Washington, Sept.22 : A renewable energy source designed to reduce greenhouse gas emissions is contributing more to global warming than fossil fuels, a study has suggested.

Measurements of emissions from the burning of biofuels derived from rapeseed and maize have been found to produce more greenhouse gas emissions than they save. Other biofuels, especially those likely to see greater use over the next decade, performed better than fossil fuels but the study raises serious questions about some of the most commonly produced varieties.

Rapeseed and maize biodiesels were calculated to produce up to 70 per cent and 50 per cent more greenhouse gases respectively than fossil fuels. The concerns were raised over the levels of emissions of nitrous oxide, which is 296 times more powerful as a greenhouse gas than carbon dioxide.

Scientists found that the use of biofuels released twice as much as nitrous oxide as previously realised. The research team found that three to five per cent of the nitrogen in fertiliser was converted and emitted. In contrast, the figure used by the International Panel on Climate Change, which assesses the extent and impact of man-made global warming, was two per cent.

The findings illustrate the importance of ensuring that measures designed to reduce greenhouse-gas emissions are assessed thoroughly before being hailed as a solution.

The research is published in the journal Atmospheric Chemistry and Physics, where it has been placed for open review. The research team was formed of scientists from Britain, the US and Germany, and included Professor Paul Crutzen, who won a Nobel Prize for his work on ozone. (With inputs from ANI)