A group of forest scientists, ecologists and climate researchers has sent a strongly worded letter to the U.S. Senate, arguing that pending bipartisan energy legislation incorrectly claims that burning trees for energy is carbon neutral.

“Legislating scientific facts is never a good idea, but is especially bad when the ‘facts’ are incorrect,” say the researchers, led by Phil Duffy, president of the Woods Hole Research Center. “We urge you and other members of the Senate to reconsider this well-intentioned legislation and eliminate the misrepresentation that forest bioenergy is carbon-neutral.”

The letter is endorsed by 65 researchers, including a number of leaders of forest science, and also endorsed by several scientific societies.

The amendment being objected to, introduced by Sen. Susan Collins of Maine with 7 bipartisan cosponsors, states that leaders of the federal government must take actions that “reflect the carbon neutrality of forest bioenergy and recognize biomass as a renewable energy source.” It is part of a sweeping bipartisan energy bill that the Senate is considering at the moment, and passed by voice vote in early February.

Shortly after its passage, a press release by Collins hailed the amendment, which, she said, would “help ensure that federal policies for the use of renewable biomass are clear, simple, and reflect the importance of biomass for our energy future.” The release noted the support of groups including the American Forest and Paper Association and the American Wood Council.

In theory, it makes perfect sense — if you burn wood or wood pellets in a power plant, you generate electricity and carbon dioxide emissions just like you do when you burn, say, coal. The difference, though, is that trees grow back again, and resequester carbon.

That sure sounds carbon neutral, and such reasoning has fueled a growing biomass-for-energy industry, driven in significant measure by European policies on biomass. But this practice, the researchers charge, may not be so beneficial for the climate as is being claimed.

A key problem, say the scientists, is that it takes a long time for trees to grow back after they’re cut down — and a lot can happen in that span of time.

“Wood is burned in minutes and it takes decades to a century or more for it to absorb the carbon dioxide that was released and grow back,” says William Moomaw, one of the letter’s signers and co-director of Global Development and Environment Institute Tufts University (Moomaw is also a board member of the Woods Hole Research Center, which released the letter). “All that time carbon dioxide is in the air absorbing radiant heat from the earth and raising the temperature.”

Moomaw adds that the researchers are concerned that “not all trees planted reach maturity because of fire, insects, disease and repurposing of land.” Thus, they fear that they may not be replaced and carbon neutrality may not be achieved, even on long time frames.

However, there are scientists on the other side of this question too, and many defenders of forest bioenergy. Indeed, this is not the first time this debate has reared its head.

In a letter two years ago, an even larger group of scientists, and many of the very same ones behind the current letter, called on the EPA to “rigorously assesses the incremental carbon emissions impacts of bioenergy production.” However, another large group of scientists at the time wrote a letter of their own supporting biomass, arguing that “Most debates regarding the carbon benefits of forest biomass energy are about the timing of the benefits rather than whether they exist.”

Indeed, Annie Clark, communications director for Sen. Collins, sent the Post a statement referring to this letter and commenting, “One hundred nationally recognized forest scientists, representing 80 universities, have written to the EPA stating the long-term carbon benefits of forest bioenergy. This group of forestry experts weighed a comprehensive synthesis of the best peer-reviewed science and affirmed the carbon benefits of biomass.”

The current amendment does have strong support from many in the forest community, including the National Alliance of Forest Owners, whose president and CEO, Dave Tenny, told the Post in a statement that “It doesn’t appear that the authors of the letter read the legislation. The amendment clearly states that biomass is renewable and carbon neutral ‘provided the use of forest biomass for energy production does not cause conversion of forests to non-forest use.'”

The amendment was indeed modified before passage to qualify the definition of carbon neutrality in this way, something that was highlighted on the Senate floor by Sen. Maria Cantwell (D-Wash.), one of the broader energy bill’s chief sponsors. “We agree that some biomass is clearly ‘carbon neutral’ and some biomass is not ‘carbon neutral,’” Cantwell said then.

“We specifically modified the amendment, prior to voting on it, to ensure we are encouraging forest owners to keep their lands in forests,” she continued.

But Moomaw says the update doesn’t take away the scientists’ concerns. “The additions were put in to improve the amendment, but fail to do so,” he said by email.