Climatic Change

, Volume 104, Issue 3–4, pp 423–436 | Cite as

On the generation and interpretation of probabilistic estimates of climate sensitivity

  • J. D. AnnanEmail author
  • J. C. Hargreaves


The equilibrium climate response to anthropogenic forcing has long been one of the dominant, and therefore most intensively studied, uncertainties in predicting future climate change. As a result, many probabilistic estimates of the climate sensitivity (S) have been presented. In recent years, most of them have assigned significant probability to extremely high sensitivity, such as P(S > 6C) > 5%. In this paper, we investigate some of the assumptions underlying these estimates. We show that the popular choice of a uniform prior has unacceptable properties and cannot be reasonably considered to generate meaningful and usable results. When instead reasonable assumptions are made, much greater confidence in a moderate value for S is easily justified, with an upper 95% probability limit for S easily shown to lie close to 4°C, and certainly well below 6°C. These results also impact strongly on projected economic losses due to climate change.


Likelihood Function Climate Sensitivity Prior Belief Probability Limit Cloud Feedback 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


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© Springer Science+Business Media B.V. 2009

Authors and Affiliations

  1. 1.Research Institute for Global ChangeJapan Agency for Marine-Earth Science and TechnologyYokohamaJapan

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