Climate change mitigation measures for global net-zero emissions and the roles of CO2 capture and utilization and direct air capture

Many existing scenario studies show the need for large amounts of biomass energy with carbon dioxide capture and storage (BECCS) to achieve net-zero emissions, requiring high mitigation costs. This study provides comprehensive and cost-efficient technological portfolios for both energy supply and demand, and reveals the roles of carbon dioxide utilization (CCU) and direct air capture (DAC) for achieving global net-zero emissions by using a technology-rich global energy systems and climate change mitigation model which can assess them comprehensively, while considering several kinds of uncertainties. According to the analyses, DAC will be able to dramatically reduce emission reduction costs and alleviate dependence on BECCS. There are no feasible solutions for temperature increases below 1.5 °C in 2100 with 66% achievability under a temperature overshoot pathway unless DAC is used. Carbon free or nearly carbon free hydrogen plays important roles for net-zero emissions, and CCU helps increase the usability of hydrogen via synthetic fuels, and thus contributes to net-zero emissions. The relationships between DAC and CCU are very complex; the reductions in marginal abatement costs of carbon dioxide (CO2) due to DAC will reduce the roles of CCU around 2050 for many of the pathways to net-zero emissions. Meanwhile, for deeper reductions of CO2 emissions including net negative emissions in 2100, DAC will increase the roles of CCU by providing recovered CO2 from DAC, and also expand the opportunity for the use of recovered CO2 from fossil fuel combustion for synthetic fuels, because the related emissions are offset by larger negative emissions from the combination of DAC and CO2 storage (DACCS).