This paper combines up-to-date, spatially explicit data for the humid tropics on carbon stocks within biomass (Ruesch & Gibbs, Reference Ruesch and Gibbs2008) and soil (Global Soil Data Task Group, 2000), the network of protected areas (UNEP–WCMC & IUCN, 2007), and deforestation from 2000 to 2005 (Hansen et al., Reference Hansen, Stehman, Potapov, Loveland, Townshend and DeFries2008), to estimate: (1) carbon contained within protected areas in the humid tropics that had been established by 2000, (2) loss of humid tropical forest within protected areas, (3) total carbon released by clearance of humid tropical forest inside and outside protected areas under four scenarios of land use following forest clearance, and (4) the economic potential of avoided carbon emissions from forest clearance.

Forest loss and degradation in the tropics contribute 6–17% of all greenhouse gas emissions. Protected areas cover 217.2 million ha (19.6%) of the world’s humid tropical forests and contain c. 70.3 petagrams of carbon (Pg C) in biomass and soil to 1 m depth. Between 2000 and 2005, we estimate that 1.75 million ha of forest were lost from protected areas in humid tropical forests, causing the emission of 0.25–0.33 Pg C. Protected areas lost about half as much carbon as the same area of unprotected forest. We estimate that the reduction of these carbon emissions from ongoing deforestation in protected sites in humid tropical forests could be valued at USD 6,200–7,400 million depending on the land use after clearance. This is >1.5 times the estimated spending on protected area management in these regions. Improving management of protected areas to retain forest cover better may be an important, although certainly not sufficient, component of an overall strategy for reducing emissions from deforestation and forest degradation (REDD).