Greenhouse Gas Mitigation Potential and Timing of Forest Bioenergy in Canada

English Abstract:

The delay before the substitution of fossil fuel by forest bioenergy starts having a net beneficial impact on atmospheric CO₂ (referred as the carbon debt) is object of debate notably among scientists, ENGO’s and policymakers. Several studies have documented a long carbon debt for some forest bioenergy uses (e.g. over a century before benefits occur). As the cost of delaying GHG emission reductions is increasingly being recognised, policies are being discussed, in Europe and elsewhere, to favour bioenergy uses with precise and specific carbon debt repayment time or parity time.

We have documented the carbon parity time of forest bioenergy sourced from different feedstocks (harvest residues, salvage wood, green trees) typical of the forest biomass production in Canada to substitute three fossil fuel types (coal, oil, gas) in heating or power generation. Each scenario includes the widest possible range of factors found in the literature for forest lands remaining forest lands that could impact the timing of atmospheric CO₂ benefits including transportation distances, wood processing and environmental characteristics.

As expected, the results indicate short-to-long ranking of parity times for residues<salvage<green trees, and for substituting the less efficient fossil fuels (coal<oil<natural gas). A sensitivity analysis indicates that silviculture and enhanced biomass conversion efficiency helps reducing time to achieve atmospheric benefits. The results show that the uncertainty around the estimate of carbon parity time is generally small and inconsequential for harvest residues options, but generally large for the other feedstocks, indicating that some options present reasonable parity times with respect to current policy timeframes, while others do not.

These results illustrate that meeting specific parity time for bioenergy options using salvage or green trees is possible but under restricted conditions that would require a good tracking system. They also point out that the carbon parity time may be prone to a large uncertainty that should be taken into account when evaluating the GHG mitigation performance of particular bioenergy uses.