As I watch the climate debate, I’ve noticed that biomass has a bad rep in some climate circles. Sometimes it is as simple as biomass is ethanol ethanol is bad therefore biomass is bad. Sometimes it is more nuanced. Seldom is it discussed in a way that reflects differences among places and the variety of possible technologies and material to be used.
Last weekend there was an article in the NY Times on a Manomet study. In this Q&A, John Hagan and Thomas Walker go into some depth describing their findings. Here are some considerations:
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.
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.
And
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.
