Fact check: False claim that replacing cornfields with solar panels exacerbates climate change

Kate S. Petersen, USA TODAY
·6 min read

The claim: Replacing cornfields with solar panels exacerbates climate change

As solar power proliferates across the U.S., some developers have sought out farmlands for their flat terrain, roadways and electric infrastructure.

However, there has been pushback in some rural areas by residents who view large solar arrays as an industrial threat to area scenery and livelihoods. In November, a post began spreading on Facebook claiming that replacing cornfields with solar panels may actually exacerbate climate change.

“Corn sequesters 36,000 lb of carbon per acre/yr. An acre of grass draws down 920 lbs of carbon. So an acre of solar panels where corn once grew will be a net loss of 35,080 lbs of carbon taken from the atmosphere,” reads the Nov. 21 post, which cites a "Michigan State study."

“Wanna cause global warming?" it continues. "Solar panels on farmland is a good place to start.”

The post was shared more than 300 times within a day. But the claim is wrong – both misquoting and misunderstanding an article on the subject.

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Corn cannot permanently remove the amount of carbon claimed in the post. Carbon dioxide is absorbed by growing corn plants but is quickly released back to the atmosphere after the corn is harvested. The claim also ignores the benefits of solar panels in mitigating climate change.

USA TODAY reached out to the social media users who shared the claim for comment.

Corn does not remove large amounts of carbon

The Facebook post appears to reference a 2007 article written by Kurt Thelen, a professor in the Michigan State University Department of Plant, Soil and Microbial Sciences.

But the post misstates Thelen's claims. While the post says 36,000 pounds of carbon are sequestered by corn, Thelen wrote an acre of corn could absorb roughly 36,000 pounds of carbon dioxide in a year.

This distinction is important because 36,000 pounds of carbon dioxide only contains about 9,800 pounds of carbon.

Either way, Thelen told USA TODAY he never said corn would permanently remove large amounts of carbon. His article spells this out.

“Of course, much of that carbon is eventually returned to the atmosphere as the corn crop residue decomposes or the grain is consumed as feed or burned as biofuel,” Thelen wrote.

There is a key distinction between carbon that is temporarily absorbed and carbon that is sequestered – meaning it is removed long-term from the atmosphere by being placed in a stable repository. For instance, an undisturbed forest can sequester carbon for a long time in the trunks of trees and in the soil.

“There's a big difference between assimilating carbon and sequestering it,” Thelen said. “(That) might be where the misunderstanding is.”

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In fact, corn production tends to result in a net addition of greenhouse gases to the atmosphere, Jordan Macknick, an environmental analyst at the National Renewable Energy Laboratory, told USA TODAY.

"Emissions come from the use of inorganic fertilizers, manure, phosphates, lime and diesel, as well as grain drying," he said in an email.

Under specific soil conditions and optimal management practices, corn can technically sequester modest amounts of carbon in the soil for a time, according to Keith Paustian, a professor of soil and crop sciences at Colorado State University. However, eventually, the soil will reach "equilibrium" and no additional carbon will be sequestered.

"Under most cases, agricultural land is a net greenhouse gas emitter at some level," he told USA TODAY, though he emphasized that low carbon agriculture was possible with the right management practices.

Solar energy helps reduce CO2 emissions

On the other hand, solar technology helps prevent carbon dioxide emissions from being released in the first place. It provides a substitute energy source for greenhouse gas-emitting fossil fuels.

Macknick said calculating the precise CO2 mitigation potential of one acre of solar panels is complicated.

Solar panels provide energy on the Hardin family farm in Danville, Indiana, on Aug. 7, 2019.
Solar panels provide energy on the Hardin family farm in Danville, Indiana, on Aug. 7, 2019.

Different regions of the U.S. have different weather patterns and rely on different proportions of natural gas, coal, nuclear and renewable energy. Each solar installation is unique, too.

However, Macknick said 70 to 110 metric tons per acre per year is a conservative estimate for the amount of CO2 emissions solar technology can prevent. That estimate is based on solar power generation averages from Seattle and San Deigo, assuming a smaller-scale installation.

Michele Boyd, program manager for the Department of Energy’s Solar Energy Technologies Office, calculated an even higher value based on a different set of estimates. She put the number at more than 300 metric tons per acre.

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"These reductions would continue year after year," she said.

Our rating: False

Based on our research, we rate FALSE the claim that replacing cornfields with solar panels exacerbates climate change. But this is based on a misunderstanding of an article on the topic. Experts say carbon storage in corn is temporary, and agricultural space like a cornfield is actually a net emitter of carbon in most cases. Solar panels, on the other hand, significantly reduce carbon dioxide emissions in the long term. Solar panels can prevent an estimated 70 to 300 metric tons of CO2 from being released per acre per year.

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This article originally appeared on USA TODAY: Fact check: Solar panels better than cornfields for carbon emissions