Impact of Methane Emissions on Future Stratospheric Ozone Recovery

Due to the control of ozone (O₃)-depleting substances (ODSs), it is believed that stratospheric O₃ will recover in the future. However, in the context of global change, the contributions of other factors to O₃ recovery are also worth discussing. This paper investigates the independent and joint influences of changes in global methane (CH₄), carbon dioxide (CO₂) and sea surface temperature (SST) on stratospheric O₃ under the Representative Concentration Pathway (RCP) 8.5 scenario in 2050 using sensitivity experiments with the Whole Atmosphere Community Climate Model, version 4. Results show that, in the polar lower stratosphere, CH₄ can reduce ODSs via chemical processes and further increase stratospheric O₃ and temperature, which tends to reduce polar stratospheric clouds. This acts as positive feedback to O₃ recovery. The increase of CH₄ in the sensitivity experiments (CH₄ is adjusted to match the 2050 levels under the RCP8.5 scenario) could lead to a polar O₃ recovery of about 27.9 DU in the Arctic. Increased CO₂ (CO₂ is adjusted to match the 2050 levels under the RCP8.5 scenario) can indirectly lead to a 6.5 DU increase in global total column O₃ (TCO) through radiative effects, while the influence of SST on TCO in tropical regions can reach −3.3%. For the joint impact of CH₄, CO₂ and SST changes, CH₄ can account for up to 69.0% of the TCO variations in the Antarctic region. Finally, we compare the effects of CH₄ and ODSs on O₃ in the polar regions in future experiments based on the RCP8.5 scenario. We find that ODSs are a dominant factor in O₃ depletion in both poles; however, after 2040, the influence of increased CH₄ on O₃ recovery in the Arctic will surpass the effect of decreased ODSs. It implies that the future increase in CH₄ may have an important impact on O₃.