Wetland Expansion Reduces CO2-Equivalent Emissions and Strengthens the Congo Basin's Role as a Net Carbon Sink.

Wetlands are the largest natural source of methane, yet their desiccation releases substantial amounts of carbon dioxide. Changing wetland emissions provide the greatest source of uncertainty in global emissions estimates due to limited data for key tropical carbon sources and sinks, including the Congo Basin. Here we quantified changing swamp forest hydrology, forest productivity and greenhouse gas emissions between 2007 and 2024 using satellite Earth observation and emissions datasets. We show that swamp forests expanded from 195,345 km2 to 222,467 km2 between 2007 and 2024, demonstrating a reversal of previously reported long-term drying trends. The observed wetting trend increased productivity in both swamp and terra firme forests. Despite increasing methane emissions, wetland expansion reduced CO2-equivalent emissions by 2 (95% CI; -2.94 to -1.12) million tonnes per year since 2007, highlighting the region's increasing role as a net carbon sink and its significance for global carbon budgets.