In today’s climate of absence of debate on the climate issue, some contribute to build up well funded opinions, and others just claim beliefs and dogmas in the general medias and at the COP22 conference in Marrakesh.

Prof Judith Curry, a climatologist who specializes in the thermodynamics of atmospheres and oceans and is not an appointed expert of IPCC (why?), just issued a summary [1] about global climates models (GCM). The bulk of this exposé is a sound lecture about what modelling is, what models are useful for, and for what purpose they should or should not be used. This is an excellent piece of which I allow myself to reproduce the Executive Summary, understandable for anyone, even without scientific or technical background.

There is considerable debate over the fidelity and utility of GCM climate models. This debate occurs within the community of climate scientists, as scientists disagree about the amount of weight to give to climate models relative to observational analyses. Climate model outputs are also used by economists, regulatory agencies and policy makers. Hence, GCMs have received considerable scrutiny from a broader community of scientists, engineers, software experts, and philosophers of science. This report attempts to describe the debate surrounding climate models to an educated but nontechnical audience.

Key summary points:

• GCMs have not been subject to the rigorous verification and validation procedure s that is the norm for engineering and regulatory science.
• There are valid concerns about a fundamental lack of predictability in the complex nonlinear climate system.
• There are numerous arguments supporting the conclusion that climate models are not fit f or the purpose of identifying with high confidence the proportional amount of natural versus human causes to the 20^th century warming.
• There is growing evidence that climate models predict too much warming from increased atmospheric carbon dioxide.
• The climate model simulation results for the 21^st century reported by the IPCC do not include key elements of climate variability, and hence are not useful as projections for how the 21^st century climate will actually evolve.

Climate models are useful tools for conducting scientific research to understand the climate system. However, the above points support the conclusion that current GCM climate models are not fit for the purpose of attributing the causes of 20^th century warming or for predicting global or regional climate change on timescales of decades to centuries, with any high level of confidence. By extension, GCMs are not fit for the purpose of justifying political policies to fundamentally alter world social, economic and energy systems. It is this application of climate model results that fuels the vociferousness of the debate surrounding climate models.

So, if some may think that I’m only a weirdo, then they should at least trust such authority.

This is one contribution to what I call the so dearly needed “rearmament of reason”.

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[1] https://curryja.files.wordpress.com/2016/11/climate-models.pdf

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