Tech Tuesday

Getting a Better Handle on Ethanol

New data from Purdue updates greenhouse gas estimates - in the biofuel's favor.

Regardless what you think of the global warming controversy, worries over greenhouse gases will drive policy in the near future - especially for ethanol. Part of that debate is how much better ethanol is versus gasoline on the greenhouse gas front, and new information from Purdue University offers some good news.

Findings on the issue were released in a report to the U.S. Department of Energy's Argonne National Laboraty, and show that ethanol could be a somewhat better option than previously thought for reducing greenhouse gas emissions, according to a press statement. Wally Tyner, a Purdue ag economist and lead author on the report, shows that revisions to the Global Trade Analysis Project model offer good news for ethanol.

The GTAP model, with the new revisions, offered better data than a 2009 report that showed corn ethanol wouldn't significantly lower greenhouse gas emissions over gasoline. Tyner notes that the idea of measuring land-use changes is a new idea. "The difference between this report and previous reports is advances in science," he says.

The report considers land use changes when calculating total greenhouse gas emissions from biofuels based on the U.S. program to boost ethanol output to 15 billion gallons by 2015. Those changes include emissions created by converting forest or pasture land to crop land, but the new analyst predicts emissions changes related to potential land use changes at 35% lower than previous analyses.

The Purdue economists ran three simulations through that GTAP model. The first included 2001 economic data as a base; the second updated information through 2006; and the third used updated 2006 information and assumed growth in population and crop yield through 2015.

that 2009 report showed that total carbon dioxide emissions, including land use changes, per megajoule for ethanol would be 86.3 grams. But the three simulations Tyner and his colleagues ran for the three scenarios predicted 84.4 grams for the 2001 data; 81.1 grams for the 2006 information; and 77.5 grams for the predictive yield growth data.

Tyner says the most accurate simulation is the third one, which includes that predictive crop yield information. That one says carbon dioxide emissions are cut by 10%, however he warns that the model is complex, covers the entire globe and includes data and parameters from a variety of sources. This could change outcomes in the future.

There were changes to the GTAP model that make a difference too. For example, the marginal land conversion data was changed. Originally, it was estimated that converting marginal land to corn production would result in about two-thirds the production you would get on prime land. New simulations used data from another model to predict productivity for land brought into cultivation by country and by ag ecological zone.

That change had an impact on decreasing the number of hectares (1 hectare is about 2.2 acres) of land needed to produce 1000 gallons of ethanol. For example, in Brazil the production of land brought into production bested that two-third level. In fact it was closer to a 1-to-1 ratio, or about as good as land already in production.

About 60 million acres of U.S. land that had been moved from cropland to pasture and some forest were re-evaluated as well. That land, if brought back into crop production, would be more productive than original estimates as well, Tyner says.

Other changes in the model helped as well, including refined use for distillers dried grains with solubles and overall energy demand figures. The California Air Resources Board used GTAP last year for ethanol emissions when drafting its low-carbon fuel standard. In that original, ethanol didn't look too good, but Tyner sits on the CARB Expert Working Group and notes this newest data will be considered before the group submits its final report in December.

The Argonne National Laboratory was a major funder of the new study. Tyner adds that future simulations will include cellulosic biofuels.

The table below shows a summary of the original GTAP estimates using 2009 data and the three simulations based on information from Tyner and his colleagues.

Hide comments


  • Allowed HTML tags: <em> <strong> <blockquote> <br> <p>

Plain text

  • No HTML tags allowed.
  • Web page addresses and e-mail addresses turn into links automatically.
  • Lines and paragraphs break automatically.