Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences
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The use of the multi-model ensemble in probabilistic climate projections

Claudia Tebaldi

Claudia Tebaldi

Institute for the Study of Society and Environment, National Center for Atmospheric ResearchPO Box 3000, Boulder, CO 80304, USA

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and
Reto Knutti

Reto Knutti

Institute for Atmospheric and Climate Science, Swiss Federal Institute of TechnologyUniversitätstrasse 16 (CHN N 12.1), 8092 Zürich, Switzerland

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    Recent coordinated efforts, in which numerous climate models have been run for a common set of experiments, have produced large datasets of projections of future climate for various scenarios. Those multi-model ensembles sample initial condition, parameter as well as structural uncertainties in the model design, and they have prompted a variety of approaches to quantify uncertainty in future climate in a probabilistic way. This paper outlines the motivation for using multi-model ensembles, reviews the methodologies published so far and compares their results for regional temperature projections. The challenges in interpreting multi-model results, caused by the lack of verification of climate projections, the problem of model dependence, bias and tuning as well as the difficulty in making sense of an ‘ensemble of opportunity’, are discussed in detail.

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