A renewable energy source designed to reduce greenhouse-gas emissions may be contributing more to global warming than fossil fuels, a study suggests.
Measurements of emissions from the burning of biofuels derived from rapeseed and corn 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.
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Rapeseed and corn biodiesels were calculated to produce up to 70 percent and 50 percent 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 a greenhouse gas than carbon dioxide.
Scientists found that the use of biofuels released twice as much as nitrous oxide as previously realized. The research team found that 3 to 5 percent of the nitrogen in fertilizer 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 2 percent.
The findings illustrated the importance, the researchers said, of ensuring that measures designed to reduce greenhouse-gas emissions are assessed thoroughly before being hailed as a solution.
"One wants rational decisions rather than simply jumping on the bandwagon because superficially something appears to reduce emissions," said Keith Smith, a professor at the University of Edinburgh in Scotland and one of the researchers.
Corn for ethanol is the prime crop for biofuel in the U.S., where production for the industry has recently overtaken the use of the plant as a food. In Europe the main crop is rapeseed (one variety of which is canola), which accounts for 80 percent of biofuel production.
"The significance of it is that the supposed benefits of biofuels are even more disputable than had been thought hitherto," Smith told Chemistry World magazine.
It was accepted by the scientists that other factors, such as the use of fossil fuels to produce fertilizer, have yet to be fully analyzed for their impact on overall figures.
But they concluded that the biofuels "can contribute as much or more to global warming by N2O [nitrous oxide] emissions than cooling by fossil-fuel savings."
The research is published in the journal Atmospheric Chemistry and Physics, where it has been placed for open review.
The research team consisted of scientists from Britain, the U.S. and Germany, and included Professor Paul Crutzen, who won a Nobel Prize for his work on ozone.
Dr. Franz Conen, of the University of Basel in Switzerland, described the study as an "astounding insight."
"It is to be hoped that those taking decisions on subsidies and regulations will in future take N2O emissions into account and promote some forms of 'biofuel' production while quickly abandoning others," he told the journal's discussion board.
Dr. Dave Reay, also of the University of Edinburgh, used the findings to calculate that with the U.S. Senate aiming to increase corn-ethanol production sevenfold by 2022, greenhouse-gas emissions from transportation will rise by 6 percent.