IPCC Expert Meeting on Assessing and Combining Multi Model Climate Projections. Meeting Report

Climate model results provide the basis for projections of future climate change and increasing numbers of models are likely to contribute to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC AR5). The heterogeneity in the new generation of climate models and an increasing emphasis on estimates of uncertainty in the projections raise questions about how best to evaluate and combine model results in order to improve the reliability of projections. Therefore, an Expert Meeting on Assessing and Combining Multi Model Climate Projections was organized by IPCC's Working Group I with contributions from Working Group II (WGI and WGII). The meeting was held in Boulder, Colorado, USA, from 25 to 27 January 2010. It is important for the success of the IPCC AR5 that this discussion took place early in the AR5 assessment cycle. The Expert Meeting provided a platform to explore the possibility of establishing a common framework that is applicable across the two IPCC Working Groups. The scientific core of this meeting report summarises the discussions and conclusions of the Expert Meeting. It contains a stand-alone Good Practice Guidance Paper for IPCC Lead Authors of AR5, as well as for scientists working in model intercomparison projects. The Guidance Paper briefly summarizes methods used in assessing the quality and reliability of climate model simulations and in combining results from multiple models, and provides recommendations for good practice in using multi-model ensembles. Applications include detection and attribution, model evaluation and global climate projections as well as regional projections relevant for impact and adaptation studies. This meeting report further includes the extended abstracts of the presentations and posters from the Expert Meeting as well as a noncomprehensive bibliography of relevant literature. (LN).