EXERCISE CAUTION: Manomet Center Warns Readers Not to Generalize Too Widely

From the June 2010 Forest2Fuel newsletter.

If you haven’t read the Manomet Center for Conservation Sciences “ Biomass Sustainability and Carbon Policy Study” yet, you may want to start by turning to page 113, the next-to-last page of the study. On this page, the Manomet Center lays out its final considerations. In this section, the Center writes extensively on the caveats that come along with the study. The gist of these caveats: Don’t generalize this study too widely. Here is the rundown on the applicability of this study beyond Massachusetts:

• The Center used “average and/or typical values for GHG emissions from biomass and fossil fuel energy facilities. With continually evolving technology, biomass developers may be able to demonstrate lower GHG emissions per unit of usable energy.” They believe that the technology advancements on the horizon will reduce carbon emissions and shorten the time it will take to recover the carbon emitted.
• The study considered “only biomass from natural forests.” Other types of biomass, the Center admits, would pay off their carbon debts more quickly. “Our results for biomass from natural forests likely understate the benefits of biomass energy development relative to facilities that would rely primarily on these other wood feedstocks.”
• The study’s estimates of carbon recovery focused on typical forest conditions in Massachusetts. The study looked solely at mixed oak, white pine, northern hardwoods, hemlock and mixed hardwood stands. In effect, the study acknowledges that all forests are different, and therefore all carbon calculations will be different.
• The study used historical harvest trends when determining which harvest regimes to include in its modeling, as the Center believes these trends are likely to remain intact. However, they acknowledge other scenarios could “change the carbon recovery results in important ways.” Massachusetts uses primarily manual logging techniques, specifically because they do a lot of high grading (selectively removing only the best and biggest trees and leaving lower quality trees behind) and because the tops and limbs of hardwoods are so heavy it is more efficient to fell the tree manually and delimb and top it where it falls before sending it to the landing. Techniques other than this will result in "different carbon debts and recovery profiles."
• “Views about how long it will take before we have truly low or no carbon energy sources play a critical role in biomass policy decisions. If policy makers believe it will take a substantial amount of time to develop and broadly apply low or no carbon sources of energy, they may be more inclined to promote the development of biomass.” In this case, if a state has a renewable profile that is different than that of Massachusetts—less wind or solar opportunity, for instance—different policy decisions will be required regardless of study results.

“In light of all these factors,” the study concludes, “we stress that our work should be viewed as providing general indicators of the time frames for recovery of biomass carbon and the key factors that influence these estimates. Uncertainties remain and we have tried to be transparent about them. For the variety of reasons discussed above, the carbon recovery and dividend profile for a specific facility is likely to deviate from the average facilities analyzed in this report. As such, we suggest that new energy and environmental policies that rely on insights from this study should clearly take into account the impacts of various uncertainties embedded in the report’s analytic framework, assumptions and methods.”

The Manomet Center deserves credit for being so transparent about the uncertainties they faced while attempting to quantify the life cycle carbon effects of different energy sources. It is, admittedly, a highly complex scientific undertaking. As the Center concedes, the carbon recovery and dividend profile of every facility is likely to deviate from the results of the report. Every facility will use a different fuel mix, and every fuel mix will come with its own carbon footprint. Every forest sequesters carbon at a different rate. Every boiler has a different efficiency rating. W e've been saying much the same thing for more than two years: Every facility will have unique characteristics that demand individualized study.

The entire study can be found here.

To register and read more about the Forest2Fuel e-Newsletter, click here.