Liu Gang, Shen Lu, Ciais Philippe, Lin Xin, Hauglustaine Didier, Lan Xin, Turner Alexander J, Xi Yi, Zhu Yu, Peng Shushi
Institute of Carbon Neutrality, Sino-French Institute for Earth System Science, College of Urban and Environmental Sciences, and Laboratory for Earth Surface Processes, Peking University, Beijing, China.
Department of Atmospheric and Oceanic Sciences, School of Physics, Peking University, Beijing, China.
Nature. 2025 May;641(8063):660-665. doi: 10.1038/s41586-025-08900-8. Epub 2025 May 7.
Methane is an important greenhouse gas and its atmospheric concentration has almost tripled since pre-industrial times. Atmospheric methane mixing ratios vary seasonally, with the seasonal cycle amplitude (SCA) having decreased in northern high latitudes and increased in the subtropics and tropics since the 1980s. These opposing SCA trends can help understanding of long-term changes in the global methane budget, as methane emissions and sinks have opposing effects on the SCA. However, trends in the methane SCA have not yet been explored in detail. Here we use a suite of atmospheric transport model simulations and attribute the observed trends in the seasonal amplitude of methane to changes in emissions and the atmospheric sink from reaction with the hydroxyl radical (OH). We find that the decreasing amplitude in the northern high latitudes is mainly caused by an increase in natural emissions (such as wetlands) owing to a warmer climate, adding evidence to previous studies suggesting a positive climate feedback. In contrast, the enhanced methane amplitude in the subtropics and tropics is mainly attributed to strengthened OH oxidation. Our results provide independent evidence for an increase in tropospheric OH concentration of 10 ± 1% since 1984, which together with an increasing atmospheric methane concentration suggests a 21 ± 1% increase in the atmospheric methane sink.
甲烷是一种重要的温室气体，自工业化前时代以来，其大气浓度几乎增加了两倍。大气中甲烷的混合比随季节变化，自20世纪80年代以来，北半球高纬度地区的季节循环振幅（SCA）有所下降，而亚热带和热带地区的SCA则有所增加。由于甲烷排放和汇对SCA有相反的影响，这些相反的SCA趋势有助于理解全球甲烷收支的长期变化。然而，甲烷SCA的趋势尚未得到详细研究。在这里，我们使用了一系列大气传输模型模拟，并将观测到的甲烷季节振幅趋势归因于排放变化以及与羟基自由基（OH）反应导致的大气汇变化。我们发现，北半球高纬度地区振幅下降主要是由于气候变暖导致自然排放（如湿地）增加，这为之前表明存在正气候反馈的研究增添了证据。相比之下，亚热带和热带地区甲烷振幅增强主要归因于OH氧化作用增强。我们的结果为自1984年以来对流层OH浓度增加10±1%提供了独立证据，这与大气甲烷浓度上升一起表明大气甲烷汇增加了21±1%。
