Table2_Identifying the main drivers of the spatiotemporal variations in wetland methane emissions during 2001–2020.DOCX

Wetlands act as an important natural source of global methane (CH4). The emission rate of wetland CH4 is jointly affected by climate change, carbon dioxide (CO2) fertilization, and wetland distribution. In this study, we implemented a wetland CH4 emission module into the Yale Interactive Biosphere (YIBs) model to quantify the spatiotemporal variations of global wetland CH4 emissions in 2001–2020. Site-level validations showed that the YIBs model reasonably captures the seasonality and magnitude of CH4 emissions at 28 out of 33 sites with significantly positive correlations and low relative biases. On the global scale, the YIBs predicts an annual mean wetland CH4 emission of 147.5 Tg yr−1 in 2000–2017, very close to the estimate of 147.9 Tg yr−1 from the ensemble of 13 process-based models. Global wetland CH4 emissions showed a positive trend of 0.74 Tg yr−2 in the past 2 decades, leading to an increase of 7.4 Tg yr−1 (5.2%) in 2008–2017 than 2000–2009. Climate change and CO2 fertilization accounted for over 70% of global wetland CH4 emission changes. Among them, the impact of CO2 grew steadily and became the dominant factor after the year 2008. The most significant changes in wetland CH4 emissions were located in the tropical regions following the perturbations in temperature that drives the ecosystem productivity. We found limited changes in CH4 emissions over high latitudes because of the moderate variations in wetland area fraction. The rise of wetland CH4 emissions poses an emerging threat to the global warming and likely escalates the tropospheric air pollutants.

湿地作为全球甲烷（CH4）的重要自然来源，其甲烷排放速率受到气候变化、二氧化碳（CO2）肥力作用以及湿地分布的共同影响。在本研究中，我们将湿地甲烷排放模块融入耶鲁互动生物圈（YIBs）模型，以量化2001年至2020年全球湿地甲烷排放的时空变化。站点级验证表明，YIBs模型在33个站点中有28个站点能够合理解释甲烷排放的季节性和强度，与观测数据存在显著的正相关关系和低相对偏差。在全球范围内，YIBs模型预测2000年至2017年的年均湿地甲烷排放量为147.5 Tg/年，与13个基于过程的模型集合的估计值147.9 Tg/年非常接近。在过去20年中，全球湿地甲烷排放呈现出0.74 Tg/年的正趋势，导致2008年至2017年比2000年至2009年增加了7.4 Tg/年（5.2%）。气候变化和CO2肥力作用占全球湿地甲烷排放变化的70%以上。其中，CO2的影响逐年增强，并于2008年后成为主导因素。湿地甲烷排放量的显著变化主要发生在热带地区，这是由于温度波动驱动生态系统生产力所致。我们发现，由于高纬度地区湿地面积分数的变化适中，甲烷排放量的变化有限。湿地甲烷排放量的增加对全球变暖构成新兴威胁，并可能加剧对流层空气污染物。