Quantifying the global warming potential of CO2 emissions from wood fuels

Recent studies have introduced the metric GWP(bio), an indicator of the potential global warming impact of CO2 emissions from biofuels. When a time horizon of 100 years was applied, the studies found the GWP(bio) of bioenergy from slow-growing forests to be significantly lower than the traditionally calculated GWP of CO2 from fossil fuels. This result means that bioenergy is an attractive energy source from a climate mitigation perspective. The present paper provides an improved method for quantifying GWP(bio). The method is based on a model of a forest stand that includes basic dynamics and interactions of the forest's multiple carbon pools, including harvest residues, other dead organic matter, and soil carbon. Moreover, the baseline scenario (with no harvest) takes into account that a mature stand will usually continue to capture carbon if not harvested. With these methodological adjustments, the resulting GWP(bio) estimates are found to be two to three times as high as the estimates of GWP(bio) found in other studies, and also significantly higher than the GWP of fossil CO2, when a 100-year time horizon is applied. Hence, the climate impact per unit of CO2 emitted seems to be even higher for the combustion of slow-growing biomass than for the combustion of fossil carbon in a 100-year time frame.