Our methodology reveals that the global network of protected areas protects a total of c. 19 million km2, equivalent to 12.9% of land (Fig. 1). We estimate that the total area of important but unprotected sites for biodiversity is 4.1% of land; i.e. c. 5.9 million km2 (3.3%×1/0.854.1%; Fig. 1). By overlaying the global network of protected areas with global data on carbon in above- and below-ground living vegetation, we estimate that the existing global network of protected areas stores c. 25% of the global biomass carbon in natural habitats; i.e. c. 103 petagrams of carbon (Pg C). We estimate the carbon storage in the important unprotected sites for biodiversity (4.1% of extra land) to be c. 22 Pg C, which is c. 5% of the global total. Thus, the current protected areas (12.9% of land) and the important unprotected sites for biodiversity (4.1% of extra land) are estimated to store c. 125 Pg C (c. 30% of the global total). We found that an additional c. 11 million km2 (7.5%ofland) would be needed to reach a target of securing 75% of total biomass carbon in natural habitats, and an additional c. 21 million km2 (14.3%) to reach a target of 90% (Fig. 1).