A review was conducted to evaluate the science behind the Manomet biomass report and the validity of the report’s main conclusions concerning net carbon emissions from biomass energy, relative to fossil fuels. The Manomet report comes to two main conclusions:
1. For utility-scale generation, net emissions are higher from biomass than fossil fuels. When biomass is used to generate electricity in utility-scale plants, the net emissions after 40 years, even taking forest regrowth into consideration, are still higher than if the power had been generated with natural gas or coal (exhibit 6-14, p. 112).
2. Net emissions profiles from biomass thermal and CHP plants may be better. The Manomet study concludes that when biomass replaces fossil fuels for small-scale thermal applications and in combined heat and power plants, net emissions by 2050 can be lower than would occur if oil had been burned, but are still significantly higher than if natural gas were used as fuel.
The science and modeling behind the Manomet study are sound. However, the study relies on a number of assumptions to achieve these conclusions, all of which minimize the calculation of net carbon emissions from biomass, meaning that actual emissions are likely significantly greater than the study concludes. Thus, the first conclusion of the report – that net emissions from biomass are greater than from coal and especially natural gas even after forty years of regrowth by forests – is qualitatively correct, it likely underestimates the magnitude of biomass emissions. The second conclusion, that small-scale thermal and CHP biomass facilities may yield a carbon “dividend” relative to fossil fuels after forty years is likely not correct, since actual biomass emissions likely exceed fossil fuel emissions even under the thermal and CHP scenarios.
This work was supported by the Clean Air Task Force, which along with the Center for Biological Diversity have been in the forefront of sound thinking on the biomass issue. The Clean Air Task Force has the Manomet evaluation posted here.