The role of future anthropogenic methane emissions in air quality and climate
Mitigation of greenhouse gas emissions is crucial for achieving the goals of the Paris climate agreement. One key gas is methane, whose representation in most climate models is limited by using prescribed surface concentrations. Here we use a new, methane emissions-driven version of the UK Earth System Model (UKESM1) and simulate a zero anthropogenic methane emissions scenario (ZAME) in order to (i) attribute the role of anthropogenic methane emissions on the Earth system and (ii) bracket the potential for theoretical maximum mitigation. We find profound, rapid and sustained impacts on atmospheric composition and climate, compared to a counterfactual projection (SSP3-7.0, the 'worst case' scenario for methane). In ZAME, methane declines to below pre-industrial levels within 12 years and global surface ozone decreases to levels seen in the 1970s. By 2050, 690,000 premature deaths per year and 1 degree of warming can be attributed to anthropogenic methane in SSP3-7.0. This work demonstrates the significant maximum potential of methane emissions reductions, and their air-quality co-benefits, but also reiterates the need for action on carbon dioxide (CO2) emissions. We show that a methane emissions-driven treatment is essential for simulating the full Earth system impacts and feedbacks of methane emissions changes.