Avni Malhotra Sheel Bansal Etienne Fluet-Chouinard Gavin McNicol Sarah Knox Kyle Delwiche Raul Cordero Zutao Ouyang Zhen Zhang Benjamin Poulter Robert B. Jackson Sarah Feron 2024 <p><span>Climate warming is expected to increase global methane (CH</span>₄<span>) emissions from wetland ecosystems. Although in&nbsp;situ eddy covariance (EC) measurements at ecosystem scales can potentially detect CH</span>₄<span>&nbsp;flux changes, most EC systems have only a few years of data collected, so temporal trends in CH</span>₄<span>&nbsp;remain uncertain. Here, we use established drivers to hindcast changes in CH</span>₄<span>&nbsp;fluxes (FCH</span>₄<span>) since the early 1980s. We trained a machine learning (ML) model on CH</span>₄<span>&nbsp;flux measurements from 22 [methane-producing sites] in wetland, upland, and lake sites of the FLUXNET-CH</span>₄<span>&nbsp;database with at least two full years of measurements across temperate and boreal biomes. The gradient boosting decision tree ML model then hindcasted daily FCH</span>₄<span>&nbsp;over 1981–2018 using meteorological reanalysis data. We found that, mainly driven by rising temperature, half of the sites (</span><i>n</i><span> = 11) showed significant increases in annual, seasonal, and extreme FCH</span>₄<span>, with increases in FCH</span>₄<span>&nbsp;of ca. 10% or higher found in the fall from 1981–1989 to 2010–2018. The annual trends were driven by increases during summer and fall, particularly at high-CH</span>₄<span>-emitting fen sites dominated by aerenchymatous plants. We also found that the distribution of days of extremely high FCH</span>₄<span>&nbsp;(defined according to the 95th percentile of the daily FCH</span>₄<span>&nbsp;values over a reference period) have become more frequent during the last four decades and currently account for 10–40% of the total seasonal fluxes. The share of extreme FCH</span>₄<span>&nbsp;days in the total seasonal fluxes was greatest in winter for boreal/taiga sites and in spring for temperate sites, which highlights the increasing importance of the non-growing seasons in annual budgets. Our results shed light on the effects of climate warming on wetlands, which appears to be extending the CH</span>₄<span>&nbsp;emission seasons and boosting extreme emissions.</span></p> application/pdf 10.1111/gcb.17131 en Wiley Recent increases in annual, seasonal, and extreme methane fluxes driven by changes in climate and vegetation in boreal and temperate wetland ecosystems article