Large differences in the climate impact of biofuels

Nov 15, 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 creates a 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 at the University of Gothenburg.

The use of affects ecosystem over time in either a positive or negative way. Biofuels where the combustion related emissions are compensated rapidly have a lower 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 .

In his PhD thesis, Lars Zetterberg analyses how different types of biofuels affects the ecosystem carbon stock over time, and the consequent climate impact. The results show that 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. Results from this study can help decision makers to understand the climate impacts from different bioenergy types in order to prioritize between different bioenergy alternatives.

"The over which the analysis is done is crucial for the result. Over a 100 year perspective the use of stumps for energy has a significantly lower climate impact than coal, but over a 20 year time perspective, stumps have a higher climate impact than natural gas. Using logging residues in the form of branches and tops for energy reduces carbon dioxide emissions in both the short term and the long term."

If environmental legislation, for instance the EU renewables directive, requires that climate benefits of biofuels are calculated over a 20 year period, biofuels that need longer time to reach carbon neutrality may be regarded as not renewable..

"If we want to do reduce global carbon emissions quickly, we should prioritize fuels that are beneficial on a short time scale, for instance 20 years In addition, over a longer time scale it will be beneficial to replace coal with stumps, even if we will not see a result until after 20 years."

In the thesis, Lars Zetterberg also addresses how the EU Emissions Trading System should be designed in order to incentivize the use of carbon dioxide efficient fuels.

Explore further: Conservation scientists asking wrong questions on climate change impacts on wildlife

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dschlink
5 / 5 (1) Nov 15, 2011
Biomass can't be carbon-neutral because there will always be an energy cost associated with gathering and processing the material. Use of lumbering waste deprives the site of critical organics, degrading the soil and slowing the regrowth.
Howhot
not rated yet Nov 16, 2011
You are looking at it wrong @dschkink. Look at biomass like you would a solar panel; sure it takes energy to make a solar panel and that will be input to CO2 equation, but once built it can provide nearly unlimited carbon free energy.

In the same way, biomass would in a generation or two be self-sustaining.
Callippo
not rated yet Nov 17, 2011
Biofuels are the most advanced form of environmental devastation. If you really want to save the planet, support the cold fusion research.
Howhot
not rated yet Nov 17, 2011
Here is my thinking on biofuels. We are always going to need oil based for specialized big engine tasks. Things like Jets, Semi-tractor trailers, bulldozers, tugboats...; The energy storage density for liquid diesel just can not be replaced with lithium/ion electric. So that is where biofuels come into play in the efforts to reduce the Carbon.

I agree with you Calippo, Biomass creation using current methods does do a lot of damage. Look at corn ethanol for example which has caused spikes in food prices. Switch-grass
may be something else.

So anyway, I see moving big engines to biofuels as about the only way to turn some machines green.