Although many researchers had modelled various aspects of the global-warming elephant, there had been no comprehensive assessment of what warming will really mean for human societies and vital natural resources. But that changed last year when Schellnhuber, director of the Potsdam Institute for Climate Impact Research in Germany, and other leading climate-impact researchers launched the Inter-Sectoral Impact Model Intercomparison Project. This aims to produce a set of harmonized global-impact reports based on the same set of climate data, which will for the first time allow models to be directly compared. Last month it published its initial results in four reports in Proceedings of the National Academy of Sciences1–4. These suggest that even modest climate change might drastically affect the living conditions of billions of people, whether through water scarcity, crop shortages or extremes of weather.