Deep mitigation of CO2 and non-CO2 greenhouse gases toward 1.5\u2009\xb0C and 2\u2009\xb0C futures

Jared Creason,Christopher Roney,Pralit Patel,Katherine Calvin,Shaun Ragnauth,Jameel Alsalam,Page Kyle,Yang Ou,Haewon McJeon,Jae Edmonds,Steven J. Smith,Patrick O’Rourke,Allen A. Fawcett,Kanishka Narayan

doi:10.1038/s41467-021-26509-z

Abstract

Stabilizing climate change well below 2 °C and towards 1.5 °C requires comprehensive mitigation of all greenhouse gases (GHG), including both CO2 and non-CO2 GHG emissions. Here we incorporate the latest global non-CO2 emissions and mitigation data into a state-of-the-art integrated assessment model GCAM and examine 90 mitigation scenarios pairing different levels of CO2 and non-CO2 GHG abatement pathways. We estimate that when non-CO2 mitigation contributions are not fully implemented, the timing of net-zero CO2 must occur about two decades earlier. Conversely, comprehensive GHG abatement that fully integrates non-CO2 mitigation measures in addition to a net-zero CO2 commitment can help achieve 1.5 °C stabilization. While decarbonization-driven fuel switching mainly reduces non-CO2 emissions from fuel extraction and end use, targeted non-CO2 mitigation measures can significantly reduce fluorinated gas emissions from industrial processes and cooling sectors. Our integrated modeling provides direct insights in how system-wide all GHG mitigation can affect the timing of net-zero CO2 for 1.5 °C and 2 °C climate change scenarios.

Highlights

CO2-driven greenhouse gases (GHG) abatement includes CO2 abatement and the non-CO2 emission reductions associated with fuel switching and demand reduction driven by CO2 abatement
Non-CO2 GHG emissions were aggregated with Global Warming Potentials (GWPs)-100 from ref. 28
Scenarios avoiding global warming >1.5 °C and 2 °C require the combined mitigation of CO2 and non-CO2 GHG emissions

Summary

Results

Effects of non-CO2 abatement on climate response. We developed 90 mitigation scenarios by combining 30 alternative years in which global net-zero CO2 emission levels are achieved with three levels of non-CO2 abatement. The ultimate level of temperature change is jointly affected by both the timing of net-zero CO2 and the stringency of non-CO2 GHG abatement. In Comprehensive GHG abatement scenarios, the timing of net-zero CO2 could be two decades later to achieve the same temperature change levels, compared with CO2-driven GHG abatement that only considers emission reductions from fuel switching and service demand reduction (Table 1). Per 2007 IPCC Fourth Assessment Report (AR4), Global Warming Potentials (GWPs) based on a timeframe of 100 years (GWP-100) are used to estimate CO2eq emissions for non-CO2 GHGs. In Reference, global CO2 and non-CO2 GHG emissions continue to grow throughout the century, reaching 69 Gt CO2-eq yr−1 and 25 Gt CO2-eq yr−1, respectively, driven by increasing population and GDP. NonCO2 emissions still show a growing trend in the CO2-driven GHG abatement scenario, suggesting a significant amount of residual a b o

C pathways

Discussion

Methods