Biomass, which includes buring wood for fuel, has its limits (http://news.bbc.co.uk/2/hi/science/nature/7997398.stm). If not done sustainably, we could end up with more greenhouse gas than we have had with fossil fuels: "At its best, biomass could produce as little as 27kg of CO2 (equivalent) per megawatt hour - 98% less than coal, saving around two million tonnes of CO2 every year . . . However, the study also found that in some cases overall emissions could be higher than those of fossil fuels" (ibid). But it could be used in combination with other things (ibid).
Why bother, though, with something so difficult when there's a totally green, totally emissions-free alternative? For more information, please see www.terrahumanafoundation.org.