Nelson researchers use satellite data to study carbon emissions from expanding ethanol cropland

December 15, 2017

Like many of our Nelson Faculty, Holly Gibbs is concerned about the effects of human activity on the landscape and local ecosystems. But she uses a true “top-down” approach in her research, supplementing the standard place-based richness of field surveys with high-resolution satellite imagery which allows her to see an entirely different view of the Earth from above.

Gibbs is professor of Environmental Studies and Geography at the Center for Sustainability and the Global Environment and leads a highly trained team of scientists at the Gibbs Land Use and Environment (GLUE) Lab. Along with researchers Tyler Lark and Seth Spawn, Gibbs recently completed a research study of the effects of U.S. cropland expansion on the amount of carbon emitted to the atmosphere between 2008 and 2012.

Several previous studies from the Gibbs lab have suggested the amount of carbon emissions saved from biofuels production was not enough to offset the carbon released from converting natural landscapes to agricultural crop fields.

“The biofuel mandate is aiming to reduce climate change, however, our work calculating the carbon emissions from ongoing land conversions shows that it might in fact be making climate change worse,” Gibbs said.

Lark and Spawn recently presented their findings at the National Wildlife Federation’s 2017 America’s Grassland Conference in Fort Worth, Tex. Lark said this research is the first comprehensive study of carbon emissions from recent cropland expansion across the nation.

“We saw a real need and opportunity for rigorous science to fill in the knowledge gap at the national scale and say, ‘What’s happening across our country?’” Lark said.

The new research built upon a previous study that identified sites of cropland expansion, and paired it with high resolution maps of the amount of carbon stored in plants and soils across the U.S. landscape. By using annual satellite-based data, Lark said they could see not only what types of vegetation used to be present, but measure the time and scale of the coupled changes in carbon land use.

Cropland largely expanded onto grassland, which was the main contributor towards the total carbon emissions. Nearly 90 percent of the carbon emissions were due to cropland expansions onto grasslands, according to the study.While the expansion did mainly affect grasslands, Lark said other types of lands were converted as well, including shrublands, forests and wetlands, which typically offer more carbon storage per unit area. Spawn said natural landscapes hold more carbon than croplands can, so replacing the natural landscape for biofuel crops acts counter to the ultimate goal of reducing carbon emissions.

“Any time land is cleared, much of the carbon that was stored on that land is emitted to the atmosphere,” Spawn said. “If we’re clearing land to grow more biofuel feedstocks, we’re undermining the carbon neutrality that we’re trying to achieve through the use of biofuels.”

Wisconsin was one of six states responsible for the highest rates of expansion onto carbon rich landscapes. Collectively, those six states made up more than 35 percent of total annual emissions resulting from cropland expansion.

Field crops like corn, soy and wheat accounted for a majority of the new cropland, which are all potential feedstocks for biofuel production, Spawn said. But in an agriculturally profitable state like Wisconsin, he was quick to note the distinction between using existing agricultural land versus converting new land for added production.

“It’s important to remember that this research is about cropland expansion and not cropland in general,” Spawn said. Spawn added the goal was to point out agricultural trends and outcomes that were not consistent with combatting climate change, and Gibbs agreed.

Ultimately, Gibbs believes these findings should be used to inform state and national policy decisions regarding carbon emissions and biofuel regulations. As a regularly consulted expert for biofuel policy, Gibbs noted there is frequent debate between stakeholders from environmental groups, agricultural interests and government bodies. When offering her opinion, Gibbs said she is careful not to take any one side. Her goal is to provide the information necessary to help these groups make proper policy decisions.

“We aim to provide the rigorous science to help inform all sides to help reduce that debate and move the policy forward,” Gibbs said.

This research is just one part of a larger investigative project titled “Quantifying the impact of the Renewable Fuel Standard on America’s Water and Land Resources.” Gibbs and Lark co-lead this half million-dollar research initiative, with the goal of bringing together experts from across multiple disciplines to solve problems that America’s natural resources face today.