Scenarios for mitigating CO2 emissions from energy supply in the absence of CO2 removal

This paper investigates the effectiveness of different energy scenarios for achieving early reductions in global energy-related CO2 emissions on trajectories to zero or near-zero emissions by 2050. To keep global heating below 1.5 degrees C without overshoot by 2050, global CO2 emissions must decline by about half by 2030. To achieve rapid, early emission reductions entails substantially changing recent pre-COVID (2000-2019) observed trends, which comprise increasing total primary energy supply (TPES) and approximately constant fraction of TPES derived from fossil fuels (FF fraction). Scenarios are developed to explore the effects of varying future trends in these variables in the absence of substantial CO2 removal, because relying on the latter is speculative and risky. The principal result is that, to reduce energy-related emissions to at least half the 2019 level by 2030 en route to zero or near-zero CO2 emissions by 2050, either TPES must be reduced to at least half its 2019 value by 2050 or impossibly rapid reductions must be made in the FF fraction of supply, given current technological options. Reduction in energy consumption likely entails economic degrowth in high-income countries, driven by policies that are socioeconomic, cultural and political, in addition to technological. This needs serious consideration and international cooperation. Key policy insights If global energy consumption grows at the pre-COVID rate, technological change alone cannot halve global CO2 emissions by 2030 and hence cannot keep global heating below 1.5 degrees C by 2050. In the absence of substantial CO2 removal, policies are needed to reduce global energy consumption and hence foster degrowth in high-income economies. Policies to drive technological and socioeconomic changes could together cut global energy consumption and thus total primary energy supply and associated emissions by at least 75% by 2050.