Speaking at a corn-ethanol industry conference last month, EPA administrator Gina McCarthyGina McCarthyTrump plans to roll back environmental rule everyone agrees on EPA chief to visit Colorado mine spill site In the fight between Rick Perry and climate scientists, Perry is winning MORE characterized the Renewable Fuel Standard (RFS) as “a crucial part of a broad, Administration-wide strategy to act on climate change and propel us even faster toward a clean energy future.”

Signed into law a decade ago by President George W. Bush, and greatly expanded by Congress in 2007, the RFS was sold to the American public as a winning solution -- a win for energy security; a win for rural development; a win for our environment. It was a way to cut our dependence on foreign oil, slash air emissions, and, while we’re at it, provide a significant economic boost to the country’s struggling farm belt.

But 10 years removed from that landscape, we now know that this policy has fallen short of its goals, not to mention corn ethanol’s impact on commodity prices and the environment.

A decade’s worth of data and experience has taught us a lot about corn-ethanol’s performance in the real world, and the picture that data paints is not very attractive. Soil erosion, a significant increase in the use of agricultural chemicals and fertilizer, the diversion of more than 40 percent of the nation’s corn crop to ethanol – these are just some of the many consequences of having an RFS policy that acts as an engine of forced corn-ethanol production.

On top of the agricultural impacts, corn ethanol’s record on air emissions is called into question. Indeed this might represent perhaps its greatest failure to date. Not only hasn’t ethanol improved our air quality, across so many categories – carbon dioxide, ozone, particulate matter, volatile organics – it actually may have made it worse.

In our study, we look at what agricultural emissions levels would have been today had corn ethanol not qualified as an eligible fuel source under the RFS (absent political intervention, it would not qualify if the decision were being made today, according to EPA’s own data). We wanted to know what would have happened to emissions had that mandated market share gone to advanced biofuels instead of corn. And we also wanted to know what those emissions figures would look like if the RFS had never been implemented at all.

So what did we find? For starters, we saw significant drops in carbon emissions under both scenarios, with a 10 percent decrease under the “no RFS” scenario, and a nearly 17 percent reduction that could have been realized if the RFS were structured in a way that favored advanced biofuels over corn. We also found that soil erosion would have been reduced by 47 million tons if the RFS hadn’t passed, and by 112 million tons under the cellulosic replacement scenario.

As it stands, the RFS focuses almost exclusively on a single crop from a concentrated region of the country. But as innovations continue to be made in the advanced biofuels industry, we believe a very real opportunity now exists to reform the RFS as a means of providing the intended environmental benefits we were promised, while spurring greater, more widespread economic growth.

President Obama has made climate change and environmental policy a centerpiece of his presidency -- but the RFS, as currently constituted, works against those goals. Before the president travels to France for the United Nations climate conference this year, his administration should seize on the opportunity available to it to modernize a broken RFS policy and put the nation and our environment on a more sustainable path forward.

Leading environmental advocates who once supported corn ethanol -- including Al GoreAl GoreOPINION | Bolton: China is our last diplomatic hope for North Korea How the New South became a swing region Bill Maher compares Republican Party to trolls MORE -- have acknowledged its shortcomings. Having government pick winners and losers in the renewable fuel space, with favoritism weighted toward corn ethanol, “is not a good policy” and “was a mistake,” said the former vice president.

Our research – which adds to a growing body of other studies, reports, and fact-based data points – certainly reflects that realization. After 10 years under the RFS, we have yet to see commercially viable next-generation biofuels emerge. Now is the time to reform the RFS and position the country to realize meaningful environmental benefits associated with advanced biofuel growth.

English and De La Torre Ugarte are professors at the University of Tennessee’s Institute of Agriculture.