Corn Ethanol or Conservation? What Do You Think?

U.S. corn ethanol production has been on the rise. That’s good for our country’s carbon footprint, right? A new study suggests not.

The federal government has had a love affair with corn ethanol. In the Energy Independence and Security Act of 2007, Congress increased the mandate for renewable biofuels production in the United States by a factor of almost 7 — from 5.4 billion gallons in 2008 to 36 billion gallons by 2022 — the vast majority of which would have to come at least in the near term from corn ethanol. Even President Obama has gotten into the act, proposing that the amount of ethanol in gasoline be increased from 10 percent to 12 or 13 percent.

Good for the climate, right? After all, the carbon in a biofuel comes from plant materials, which got their carbon by taking carbon dioxide (CO2) from the atmosphere during photosynthesis. So burning fuel just sends that same carbon back into the atmosphere — no net change in carbon dioxide and no climate impact. Right? Wrong.

No Climate Benefit from Corn Ethanol at Present

In principle that’s the way it works, but in practice it’s more complicated.

Growing crops requires energy in the form of fossil fuels and requires fertilizers, which also emit greenhouse gases. Those factors reduce the energy and greenhouse benefits of using corn as a feedstock for ethanol.

However, recent studies suggest that corn ethanol production, using modern, energy-efficient practices, has a net energy benefit and an apparent climate benefit — it's apparent because if you take into account the probable land-use changes that adding new, domestic corn ethanol capacity will require, the climate benefits evaporate.

Problems arise because increasing the country’s production of corn ethanol requires farmers to place more land into corn cultivation. Ultimately, that means that land not in cultivation somewhere must be cultivated to make up the difference. And when you put otherwise fallow land into production, a significant fraction of the carbon stored in its soil is sent into the atmosphere as CO2, one of the most abundant greenhouse gases.

A couple of papers published in Science last year (see here and here) showed that often the new cultivated acreage comes from converting tropical rain forests in Brazil into soybean farms. The result: significant net emissions of greenhouse gas emissions.

Converting Land Set Aside for Conservation Into Ethanol-Producing Lands Is Not a Good Idea

But there is another, less exotic source of new land for cultivation, one closer to home and even more under our control. It comes from land set aside in the federal government's Conservation Reserve Program (CRP) — a voluntary program that effectively pays farmers to take land out of production. In the CRP, land owners sign a lease for a 10-15 year period to allow specific ranch or farmland to go fallow with grasses and trees. Environmental benefits of the CRP include: improved soil and water quality, more wildlife habitat, and increases in the amount of soil carbon. This last benefit is important, because the more carbon stored in the soil, the less CO2 in the atmosphere.

However, as demand for corn increases, farmers are under increasing pressure to take their land out of the CRP when their leases expire and cultivate them again.

Right now about 33 million acres of land [pdf] are enrolled in the CRP. But that acreage has started to drop off in recent years, and, believe it or not, Congress reduced the cap on CRP lands from 39.2 million acres to 32 million acres in the Farm Bill of 2008.

New Study: Conservation to Corn Is Like Fueling the CO2 Fire

What happens when CRP lands are converted to corn cultivation to produce corn ethanol? My colleague at Duke, Rob Jackson, and his co-authors report in the latest issue of Ecological Applications that at least in terms of greenhouse gases the results are not pretty. Because of the loss of soil carbon, producing corn ethanol on former CRP lands releases almost 40 tons of CO2 per hectare in the first decade. This means that switching just 10 percent of CRP land to corn cultivation would add nearly 50 million more tons of CO2 to the atmosphere in 10 years. That’s about the same amount of emissions as putting an additional 850,000 cars on the roads over the same time period.

Over time, the benefits of displacing gasoline with corn ethanol do begin to pay off. After about 30 years, converting CRP lands to corn ethanol production would break even in terms of greenhouse gas emissions. And after some 50-70 years, the conversion would begin to outdo just leaving the CRP land in place.

A Winner in the Making: Cellulosic Ethanol

The good news is that Jackson and colleagues do find a potential greenhouse-gas winner in the biofuels sweepstakes: cellulosic ethanol. Cellulosic ethanol can be produced from grasses grown with little or no cultivation — thus allowing carbon to build up in the soil at the same time the grasses are harvested for ethanol. (The big assumption here is that since cellulosic ethanol can be grown on degraded rather than prime agricultural lands, it won’t drive the same land-use changes that ultimately make corn-ethanol production a net greenhouse gas loser.)

So here’s the thing. Cellulosic ethanol is on a track to become commercially available in a matter of years. Once it does, it will make corn ethanol yesterday’s news. So why set up policies to force extra production of corn ethanol now and encourage the loss of CRP lands for a questionable, short-term benefit in terms of biofuel availability and a definite step backward in terms of climate mitigation?

Of course, with the collapse of gasoline demand and prices, the federal policy on corn ethanol makes even less sense than it did before. In fact some U.S. corn ethanol plants are going out of business (see here and here).

So, rather than encouraging corn ethanol production to address our energy and climate problems, here’s an idea: push conservation — conservation of carbon sequestering lands by beefing up the CRP acres and conservation of gasoline by enhancing mass transit as well as fuel-economy standards.