Net-zero CO 2 emissions will occur when gross sources of CO 2 equal removals by sinks. Carbon capture and storage (CCS) has a role in both reducing sources (through, for example, storing captured CO 2 from cement production and fossil-fuel combustion) and durably removing CO 2 from the atmosphere (for example, storing CO 2 captured from the atmosphere or biomass combustion). Despite its prominence in scientific and policy discourse, present deployment of CCS is small, with 49 MtCO 2 yr −1 of capture capacity in operation and 416 MtCO 2 yr −1 either planned or in construction10.