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Globe Editorial

The bloom is off the biomass

July 10, 2010

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IS THERE any better symbol of energy independence than a Berkshire oak replacing oil from Saudi Arabia? Apparently, there is.

Even though burnt wood produces carbon dioxide, policy makers have long insisted that it should be considered a renewable alternative to fossil fuels because trees are carbon neutral — after some are cut down to burn, the new growth that replaces them absorbs CO2. On that ground, the state has sought to make “biomass’’ a priority for its energy future. But it’s now reconsidering, and probably with good reason.

A new study by a Massachusetts environmental think tank casts some doubt on the benefits of biomass. It spells out, in a variety of scenarios, just how long it would take for the regrowth to offset both the carbon emitted by a burned tree and the loss of that tree as a carbon absorber.

The payback time can be as short as five years if the wood-burning plant is simply used for heat and replaces an oil-fired facility. But if the wood is replacing an electric generator fueled by natural gas, the first global-warming dividends will not come for 90 years. Overall, the study by the Manomet Center for Conservation Sciences casts a cloud on proposals to use wood-fueled power as a way to meet the state’s mandated goal of reducing greenhouse gas emissions 80 percent by 2050.

Of course, curbing global warming is just one reason to favor wood energy as an alternative to fossil fuels. Its emissions of sulfur, a toxic combustion pollutant, are a fraction of oil’s or coal’s. Moreover, harvesting trees runs no risk of offshore oil spills or coal-mining disasters. The jobs in supplying and running wood-burning plants would all be local.

Backers of wood-burning energy plants and the author of the study disagree on whether the state has enough wood from storm damage, landscaping, building-site clearing, mill waste, and construction debris to supply much of the fuel for wood facilities. Wood from such sources has a much lower carbon profile, since it is no longer absorbing carbon dioxide and, if burned in a field or left to rot, would emit it anyway.

After hearings next month on the implications of the Manomet study, the state will revise its rules governing wood energy’s role in helping the state meet its renewable-energy goals. One thing is clear: the study has left wood energy a lighter shade of green.

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