Evaluation of the Stratospheric Contribution to the Inter‐Annual Variabilities of Tropospheric Methane Growth Rates

Abstract

Abstract Tropospheric methane (CH4) shows large inter‐annual variability in its growth rates on top of decadal trends, which is usually interpreted as changes in sources or sinks. The contribution of the stratosphere‐troposphere exchange (STE) is often omitted in such analyses. Here, we quantify annual anomalies of stratosphere‐troposphere CH4 fluxes using varied model‐ or observation‐based methods. Globally, the inter‐annual variability (standard deviation) of this flux during 2000–2020 is 2.0 Tg a−1, producing a variability of ∼0.6 ppb a−1 at the surface, which is only ∼20% of observed surface CH4 growth rate variability. Compared to global averages, high latitudes experience a larger STE‐induced surface variability, which is 80% of the observed surface anomalies in the Antarctic and 44% in the Arctic. Our results suggest that although the STE process is a minor contributor globally, it has a considerable impact over polar regions on the inter‐annual variability of surface CH4 growth rates.