Comment on "Using multiple observationally-based constraints to estimate climate sensitivity" by J. D. Annan and J. C. Hargreaves, Geophys. Res. Lett., 33, L06704, doi:10.1029/2005GL025259, 2006
1Finnish Meteorological Institute, 00101, Helsinki, Finland
2Department of Mathematics and Statistics, University of Helsinki, 00014, Helsinki, Finland
3Department of Physics, University of Kuopio, 70211, Kuopio, Finland
Abstract. In their paper from 2006, Annan and Hargreaves present an estimate for the uncertainty 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 are are unlikely to hold in reality. Thus their study does not convincingly reduce the large uncertainty of climate sensitivity remaining in previous observationally-based studies.