In recent months, two noteworthy letters have been sent to Congress by eminent scientists examining the merits—or demerits—of biofuels in the climate debate.
The first, sent May 17 by 90 scientists to House Speaker Nancy Pelosi (D-Calif.) and Senate Majority Leader Harry Reid (D-Nev.), questioned the treatment of all biomass energy as carbon-neutral, arguing that such treatment could undermine legislative emission-reduction goals.
The second, sent July 20 to Senate Environment and Public Works Committee Chair Barbara Boxer (D-Calif.) by 110 scientists, expressed concern over equating biogenic carbon emissions with fossil fuel emissions, such as contemplated in the Environmental Protection Agency’s greenhouse gas tailoring rule. Such an approach, it is feared, encourages further fossil fuel energy production.
The first letter notes correctly that the "replacement of fossil fuels with bioenergy does not directly stop carbon dioxide emissions from tailpipes or smokestacks." Thus, biomass—fuels derived from wood or other plant waste—is unlike other renewables, such as wind or solar, which have no smokestack emissions. The second letter notes, also correctly, that carbon dioxide released from the combustion of wood biomass is part of the global cycle of biogenic carbon and "does not increase the amount of carbon in circulation," as would fossil fuel emissions.
These two points are not fundamentally in conflict. While biomass is like fossil fuels in that burning releases carbon into the biosphere—the biosphere being the whole area of Earth’s surface, atmosphere, and sea that is inhabited by living things—these carbon releases are different from those of fossil fuels in that the process does not release net additional amounts of carbon into the biosphere. By contrast, carbon found in fossil fuels—coal, oil and natural gas—which holds carbon captive, does release net permanent additional amounts of carbon to the biosphere upon energy generation. This impact on the amount of carbon in the biosphere can be critical to climate change in the long term, but is much less important in meeting short term objectives.
It is this lack of equivalence in the broader impact on the biosphere that is at the crux of the question of carbon neutrality. In the case of fossil fuels, the release of carbon dioxide is a net addition to the amount in the biosphere. For biomass, by contrast, the amount of carbon in the biosphere has not changed. Only the form has changed since it moves from being captured in the biomass to being released in the atmosphere.
This is not without consequence. In the short term the emissions, whether from biomass or fossil fuels, will accumulate in the atmosphere and contribute to global warming.
Moreover, a portion of them, without regard to source, will be captured in biological growth. Over the longer term, however, the carbon paths will diverge. Fossil fuel emissions will add to the total stock of permanent carbon in the biosphere—both in the atmosphere and in biomass—whereas biomass energy will merely involve the recycling of carbon within the components of the biosphere. An energy diet of strictly biomass will not generate the long-term problem of global warming (nor related issues such as the acidification of the oceans).
The question arises as to what time frame is most relevant for purposes of mitigating global warming. Obviously, contemporary society cannot move instantly, or perhaps ever, to an all-biomass energy diet. However, to the extent that biomass substitutes for fossil fuels, the buildup of carbon dioxide is reduced. Some have noted that warming is already occurring and thus argue for immediate short-term responses. However, a response that slows near-term warming while exacerbating the problems in the long term does little to ensure the future of humanity. Indeed, there is evidence published by the Intergovernmental Panel on Climate Change that modest warming of up to 2 degrees Celsius (3.8 degrees Fahrenheit) could generate net positive benefits globally. Thus, humans do have some room for calibration.
The use of biomass, although it may generate slightly more carbon emissions per unit of energy, also provides its own offsetting process in subsequent biological growth that recaptures the carbon. Additionally, biofuels offer the best current alternative to fossil fuels for a liquid transport fuel. If biomass energy restrictions result in society being forced to use fossil fuels, those emissions are irreversible and cannot be returned to their fossil fuel source. Of course, they can be captured in vegetation but only by reducing the opportunities for future vegetative capture, since the global biosphere potential to capture carbon presumably is limited. Thus, at any future point in time, carbon dioxide in the biosphere will be greater if biomass were not allowed to substitute for fossil fuels.
Global warming is indeed a long-term challenge to humanity, and long-term sustainable solutions are required. The contest is a marathon, not a sprint. Having the lowest emissions to the year 2020 does not address the real problem, which is long term. There is no silver bullet solution to climate change. We need all the tools we can bring to bear. An important role can be played by biomass energy, which, if correctly utilized, can contribute significantly to addressing the long-term climate issue.
—Roger A. Sedjo is a senior fellow and the director of Resources for the Future forest economics and policy program. This commentary first appeared in The Energy Daily.