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 Biodiesel may worsen global warming relative to petroleum diesel

23/4/07 (mongabay.com)  -  Biodiesel and petroleum diesel have similar environmental impact

Biodiesel made from rapeseed could increase rather than reduce greenhouse emissions compared to conventional diesel fuels, reports a new study published in the journal Chemistry & Industry. Overall the researchers found that petroleum diesel and rapeseed biodiesel, presently the main biofuel used across Europe, have a similar environmental impact. The results suggest that efforts to mitigate climate change through the adoption of rapeseed biodiesel may be of little use beyond energy security.

Comparing the full lifecycle emissions of greenhouse gases by the two fuels from production through combustion in cars, Eric Johnson, editor of Environmental Impact Assessment Review, and Russell Heinen, Vice President of SRI Consulting, found that "biodiesel derived from rapeseed grown on dedicated farmland emits nearly the same amount of greenhouse gas emissions (defined as CO2 equivalents) per km driven as does conventional diesel."

They show that about two-thirds of greenhouse gas emissions from rapeseed biodiesel occur during the farming of rapeseed, when nitrous oxide (N2O), which is 200-300 times as potent a greenhouse gas as CO2 otherwise, is released into the atmosphere. In contrast, petroleum diesel releases roughly 85 percent of its greenhouse gas emissions during combustion in a vehicle's engine, the final use stage.


Biodiesel yield (gallons per acre) of various crops. 

The researchers say that the difference may be greater depending on land use.

"If the land used to grow rapeseed was instead used to grow trees, petroleum diesel would emit only a third of the CO2 equivalent emissions as biodiesel," stated a release from the Society of Chemical Industry, publisher of Chemistry & Industry.

The authors say their study has implications for European policymakers looking to meet binding commitments under the Kyoto Protocol.

"Our study suggests that farmers in Europe who are growing rapeseed for biodiesel might combat global warming in a more effective way, namely by converting those fields into forests and using conventional diesel for fuel," Johnson told mongabay.com. "It also suggests that rapeseed biodiesel does not deliver the global warming benefit over conventional diesel that is so often presumed by EU member states."

Overall the study found that biodiesel and petroleum diesel have similar environmental impact.

"In addition to our study of global warming, we also compared the two fuels in terms of a range of other environmental impacts – from eco and biological toxicity to ozone layer depletion and acidification," the authors wrote. "To do so, we weighted the complete emissions inventories of each system, not just greenhouse gases, by using a commonly used impact assessment method. The answer is equivocal: petroleum diesel comes out ahead in five categories; biodiesel comes out ahead in the other five."

Johnson is now looking at the lifecycle climate impact of other sources of biodiesel, like soybeans and oil palm.

"We are studying [palm oil and soybeans] at present and hope to have answers in a few months' time," Johnson said. "A key factor here will be - as it was for rapeseed - nitrous oxide (N2O, or laughing gas) emissions from their farming. N2O is a significant global warmer, with a 100-year global warming potential of 296 (carbon dioxide's GWP is 1). There is much research and debate going on about N2O emissions, and I'm trying to get abreast of it for these other crops."

Transportation currently accounts for more than a 20 percent of all EU greenhouse gas emissions, according to a statement from the Society of Chemical Industry. The 2003 EU Biofuels Directive seeks to increase the levels of biofuels to 5.75 percent of all transport fuels by 2010 and 10 percent by 2020, up from about 2% today.

Eric Johnson and Russell Heinen (2007). Petroleum diesel vs biodiesel: The race is on. Chemistry & Industry — 23 22 April 2007.

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