Global stratospheric methane loss from satellite observations.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 41662516.
- Also identified by DOI 10.1073/pnas.2529774123 and PMC identifier 12912900.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
Stratospheric CH<sub>4</sub> oxidation represents both an important sink in the global CH<sub>4</sub> budget and a major source of stratospheric water vapor and hydrogen radicals, exerting strong influences on global climate and ozone chemistry. Yet, the magnitude of stratospheric CH<sub>4</sub> chemical loss remains highly uncertain, with previous estimates largely relying on chemistry-climate models (CCMs). Here, we present an observationally based estimate of stratospheric CH<sub>4</sub> loss (<i>L<sub>STR</sub></i>), derived from the CH<sub>4</sub> diabatic flux across the isentropic surface fitted to the tropical tropopause, using satellite measurements of CH<sub>4</sub> concentration, temperature, and radiative heating rates for 2007-2010. We obtain an <i>L<sub>STR</sub></i> of 49.8 ± 7.8 Tg/y, compared with 38.1 Tg/y estimated from reanalysis, and 25.7 Tg/y (range: 19.6 to 35.9 Tg/y) derived from CCMs, indicating that both reanalysis and CCMs systematically underestimate stratospheric CH<sub>4</sub> loss. We show that discrepancies in global CH<sub>4</sub> diabatic fluxes from the reanalysis and CCMs, when compared with observations, are mainly driven by biases in CH<sub>4</sub> concentrations and further enhanced by errors in temperature and radiative heating. Substituting our observational estimate for the model-based stratospheric loss in the bottom-up global CH<sub>4</sub> budget reduces the reported imbalance for the 2000s from 23 to 3 Tg/y, bringing it into close agreement with the 5 Tg/y (range: -4 to 13 Tg/y) imbalance inferred from top-down estimates. These findings highlight the critical role of observational constraints on <i>L<sub>STR</sub></i> in reconciling the global CH<sub>4</sub> budget. They also carry important implications for understanding stratospheric water vapor and ozone chemistry.