UNIVERSITY PARK, Pa. — Plant-based biofuels can play a key role in reducing greenhouse gas emissions and removing excess carbon dioxide from the atmosphere, and growing these crops in certain landscapes offers net climate benefits compared to other land use options, according to a team of international scientists.
“For the last decade, there have been a lot of questions about whether there’s an important role for bioenergy in a sustainable energy future,” said Tom Richard, professor of agricultural and biological engineering and director of the Penn State Institutes of Energy and the Environment. “We’ve documented that if it’s done right, there is a clear role for bioenergy, and we’ve pointed toward the places and approaches necessary for those systems to have a positive benefit.”
Biofuels are a common source of renewable energy in the United States, but some scientists have questioned the environmental benefits of growing these crops compared to other land use alternatives like planting forests.
“Many ecologists are concerned that biofuels could displace forests or cause other indirect changes to areas that support food production, while not providing enough climate benefits,” said Erica Smithwick, the E. Willard and Ruby S. Miller Professor in Geography at Penn State. “This study allowed us to take a full account of the impacts of biofuels from soil to tailpipe emissions and do a full accounting of the carbon flows to see how fair that criticism really is.”
In the comprehensive study, a team of interdisciplinary researchers, including plant scientists, ecologists and engineers, used models to simulate switchgrass cultivation, biofuel production and carbon capture and storage, tracking the carbon and ecosystem impacts. They compared the results with other ways to store carbon on land, like growing forests or grasslands.
They found that growing switchgrass, a leading candidate for next generation biofuels, on lands transitioning away from crops or pasture has climate benefits comparable with reforestation and greater than grassland restoration. While the analysis does not support replacing mature forests with biofuels, technological advances like carbon capture and storage could result in biofuels producing several times the benefit of other land use options, the scientists said.
The findings, reported in the journal Proceedings of the National Academy of Sciences, offer a roadmap for how and where to pursue biofuels, and reassert the prominent role the technology can play in combating climate change, the scientists said.
“I’ve become quite convinced through the work on this project that there is an opportunity to integrate biofuels into some land use decisions so that we can create more sustainable solutions to the climate challenge,” Smithwick said. “We are in a climate crisis. And biofuels provide sustainable energy sources that don’t release excess carbon dioxide into the atmosphere while providing us with the energy that we need.”
Biofuels have traditionally come from food products like corn, which produces ethanol as it ferments. That can be added to fossil fuels used to power cars, airplanes and boats, curbing some carbon dioxide emissions. Next generation biofuels, or cellulosic biofuels, will be made from non-edible, fibrous parts of plants like switchgrass. As part of the study, the researchers created models to simulate how a cellulosic biofuel refinery would handle carbon capture and storage.
“What we found is that around half of the carbon in the switchgrass that comes into the refinery becomes a byproduct that would be available for carbon capture and storage,” said John Field, research scientist at Colorado State University and lead author on the study. “The resulting byproduct streams of high-purity carbon dioxide would not require much separation or clean-up before being stored underground.”
These cellulosic biofuels are considered carbon negative because they remove and store more carbon dioxide than they emit into the atmosphere when used as a fuel source.
“We need negative carbon systems,” Richard said. “Ideally, they’re going to be profitable systems that can be the foundation for a carbon negative, climate positive economy. And if we build that economy based on photosynthesis, like we’ve demonstrated in this case, then we have a path toward growing our economy at the same time we address climate change.”
Scientists said because of the current delays in tackling climate change, it’s imperative to take a more proactive stance on biofuels and other negative emissions technologies if countries like the U.S. want to limit the impacts of global warming to 1.5 degrees Celsius above pre-industrial levels.
The U.S. Department of Agriculture’s National Institute of Food and Agriculture, the Department of Energy’s Center for Bioenergy Innovation and the São Paulo Research Foundation in Brazil provided funding for this research.
Other researchers on the project were Lee Lynd and Mark Laser, Dartmouth College, Hao Cai, Michael Wang and Zhangcai Qin, Argonne National Laboratory, David LaBauer, University of Arizona, Stephen Long, University of Illinois at Urbana-Champaign, Keith Paustian and John Sheehan, Colorado State, and Pete Smith, University of Aberdeen.