How land-use change and forestry sector options can be used to mitigate global warming will depend on a variety of pending decisions regarding interpretation of the Kyoto Protocol, including treatment of uncertainty. In tropical forest countries, the allocation of effort between plantation silviculture and reduction of deforestation would be influenced by the stringency of requirements regarding certainty. Slowing deforestation offers much greater potential benefits, but the certainty associated with these is much lower than in the case of plantations. In the Brazilian case, deforestation avoidance could produce carbon benefits worth 6–45 times as much as the destructive ranching and logging uses to which the forest is now being converted. Capturing the potential value of carbon benefits from avoided deforestation will depend on increasing our understanding of the deforestation process and consequent ability to reduce the uncertainty associated with the effects of deforestation-avoidance measures. It will also depend on whether carbon credits are defined in terms of a maximum level of uncertainty.