Bio-ethanol could be significant contributor to global warming

Corn-based ethanol, which has historically been used a mixer with gasoline sold at US gas stations, could be a much bigger contributor to global warming than straight gasoline, according to a new study.

Under the US Renewable Fuel Standard (RFS), a law enacted in 2005, the nation’s oil refiners are required to mix some 15 billion gallons of corn-based ethanol into the nation’s gasoline annually.

The study, published in the Proceedings of the National Academy of Sciences, follows in the wake of previous research commissioned by the US Department of Agriculture (USDA) showing ethanol and other biofuels to be relatively green.

The study comes as President Joe Biden’s administration is reviewing policies on biofuels as part of a broader effort to decarbonize the US economy by 2050 in a bid to counter climate change.

“Corn ethanol is not a climate-friendly fuel,” said Dr Tyler Lark, assistant scientist at University of Wisconsin-Madison Center for Sustainability and the Global Environment and lead author of the study.

The research, which was funded in part by the National Wildlife Federation and US Department of Energy, found that ethanol is likely at least 24% more carbon-intensive than gasoline due to emissions resulting from land use changes to grow corn, along with processing and combustion.

Geoff Cooper, president and CEO of the Renewable Fuels Association, the ethanol trade lobby, called the study “completely fictional and erroneous,” arguing the authors used “worst-case assumptions [and] cherry-picked data.”

The RFS fuel policy was intended to reduce emissions, support farmers, and cut US dependence on energy imports.

As a result of the mandate, corn cultivation grew 8.7% and expanded into 6.9 million additional acres of land between 2008 and 2016, the study found.

However, it has also suggested that the law led to widespread changes in land use, including the tilling of cropland that would otherwise have been retired or enrolled in conservation programs and the planting of existing cropland with more corn, the study found.

Tilling fields releases carbon stored in soil, while other farming activities, like applying nitrogen fertilizers, also produce emissions.

A 2019 study from the USDA, which has been broadly cited by the biofuel industry, found that ethanol’s carbon intensity was 39% lower than gasoline, in part because of carbon sequestration associated with planting new cropland.

However, that research underestimated the emissions impact of land conversion, Lark said.

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