Is Jean-Pascal van Ypersele (IPCC) able to read?

Is Jean-Pascal van Ypersele (ex-IPCC) able to read?

During a debate on the Belgian TV network RTL on Sunday, September 20, 2020, the charming Jean-Pascal van Ypersele, unfortunate candidate for the Intergovernmental Panel on Climate Change (IPCC) chairmanship, disputed that the IPCC had recognized, in its third report (AR3), the impossibility of predicting the climate in the long term.

Continuing the debate on Twitter — a technique typical of those who lost the argument live — the charming van Ypersele broadcasted these two tweets just after the televised debate:

In English, this states: “The IPCC text correctly refers to the impossibility of predicting the long-term state of the climate system at a given time (e.g. the weather of 21 July 2100). The IPCC then explains that this does not prevent the prediction of the probable distribution of these states, i.e. the climate.”

“Here then, on the IPCC website, the famous page 774 of AR3 which would have been censored by the … IPCC according to Samuel Furfari, a guest, like me, of @dimancheRTL. In addition, he did not understand what was written there: https://ipcc.ch/site/assets/uploads/2018/03/WGI_TAR_full_report.pdf #dimancheRTL.”

Could we invite Mr. van Ypersele to reread himself carefully before publishing?

Let’s start again, slowly:

In its third report (AR3), the IPCC writes: “In sum, a strategy must recognise what is possible. In climate research and modelling, we should recognise that we are dealing with a coupled non-linear chaotic system, and therefore that the long-term prediction of future climate states is not possible. The most we can expect to achieve is the prediction of the probability distribution of the system’s future possible states by the generation of ensembles of model solutions. This reduces climate change to the discernment of significant differences in the statistics of such ensembles.”

According to van Ypersele, what the IPCC argues in this passage is (1) that weather is unpredictable in the long term, but (2) climate is indeed predictable in the long term. The wording of van Ypersele’s tweet is clear: “The IPCC text correctly refers to the impossibility of predicting the long-term state of the climate system at a given time (e.g. the weather of 21 July 2100). The IPCC then explains that this does not prevent the prediction of the probable distribution of these states, i.e. the climate.”

Problem: the IPCC does not talk about the weather in the passage in question, only about “future climate states”. But does the IPCC refer to the weather in the expression “future climate states”? The answer to this question appears on the same page 774 of the IPCC report, which states: “Climate states are defined in terms of averages and statistical quantities applying over a period typically of decades.”

It seems clear that, contrary to the allegations of the unfortunate candidate, the expression “climate states” in the passage of the AR3 referred to by Prof. Furfari does not expressly refer to the weather, but to averages and statistical quantities applied over periods of several decades, that is to say… the climate! The perfect negation of the notion of “the weather of 21 July 2100” (© van Ypersele).

In conclusion, contrary to van Ypersele’s fanciful claims, the IPCC does indeed recognize in its AR3 the impossibility of predicting the climate in the long term. The only way offered, still by the IPCC and in the same report, is the construction of computer models that allow us to discern the possibility, in the form of probabilistic distributions, of certain climate “scenarios”. This ambition is problematic in itself, because it concerns chaotic systems, but it is infinitely more humble and modest than Mr. van Ypersele’s lyrical flights of fancy in the style of Madame Soleil.

On a personal note, we were very saddened by van Ypersele’s failure as president of the IPCC. But how can we fail to understand that the IPCC refuses to put at its head an amateur who is not capable of reading the IPCC reports with rigor and lucidity?

Drieu Godefridi, PhD, September 22, 2020