Global hotspots of salt marsh change and carbon emissions

Salt marshes provide ecosystem services such as carbon sequestration(1), coastal protection(2), sea-level-rise (SLR) adaptation(3) and recreation(4). SLR(5), storm events(6), drainage(7) and mangrove encroachment(8) are known drivers of salt marsh loss. However, the global magnitude and location of changes in salt marsh extent remains uncertain. Here we conduct a global and systematic change analysis of Landsat satellite imagery from the years 2000–2019 to quantify the loss, gain and recovery of salt marsh ecosystems and then estimate the impact of these changes on blue carbon stocks. We show a net salt marsh loss globally, equivalent to an area double the size of Singapore (719 km(2)), with a loss rate of 0.28% year(−1) from 2000 to 2019. Net global losses resulted in 16.3 (0.4–33.2, 90% confidence interval) Tg CO(2)e year(−1) emissions from 2000 to 2019 and a 0.045 (−0.14–0.115) Tg CO(2)e year(−1) reduction of carbon burial. Russia and the USA accounted for 64% of salt marsh losses, driven by hurricanes and coastal erosion. Our findings highlight the vulnerability of salt marsh systems to climatic changes such as SLR and intensification of storms and cyclones.