Ethanol Study Rebuttal – Correcting Misrepresentations with Data

A February 2022 report released in the Proceedings of the National Academy of the Sciences (PNAS) by Tyler Lark and other authors brought to life several misrepresentations on the environmental outcomes of the Renewable Fuel Standard (RFS). American Coalition for Ethanol and Dakota Ethanol Board Member, and Corn Farmer, Ron Alverson, corrected three, key misrepresentations in the study, and provides further analysis on the major points of contention in the following rebuttal utilizing industry resources and historical data. 

For more technical comments in response to Lark et al., read those released 3.21.22 by the Department of Energy's Argonne National Labratory - CLICK HERE.

  1. Lark et al. estimated that corn prices increased 30% during the study period of 2008 to 2016 due corn demand induced by the Renewable Fuels Standard (RFS).

Fact:  Corn prices decreased from 2008 to 2010, increased from 2010 to 2013, and then decreased from 2013 to 2016.  Overall, corn prices decreased about 25% from 2008 to 2016. Lark got even this simple fact wrong, which calls into question the strange assumptions and estimations he makes in the rest of his so-called study.

Over the long term, corn price has been correlated far more closely with the price of crude oil than it has with corn ethanol production. Below shows corn price, crude oil price, and corn ethanol production trends over the longer term:

Correlation of corn price to crude oil price was also noted in this research paper: 

  1. As noted earlier, Lark et al. incorrectly estimated corn prices increased 30%, and then used this faulty estimation to suggest cropland increased 2.1 million hectares (5.2 million acres). Lark et al. used economic modeling and satellite images to estimate this cropland increase. 

USDA NASS Cropland Area: 

Fact: USDA NASS cropland planted data indicate little change as illustrated in the above chart.  Furthermore, the Renewable Fuels Association (RFA) and many others have pointed out the use of satellite images to determine Land Use Change (LUC) have proven to be inaccurate.                                                                    



  1. Lark et al. estimated 30-year soil CO2 emissions of 181 megagrams per hectare from Land Use Change soil organic carbon (SOC) losses on 1.71 million hectares. This is equivalent to a 49.4 megagram SOC loss per hectare before SOC stocks reached a new equilibrium.

Fact: However, the Poeplau et al. global meta-analysis (cited by Lark) found that total SOC losses when grasslands were converted to croplands (45 studies) were 36 megagrams SOC before reaching a new equilibrium.  


Furthermore, the 45 studies cited by Poeplau et al. represented grassland conversions to cropland that occurred decades ago when crop production practices and yields (intense tillage and low yields/carbon returns to soil from crop residues and roots) were a fraction of today.

When grasslands are converted to cropland in recent years, SOC losses are minimal due to reduced tillage and higher yields/residue and root carbon additions. 


These data indicate that if indeed there has been 1.71 million hectares of recent grassland to cropland LUC, SOC losses have been a small fraction of Lark et al. estimations

  1. Lark et al. estimated that Conservation Reserve Program enrollments were reduced because of RFS induced corn demand and higher corn prices.

Fact: As RFA has pointed out, the Conservation Reserve Program statutory acreage cap has been reduced multiple times since 2009:

Chart Source:

  1. Lark et al. estimated that total N2O emissions for corn production increased 9 grams CO2e per megajoule due to increased corn area and higher nitrogen fertilizer application rates.

Facts: Currently, the U.S. Department of Energy GREET model estimates that N2O emissions during corn production is 13.2 grams/megajoule. A 9 gram/megajoule increase represents an unlikely and unbelievable 68% increase in corn production N2O emissions! However, current corn ethanol GHG life cycle N2O emissions are accounted for on a “Nitrogen use per bushel of production” basis. Therefore, N2O emissions from any RFS induced increase in corn production is fully accounted for by current life cycle assessment methodology.

Furthermore, corn Nitrogen fertilizer use efficiency (lbs. N/bu.) continued to improve during the 2008 to 2018 time period, a continuation of the long-term trend. Corn producers have reduced Nitrogen fertilizer use per bushel by 42% during the past five decades.

Nitrogen Fertilizer Prices have increased more than 800% since 1970, driving down application rates.

  1. Finally, Lark et al. estimated total RFS induced 5.5 billion gallons of additional ethanol production during 2008 to 2016, and that this will cause soil carbon and Nitrous Oxide emissions totaling 514 Teragrams of CO2e emissions over the following 30 years. The 5.5 billion gallons of annual ethanol production will produce 13.3 trillion megajoules of energy over the next 30 years. This results in a corn ethanol LUC penalty of 38.7 grams/megajoule on those 5.5 billion gallons of annual ethanol production. However, Lark et al. seems to imply that this annual 38.7 grams/megajoule LUC penalty should be applied to all 16 billion gallons of annual U.S. ethanol production.

Figure 3 in Lark et al.

Fact: However, there is no LUC CO2e emission penalty association with pre-RFS U.S. corn ethanol production (10.5 billion gallons per year).  Therefore, to determine the LUC penalty for the entire U.S. corn ethanol industry annual production, the Lark et al. estimated CO2e emissions of 514 Teragrams due to RFS-induced LUC should be divided by the total U.S. corn ethanol 30-year energy production of 38.66 trillion megajoules. This means that even if the Lark et al. LUC emission estimation is correct (doubtful), the LUC emissions penalty for U.S. corn ethanol is 13.3 grams CO2e/megajoule, rather than 38.7 grams CO2e/megajoule.

Calculation of LUC emissions penalty:

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