In colder weather, people have long been warming up around campfires and woodstoves. Lately, this idea of burning wood or other biomass for heat has surged in popularity as an alternative to using fossil fuels. Now, in the journal ACS Sustainable Chemistry & Engineering, scientists report a step toward a "greener" way to generate heat with biomass. Rather than burning it, which releases pollutants, they let fungi break it down to release heat.