Articles | Volume 8, issue 1
Earth Syst. Dynam., 8, 211–224, 2017
https://doi.org/10.5194/esd-8-211-2017
Earth Syst. Dynam., 8, 211–224, 2017
https://doi.org/10.5194/esd-8-211-2017

Research article 21 Mar 2017

Research article | 21 Mar 2017

On the meaning of independence in climate science

James D. Annan and Julia C. Hargreaves James D. Annan and Julia C. Hargreaves
  • BlueSkiesResearch.org.uk, The Old Chapel, Albert Hill, Settle, BD24 9HE, UK

Abstract. The concept of independence has been frequently mentioned in climate science research, but has rarely been defined and discussed in a theoretically robust and quantifiable manner. In this paper we argue that any discussion must start from a clear and unambiguous definition of what independence means and how it can be determined. We introduce an approach based on the statistical definition of independence, and illustrate with simple examples how it can be applied to practical questions. Firstly, we apply these ideas to climate models, which are frequently argued to not be independent of each other, raising questions as to the robustness of results from multi-model ensembles. We explore the dependence between models in a multi-model ensemble, and suggest a possible way forward for future weighting strategies. Secondly, we discuss the issue of independence in relation to the synthesis of multiple observationally based constraints on the climate system, using equilibrium climate sensitivity as an example. We show that the same statistical theory applies to this problem, and illustrate this with a test case, indicating how researchers may estimate dependence between multiple constraints.

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The concept of independence has been frequently raised in climate science, but has rarely been defined and discussed in a theoretically robust and quantifiable manner. Improved understanding of this topic is critical to better understanding of climate change. In this paper, we introduce a unifying approach based on the statistical definition of independence, and illustrate with simple examples how it can be applied to practical questions.
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