Ironically, converting new land to produce alternative fuels from crops and grasses can cause emissions of carbon dioxide 420 times more than the annual savings from replacing fossil fuels, according to Minnesota-based scientists. Policymakers in the European Union and the US have identified biofuels as a tool to fight global warming, as they emit less greenhouse gases than burning fossil fuels. The US recently enacted legislation boosting biofuel production to 36 billion gallons in 2022 from 7.5 billion gallons in 2012. EU requires 10 per cent of the transportation to use biofuels by 2020. Converting forests and peatlands that absorb carbon dioxide from the atmosphere to grow the crops may cause emissions that may far outweigh the annual benefits of burning the new fuels, creating a "carbon debt' lasting centuries, the researchers at the University of Minnesota, St Paul and the Minneapolis-based Nature Conservancy said in the journal Science. "If you're trying to mitigate global warming, it simply does not make sense to convert land for biofuels production,'' lead author Joe Fargione said in a statement. "All the biofuels we use now cause habitat destruction, either directly or indirectly.'' The scientists studied different cases of natural habitat conversion, and used data from previous studies to determine the carbon debt accrued. They found that converting Indonesian or Malaysian peatlands into palm plantations incurred a carbon debt that took 423 years to neutralise. Replacing tropical rainforests in those two nations with the same crop led to an 86-year debt. US crops US biofuels can also lead to a debt lasting decades, the scientists found. When corn for ethanol is planted on grassland, it takes 93 years for the benefits to set in, while placing the same crops on abandoned agricultural land led to a 48-year lag. In Brazil, the benefits from converting savanna grassland to cultivate soybeans took 37 years to set in, while replacing wooded savanna with sugarcane led to a 17-year lag. When rainforest is felled to grow soybean, a 319-year debt is incurred, they said. Not all biofuels led to significant carbon debts. Allowing prairie grasses to grow on abandoned or fertile cropland led to a debt lasting as long as a year, according to the study. "In finding solutions to climate change, we must ensure that the cure is not worse than the disease,'' Jimmie Powell, leader of The Nature Conservancy's energy team, said in the statement. "These findings should be incorporated into carbon emissions policy going forward.''