The EPA says burning wood to generate power is 'carbon-neutral.' Is that true?
Posted by admin on 8th May 2018

Environmental Protection Agency Administrator Scott Pruitt recently told a group of forestry executives and students that from now on the U.S. government would consider burning wood to generate electricity, commonly known as forest or woody biomass, to be “carbon neutral.”

The executives, who had gathered at an Earth Day celebration in Georgia, greeted the news with enthusiasm. But I did not.

Biomass does not introduce new carbon into the system, as its supporters point out. Yet it does transfer carbon from forests to the atmosphere, where it traps heat and contributes to climate change.

As a scientist and the coordinating lead author of the Intergovernmental Panel on Climate Change report on renewable energy, I have concluded from extensive scientific studies that converting forests into fuel is not carbon neutral. I have also been working with many other scientists to inform governments about the potential for forests to remove carbon dioxide from the atmosphere, and the climate perils of burning wood and forestry waste at an industrial scale for electric power.

Wood pellets like this one are burned to generate heat or power.
AP Photo/John Flesher

Turning forests into fuel

Energy can be renewable. Or sustainable. Or carbon neutral. Or some combination. These terms are often used interchangeably, but they mean quite different things. Wind power and solar energy clearly have all three attributes. What about bioenergy – the heat released from burning wood and other plants?

Trees can eventually grow to replace those that were felled to produce wood pellets that are burned to produce electricity. That makes biomass very slowly renewable, if the replacement trees actually do grow enough to absorb all the carbon dioxide previously discharged.

Environmentalists generally oppose forest biomass because it contributes to climate change while disrupting important ecosystems and the biodiversity they support. They also object to this source of energy because it appears that burning biomass releases pollutants that endanger public health.

The scientists who study climate change, the global carbon cycle and forest ecology tend to reject the notion of biomass carbon neutrality. Some forest economists and forestry scientists, however, support the notion of carbon neutrality, depending on the circumstances.

Carbon accounting

To settle this debate, many of my colleagues and I believe it is essential to accurately account for all the emissions from burning wood for electric power. This is more than an academic exercise as biomass already produces significant emissions and industry observers foresee a nearly seven-fold increase in its use by 2050 from 2013 levels.

Forests can, at least theoretically, be managed sustainably as long as annual harvesting doesn’t exceed annual growth rates. Suppliers claim to use residues from timber harvesting, thinnings – trees growing too close to other trees to thrive – and sawdust for this purpose. However, large-scale biomass has led to clear-cutting and the harvesting of whole trees.

Also, experts see the carbon neutrality of forest biomass differently depending on the time frames they consider, and on their assumptions regarding the likelihood that saplings planted to replace burned trees grow sufficiently to offset all of the associated carbon emissions.

Trees at the Georgia Biomass pellet facility in Waycross.
Marlboro Productions, CC BY-ND

Carbon neutrality supporters

Bioenergy supporters say it’s possible for replacement trees to eventually remove all the carbon emitted through biomass from the atmosphere.

But this would require growing trees and forests that are bigger than the ones already harvested and burned for fuel. In addition to the emissions from combustion, carbon is released from forest soils when trees are felled. And it takes large amounts of energy to prepare wood pellets and transport them to where they are burned.