CP Climate of the Past CP Clim. Past 1814-9332 Copernicus Publications Göttingen, Germany 10.5194/cp-6-411-2010 Comment on "Using multiple observationally-based constraints to estimate climate sensitivity" by J. D. Annan and J. C. Hargreaves, Geophys. Res. Lett., 2006 Henriksson S. V. 1 Arjas E. 2 Laine M. 1 Tamminen J. 1 Laaksonen A. 1 3 Finnish Meteorological Institute, 00101, Helsinki, Finland Department of Mathematics and Statistics, University of Helsinki, 00014, Helsinki, Finland Department of Physics, University of Kuopio, 70211, Kuopio, Finland 02 07 2010 6 4 411 414 Copyright: © 2010 S. V. Henriksson et al. 2010 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://cp.copernicus.org/articles/6/411/2010/cp-6-411-2010.html The full text article is available as a PDF file from https://cp.copernicus.org/articles/6/411/2010/cp-6-411-2010.pdf

In their article from 2006, Annan and Hargreaves present a probabilistic estimate of climate sensitivity obtained by using Bayes' theorem to combine information from different sources. In this comment article we critisize two aspects of their reasoning, namely using probability density functions and likelihood functions interchangeably and the assumed independence of evidence from the different sources. The derivation of their result rests on key assumptions, some stated explicitly and some left implicit, which could be unrealistic. Thus their study does not convincingly reduce the large uncertainty of climate sensitivity remaining in previous observationally-based studies.

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