Initially sold as a dual path to energy independence and a cleaner environment, the Renewable Fuel Standard (RFS) was adopted as part of the 2005 amendments to the Clean Air Act. Today, research on the RFS is nearly unanimous that its corn ethanol mandate degrades the environment. The policy’s consequences extend to a wide variety of ongoing environmental problems, including water pollution and water scarcity, habitat degradation, and air pollution.
The Environmental Protection Agency, which administers the standard, will soon have an opportunity to adjust ethanol mandate volumes under the RFS. Unfortunately, recent reporting suggests that the agency may treat the RFS as if it were a part of the Farm Bill, not the Clean Air Act, which would mean more mandated ethanol, not less. As the EPA considers altering the RFS, it should give special attention to the unintended harmful environmental consequences that the ethanol mandate creates.
RFS Design and Implementation
The RFS is a volumetric consumption mandate, obligating refiners and fuel importers to buy biofuels and blend them into transportation fuels. The mandate started small in the mid‐2000s but crescendos to 36 billion gallons in 2022.
The total mandate is made up of four nested mandates: cellulosic, biomass‐based diesel, “advanced,” and the total mandate. Cellulosic biofuels and biomass‐based biodiesel count toward their own, smaller mandates as well as the advanced and total mandates. Advanced biofuels—primarily ethanol produced using sugarcane as the feedstock—similarly meet their own mandate and the larger total mandate. Whatever is left of the total mandate after refiners meet their obligations to the cellulosic, biomass‐based diesel, and advanced mandates is generally met with conventional biofuels like corn ethanol.
The original idea was that conventional biofuels would transition the fuel industry to using much higher sums of ethanol, paving the way for better (i.e., cellulosic) biofuels to take over. That’s why the non‐advanced remainder of the total mandate that conventional biofuels are left to fill was supposed to cap out at 15 billion gallons in 2015. After that, biofuel growth was supposed to be driven by the higher‐level mandates. The idea of widespread cellulosic biofuel use was particularly enticing because it would allow wastes like corn husks and stalks or specialty energy crops grown on otherwise useless land to be turned into valuable fuel.
But cellulosic biofuel development has been a disappointment by any measure. Despite a consumption mandate for whatever cellulosic ethanol is produced, a production tax credit, and millions of dollars in research and development support from the government and billions more from oil companies, cellulosic ethanol production in the United States is an order of magnitude lower than its mandated levels, forcing the EPA to drastically modify the cellulosic mandate downward year after year. The 2019 final rule set a cellulosic mandate of 418 million gallons, a mere sliver of the 8.5 billion gallons set in statute. If cellulosic ethanol growth continues at anywhere near this sluggish pace, conventional biofuels will continue to make up a majority of the mandate, as they have every year since the law’s inception. According to a retrospective piece by University of California, Davis agricultural economist Aaron Smith, written to guide future climate policy, the lesson is: “Do not mandate things that don’t exist.”
E10 gasoline (motor fuel containing up to 10% ethanol) is now ubiquitous, car manufacturers attempt to sell “flex fuel” vehicles that can handle E85 (up to 85% ethanol), and the Trump administration recently made regulatory reforms that will allow for year‐round sales of E15. Without the materialization of a cellulosic ethanol industry (and none appears on the horizon), the RFS’s chief result has been the dramatic expansion of a biofuel that’s older than the Model T: corn ethanol.
The RFS and the Environment
The entire point of the RFS is incentivizing the production of more biofuels. Because corn ethanol is cheaper than other types of biofuels, refiners use it to meet as much of the mandate as possible. Producing the ethanol to meet that demand required a major expansion of corn production.
Most of the environmental consequences of the RFS result from expanded corn production. Farms increase production in two ways: by intensifying production on current cropland and by putting new land into production. Farmers initially tried the former approach to the RFS, skipping crop rotations so that they could produce more corn in the short‐term. In the long run, farms increased the amount of land they have under the plow. Because the best areas for growing corn were already being farmed, expansions occurred in areas that weren’t as well‐suited to production. Those areas were often environmentally sensitive or “marginal” land.
Some of this marginal land had previously been protected by the Conservation Reserve Program (CRP), which pays farmers to leave particularly sensitive areas fallow. In the six years following the RFS’s 2007 expansion, nearly half of expiring CRP signatories elected not to re‐enroll. Throughout the Corn Belt’s periphery, grasslands, shrublands, wildlife habitat, and high‐risk erosion zones have been put into production. Between 2008 and 2012, 4.2 million acres converted to cropland within 100 miles of a biorefinery. The National Wildlife Federation documented that these significant losses in habitat for grassland birds caused a drop in both species diversity and abundance in the Prairie Pothole Region.
Corn fields on marginal lands require more inputs like water and fertilizer than their more productive counterparts. Unlike most Iowa cropland, new corn plantings in places like Nebraska require irrigation. Though ethanol from any feedstock consumes more water than gasoline—E85 from unirrigated corn grain requires more than twice as much water per vehicle mile traveled—irrigating the feedstock magnifies the problem more than 100‐fold. It requires an average of 28 gallons of irrigation water to produce enough biofuel for a vehicle to travel a single mile on E85 fuel as compared to about a fourth of a gallon if the corn is not irrigated. (See Table 1.) Much of this irrigation is sourced from groundwater, including the Ogallala Aquifer, whose unsustainable drawdown rate has been well‐publicized.
Producing corn on marginal lands and intensifying production on existing farms also results in additional nitrogen fertilizer application. Runoff from that fertilizer enters nearby waterways and, in the heartland, eventually makes its way to the Gulf of Mexico. This results in the water oxygen depletion that drives the growing hypoxic dead zone. For every billion gallons of ethanol production, environmental economists estimate the dead zone grows by roughly 30 square miles.
The litany of environmental effects from ethanol production makes the new politics of RFS regulation bizarre and unique. On what other issues do Exxon Mobil, the Sierra Club, Chevron, the National Wildlife Federation, and the Clean Air Task Force align?
What about the Climate?
Transportation accounts for 29% of U.S. greenhouse gas (GHG) emissions, and reducing emissions from this sector is notoriously difficult. President George W. Bush often referred to GHG reduction as an important benefit of the RFS. As concerns about energy independence waned in response to the fracking boom, GHG reduction became the chief purported benefit of biofuel production.
