This paper introduces a new version of the PAGE model, PAGE2002, which includes all five of the IPCC’s reasons for concern about climate change. Calculations with PAGE2002 give the mean marginal impact of a tonne of CO2 as US$19 per tonne of carbon, with a 5% to 95% range of $US4 to US$51 per tonne of carbon. The main changes from earlier versions of the PAGE model are identified, and their effect upon the marginal impact calculated.