Editor's note: Nathanael Greene is director of renewable energy policy for the Natural Resources Defense Council, a nonprofit environmental organization.

(CNN) -- Wednesday is the six-month anniversary of the BP blowout that continues to devastate Gulf communities and remind us of our need to find new clean energy sources for our cars, homes and businesses.

One of those clean energy sources can be biofuels -- energy grown right here on our land rather than drilled for deep underneath the Earth's surface. But despite the huge opportunities in this area, big industry and shortsighted planning are once again derailing us from a truly clean green path.

Here's the simple reality -- not all biofuels are created equal. Some reduce pollution, but some, like corn-based ethanol in particular, do more harm than good. When all direct and indirect impacts are factored in, corn ethanol production causes more global warming pollution than the oil it is meant to replace, contaminates our waterways and raises the price of food and feed in our stores.

Meanwhile, emerging, better-performing biofuels made from perennial grasses such as switchgrass and winter-cover crops get the short end of the stick.

Thanks to a step backward last week by the Environmental Protection Agency and ongoing subsides to the oil industry for using more and more corn ethanol, we've moved further down a path toward old, dirty biofuels at the expense of newer, cleaner, advanced biofuels. And -- as always -- we the taxpayers are paying for the privilege.

Here's the situation: The EPA said it will raise the limit on how much corn ethanol can be blended into our gasoline from 10 percent to 15 percent for vehicles made since 2007. A broad coalition -- from public health advocates to livestock ranchers to automakers -- oppose this move because it actually poses serious risks to engines, wildlife, water and the air we all breathe.

Burning ethanol can cause toxic air pollution from vehicle tailpipes, especially at levels as high as this new blend -- called E15 -- and especially when used in older cars. Because ethanol burns hotter than gasoline, it causes catalytic converters to break down faster.

Cars with broken tailpipe controls are disproportionately responsible for air pollution from vehicles, posing serious risks to public health and the health of our environment. While newer cars are equipped to prevent this breakdown, cars made before 2007 are not. Unless you're one of the few people who follow these things closely, you run the risk of damaging your engine by accidentally using the wrong fuel.

Despite EPA's claims of plans to educate consumers about these risks, the "pump first, ask questions later" attitude means the agency's planned safeguards are unlikely to work in the real world. It's no wonder the corn ethanol lobby is seeking a liability waiver for oil companies and fuel retailers to protect against consumer lawsuits when those engines go kaput. It also seems unlikely that any consumer whose engine dies because of this will return to biofuels any time soon.

In short -- the EPA and the corn ethanol industry are guaranteeing a short-term win for this faulty product while putting the future of advanced biofuels at risk.

On top of that, it should be noted that over the last four years, the biggest government incentive program for biofuels has handed over more than $20 billion in taxpayer subsidies to oil companies in exchange for blending more and more corn ethanol into our gasoline supply, something they are already required to do by law.

That's right; our taxpayer dollars are fueling corporate giants and their dirty fuels instead of supporting the transition away from old, polluting corn ethanol toward the newer, cleaner, advanced biofuels we need. And in spite of its polluting record, the corn ethanol lobby continues to push for more -- an extension of these subsidies at a cost to U.S. taxpayers of nearly $6 billion next year alone.

Despite these major missteps, it's not too late for the government to get us back on track. Advanced biofuels still hold huge potential for moving us away from polluting gas tanks. But we need to end subsidies for oil and corn ethanol that do nothing but lock dirty fuels into our marketplace.

Instead, we should get more for our taxpayer dollars by focusing on the commercialization of really clean biofuels, which can provide more homegrown fuel, more homegrown jobs, more energy security and cleaner air.

Big Oil and Old Ethanol have us driving in circles, while moving to advanced biofuels will move us forward. It's time to invest in new technologies that can jumpstart a truly clean fuel industry in America.

The opinions expressed in this commentary are solely those of Nathanael Greene.