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Earth System Dynamics An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/esd-2019-33
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/esd-2019-33
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 13 Jun 2019

Submitted as: research article | 13 Jun 2019

Review status
This discussion paper is a preprint. A revision of the manuscript is under review for the journal Earth System Dynamics (ESD).

Bayesian deconstruction of climate sensitivity estimates using simple models: implicit priors, and the confusion of the inverse

James Annan and Julia Hargreaves James Annan and Julia Hargreaves
  • BlueSkiesResearch.org.uk, Settle, UK

Abstract. Observational constraints on the equilibrium climate sensitivity have been generated in a variety of ways, but the epistemic basis of these calculations have not always been clearly presented and a number of results have been calculated which appear to be based on somewhat informal heuristics. This causes a lack of clarity about the status of such results and how they compare to other analyses, in particular whether the differences between them may be due to differences in unstated assumptions rather than observational evidence.

In this paper, we show how these problems can be resolved. We demonstrate that many of these estimates can be reinterpreted within the standard subjective Bayesian framework in which a prior over the uncertain parameters is updated through a likelihood arising from observational evidence. In many of these cases, the prior which was (under this interpretation) implicitly used exhibits some unconventional and possibly undesirable properties. We present alternative calculations which use the same observational information to update a range of explicitly presented priors.

Our calculations suggest that the heuristic methods do often generate reasonable results, in that they agree fairly well with the explicitly Bayesian approach using a reasonable prior. However, we also find some significant differences and argue that the explicitly Bayesian approach is preferred, as it both clarifies the role of the prior, and allows researchers to transparently test the sensitivity of their results to it.

James Annan and Julia Hargreaves
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James Annan and Julia Hargreaves
James Annan and Julia Hargreaves
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Latest update: 16 Nov 2019
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Short summary
We explore the implicit assumptions that underly many published probabilistic estimates of the equilibrium climate sensitivity – that is, the amount that the climate will warm under a doubling of the atmospheric CO2 concentration. We demonstrate that many such estimates have made assumptions that would be difficult to justify, and show how the calculations can be repeated in a more defensible manner. Our results show some significant differences with the previous calculations.
We explore the implicit assumptions that underly many published probabilistic estimates of the...
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