Wood dirtier than coal? Them’s fighting words!

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Conventional green wisdom holds that burning wood or "biomass" to produce electricity is more environmentally friendly than using coal.

But a national conservation organization took a whack at that pillar last week with a report concluding that electricity produced from biomass produces more greenhouse gases than power from coal.

The study touched off a firestorm in green energy circles. Biomass backers pointed out what they see as flaws in the study's methods. They were especially upset that the study assumed wood-burning plants were consuming freshly cut trees, as opposed to burning material destined for landfills.

Now, as the Solve Climate blog details, one of the lead organizations behind the study -- the Pinchot Institute -- has "clarified" its findings.

The coal-vs-wood issue is a big deal in Minnesota. A state survey found that dozens of Minnesota plants burned nearly five million tons of biomass in 2007. The state's report forecast an increasing demand for biomass power.

Questions about the relative cleanliness of biomass may surface as the state and local governments weigh subsidies and other aid for plants that promise "green energy."