Energy crunch: sugar cane is used for ethanol production in Brazil
Biofuels crops ‘may speed global warming’
Most crops grown in the US and Europe to make "green" transport fuels actually speed up global warming because of industrial farming methods, says a report by Nobel prize winning chemist Paul J. Crutzen.
The findings could spell particular concern for alternative fuels derived from rapeseed, or canola, used in Europe, which the study concluded could produce up to 70% more planet-warming greenhouse gases than conventional diesel.
The study suggested scientists and farmers focus on crops which required less intensive farming methods to produce better benefits for the environment.
Biofuels are derived from plants which absorb the planet-warming greenhouse gas carbon dioxide as they grow, and so are meant as a climate-friendly alternative to fossil fuels.
But the new study shows that some biofuels actually release more greenhouse gases than they save, because of the fertiliser used in modern farming practices.
Fertilisers release nitrous oxide, which is about 300 times more insulating than the commonest greenhouse gas carbon dioxide.
"The nitrous oxide emission on its own can cancel out the overall benefit," co-author Professor Keith Smith told Reuters in a phone interview.
The results, published in "Atmospheric Chemistry and Physics Discussions," were based on the finding that fertiliser use on farms was responsible for three to five times more such greenhouse gas emissions than previously thought. http://www.atmos-chem-phys-discuss.net/7/11191/2007/acpd-7-11191-2007.pdf
Other critics have linked increased biofuels production to other unintended side effects such as rainforest clearance and raised food prices, from competition with forests and food for land.
Brazil and the US produce most of the world's bioethanol as a substitute for gasoline, while the EU is the main supplier of biodiesel.
Using biodiesel derived from rapeseed would produce between 1 and 1.7 times more greenhouse gas than using conventional diesel, the study estimated.
Biofuels derived from sugar cane, as in Brazil, fared better, producing between 0.5 and 0.9 times as much greenhouse gases as gasoline, it found.
Maize is the main biofuels feedstock used in the US, and produced between 0.9 and 1.5 times the global warming effect of conventional gasoline, it said.
"As it's used at the moment, bioethanol from maize seems to be a pretty futile exercise," Smith said.
The study did not account for the extra global warming effect of burning fossil fuels in biofuel manufacture.