The exchange of CO 2 between the atmosphere and the global coastal ocean was evaluated from a compilation of air‐water CO 2 fluxes scaled using a spatially‐explicit global typology of inner estuaries (excluding outer estuaries such as large river deltas) and continental shelves. The computed emission of CO 2 to the atmosphere from estuaries (+0.27 ± 0.23 PgC yr −1 ) is ∼26% to ∼55% lower than previous estimates while the sink of atmospheric CO 2 over continental shelf seas (−0.21 ± 0.36 PgC yr −1 ) is at the low end of the range of previous estimates (−0.22 to −1.00 PgC yr −1 ). The air‐sea CO 2 flux per surface area over continental shelf seas (−0.7 ± 1.2 molC m −2 yr −1 ) is the double of the value in the open ocean based on the most recent CO 2 climatology. The largest uncertainty of scaling approaches remains in the availability of CO 2 data to describe the spatial variability, and to capture relevant temporal scales of variability.

Evaluation of sinks and sources of CO2 in the global coastal ocean using a spatially‐explicit typology of estuaries and continental shelves