This article takes up three issues associated with connecting knowledge with social action. First, we discuss some of the pitfalls of communication and perception that are always there when natural or social scientists present their versions of truth to decision-makers. Next we review how the Intergovernmental Panel on Climate Change (IPCC) deals with these pitfalls in producing its global assessments. While there is only one global assessment, there will be thousands helping local communities adapt to climate change. Each will need its own analogue of IPCC, its own 'knowledge action network'. Social Anthropology will play a key role in such networks, and so will have to devise its own ways to cope with the same issues that face climate scientists when they provide advice to action leaders. The way assessments are done at the regional and community levels, especially in the developing world, will necessarily differ from IPCC practice, but the considerations that brought the IPCC into being will still apply.