As I wrote in an article over the weekend, electricity derived from burning organic matter, particularly wood, has long enjoyed a reputation as a green alternative to coal-fired power — and why not? Trees and plants, renewable by definition, release planet-warming gases into the atmosphere when they burn, and absorb it again when they are growing.
It’s sustainable and climate-friendly to boot — or so the logic has long held.
As with biofuels and questions surrounding their impact on land use around the world, however, the science on biomass is proving a bit more nuanced.
The Manomet Center for Conservation Sciences in Massachusetts recently completed an analysis of the potential impact of using wood for energy in that state, where a handful of new biomass plants are in the development pipeline. The study was commissioned by the Massachusetts Department of Energy Resources, and its findings — broadly oversimplified by some of the news media, the center has said — are likely to have implications in other states contemplating their own expansion of woody biomass power.
I sent some questions to John M. Hagan, the president of the Manomet Center, and Thomas Walker, the study’s team leader. The queries and responses are below.
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Q.Among the headlines that heralded the arrival of the Manomet Center’s biomass study were many like these: “Mass. Study: Wood Power Worse Polluter Than Coal,” "Manomet: Biomass Isn’t Green,” “Biomass Benefits Refuted.” Do they capture the essence of the study?
A.No, all three headlines fail to recognize that over time using wood for energy can lead to lower atmospheric greenhouse gas levels. While emissions from burning wood are initially higher than from fossil fuels, regrowing forests sequesters carbon, a process that eventually can yield greenhouse gas levels lower than would have resulted from continued burning of fossil fuels.
The key issue, and the focus of the Manomet study, is the timing and magnitude of these effects. Energy and environmental policymakers will need to carefully weigh these short- and long-term trade-offs of biomass energy development. All the headlines miss the details and therefore serve to misinform rather than inform the public. It’s unfortunate that the story can’t be reduced to simple sound bites, but these types of life cycle analyses inevitably are complicated.
To further complicate the story, while our life cycle analysis looked at greenhouse gas emissions from production and transport of both biomass and fossil fuels, we couldn’t evaluate every possible environmental impact of energy production, such as broken blowout preventers 5,000 feet under water or mountaintop removals to access coal. Rarely (maybe never) does society really weigh the full array of costs and benefits of our decisions. But as the world gets more complicated, and as resources get more scarce, and as the human population climbs to nine billion (and then some), we’re going to have to become more serious about analyzing these kinds of trade-offs.
Q.To what extent do the study’s findings have wider implications for biomass power generation in other parts of the country?
A.The framework we developed for carbon accounting could be used for an individual power facility, a state, a country, or even the European Union (which is importing wood chips from the U.S. and other countries to meet its renewable-energy goals). In order to assess the greenhouse gas implications of using wood for energy, you have to know four things:
• The life cycle of the wood (e.g., logging debris, whole trees, trees vulnerable to catastrophic events) in the absence of the biomass energy opportunity.
• The type of energy that will be generated (heat, electricity, combined heat and electricity), because different types have different efficiencies and thus different CO2 emissions profiles.
• The type of fossil fuel being displaced (coal, oil, or natural gas), because different fuels have different emissions profiles.
• The management of the forest — management can either slow or accelerate forest growth, and therefore recovery of carbon from the atmosphere.
We plugged in data for Massachusetts to get an answer for the Massachusetts Department of Energy Resources. But you could plug in data from anywhere and get an answer for that place, and that’s what you need to do in order to get the right answer for the greenhouse gas footprint. The European Union might benefit from applying our framework to find out exactly what the benefits (or costs) might be to the atmosphere of using wood to achieve its 20 percent renewable-energy goal by 2020. Without doing this analysis, the E.U. could conceivably be making the climate worse in the near term (10 to 30 years), and this might not be smart climate policy.
Q.Some critics — including the biomass industry — have said the study failed to make clear the benefits of using forest and agricultural residues for biomass power generation, as opposed to growing crops and forests specifically for energy generation. Is this a fair charge?
A.Actually, the report was painstakingly transparent with respect to what we analyzed and what we didn’t. In the case of greenhouse gas emissions, the study addressed only the carbon cycle implications of biomass harvested from actively managed, natural forests. In the third paragraph of the report’s executive summary, we clearly made this point:
We do not consider nonforest sources of wood biomass (e.g., tree care and landscaping, mill residues, construction debris), which are potentially available in significant quantities but which have very different greenhouse gas implications.
These materials can be important potential sources of biomass — ones that likely have very different carbon cycle implications than biomass from natural forests — and merit careful and separate consideration in biomass policy development. Our carbon accounting framework would capture these differences.
Q.Some biomass opponents say that if the benefits of biomass power are limited and/or marginal, society shouldn’t waste time or money investing in it, channeling money instead toward further development of solar, wind and other nonpolluting sources. Do you see a role for biomass power in the nation’s overall energy portfolio?
A.This is really an issue for policymakers at the state and national levels. But our study suggests that it’s important to be specific about how you define biomass. Energy generation from harvests of live whole trees from natural forests has different life cycle implications than energy generation from wood wastes that otherwise would have released their carbon to the atmosphere relatively quickly. The choice of biomass energy generation technologies also matters. Biomass fueling thermal and combined heat and power systems typically produce greenhouse gas benefits sooner than large-scale biomass electricity generation.
Finally, we’d emphasize that there are many other considerations besides greenhouse gas emissions when making energy policy — these include energy security, air quality, forest recreation values, local economics, other environmental impacts of extracting fossil fuels (and not just greenhouse gas emissions of burning fossil fuels), and quality of place, among others. Policymakers need to weigh all these factors in making energy policy.
What we’ve done is put a much sharper point on one piece of the story — greenhouse gas emissions. Until our study came out, it was widely assumed that using wood for energy was immediately carbon- neutral. How this new insight factors into the public’s view of using wood for energy remains to be seen.
As for Manomet, our role is to inform society with science, with the hope that a better informed society will make better decisions.
