Benoît Rittaud: Climate Models Capable of Anything

Benoît Rittaud is a maths lecturer and blogger at “Changement Climatique”. This article, from November 11th 2014 is one of a series analysing a recent series of reports by Meteo France containing climate predictions for France (Metropolitain and Overseas). The original article is at http://www.skyfall.fr/?p=1366

The Climate Models Are Capable of Anything (That’s how you recognise a Climate Model.)

by Benoît Rittaud

A quick glance at this August 2014 report on the Climate in France in the 21st century prepared for the Ministry of Ecology and Sustainable Development is good for a laugh.

http://www.developpement-durable.gouv.fr/Volume-4-Scenarios-regionalises.html

See for example on page 17 this Table of Doom, the terrifying pith and moment of which has been reproduced just about everywhere in the media.

grostableauquifaitpeur

This table summarises the mean temperature anomalies for the periods 2020-2050 and 2071-2100 in comparison to the reference period 1976-2005 according to the climate models WRF and Aladin-Climat for each of the three scenarios RCP2.6, RCP4.5 and RCP8.5. The columns C25 and C75 correspond to the 25th and 75th centiles of an ensemble of regional models. WRF and Aladin-Climat are the two models considered in detail in the report. RCP means “representative concentration pathways.” The important thing to note is that the higher the number after the letters RCP, the greater the emissions of CO2 envisaged and therefore, according to the IPCC, the higher the resulting temperature. I see no other way that a model can be compatible with the findings of the IPCC.

However, in the table above, this necessary characteristic is flouted in no less than six places.

MoreCO2Lesswarming

Whichever column you look at, you’ll find at least one case in which higher emissions lead to to less warming. The WRF model is the clear winner of the prize for the most bizarre results. For the period 2021-2050, which is practically tomorrow in terms of climate, in two out of four cases WRF predicts less warming for France in a scenario with a far higher level of CO2. And the differences are not negligible: from +1°C to +0.6°C in the summer, and from 1.3°C to 0.8°C inwinter. An English-speaker might be tempted to rename the WRF model, replacing the R by a T…

When I was a young university student, a physics lecturer had the bright idea of introducing us to the notion of the criterion of relevance. The idea is that when you’ve finished a calculation, that doesn’t mean your work is over. You still have to cast a critical eye on the result and the way in which it was obtained, in order to spot any possible error.

The fact that not one of the six climate scientists who worked on this report considered applying such a simple and obvious criterion of relevance as the one detailed above tells us much unfortunately about certain practices in climatology: worship of the Great Computer, devotion to “statistics”, and a complete lack of a critical spirit.

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4 Responses to Benoît Rittaud: Climate Models Capable of Anything

  1. Dear Geoff, thank you so much for this very nice translation.
    I send you by e-mail an English version of the “more CO2, less warming” table.

  2. Thanks Benoît
    I really don’t enjoy translating. An article like yours on a scientific subject is easier than one expressing an opinion, but there is still plenty of room for misunderstanding. Note for example that when I say “case” I mean “cas” and not “case”😉
    I’m going to write a summary of your experiences with Méteo France, since they may prove to be important in the run up to Paris 2015. So watch this space, and keep in touch.

  3. Nicias says:

    The tittle link to “Les tontons flingueurs”. An old french film well known for its dialogues. Original transcript : “Les cons ça osent tout, c’est même à ça qu’on les reconait”.

  4. Nicias says:

    @Geoff
    Je vous ai envoyé un mail à votre adresse Orange laissée sur Skyfall.

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