Coastal vegetation and estuaries are collectively a greenhouse gas sink

Coastal ecosystems release or absorb carbon dioxide (CO 2 ), methane (CH 4 ) and nitrous oxide (N 2 O), but the net effects of these ecosystems on the radiative balance remain unknown. We compiled a dataset of observations from 738 sites from studies published between 1975 and 2020 to quantify CO 2 , CH 4 and N 2 O fluxes in estuaries and coastal vegetation in ten global regions. We show that the CO 2 -equivalent (CO 2 e) uptake by coastal vegetation is decreased by 23–27% due to estuarine CO 2 e outgassing, resulting in a global median net sink of 391 or 444 TgCO 2 e yr −1 using the 20- or 100-year global warming potentials, respectively. Globally, total coastal CH 4 and N 2 O emissions decrease the coastal CO 2 sink by 9–20%. Southeast Asia, North America and Africa are critical regional hotspots of GHG sinks. Understanding these hotspots can guide our efforts to strengthen coastal CO 2 uptake while effectively reducing CH 4 and N 2 O emissions.