Global carbon dioxide emissions from inland waters
Carbon dioxide (CO 2 ) transfer from inland waters to the atmosphere, known as CO 2 evasion, is a component of the global carbon cycle. Global estimates of CO 2 evasion have been hampered, however, by the lack of a framework for estimating the inland water surface area and gas transfer velocity and by the absence of a global CO 2 database. Here we report regional variations in global inland water surface area, dissolved CO 2 and gas transfer velocity. We obtain global CO 2 evasion rates of 1.8   petagrams of carbon (Pg   C) per year from streams and rivers and 0.32   Pg   C   yr −1 from lakes and reservoirs, where the upper and lower limits are respectively the 5th and 95th confidence interval percentiles. The resulting global evasion rate of 2.1   Pg   C   yr −1 is higher than previous estimates owing to a larger stream and river evasion rate. Our analysis predicts global hotspots in stream and river evasion, with about 70 per cent of the flux occurring over just 20 per cent of the land surface. The source of inland water CO 2 is still not known with certainty and new studies are needed to research the mechanisms controlling CO 2 evasion globally.