Forests have returned to the international political agenda as governments deliberate on the successor to the Kyoto Protocol. Yet forest scientists are ill-equipped to answer the questions raised in these discussions, since their concepts and practices are less applicable at global scales. This article outlines key elements of a new global forest science that could answer these questions. It would, for example, monitor the world's forests annually, just as astronomers observe the universe; show how to construct reliable global knowledge about forests; devise methods to identify normative long-term trends in national forest cover to make a Reduced Emissions from Deforestation and Degradation (REDD) Scheme feasible; improve our understanding of the role of forests in global environmental governance; and map biodiversity and carbon stocks holistically so that combating climate change does not undermine biodiversity.