President Obama's commitment to take on climate change and put science over politics is about to be tested as his administration faces a politically sensitive question about the widespread use of ethanol -- Does it help or hurt in the fight against global warming?
The Environmental Protection Agency is close to proposing ethanol standards. But two years ago, when Congress ordered a huge increase in ethanol use, lawmakers also told the agency to verify that ethanol would produce less pollution linked to global warming than would gasoline.
So how will the EPA define greenhouse gas emissions from ethanol production and use? Given the political clout of farm interests, will the science conflict with the politics?
Environmentalists, citing studies and scientific papers, say the agency must factor in more than just the direct, heat-trapping pollution from ethanol and its production. They also point to "indirect" impacts on global warming from worldwide changes in land use, including climate-threatening deforestation, as land is cleared to plant corn or other ethanol crops.
Ethanol manufacturers and agriculture interests contend the fallout from potential land-use changes in the future, especially those outside the United States, have not been adequately proven or even quantified, and should not count when the EPA calculates ethanol's climate impact.
"It defies common sense that EPA would publish a proposed rule-making with harmful conclusions for biofuels based on incomplete science and inaccurate assumptions," complained Sen. Charles E. Grassley, Iowa Republican.
He was one of 12 farm-state senators, both Democrats and Republicans, who wrote to EPA Administrator Lisa P. Jackson in March, urging the agency to stick to assessing only the direct emissions.
Ethanol, which in the future may come from cellulosic sources such as switchgrass and wood chips, is promoted by its advocates as a "green" substitute for gasoline that will help the United States reduce its reliance on fossil fuels, especially foreign oil. That transition is a priority of the Obama White House.
In 2007, Congress ordered huge increases in ethanol use, requiring refiners to blend 20 billion gallons with gasoline by 2015 and a further expansion to 36 billion gallons per year by 2022.
Congress said any fuel produced in plants built after 2007 must emit 20 percent less in greenhouse gases than gasoline if it comes from corn, and 60 percent less if from cellulosic crops.
Meeting the direct emissions would not be a problem. But if indirect emissions from expected land use changes are included, ethanol probably would fail the test.
Nathaniel Greene, director of renewable energy policy at the Natural Resources Defense Council, an environmental advocacy group, said that wouldn't mean the end of ethanol.
Ethanol from existing production facilities will be grandfathered, Mr. Greene said, and "there are ways to produce advanced ethanols that would comply with the greenhouse thresholds" even using land-use climate impacts if the industry chose to adopt them.
But farm interests and their allies in Congress are pushing to get the EPA to at least postpone any consideration of the land-use impacts issue, arguing the science surrounding the issue is uncertain.
The senators' letter said that overreaching regulation by the EPA on ethanol's link to climate change "could seriously harm our U.S. biofuels growth strategy by introducing uncertainty and discouraging future investments."
Environmentalists say there have been enough studies on the indirect impacts of ethanol on greenhouse pollution to justify the science.
EPA spokeswoman Andora Andy declined to say when an agency proposal - a holdover issue from the previous administration - would be issued. Interest groups on both sides of the debate said it could come in days. The White House Office of Management and Budget concluded its review of the EPA proposal last week.