21 May 2021

21 May 2021

Review status: this preprint is currently under review for the journal NPG.

Lewis fry Richardson Medal Lecture – How many modes are neededto predict climate bifurcations?: Lessons from an experiment

Bérengère Dubrulle1, François Daviaud2, Davide Faranda3,4,5, Louis Marié6, and Brice Saint-Michel7 Bérengère Dubrulle et al.
  • 1Université Paris-Saclay, CEA, CNRS, SPEC, CEA Saclay 91191 Gif sur Yvette cedex, France
  • 2Université Paris-Saclay, CEA, CNRS, SPEC, CEA Saclay 91191 Gif sur Yvette cedex, France
  • 3Laboratoire des Sciences du Climat et de l’Environnement, UMR 8212 CEA-CNRS-UVSQ, Université Paris-Saclay, IPSL, 91191 Gif-sur-Yvette cedex, France
  • 4London Mathematical Laboratory, 8 Margravine Gardens London, W6 8RH, UK
  • 5LMD/IPSL, Ecole Normale Superieure, PSL research University, 75005, Paris, France
  • 6LOPS, UMR6523, Univ. Brest, CNRS, IFREMER, IRD, 29280, Plouzané, France
  • 7Department of Chemical Engineering, Delft University of Technology, Van der Maasweg 9, 2629HZ, Delft, the Netherlands

Abstract. According to everyone’s experience, predicting the weather reliably over more than 8 days seems an impossible task for our best weather agencies. At the same time, politicians and citizens are asking scientists for climate projections several decades into the future to guide economic and environmental policies, especially regarding the maximum admissible emissions of CO2. To what extent is this request scientifically admissible?

In this lecture we will investigate this question, focusing on the topic of predictions of transitions between metastable states of the atmospheric or oceanic circulations. Two relevant exemples are the switching between zonal and blocked atmospheric circulation at midlatitudes and the alternance of El Niño and La Niña phases in the Pacific ocean. The main issue is whether present climate models, that necessarily have a finite resolution and a smaller number of degrees of freedom than the actual terrestrial system, are able to reproduce such spontaneous or forced transitions. To do so, we will draw an analogy between climate observations and results obtained in our group on a laboratory-scale, turbulent, von Kármán flow, in which spontaneous transitions between different states of the circulation take place. We will detail the analogy, and investigate the nature of the transitions, the number of degrees of freedom that characterizes the latter and discuss the effect of reducing the number of degrees of freedom in such systems. We will also discuss the role of fluctuations and their origin, and stress the importance of describing very small scales to capture fluctuations of correct intensity and scale.

Bérengère Dubrulle et al.

Status: open (until 16 Jul 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CC1: 'Comment on npg-2021-19', Paul PUKITE, 29 May 2021 reply
    • AC1: 'Reply on CC1', Berengere Dubrulle, 14 Jun 2021 reply
  • RC1: 'Comment on npg-2021-19', Anonymous Referee #1, 15 Jun 2021 reply

Bérengère Dubrulle et al.

Bérengère Dubrulle et al.


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Short summary
Present climate model discuss climate change, but show no sign of bifurcation in the future. Is this because there is none, or because they are by essence too simplified to be able to capture them? To get elements of answer, we ran a laboratory experiments, and discovered that the answer is not so simple.