ACE corrects misrepresentations of RFS environmental outcomes

In South Dakota, the American Coalition of Ethanol said a report released recently in the Proceedings of the National Academy of the Sciences by Tyler Lark and others brought to life several misrepresentations of the environmental outcomes of the Renewable Fuel Standard (RFS) and refutes three key misrepresentations from the report.

American Coalition for Ethanol and Dakota Ethanol Board Member, Corn Farmer, and self-described “student” of corn production and greenhouse gas (GHG) accounting and modeling, Ron Alverson, refutes three key misrepresentations with the facts.

Misrepresentations in Lark et al. 2022

1. Lark et al. estimated that “the RFS increased corn prices by 30% and the prices of other crops by 20%” which, in turn, expanded U.S. corn cultivation by 2.8 million hectares (8.7%) and total cropland by 2.1 Mha (2.4%) in the years following policy enactment (2008 to 2016)”.

Facts: Corn prices during the 5-year period of 2008 through 2012 averaged $5.40 per bushel and during the 4-year period of 2013 through 2016 averaged $4.35 per bushel. A 19% reduction (Chicago Board of Trade Monthly Futures Prices). The corn cultivated area increased 2.3% during these same time periods and total cropland cultivated area increased just 8 tenths of 1% (USDA databases).

2. Lark et al. estimated that 30-year emissions associated with RFS-induced conversions to cropland were 320.4 Tg CO2e, or approximately 181 metric tons of CO2 per hectare per year.

Facts:  Grasslands and pasturelands contain about 150 metric tons per hectare of soil organic carbon in the top 3 feet of soil.  If 100% of the carbon decomposed in the 3-foot layer of soil over a hectare, the total CO2 emissions would be 550 metric tons of CO2.  Lark’s claim of 181 metric tons of CO2 per hectare per year implies that the entirety of soil organic carbon (SOC) in the top 3 feet of soil in converted cropland would decompose in only 3 years, and then corn ethanol is charged with 181 metric tons of CO2 emissions per hectare per year for another 27 years, even though Lark et al. claims the entire SOC stock will be decomposed after 3 years.  Furthermore, soil scientists have determined that from about 1900 to 1950, grasslands that were converted to cropland lost about 50% of the original SOC in the top 8 inches of soil.  This is an annual loss rate of .4 metric tons of C per hectare per year (1.5 metric tons soil CO2 emissions per hectare per year).  Lark’s soil CO2 emission estimate of 181 metric tons of CO2 per hectare per year is more than 100 times the soil CO2 emission rate than was experienced during the first 5 decades of the past century. During the first 5 decades of the past century, grain and residue yields were very low resulting in an extremely negative crop/soil carbon balance.  Modern corn production’s high grain/residue yields, along with reduced tillage intensity, result in a positive crop/soil carbon balance and thousands of well-managed corn fields are sequestering CO2 at the rate of .5 metric tons of CO2 per hectare per year.

3. Lark et al. claims that nitrous oxide emissions due to higher Nitrogen fertilizer use during corn production, and Land Use Change, results in a 9-gram CO2e per megajoule increase in corn production GHG emissions. A 9 gram per megajoule increase in corn production nitrous oxide emissions implies a 68% increase in nitrous oxide emissions on all corn production used for ethanol. This would also imply that nitrogen use rates on corn must have increased by 68%.

Facts: USDA fertilizer use data indicate that total Nitrogen (N) fertilizer use per bushel of corn production was .88 lbs N per bushel in 2010, .82 lbs N per bushel 2016, and .85 lbs per bushel in 2018.  These data do not indicate dramatically higher nitrogen use or nitrous oxide emissions from N fertilizer use on corn.

Alverson poses the question: Why does Lark et al. use modeling to estimate biofuel GHG emissions? It is understandable to use modeling to estimate future impacts, but why use modeling when a track record of historical facts are available?  “I think we know why,” Alverson says.  “Modeling outcomes can be manipulated and biased by small changes in modeling factors.”