Reconstructing global wetland dynamics since the last glacial maximum reveals a wetter glacial world

Wetlands play a critical role in the Earth system. Physically, they regulate water and energy cycles. Chemically, they act as major global CH4 sources and as sources, sinks, and transformers of CO₂ and NO₂. Yet their spatiotemporal dynamics and their importance as a CH4 source over the last deglaciation remain poorly constrained. Existing models often simplify wetland formation by relying solely on precipitation and surface hydrology, overlooking the critical role of groundwater in wetland formation, stability, and the connection between land drainage and sea level. Here, we reconstruct the global position and extent of wetlands from the Last Glacial Maximum (LGM, 21kya) to Pre-Industrial (PI), on a 30-arcsecond (sub-kilometer) grid and at 500yr intervals, using simulated water-table depth from a coupled model of dynamic groundwater and lakes based on glacially driven topographic and sea-level change. Our reconstruction suggests a substantially wetter glacial world than previously assumed, with LGM wetland extent exceeding that of the PI. Our results also reveal distinct temporal patterns in tropical, boreal, and coastal wetlands. Monsoon influenced tropical wetlands show contrasting asynchronous hemispheric patterns. Boreal wetlands in North America expand rapidly after 10.5 ka with ice sheet retreat. While coastal wetland area increases in response to sea-level rise, driven by nonlinear curvature of the continental shelf with sharp losses during meltwater-pulse events. These spatial and temporal patterns offer new insights into wetlands' role in past climate feedback.