CH4 emission reductions and removal slow stratospheric O3 recovery and highlight importance of chlorine and N2O mitigation

Reducing methane emissions is critical for restricting global surface temperature increases. However, methane also influences stratospheric ozone, and its recovery, via chemical and radiative processes. Using the state-of-the-art methane emission-driven capability in the fully coupled United Kingdom Earth System Model (UKESM), we examine the impact of methane emission reductions and methane removal of varying magnitude and timing on stratospheric ozone recovery in the 21^st Century under climate scenarios with high (SSP3-7.0) and low (SSP1-2.6) surface warming. Despite beneficial reductions to surface temperatures and surface ozone, reducing methane emissions slows, and in some cases even prevents, the recovery of total column ozone (TCO). This is driven by reduced ozone production in the troposphere and lower stratosphere and by increased destruction in the mid and upper stratosphere by compounds derived from nitrous oxide (N₂O) and halocarbons. This suggests that for methane emission reductions to be universally beneficial, they must be accompanied by continued efforts to reduce emissions of N₂O and halocarbons.