The willingness to try, fail and try again is the essence of scientific progress. The same sometimes holds true for public policy. It is in this spirit that we call upon Congress to revisit recently enacted federal mandates requiring the diversion of foodstuffs for production of biofuels. These "food-to-fuel" mandates were meant to move America toward energy independence and mitigate global climate change. But the evidence irrefutably demonstrates that this policy is not delivering on either goal. In fact, it is causing environmental harm and contributing to a growing global food crisis.

Food-to-fuel mandates were created for the right reasons. The hope of using American-grown crops to fuel our cars seemed like a win-win-win scenario: Our farmers would enjoy the benefit of crop-price stability. Our national security would be enhanced by having a new domestic energy source. Our environment would be protected by a cleaner fuel. But the likelihood of these outcomes was never seriously tested, and new evidence has shown that the justifications for these mandates were inaccurate.

It is now abundantly clear that food-to-fuel mandates are leading to increased environmental damage. First, producing ethanol requires huge amounts of energy — most of which comes from coal. Second, the production process creates a number of hazardous byproducts, and some production facilities are reportedly dumping these in local water sources.

Third, food-to-fuel mandates are helping drive up the price of agricultural staples, leading to significant changes in land use with major environmental harm. Here in the United States, farmers are pulling land out of the federal conservation program, threatening fragile habitats. Increased agricultural production also means increased fertilizer use. The National Academy of Sciences reported last month that meeting the congressional food-to-fuel mandate by 2022 would lead to a 10 to 19 percent increase in the size of the Gulf of Mexico's "dead zone" — an area so polluted by fertilizer runoff that no aquatic life can survive there.

Most troubling, though, is that the higher food prices caused in large part by food-to-fuel mandates create incentives for global deforestation, including in the Amazon basin. As Time magazine reported this month, huge swaths of forest are being cleared for agricultural development. The result is devastating: We lose an ecological treasure and critical habitat for endangered species, as well as the world's largest "carbon sink." And when the forests are cleared and the land plowed for farming, the carbon that had been sequestered in the plants and soil is released. Princeton scholar Tim Searchinger has modeled this impact and reports in Science magazine that the net impact of the food-to-fuel push will be an increase in global carbon emissions — and thus a catalyst for climate change.

Meanwhile, the mandates are not reducing our dependence on foreign oil. Last year, the United States burned about a quarter of its national corn supply as fuel — and this led to only a 1 percent reduction in the country's oil consumption.

Turning one-fourth of our corn into fuel is affecting global food prices. U.S. food prices are rising at twice the rate of inflation, hitting the pocketbooks of lower-income Americans and people living on fixed incomes. Globally, the United Nations and other relief organizations are facing gaping shortfalls as the cost of food outpaces their ability to provide aid for the 800 million people who lack food security. Deadly food riots have broken out in dozens of nations in the past few months, most recently in Haiti and Egypt. World Bank President Robert Zoellick warns of a global food emergency. The immediate necessary step is a major increase in global food aid. But beyond that, America must stop contributing to food price inflation through mandates that force us to use food to feed our cars instead of to feed people.

Taking these together — the environmental damage, the human pain of food price inflation, the failure to reduce our dependence on oil — it is impossible to avoid the conclusion that food-to-fuel mandates have failed. Congress took a big chance on biofuels that, unfortunately, has not worked out. Now, in the spirit of progress, let us learn the appropriate lessons from this setback, and let us act quickly to mitigate the damage and set upon a new course that holds greater promise for meeting the challenges ahead.

Lester Brown is founder and president of the Earth Policy Institute. Jonathan Lewis is a climate specialist and lawyer with the Clean Air Task Force. They wrote this commentary for The Washington Post.