My Google Alert for “Manomet Study” has been pretty quiet lately, and no wonder since our "Massachusetts Biomass Sustainability and Carbon Policy Study" was initially published in 2010 (with a subsequent peer-reviewed publication in the Journal of Sustainable Forestry in early 2013). So I was a bit surprised to see one pop up on Friday afternoon (November 1st, 2013). This one took me to a link for a Biomass Magazine blog by Anna Simet featuring the comments of an engineer recycling an argument from 2010. Based on what the engineer said, it appears as though they did not understand the carbon accounting methodology employed in the study. The engineer was making the case that “As long as you don’t harvest the trees faster than they regrow, you are essentially producing electricity from solar energy. There is no net carbon emission from this model.” With training and practical experience in forest management, this was in fact my view of the issue before we embarked on the Manomet Study. But I've come to learn that this is a flawed and incomplete view of forest biomass energy carbon accounting. We've addressed this topic before in a piece in Global Change Biology – Bioenergy and in a Renewable Energy World article, so I won’t go into great detail here. I now see it is very easy to demonstrate that even if the forest stocks at whatever scale you choose remain the same or increase, following the fate of the harvested and unharvested material can lead you to very different conclusions about the emissions the atmosphere will receive. It is not easy, however, to overcome the conventional forestry wisdom that “sustained yield = carbon neutral”. In the dynamic baseline approach we used in the Manomet Study, the unharvested (and generally growing) forest landscape is doing what it does in both the baseline and biomass energy scenarios. While we could not (and cannot) perfectly predict the future fate of forests in the baseline and bioenergy scenarios we used, our projections were associated with an economic analysis of biomass supply based in part on the historical (and fairly consistent) behavior of landowners in the region. This grounded our modeling much closer to reality than I think many detractors realize.
I say all this as a background introduction to my main point in responding to the Biomass Magazine blog post. I believe that the conversation needs to move beyond the “Manomet Study” and instead focus the rapidly emerging body of science from around the world. It is a very rich area of scientific inquiry that has increased rapidly since 2010. The scientific community appears to be developing common themes that move beyond the view that biogenic energy sources are inherently carbon neutral. Among those themes is the development of a dynamic baseline evaluation framework that incorporates the complexity of forest management and the forest products sector.
Anna Simet’s call for a “new study on biogenic emissions” to come out is illustrative of the gap in understanding between the scientific community completing these studies and the biomass energy industry. We need to close this gap. Actually, there have been many studies on biogenic emissions published since the Manomet Study. In fact, my colleague Thomas Buchholz at the Spatial Informatics Group and I have found nearly 60 studies that look at the question of woody biomass emissions compared to fossil fuel equivalents. Similarly, a group in Europe (see Lamers and Junginger, 2013) recently completed a thorough review of several carbon accounting studies. Both efforts have concluded that the overwhelming majority of these studies identify a carbon payback (or carbon debt) period before bioenergy scenarios are favorable to fossil energy scenarios from an emissions standpoint. Most of the studies that were reviewed in these two meta-analyses have been published since 2010. A report from several industry groups in Europe, Canada and the US was also recently released that acknowledges that there is a carbon debt. The overwhelming majority of the studies coming out since 2010 fundamentally conclude the same thing as the Manomet Study: when you use biomass from the forest for energy, there will be an initial emission of greenhouse gases that is greater than fossil fuels (per unit of energy generated), but these emissions are removed from the atmosphere as the harvested forests re-grow. Some scenarios have shorter “debt” period than others, and there are contexts where the debt is paid off immediately. We are completing a meta-analysis of these published studies to try to understand the many factors that drive the length of carbon payback period. We hope to have this work written up in the next few months to synthesize and bring greater awareness to the current scientific thought on this topic.
Again, I firmly believe that the conversation needs to move beyond the “Manomet Study” and instead focus on what the rapidly emerging science is telling us about where the development of biomass energy from forests is a low risk proposition from an atmospheric emissions perspective. I agree with Anna Simet, it really is all about the carbon math. It’s complicated math, but necessary to do to drive activities that best use our forests as a climate mitigation tool.
Gunn, J.S. 2011. The Biomass Carbon Debate: When to start counting? Renewable Energy World Magazine North America September/October 2011 Volume 3:5 pg. 58-59.
Gunn, J.S., D. Ganz, W.S. Keeton. 2012. Biogenic vs. geologic carbon emissions and forest biomass energy production. Global Change Biology – Bioenergy. 4:239-242.