The biomass industry pushed back strong on the report, calling the science in it neither “factual nor new.”

“Biomass is a clean, renewable energy source that our nation relies upon to reduce our dependence on fossil fuels,” said Bob Cleaves, president of the Biomass Power Association, in a statement.

“Our industry uses residuals from forest maintenance as well as wood already used for other purposes like construction. These materials have no other use; they would otherwise decompose either in landfills, emitting the harmful methane gas, or on a forest floor where they would provide kindling to wildfires.”

The report highlights one comparison that shows a biomass power plant had higher allowable emission rates than a coal or gas plant in carbon monoxide, nitrogen oxides, filtered particulate matter 10 (PM 10) and volatile organic compounds. Only the coal plant had higher sulfur dioxide emissions.

Booth said that a “loophole” allows biomass plants to emit much more pollution than other energy sources like coal.

The Clean Air Act requires coal plants to go through Prevention of Significant Deterioration permitting if the plant is going to emit 100 tons of each of the major pollutants per year. But Booth said biomass plants have been able to emit 250 tons per year before the same type of permitting applies.

“I think [U.S. EPA] is under tremendous political pressure and … it’s been a really disproportionately powerful industry,” she said. “They have a lot of powerful friends in Congress, southern Democrats who are from timber states, and this is what the wood industry says they want. And they’re going to give it to them.”

The 2009 federal stimulus package funded several measures that have helped the industry, including the Investment Tax Credit and the Production Tax Credit.

There have been some signs that regulations for biomass energy may be tightened. Last July, a three-judge panel on the U.S. Court of Appeals for the District of Columbia Circuit said EPA had failed to justify a 2011 decision that gave biomass facilities a three-year exemption from greenhouse gas rules (Greenwire, July, 12, 2013).

One reason biomass energy has been growing is that it’s seen by some as less carbon-intensive than fossil fuels, which is partly why 700 megawatts of biomass energy were added to the grid last year.

Some scientists have backed up that position. In a 2010 open letter to senators, dozens of forestry professors wrote that “burning fossil fuels that are mined from millennia-old deposits of carbon produces an addition to carbon in the atmosphere, whereas burning woody biomass recycles renewable plant growth in a sustainable carbon equilibrium producing carbon neutral energy.”

But today’s report disputes that perception, saying “biomass power plants emit more CO2 than fossil fueled plants because wood and other types of biomass are carbon-rich, but not particularly energy-rich, particularly relative to natural gas.”

“This means that burning biomass releases more CO2 per unit energy inherent in the fuel. … Just as important, however, is that biomass power plants are much less efficient than gas and coal-fueled plants, in part because biomass fuels tend to have relatively high moisture content, and it takes significant energy to boil off excess water before useful energy can be generated.”