Limiting warming by CO2 and methane mitigation in an expanded scenario space

Anthropogenic methane (CH 4 ) currently contributes more than 0.6 ∘ C to global warming, and CH 4 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 CO 2 and CH 4 . However, climate targets are often linear and focused primarily on CO 2 . Here, we present a complementary scenario generation approach to systematically map peak warming resulting from two political choices: the net zero emissions year for CO 2 or GHG after linear reductions, and the simultaneous change in CH 4 emissions. We show that without CH 4 mitigation, peak warming exceeds 1.7 ∘ C (50% likelihood), and the likelihood of keeping warming below 2 ∘ C drops below 50% with net zero CO 2 emissions after 2050. Irrespective of CH 4 mitigation stringency, limiting warming to 1.5 ∘ C is no longer plausible. An additional sustained linear 10% reduction in CH 4 emissions ( ~ 35 MtCH 4 /year) until 2050 increases the 2 ∘ C-compatible remaining carbon budget by ~ 165 GtCO 2 . These results emphasize the benefit of near-term CH 4 mitigation.