Environmental Outcomes of the US Renewable Fuel Standard: A Reply
Since 2013, 10% of essentially every gallon of US gasoline has been ethanol made from corn. In February, my co-authors and I published a peer-reviewed paper in the Proceedings of the National Academy of Sciences arguing that additional corn ethanol does not reduce carbon emissions relative to gasoline once you account for changes in land use.
In essence, more ethanol means an increase in demand for corn, which pushes up corn prices, which incentivizes farmers to plant more corn on existing cropland and to plant crops on land that was not previously being used for crops. Converting land to crops releases carbon from the soil. Our research discovered that the land that was converted due to the Renewable Fuel Standard (aka the ethanol mandate) released a lot of carbon.
Our model estimates what land use would have been if demand for corn had been 1.3b bushels lower than it was. We take a data intensive approach to answering this question. We use historical data to estimate how prices change when corn demand changes, how land use changes throughout the cornbelt when prices change, and how soil carbon changes when land use changes.
A research group lead by Farzad Taheripour posted a critique of our study on their websites. We find their conclusions to be unsupported and based upon several misunderstandings and misinterpretations of our methods and results. We have written a reply to their critique, which I link to below.
We welcome further scientific debate on this topic, especially given its importance for US climate, energy, and agricultural policies.
Our PNAS paper: Environmental Outcomes of the US Renewable Fuel Standard
Taheripour et al. comments: Comments on “Environmental Outcomes of the US Renewable Fuel Standard”