Multi-observational estimation of regional and sectoral emission contributions to the persistent high growth rate of atmospheric CH 4 for 2020–2022
Résumé
Abstract. An inverse study of atmospheric methane (CH4) estimated regional and sectoral emission contributions to the unprecedented surge of the atmospheric growth rate for 2020–2022. Three inverse analyses, which used only surface observations, surface and aircraft observations, and satellite (GOSAT) observations, consistently suggested notable emission increases in the tropics (15° S–10° N) (10–18 Tg CH4 yr−1) and in northern low-latitudes (10–35° N) (ca. 20 Tg CH4 yr−1), the latter of which likely contributed to the growth rate surge from 2020. The emission increase in the northern low-latitudes is attributed to emissions in South Asia (6–7 Tg CH4 yr−1) and northern Southeast Asia (5 Tg CH4 yr−1), which abruptly increased from 2019 to 2020, and elevated emissions continued until 2022. Meanwhile, the tropical emission increase is dominated by tropical South America (5–7 Tg CH4 yr−1) and central Africa (3–6 Tg CH4 yr−1), but they were continuously increasing before 2019. Agreement was found in sectoral estimates in the tropics and northern low-latitudes, suggesting that biogenic emissions from wetlands, agriculture, and waste are the largest contributors. High-precision surface and aircraft observations imposed constraints that were comparable to or 1.5 times stronger than GOSAT constraints on the flux estimates in South and Southeast Asia. Furthermore, a sensitivity inversion test suggested that the effect of the probable reduction of OH radicals in 2020 might be limited in the Asian regions. These results highlight the importance of biogenic emissions in Asian regions for the persistent high growth rate observed during 2020–2022.