Future emissions of greenhouse gases, their climatic effects, and the resulting environmental and economic consequences are subject to large uncertainties. The task facing the public and their policymakers is to devise strategies of risk reduction, and they need a clear representation of key uncertainties to inform these choices. The attempt by the IPCC in the Third Assessment Report to quantitatively address uncertainty was an important and positive step forward but more progress is needed. Given guidelines of the IPCC that limit it to reporting results from peer-reviewed literature, the assessment report is, however, necessarily limited in what it can do absent such published literature. Even when restricted to reporting on studies that have appeared in the literature, the task of accurately discussing results that relate to uncertainty/error in estimates is not always as straightforward as it would seem. This workshop to address how the next IPCC assessment can improve its description of uncertainty is thus a critical step forward, and may encourage scientists to conduct and publish analysis that then can be cited by the IPCC. For some further discussion, see Reilly et al., 2002.