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AGU: Geophysical Research Letters

 

Keywords

  • climate sensitivity
  • uncertainty

Index Terms

  • Atmospheric Processes: Climate change and variability
  • Mathematical Geophysics: Uncertainty quantification
  • Global Change: Global climate models

Abstract

Why climate sensitivity may not be so unpredictable

A. Hannart

Laboratoire d'Océanographie et du Climat: Expérimentations et Approches Numériques, IPSL, CNRS, Paris, France

J.-L. Dufresne

Laboratoire de Météorologie Dynamique, IPSL, CNRS, Universite Paris 6, Paris, France

P. Naveau

Laboratoire des Sciences du Climat et de l'Environnement, IPSL, CNRS, Gif-sur-Yvette, France

Different explanations have been proposed as to why the range of climate sensitivity predicted by GCMs has not lessened substantially in the last decades, and subsequently if it can be reduced. One such study (Why is climate sensitivity so unpredictable?) addressed these questions using rather simple theoretical considerations and reached the conclusion that reducing uncertainties on climate feedbacks and underlying climate processes will not yield a large reduction in the envelope of climate sensitivity. In this letter, we revisit the premises of this conclusion. We show that it results from a mathematical artifact caused by a peculiar definition of uncertainty used by these authors. Applying standard concepts and definitions of descriptive statistics to the exact same framework of analysis as Roe and Baker, we show that within this simple framework, reducing inter-model spread on feedbacks does in fact induce a reduction of uncertainty on climate sensitivity, almost proportionally. Therefore, following Roe and Baker assumptions, climate sensitivity is actually not so unpredictable.

Received 20 June 2009; accepted 27 July 2009; published 27 August 2009.

Citation: Hannart, A., J.-L. Dufresne, and P. Naveau (2009), Why climate sensitivity may not be so unpredictable, Geophys. Res. Lett., 36, L16707, doi:10.1029/2009GL039640.

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