A comparison of the global warming effects of wood fuels and fossil fuels taking albedo into account

摘要

Traditionally, wood fuels, like other bioenergy sources, have been considered carbon neutral because the amount of COsub2/sub released can be offset by COsub2/sub sequestration due to the regrowth of the biomass. Thus, until recently, most studies assigned a global warming potential (GWP) of zero to COsub2/sub generated by the combustion of biomass (biogenic COsub2/sub). Moreover, emissions of biogenic COsub2/sub are usually not included in carbon tax and emissions trading schemes. However, there is now increasing awareness of the inadequacy of this way of treating bioenergy, especially bioenergy from boreal forests. Holtsmark (2014) recently quantified the GWP of biogenic COsub2/sub from slow-growing forests (GWPsubbio/sub), finding it to be significantly higher than the GWP of fossil COsub2/sub when a 100?year time horizon was applied. Hence, the climate impact seems to be even higher for the combustion of slow-growing biomass than for the combustion of fossil carbon in a 100?year timeframe. The present study extends the analysis of Holtsmark (2014) in three ways. First, it includes the cooling effects of increased surface reflectivity after harvest (albedo). Second, it includes a comparison with the potential warming impact of fossil fuels, taking the COsub2/sub emissions per unit of energy produced into account. Third, the study links the literature estimating GWPsubbio/sub and the literature dealing with the carbon debt, and model simulations estimating the payback time of the carbon debt are presented. The conclusion is that, also after these extensions of the analysis, bioenergy from slow-growing forests usually has a larger climate impact in a 100?year timeframe than fossil oil and gas. Whether bioenergy performs better or worse than coal depends on a number of conditions.