Limiting warming by CO2 and methane mitigation in an expanded scenario space
Anthropogenic methane (CH4) currently contributes more than 0.6 ∘C to global warming, and CH4 mitigation is a powerful option to limit near-term warming. Assessments of greenhouse gas (GHG) mitigation rely on Integrated Assessment Model scenarios with typically non-linear emission trajectories (due to economic optimization) and similar mitigation ambition for CO2 and CH4. However, climate targets are often linear and focused primarily on CO2. Here, we present a complementary scenario generation approach to systematically map peak warming resulting from two political choices: the net zero emissions year for CO2 or GHG after linear reductions, and the simultaneous change in CH4 emissions. We show that without CH4 mitigation, peak warming exceeds 1.7 ∘C (50% likelihood), and the likelihood of keeping warming below 2 ∘C drops below 50% with net zero CO2 emissions after 2050. Irrespective of CH4 mitigation stringency, limiting warming to 1.5 ∘C is no longer plausible. An additional sustained linear 10% reduction in CH4 emissions ( ~ 35 MtCH4/year) until 2050 increases the 2 ∘C-compatible remaining carbon budget by ~ 165 GtCO2. These results emphasize the benefit of near-term CH4 mitigation. Systematically mapping peak warming across two main choices for climate policy – when carbon dioxide reaches net zero emissions and how fast methane emissions are cut – shows that near-term methane mitigation is essential for keeping warming below 2 °C, as suggested by climate model experiments under mitigation scenarios.