CALIFORNIA has led the charge in enforcing stricter air emissions requirements.
For ethanol, an initial analysis from Purdue University made ethanol seem less attractive at reducing greenhouse gas (GHG) emissions compared to other alternatives. Now, a revision to the Purdue economic analysis is showing that ethanol could be a somewhat better option than previously thought.
Wally Tyner, a Purdue agricultural economist and the report's lead author, said revisions to the Global Trade Analysis Project (GTAP) model better reflect market conditions and land productivity than a 2009 report showing that corn-based ethanol wouldn't significantly lower GHG emissions over gasoline.
"The difference between this report and previous reports is advances in science," Tyner said. "With any issue, your first cut may not be the best, but when you get new data and new methods, you improve."
The report considers land use changes when calculating total GHG emissions from biofuels based on the U.S. program to increase corn ethanol production to 15 billion gal. by 2015. Those changes include emissions created by converting forests or pastures to cropland. The new analysis predicts emissions related to land use change to be 35% lower than previous analyses.
Purdue economists ran three new simulations through the GTAP model. The first used 2001 economic data as a base, the second updated the data through 2006 and the third used the updated 2006 data and assumed growth in population and crop yield through 2015.
The 2009 report showed total -- including with land use changes -- carbon dioxide emissions per megajoule (MJ) for ethanol to be 86.3 g, while the three simulations in the new report predicted 84.4 g, 81.1 g and 77.5 g, respectively (Table).
The third simulation, which Tyner said is probably the most accurate, reduced the amount of carbon dioxide that would be emitted by about 10%, but he warned that there is still uncertainty with the numbers because the model contains many complex relationships, covers the entire globe and includes data and parameters from diverse resources.
Revised figures
Previous reports estimated that marginal lands converted to corn production would be two-thirds as productive as prime land. The new simulations used data from another model to predict productivity for land being brought into cultivation by country and by agro-ecological zone.
Energy sector demand and supply elasticity were also revised. Tyner said new economic data show that consumers do not change consumption habits as drastically as once thought based on changes in gasoline prices.
Factors affecting the livestock sector were re-evaluated. New simulations assumed that dried distillers grains -- an ethanol co-product fed to livestock -- would go primarily to dairy and beef cattle producers, mirroring actual usage.
Board ruling
Last year, the California Air Resources Board used GTAP model predictions of ethanol emissions when drafting its low-carbon fuel standard (LCFS), which aims to lower the state's transportation-related carbon emissions 10% by 2020.
At that time, GTAP predictions using land use changes showed that ethanol wouldn't significantly reduce GHG emissions over gasoline usage.
Tyner is a member of the California Air Resources Board's Expert Working Group, which he said will consider information from the new Purdue analysis and other new data before submitting a final report to the board in December.
In a letter to Air Resources Board chair Mary Nichols, Renewable Fuels Assn. president Bob Dinneen brought up the board's promise to review and incorporate new science as it becomes available.
?We believe that the board, given its commitments, must direct the staff to adopt the new Purdue results and use the new, improved GTAP model from this point forward until such time that even better tools are available,? Dinneen wrote.
?Because regulated parties under the LCFS will imminently be making decisions about 2011 fuel purchases and related logistics, the Purdue (land use) value should be adopted in the LCFS lookup table immediately so that regulated parties have the certainty they need to make purchasing and logistical decisions for the upcoming 2011 LCFS compliance cycle,? he concluded.
Email a friend