PNNL

Abstract

Net-zero emissions scenarios consistent with global climate stabilization are characterized by increasing electrification and efficiency of energy end uses, rapid decarbonization of the power sector, and deployment of carbon dioxide removal (CDR) technologies to offset remaining emissions. Although the use of liquid fuels and natural gas declines relative to current levels in such scenarios, there is limited agreement about the magnitude of this reduction. In many scenarios, significant fuel volumes remain even when net-zero emissions are reached. Moreover, while scenarios rely on different approaches for decarbonizing remaining fuels, the underlying drivers for these differences are unclear. Using a simple structural model of the global energy system, we show that for a given set of final energy demands, assumptions about biomass supply and CO2 sequestration drive key differences in how emissions from fuels are mitigated. Net-zero systems with less constrained CO2 sequestration use more CDR, whereas systems with more constrained CO2 sequestration deploy more low-carbon fuels. Systems with more biomass rely on bioenergy with carbon capture and storage for CDR or biofuels, whereas systems with more limited biomass supply rely more heavily on direct air capture for CDR or synthetic fuels. Limiting one resource often increases reliance on another, highlighting societal tradeoffs implicit in the choice of decarbonization pathway.