greenhouse gas emissions associated with indirect land use change depend strongly on assumptions regarding social and environmental responsibilities for actions taken, cropping management approaches, and time frames involved, among other issues.

Reducing life cycle greenhouse gas emissions of corn ethanol by integrating biomass to produce heat and power at ethanol plants

A life-cycle assessment (LCA) of corn ethanol was conducted to determine the reduction in the life-cycle greenhouse gas (GHG) emissions of corn ethanol compared to gasoline by integrating biomass fuels in a 190 million liter (50 million gallon) per year dry-grind corn ethanol plant to replace fossil fuels (natural gas and grid electricity). The biomass fuels studied are corn stover and ethanol co-products [dried distillers grains with solubles (DDGS), and syrup (solubles portion of DDGS)]. The biomass conversion technologies/systems considered are process heat (PH) only systems, combined heat and power (CHP) systems, and biomass integrated gasification combined cycle (BIGCC) systems. The key inventory components of the LCA are corn production, stover production, ethanol production, fertilizer inputs, truck transport, co-product credits, ethanol transport to blending, biomass fuel conversion systems, and combustion of anhydrous ethanol (E100). The life-cycle GHG emission reduction for corn ethanol compared to gasoline (97.7 g CO2e/MJ gasoline) is 42.5% for PH with natural gas, 61.3% for PH with corn stover, 82.2% for CHP with corn stover, 81.6% for IGCC with natural gas, 127.7% for BIGCC with corn stover, and 119.1% for BIGCC with syrup and stover. These GHG emission estimates do not include indirect land use change effects. GHG emission reductions for CHP, IGCC, and BIGCC include power sent to the grid which replaces electricity from coal. BIGCC results in greater reductions in GHG emissions than IGCC with natural gas because biomass is substituted for fossil fuels. In addition, underground sequestration of CO2 gas from the ethanol plant’s fermentation tank could further reduce the life-cycle GHG emission of corn ethanol by 31.5% compared to gasoline.

Direct and indirect land use changes issues in European sustainability initiatives: State-of-the-art, open issues and future developments

The approximately 100 million tonne per year increase in the use of corn to produce ethanol in the U.S. over the past 10 years, and projections of greater future use, have raised concerns that reduced exports of corn (and other agricultural products) and higher commodity prices would lead to land-use changes and, consequently, negative environmental impacts in other countries. The concerns have been driven by agricultural and trade models, which project that large-scale corn ethanol production leads to substantial decreases in food exports, increases in food prices, and greater deforestation globally. Over the past decade, the increased use of corn for ethanol has been largely matched by the increased corn harvest attributable mainly to increased yields. U.S. exports of corn, wheat, soybeans, pork, chicken, and beef either increased or remained unchanged. Exports of distillers' dry grains (DDG, a coproduct of ethanol production and a valuable animal feed) increased by more than an order of magnitude to 9 million tonnes in 2010. Increased biofuel production may lead to intensification (higher yields) and extensification (more land) of agricultural activities. Intensification and extensification have opposite impacts on land use change. We highlight the lack of information concerning the magnitude of intensification effects and the associated large uncertainties in assessments of the indirect land use change associated with corn ethanol.

Although various studies have shown that corn ethanol reduces greenhouse gas (GHG) emissions by displacing fossil fuel use, many of these studies fail to include how land-use history affects the net carbon balance through changes in soil carbon content. We evaluated the effectiveness and economic value of corn and cellulosic ethanol production for reducing net GHG emissions when produced on lands with different land-use histories, comparing these strategies with reductions achieved by set-aside programs such as the Conservation Reserve Program (CRP). Depending on prior land use, our analysis shows that C releases from the soil after planting corn for ethanol may in some cases completely offset C gains attributed to biofuel generation for at least 50 years. More surprisingly, based on our comprehensive analysis of 142 soil studies, soil C sequestered by setting aside former agricultural land was greater than the C credits generated by planting corn for ethanol on the same land for 40 years and had equal or greater economic net present value. Once commercially available, cellulosic ethanol produced in set-aside grasslands should provide the most efficient tool for GHG reduction of any scenario we examined. Our results suggest that conversion of CRP lands or other set-aside programs to corn ethanol production should not be encouraged through greenhouse gas policies.

Can Biofuels be a Solution to Climate Change? The Implications of Land Use Change Related Emissions for Policy

The objective of this study was to estimate the effects of dairy diets, manure-handling methods, and interactions with the bio-fuels industry on the net energy intensity, greenhouse gas (GHG) emissions, and land use for milk production in Wisconsin. Five dairy diets supplemented with varying amounts of co-products from corn ethanol and soybean biodiesel production were modeled in two manure management scenarios: with and without on-farm biogas generation. The diets were characterized by different inclusion of soybean meal (SBM) and dry distillers grains with solubles (DDGS), balanced with different types forages. A partial life cycle assessment (LCA) of milk production from cradle to farm gate was performed. Milk production was used as the primary output for this analysis, since the dairy industry will remain the primary agricultural enterprise in Wisconsin for the foreseeable future. The boundaries of the milk production system were expanded to include bio-fuels production. The production of bio-fuels (corn ethanol and biodiesel) was scaled to meet the dietary requirements of each selected dairy ration. The choice of dairy ration had a substantial effect on GHG emissions and net energy intensity per energy corrected milk (ECM) produced. Land use for the integrated dairy and bio-fuels production systems ranged from 1.68 m2/kg ECM to 2.01 m2/kg ECM. Accounting for bio-fuels credits but without biogas generation, net energy intensity ranged from 0.83 MJ/kg ECM to 1.34 MJ/kg ECM, and GHG emissions ranged from 0.69 kg CO2-eq/kg ECM to 0.80 kg CO2-eq/kg ECM, depending on the diet. The average effects of including anaerobic digesters for on-farm biogas generation were reductions in GHG emissions by 0.24 kg CO2-eq/kg ECM, and in net energy intensity by 2.84 MJ/kg ECM.

Chapter 7 - Implications of biofuel production on direct and indirect land use change: Evidence from Brazil

Previous studies on the life-cycle environmental impacts of corn ethanol and gasoline focused almost exclusively on energy balance and greenhouse gas (GHG) emissions and largely overlooked the influence of regional differences in agricultural practices. This study compares the environmental impact of gasoline and E85 taking into consideration 12 different environmental impacts and regional differences among 19 corn-growing states. Results show that E85 does not outperform gasoline when a wide spectrum of impacts is considered. If the impacts are aggregated using weights developed by the National Institute of Standards and Technology (NIST), overall, E85 generates approximately 6% to 108% (23% on average) greater impact compared with gasoline, depending on where corn is produced, primarily because corn production induces significant eutrophication impacts and requires intensive irrigation. If GHG emissions from the indirect land use changes are considered, the differences increase to between 16% and 118% (33% on average). Our study indicates that replacing gasoline with corn ethanol may only result in shifting the net environmental impacts primarily toward increased eutrophication and greater water scarcity. These results suggest that the environmental criteria used in the Energy Independence and Security Act (EISA) be re-evaluated to include additional categories of environmental impact beyond GHG emissions.

BackgroundThe greenhouse gas (GHG) emissions that may accompany land-use change (LUC) from increased biofuel feedstock production are a source of debate in the discussion of drawbacks and advantages of biofuels. Estimates of LUC GHG emissions focus mainly on corn ethanol and vary widely. Increasing the understanding of LUC GHG impacts associated with both corn and cellulosic ethanol will inform the on-going debate concerning their magnitudes and sources of variability.ResultsIn our study, we estimate LUC GHG emissions for ethanol from four feedstocks: corn, corn stover, switchgrass, and miscanthus. We use new computable general equilibrium (CGE) results for worldwide LUC. U.S. domestic carbon emission factors are from state-level modelling with a surrogate CENTURY model and U.S. Forest Service data. This paper investigates the effect of several key domestic lands carbon content modelling parameters on LUC GHG emissions. International carbon emission factors are from the Woods Hole Research Center. LUC GHG emissions are calculated from these LUCs and carbon content data with Argonne National Laboratory’s Carbon Calculator for Land Use Change from Biofuels Production (CCLUB) model. Our results indicate that miscanthus and corn ethanol have the lowest (−10 g CO2e/MJ) and highest (7.6 g CO2e/MJ) LUC GHG emissions under base case modelling assumptions. The results for corn ethanol are lower than corresponding results from previous studies. Switchgrass ethanol base case results (2.8 g CO2e/MJ) were the most influenced by assumptions regarding converted forestlands and the fate of carbon in harvested wood products. They are greater than miscanthus LUC GHG emissions because switchgrass is a lower-yielding crop. Finally, LUC GHG emissions for corn stover are essentially negligible and insensitive to changes in model assumptions.ConclusionsThis research provides new insight into the influence of key carbon content modelling variables on LUC GHG emissions associated with the four bioethanol pathways we examined. Our results indicate that LUC GHG emissions may have a smaller contribution to the overall biofuel life cycle than previously thought. Additionally, they highlight the need for future advances in LUC GHG emissions estimation including improvements to CGE models and aboveground and belowground carbon content data.

Many of the sustainability concerns of bioenergy are related to direct or indirect land use change (LUC) resulting from bioenergy feedstock production. The environmental and socio‐economic impacts of LUC highly depend on the site‐specific biophysical and socio‐economic conditions. The objective of this study is to spatiotemporally assess the potential LUC dynamics resulting from an increased biofuel demand, the related greenhouse gas (GHG) emissions, and the potential effect of LUC mitigation measures. This assessment is demonstrated for LUC dynamics in Brazil towards 2030, considering an increase in the global demand for bioethanol as well as other agricultural commodities. The potential effects of three LUC mitigation measures (increased agricultural productivity, shift to second‐generation ethanol, and strict conservation policies) are evaluated by using a scenario approach. The novel modelling framework developed consists of the global Computable General Equilibrium model MAGNET, the spatiotemporal land use allocation model PLUC, and a GIS‐based carbon module. The modelling simulations illustrate where LUC as a result of an increased global ethanol demand (+26 × 109 L ethanol production in Brazil) is likely to occur. When no measures are taken, sugar cane production is projected to expand mostly at the expense of agricultural land which subsequently leads to the loss of natural vegetation (natural forest and grass and shrubland) in the Cerrado and Amazon. The related losses of above and below ground biomass and soil organic carbon result in the average emission of 26 g CO2‐eq/MJ bioethanol. All LUC mitigation measures show potential to reduce the loss of natural vegetation (18%–96%) as well as the LUC‐related GHG emissions (7%–60%). Although there are several uncertainties regarding the exact location and magnitude of LUC and related GHG emissions, this study shows that the implementation of LUC mitigation measures could have a substantial contribution to the reduction of LUC‐related emissions of bioethanol. However, an integrated approach targeting all land uses is required to obtain substantial and sustained LUC‐related GHG emission reductions in general.

This study investigates the relationship between corn prices in Brazil and the international market, considering a rise in corn ethanol production in Brazil's Midwest region since 2017. Did the entry of the corn ethanol industry in Brazil affect the relationship between domestic and international corn prices? A cointegration analysis was made with a monthly time series from May 2005 to August 2023 controlling for different exogenous events or shocks that may have affected global agricultural markets. The study's findings indicate a stable long‐term relationship between the international and Brazilian corn prices, with changes in international prices being predictors of variations in Brazilian domestic prices, while the opposite was not statistically supported. The study also found no evidence to support the claim that the entry of the corn ethanol industry into Mato Grosso state in 2017 impacted the prices paid to local producers. Therefore, the increase in Brazilian corn prices cannot be attributed to additional demand for corn by local mills, an important result that contributes to discussions such as food versus fuel and indirect land use change.

We developed an integrated model of U.S agricultural and transportation sectors to examine the impacts of corn ethanol production on the reduction in CRP enrollment and grassland conversion during the period 2007-2012. We also examine the extent to which ethanol production raised the budgetary cost of maintaining the CRP program at the 2007 level. Our simulation analysis shows that by raising crop prices and increasing opportunity costs of marginal lands, corn ethanol production led to additional 1.6 million acres reduction in CRP enrollment and grassland conversion relative to a no-biofuel policy baseline scenario. In order to maintain the CRP enrollment at the 2007 levels, a net present value of government expenditure of $1.85 billion on reenrollment would be needed under the baseline scenario for the period 2007-2012. Government expenditure will increase to $2.07 billion with the booming of corn ethanol industry.