We do need trees to take carbon dioxide out of the atmosphere, and the good news is, U.S. forests absorb and store about 10 percent of annual U.S. greenhouse gas emissions.
But the thinking on this question is evolving as human-caused emissions of carbon dioxide continue to rise, concerns about global warming have grown more urgent and scientists dig deeper into life cycle analyses of various wood-to-energy scenarios on scales ranging from a household to a major power plant.
The idea that trees are a renewable resource and burning them for energy is carbon neutral was written into the Kyoto Protocol, the 1997 international agreement to fight global warming. The European Union accepts that thinking, and as a result, with subsidies, millions of metric tons of wood pellets made from Southern U.S. forests are being burned in European power plants every year, with the resulting carbon dioxide emissions—and there are a lot—counted as zero.
Promoted by lawmakers in states with wood products industries, Congress in a 2018 appropriations bill gave the U.S. Environmental Protection Agency and other agencies direction to establish policies that “reflect the carbon-neutrality of forest bioenergy and recognize biomass as a renewable energy source, provided the use of forest biomass for energy production does not cause conversion of forests to non-forest use.”
The EPA has been working to draft regulations that will spell out under what practices wood can be burned and be considered carbon neutral.
A lot of scientists, however, are now saying, effectively, hold on a minute.
It is supposed to work like this: Burning wood to generate energy releases carbon dioxide into the atmosphere, while newly planted trees—and others—soak up an equivalent amount or more of carbon through photosynthesis. But it doesn’t work like that because burning wood pellets in power plants releases massive amounts of carbon now, when there’s an urgent need to reduce emissions, and any forest regrowth to absorb carbon dioxide will be too late, said John Sterman, a professor of management and engineering at the Massachusetts Institute of Technology, who has published peer-reviewed research on lifecycle carbon emissions from burning wood pellets.
There are also no assurances that trees that are harvested will be allowed to regrow, he pointed out.
Also, in 2018, almost 800 scientists wrote to the European Parliament, arguing that “cutting down trees for bioenergy releases carbon that would otherwise stay locked up in forests, and diverting wood otherwise used for wood products will cause more cutting elsewhere to replace them.”
Still, there are forestry experts like Robert Bonnie, who oversaw the U.S. Forest Service during the Obama administration, who argue that decades of government data show that southern forests in particular are growing so fast that they are sequestering a massive amount of carbon, even as they are being harvested for wood products. Placing a value on that carbon will give landowners the economic incentive to keep growing trees, Bonnie says.
Other experts will support smaller-scale or localized biomass production and burning, where only waste wood from mills or forest debris are burned, or when there are co-benefits of reducing wildfire risk in fire-prone areas, like California.