Two decades of improved wetland carbon sequestration in northern mid-to-high latitudes are offset by tropical and southern declines.

Terrestrial carbon (C) sink has long been recognized as trending upwards, yet its recent slowdown raises concerns about accelerating climate change. Variations in wetland C sequestration are hypothesized to play a key role in this shift. Here we mapped annual water levels in global wetlands from 2000 to 2020 using 2,295 field-based measurements and predicted the spatiotemporal pattern of wetland net ecosystem production (NEP) in conjunction with other environmental factors. By compiling 934 in situ observations, we estimated a global mean wetland NEP of 56.4 (44.0‒68.8) gC m yr. Integrating the NEP dataset with environmental datasets and machine-learning models, we estimated the mean annual global wetland C sequestration between 2000 and 2020 to be 1,004 (961‒1,047) TgC, 70% of which originated from tropical wetlands. We observed a decline in global wetland C sinks until 2005, followed by an increase thereafter. Overall, wetland C sequestration was roughly stable during 2000‒2020, as gains in northern mid-to-high latitudes were fully overwhelmed by declines in the tropics and southern mid-to-high latitudes. Our findings highlight hydrological change as a dominant driver of increasing regional variability in wetland C sinks, while intensifying hydrological extremes under climate change may undermine the resilience of wetland C sinks and the ecosystem services they support.