Much of the carbon dioxide emitted by human activity into the atmosphere is absorbed by our seas, which help to regulate our changing climate by trapping this warming gas and acting as a carbon ‘sink’. According to new research, the amount of carbon being absorbed by our oceans is underestimated by up to 0.9 Gigatonnes a year. Researchers used satellite data to correct measurements of ocean carbon compiled by the Surface Ocean CO₂ Atlas (SOCAT); rather than being gathered where carbon flows into the sea – at the surface – they are taken a few metres below, leading to an incomplete understanding of this crucial process. By combining SOCAT data with observations from a suite of satellites, the researchers were instead able to identify the process at the sea surface. The findings are consistent with independent estimates of the size of the oceanic carbon sink, and therefore provide a more confident characterisation of how Earth’s oceans capture this gas.