As the calls to curb carbon pollution grow louder, power companies face increased pressure to find cleaner sources of energy. Many have turned to woody biomass for fuel, much of which comes from forests. The wood is chipped or turned into pellets — small, compressed cylinders of woody material. These pellets are burned in power plants just like coal. Most suppliers are operating under the false assumption that, since trees can grow back and resequester carbon, then they are a carbon-neutral fuel when burned.

But recent science shows that many forms of biomass — especially from forests — produce higher carbon emissions compared to fossil fuels. In particular, a growing body of peer-reviewed, scientific studies shows that burning wood from whole trees in power plants to produce electricity can increase carbon emissions relative to fossil fuels for many decades — anywhere from 35 to 100 years.

Composition of Wood Pellets and Carbon Emissions

Under the right circumstances, true wood waste could serve as a low-carbon option for producing pellets. For example, sawdust and chips from sawmills that would otherwise quickly decompose — and release carbon anyway — can be a low-carbon source. On the other hand, burning whole trees can produce higher carbon emissions than coal, and this elevated CO2 level with respect to coal can persist in the atmosphere for decades.

NRDC therefore modeled the carbon impacts of burning wood pellets of varying composition in power plants to produce electricity. We used a carbon accounting model developed by the Spatial Informatics Group (SIG) to model scenarios in which pellets sourced from bottomland hardwood forests in Atlantic plain of North Carolina and South Carolina supplied a typical power plant in the United Kingdom. Our analysis assumed that the biomass feedstocks used to produce pellets were typical of the pellet industry:

• forestry residues: tops and limbs from forestry operations that are non-merchantable to other markets;
• whole trees: merchantable pulpwood, trees from thinning operations, and non-merchantable trees; and
• mill waste: by-products of sawmill operations such as sawdust and chips.

Using the model, we estimated the total amount of carbon released over time (cumulative CO2 emissions) for each scenario and compared those emissions with those from coal and natural gas.

Results and Implications for the Wood Pellet Industry

NRDC’s modeling shows that wood pellets made of whole trees from bottomland hardwoods in the Atlantic plain of the U.S. Southeast — even in relatively small proportions — will emit carbon pollution comparable to or in excess of fossil fuels for approximately five decades. This 5-decade time period is significant: climate policy imperatives require dramatic short-term reductions in greenhouse gas emissions, and emissions from these pellets will persist in the atmosphere well past the time when significant reductions are needed. Moreover, several studies have concluded that logging residuals alone may be unable to meet bioenergy demands in the region we modeled, and that pulpwood trees may need to be used to meet the increasing demand.

Unfortunately, the biomass wood pellet industry in the southeastern United States is expanding rapidly. Wood pellet exports from the United States doubled from 1.6 million tons in 2012 to 3.2 million tons in 2013, and they are expected to reach 5.7 million tons in 2015. This growth is driven largely by exports to Europe in response to flawed policy incentives on renewable resources that regard all biomass as carbon neutral.

Pellet manufacturer Enviva LP is the largest producer and exporter of wood pellets in the United States, and a primary biomass supplier to British utility Drax Power. Drax operates the United Kingdom’s largest coalfired power plant and is converting half of its six generating units to run solely on wood pellets. Enviva has claimed that its wood pellets are a clean source of fuel for electricity production, yet the company has not publicly disclosed the composition of its wood pellets. If Enviva’s pellets were comprised of whole trees from the modeled Southeast bottomland hardwoods — even in relatively small proportions — they would emit carbon pollution comparable to fossil fuels for decades. The company has the responsibility to come clean with the public, investors, and regulators by disclosing the makeup of its fuel, and to take steps to ensure that its pellets do not increase carbon emissions.