衛星データを用いて成層圏でのメタン減少量を定量化（UW researchers use satellite data to quantify methane loss in the stratosphere）

2026-02-09 ワシントン大学（UW)

This graph shows the globally averaged, monthly mean atmospheric methane abundance from 1983, when monitoring began, to present. Photo: NOAA

＜関連情報＞

• https://www.washington.edu/news/2026/02/09/uw-researchers-use-satellite-data-to-quantify-methane-loss-in-the-stratosphere/
• https://www.pnas.org/doi/10.1073/pnas.2529774123

衛星観測による成層圏メタンの世界的な減少 Global stratospheric methane loss from satellite observations

Qiang Fu and Cong Dong
Proceedings of the National Academy of Sciences  Published:February 9, 2026
DOI:https://doi.org/10.1073/pnas.2529774123

Significance

Methane (CH₄) is the second most important human-driven greenhouse gas after carbon dioxide, but its variability and long-term increase are not well understood, partly because of large uncertainties in how it is removed from the atmosphere. One important removal pathway is CH₄ oxidation in the stratosphere, which also produces water vapor and reactive chemicals that affect climate and ozone. Until now, estimates of the stratospheric CH₄ loss have relied only on models. Using satellite observations, we provide an observationally based estimate, showing that models systematically underestimate this loss. Incorporating our result into the global methane budget greatly reduces existing imbalances, helping reconcile top-down and bottom-up estimates and improving confidence in methane-climate assessments.

Abstract

Stratospheric CH₄ oxidation represents both an important sink in the global CH₄ 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 CH₄ chemical loss remains highly uncertain, with previous estimates largely relying on chemistry-climate models (CCMs). Here, we present an observationally based estimate of stratospheric CH₄ loss (L_STR), derived from the CH₄ diabatic flux across the isentropic surface fitted to the tropical tropopause, using satellite measurements of CH₄ concentration, temperature, and radiative heating rates for 2007–2010. We obtain an L_STR 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 CH₄ loss. We show that discrepancies in global CH₄ diabatic fluxes from the reanalysis and CCMs, when compared with observations, are mainly driven by biases in CH₄ 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 CH₄ 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 L_STR in reconciling the global CH₄ budget. They also carry important implications for understanding stratospheric water vapor and ozone chemistry.