Large differences in the climate impact of biofuels

EurekaAlert!
Public release date: 15-Nov-2011

When biomass is combusted the carbon that once was bound in the growing tree is released into the atmosphere. For this reason, bioenergy is often considered carbon dioxide neutral. Research at the University of Gothenburg, Sweden, however, shows that this is a simplification. The use of bioenergy may affect ecosystem carbon stocks, and it can take anything from 2 to 100 years for different biofuels to achieve carbon dioxide neutrality.

"Using a tree as biofuel creates a carbon dioxide debt that must be "paid back" before the fuel can be considered to be carbon dioxide neutral. Energy forest is fully neutralised after 3-5 years, while other trees grow so slowly that it can take up to 100 years before they achieve carbon dioxide neutrality" says Lars Zetterberg of the Department of Earth Sciences at the University of Gothenburg.

The use of bioenergy affects ecosystem carbon stocks over time in either a positive or negative way. Biofuels where the combustion related emissions are compensated rapidly have a lower climate impact than fuels for which it takes a long time for the emissions to be compensated. Despite this, the difference in climate impacts between slow and rapid biofuels is rarely highlighted in political contexts. Emissions from bioenergy are, for example, not included in countries' commitments under the Kyoto Protocol.

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