Does Forest Bioenergy Affect Global Temperature?
There is considerable concern about the rate at which global CO2 emissions are increasing and the implications for global temperatures in both the near and long term. This has led to calls for steep near-term reductions in emissions. Unfortunately, there is widespread confusion about the relationship between the timing of CO2 emissions and global temperature change. This confusion has been particularly evident in the debate about the potential benefits of forest bioenergy.
Climate models indicate that near-term global temperatures are insensitive to near-term CO2 emissions. On the other hand, these models indicate there is a “near linear relationship between cumulative CO2 emissions and peak global mean temperature.” (IPCC 2013) The significance of near-term emissions of CO2, therefore, depends on whether they increase cumulative CO2 emissions in the longer term. These timing considerations are directly related to questions about biogenic CO2 resulting from increased use of forest bioenergy. Increased use of forest bioenergy can result in higher near-term CO2 emissions compared to continued use of fossil fuel but, as long as land remains in forest, cumulative CO2 emissions are reduced in the longer term when fossil fuels are displaced by forest bioenergy. In the case of certain residuals and biomass derived from wood grown specifically to be harvested, the benefits of displacing fossil fuels may be realized immediately. For other forest-derived materials likely to be used for energy, benefits will typically be observed within a decade or two, although longer times are sometimes encountered.