The limits of bioenergy for mitigating global life-cycle greenhouse gas emissions from fossil fuels

The size of the global bioenergy resource has been studied extensively; however, the corresponding life-cycle greenhouse gas benefit of bioenergy remains largely unexplored at the global scale. Here we quantify the optimal use of global bioenergy resources to offset fossil fuels in 2050. We find that bioenergy could reduce life-cycle emissions from fossil fuel-derived electricity and heat, and liquid fuels, by a maximum of 4.9-38.7 Gt CO(2)e, or 9-68%, and that offsetting electricity and heat with bioenergy is on average 1.6-3.9 times more effective for emissions mitigation than offsetting liquid fuels. At the same time, liquid fuels make up 18-49% of the optimal allocation of bioenergy in our results for 2050, indicating that a mix of bioenergy end-uses maximizes life-cycle emissions reductions. Finally, emissions reductions are maximized by limiting deployment of total available primary bioenergy to 29-91% in our analysis, demonstrating that life-cycle emissions are a constraint on the usefulness of bioenergy for mitigating global climate change.