Carbon Dioxide Emission from Biofuel Forests

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Some forests in the western United States are used for fuel. Image courtesy of the National Park service

Biomasses, such as plants or forests, are considered green fuels, with zero net carbon dioxide emissions. A study published on the 23rd of October, 2011 in Nature Climate Change, however, shows that this is not always the case. Researchers found that the use of forests from the West Coast areas (US) lead to an increase in the carbon dioxide emissions.

Carbon Dioxide: Why Do We Need to Reduce CO2?

Carbon dioxide (CO2) is a natural minor component of the atmosphere. Human activities, such as fossil fuel burning, increase its concentration in the atmosphere. This increase has caused worries, due to the properties of this gas: CO2 is a greenhouse gas, and is also acidic, and has been named as a potential culprit in the acidification of the ocean.

Due to the possible damage to the environment associated with CO2, the Kyoto protocol was approved. This is an agreement was made at international level, to decrease CO2 emissions into the atmosphere.

Some Strategies for COEmission Reduction

As mentioned above, one of the main sources of CO2 in the atmosphere is the burning of fossil fuels, such as coal, oil, or gas. For this reason, one of the strategies to reduce its emission is the use of biomass to produce energy.

The principle behind its use is that biomasses, such as plants and forests, are a renewable source; when some plants are burned for energy production, they can be replaced by growing new plants. With this process, the new plants will absorb the CO2 generated with the combustion and, consequently, there will be zero net CO2 emissions.

Another way to reduce the amount of CO2 emitted in the atmosphere is the thinning of some forests, to reduce the risks of wildfire and the consequent fire-caused CO2 emissions.

Study on the Effectiveness of These Strategies

Nature Climate Change recently published the results of a study performed by the Department of Forest Ecosystems and Society of Oregon State University, US. The research was done in collaboration with the University of Leipzig, Germany, and the Laboratoire des Sciences du Climat en de l’Environnement, France.

The researchers studied the effects of these strategies in the US West Coast, a vast area which includes 3 states (Washington, Oregon and California), and it is divided into 19 different ecoregions.

They compared the CO2 emissions from the forests of these areas considering 4 possible situations: 1) business as usual (BAU), which corresponds to the current management of these forests; 2) forest thinning for fire prevention purposes; 3) forest thinning for fire prevention purposes but in a more economically viable manner;  4) forest thinning combined with further harvest to produce energy.

Carbon sinks, sources and added emissions for the 4 possible scenarios. Photo by Oregon State University.

Surprising results

Tara Hudiburg, main author of this study, told Decoded Science: “We found that, in the majority of cases (80% of the monitored area), the net carbon dioxide emissions were higher for situations 2, 3 and 4 in comparison with the first one (BAU).

The increase was particularly high for the last case, that is, when forests were used for bioenergy production: for the whole region considered, a 14% CO2 increase was observed.

This study shows that energy from biomass does not always have zero CO2 net emission; on the contrary, in some cases like the ones we studied, the emissions could be higher.”

The Figure above shows a summary of the CO2 sinks, sources, and added emissions for the scenarios 2, 3 and 4 with respect to scenario 1.

The study of Tara Hudiburg and her coworkers was based on several parameters, such as carbon life-cycle assessment and net carbon intake by plants. They also took into account both the energy and the emissions due to the acquisition and production of fossil fuels for the first scenario (BAU) and to the extra harvest for the fourth scenario (forests used to produce energy).

Biomass: A complex topic

The research carried out by these researchers covers an area with a great variety of climates and vegetations, from semi-arid woodlands to temperate rainforests. Therefore, it is reasonable to think that analogous results would be obtained if a similar study would be performed in a different area and/or country. Surely, it will be interesting to do analyze other regions, to see if this is the case or not.

These results show how the reduction of CO2 emissions is a complex topic; many features should be taken into account when deciding the strategies to achieve the decrease requested by the Kyoto protocol.

Sources

T.W. Hudiburg et al.: “Regional carbon dioxide implications of forest bioenergy production.” Nature Climate Change, 1, 419/423 (2011). Accesses November 2011.

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