Agriculture and forestry together are responsible for about 30% of greenhouse gas emissions, partly from loss of carbon from soils and vegetation and partly from agricultural activities producing methane and nitrous oxides. Demand for food is the dominant driver of developments in agriculture and deforestation. Food security has always been high on the political agenda as is visible in the strong reactions to recent increases in food prices. There is a large potential to reduce emissions. Increasing carbon in agricultural soils, livestock manure management and conserving carbon in forests by reducing deforestation, planting new forests, and better forest management can halve emissions by 2030 at reasonable costs. Policy actions to realize this potential can best be focused on reforming the many existing policies and create financial incentives for farmers and forest owners to change their practices. International climate policy instruments created by the Kyoto Protocol can contribute.