The carbon footprint of biofuels has often been a source of contention. Recently, a study out of the University of Michigan Energy Institute suggested that biofuels are worse for the climate than gasoline. However, there is significant evidence in the scientific literature to the contrary. Many respected laboratories, agencies, and researchers have used a lifecycle analysis to show that biofuels, particularly advanced biofuels, provide significant carbon benefits compared to gasoline. These benefits have increased in recent years, as biofuels have become less energy-intensive to produce while oil/gasoline has become more energy-intensive to extract and produce.
Greenhouse gas emissions for biofuels are most commonly evaluated through a lifecycle assessment. This assessment calculates the amount of greenhouse gases that are released per unit of fuel. For biofuels, this includes emissions and/or carbon sequestration as well as any land use changes from the growing of biofuel crops. Congress required EPA to use a lifecycle assessment in its evaluation of the Renewable Fuel Standard.
The Department of Energy’s Argonne National Lab has developed the Greenhouse Gases, Regulated Emissions, and Energy Use in Transportation (GREET) Model, the most comprehensive, up-to-date lifecycle assessment model for various fuels (including biofuels and petroleum-based fuels). A 2012 paper from researchers at Argonne shows that ethanol provides emissions reductions of between 19 and 48 percent compared to gasoline. This range can be attributed in part to different farming practices—more sustainable agricultural practices will lead to larger emissions reductions.
This fits with the assessment of Harvard Professor Daniel Schrag, who acts as a bioenergy impact advisor to the EPA. Schrag says, “For about 10 years there have been very careful studies of corn ethanol and all of the fossil carbon that is used to make it… and those studies have gotten a range of answers, but it is about a 20 percent reduction of net emissions relative to gasoline.”
The emissions reductions are even higher for advanced biofuels. For example, according to Argonne’s GREET model, an energy crop like miscanthus can have negative GHG emissions, meaning that over the crop’s life cycle, carbon sequestration outweighs emissions. Argonne researchers show that compared to gasoline, biofuel from energy crops can reduce emissions by 101 to 115 percent. Corn stover, a residue from corn, can reduce emissions by 90 to 103 percent.
The oft-cited increase in GHGs from biofuels is based on EPA’s Regulatory Impact Analysis for the RFS from 2010. Since 2010, better data, continual improvements in lifecycle analysis modeling, and a richer understanding of the role of co-products produced in conjunction with biofuels have significantly reduced emission estimates for corn-based biofuels, and this updated data is reflected in the GREET model. The GREET model has demonstrated that the carbon intensity for ethanol has been steadily falling in the past decade.
Measuring Carbon Uptake
The Michigan Energy Institute study used the Annual Crop Production data from the National Agricultural Statistical Service to quantify the carbon uptake of corn used for ethanol. Dr. Michael Wang, a researcher at Argonne, told the Christian Science Monitor, “The carbon uptake by the US farming systems is calculated based only on grain harvest. Carbon uptake embedded in above- and below-ground biomass is ignored…”
Others have commented that time scale needs to be taken into account. Rather than looking year to year, most assessments look at the carbon cycle of biofuels over a 30 year timeframe, allowing time for emitted carbon to be resequestered.
Argonne National Laboratory assigns an emissions credit in its GREET model to account for the carbon uptake in biofuels. Researchers from Argonne, Purdue, and the Federal Aviation Administration wrote in a response to another paper by John DeCicco, the Energy Institute study author, that the separation of emissions from combustion and carbon uptake was, “so that GREET users could always question how much, if any, CO2 uptake credit should be assigned to a given biomass feedstock. In our opinion, assignment of CO2 uptake credits for annual crops, perennial grasses, and short-term-rotation trees is a reasonable assumption.”
Biofuels Are Getting Better, Gasoline Is Getting Worse
In the years since the 2010 EPA Regulatory Impact Analysis, biofuels have become less carbon intensive. Research conducted at the University of Illinois at Chicago has shown that the corn ethanol industry’s electricity use declined 30 percent from 2001-2013, while yields increased by seven percent. Improved agricultural practices have allowed higher yields from the same amount of land, which limits land use change. In addition, sustainable agricultural practices have been increasingly adopted. These practices increase soil carbon sequestration, which means that more of the emissions associated with biofuel production are offset.
Precision agriculture can also play a role. This technology allows for specific analysis of farmland, so farmers can know how much fertilizer is needed in each area. This reduces overall nitrogen fertilizer application. Reducing fertilizer application is a benefit to the climate, as the fertilizer is energy-intensive to produce and releases nitrous oxide, a potent greenhouse gas.
On the other hand, more and more energy-intensive practices are being used to extract oil and produce gasoline. Oil from tar sands, for example, produces significantly more greenhouse gases than traditional petroleum, and is becoming a larger percentage of the fuel supply. Therefore, as biofuels replace more carbon-intensive gasoline, they provide even greater emissions reductions.
Ethanol provides many significant advantages in addition to its low-carbon intensity. In particular, ethanol is homegrown (decreasing our dependence on foreign countries), and its production results in many valuable byproducts, such as corn oil, fiber, and dried distiller’s grains or DDGs (high-protein animal feed).
Ethanol is cheaper than gasoline—according to a study by the Defour group, E10 saves consumers four cents per gallon, on average. The cost savings for ethanol are even higher when compared with premium fuel. More and more auto manufacturers are recommending premium because of its high octane content, which is necessary for increasingly efficient engine technologies. Higher ethanol blends provide the same octane benefits as premium, but with significant cost savings for the consumer.
Until we are able to produce a significant amount of electric vehicles that run on renewably-produced electricity, biofuels remain the only widely available source of clean, renewable transportation energy.
For more information see:
- Well-to-Wheels Energy Use and Greenhouse Gas Emissions of Ethanol From Corn, Sugarcane and Cellulosic Biomass for US Use, Wang et al.
- Carbon Balance Effects of U.S. Biofuel Production and Use, DeCicco et al.
- The Renewable Fuel Standard: Working as Intended? EESI
- Do Biofuels Harm the Planet More Than Gasoline? The Christian Science Monitor
- Comments on and Discussion of “The Liquid Carbon Challenge: Evolving Views on Transportation Fuels and Climate”, Wang et al.
- Request for Correction of Information, Energy Future Coalition, Urban Air Initiative, and Governors’ Biofuels Coalition
- Carbon Accounting and Vehicle Fuels: A Research Update, EESI
- Protecting Public Health Through Cleaner Fuels and Lower Emissions, EESI