biofuels have often been billed as the silver bullets of climate change. In recent times, however, their benefits have come under scrutiny. One analysis suggests that clearing forests and savannah to grow biofuels releases vast amount of carbon into the atmosphere, far more than the carbon spared from the atmosphere by substituting fossil fuels with biofuels.

Plant-based fuels were originally touted as better than fossil fuels because the carbon released from their burning was said to be balanced by the carbon absorbed when the plants grew. But the recent study has claimed this equation misses out on the destruction of natural carbon sponges to grow plants for biofuels. It was published in the journal Science (Vol 319, February 29, 2008).

The researchers calculated ghg emissions as a result of the 56 billion litres of biofuel projected to be used in the us by 2016. This will require bringing 10.8 million hectares of additional land under biofuel crops. "If this land comes out of forest or grassland, there is a quick release of carbon as a result of removing vegetation and tilling the soil,' says T Searchinger, professor at Princeton University's Woodrow Wilson School, the paper's lead author.

The researchers found that in 2015 ghg emissions could indeed reduce by 20 per cent from current levels if global biofuel use projections are met