The sobering truth about corn ethanol

PNAS March 9, 2022

Agricultural interest groups promote corn ethanol as an environmentally beneficial alternative to gasoline, but many independent scientists have long questioned this view (1–3). Nevertheless, the United States has aggressively pursued measures to expand biofuel production. The key policy has been the Renewable Fuel Standard (RFS2) in the Energy Independence and Security Act of 2007, which requires greater use of ethanol up to the current level of 15 billion gallons annually. Ethanol proponents have argued that this reduces greenhouse gas (GHG) emissions, but as Lark et al. (4) show in PNAS, the opposite occurs. The authors find that the life-cycle GHG emissions of the ethanol produced to meet RFS2 are no less than those of gasoline, and are likely even greater. This is because using more corn for biofuel has led to an increase in the intensity and the extent of corn farming in the United States. Thus, RFS2 not only fails to mitigate climate change but is actually counterproductive. Furthermore, the authors conclude that RFS2 has exacerbated other environmental problems commonly associated with row crop production, including poor water quality and soil erosion.

Findings

Lark et al. (4) present a detailed accounting of how GHG emissions from US agriculture increased due to greater demand for corn to meet RFS2-mandated ethanol volumes. Farmers responded to higher corn prices by applying more fertilizer to their fields and by reducing the diversity of crops planted in rotation so as to include more corn. They also grew corn on cropland previously planted to other crops such as soybeans and wheat, raising their prices as well. Higher crop prices led, in turn, to expansion of the total cropland area. The consequence of this intensification and extensification of US cropland has been substantially greater GHG emissions. Near the start of RFS2 over a decade ago, three independent studies showed that expanding biofuel production could result in large GHG emissions from land use change (5–7). These concerns are confirmed in the work of Lark et al. (4), which provides a retrospective look at the environmental consequences of implementing RFS2. They accomplish this by integrating economic and biophysical modeling with high-resolution land use change observations in fuel consumption in response to greater fuel supply. Other studies have indicated that emissions from these sources can be substantial in their contribution to total biofuel emissions (8–10).

See https://www.pnas.org/doi/10.1073/pnas.2200997119