The latest IPCC Report on “The Physical Science Basis” of Climate Change in 2021 has just been published. The downloaded document weighs 3949 pages and contains a “Summary for policymakers” (SPM) with 41 pages. Aside of the summary, the rest, including a 150 page “Technical Summary”, is marked “Do Not Cite, Quote or Distribute”. A 148 page “Corrigenda” can also be downloaded. If the summary is already approved, why is the bulk still in a correcting mode? Impatience and concern for communication should not be part of the climate scientists’ toolbox.

These monstrous dimensions suggest that no one can claim to master the subject, not even the hundreds of authors who have shared the task of reviewing and drawing conclusions from thousands of scientific works of varying quality. This is an ideal basis for imposing whatever interpretation one may find serving her or his purpose.

Flying over the not that easy-to-understand SPM, I’ve noted that the observed warming is deemed almost exclusively anthropogenic. A best estimate was assessed for the climate sensitivity to CO₂ at “ 3°C with a likely range of 2.5°C to 4°C (high confidence), compared to 1.5°C to 4.5°C in AR5, which did not provide a best estimate.”

Such sentence reminds us of the eternal use of ” expert ” judgements, even though they only have one laboratory and only one experiment at their disposition. Imagine psychiatrists or astronomists founding their knowledge on one only patient or one only star system. The long footnote 4 on page 4 should be the object of cognitive studies and group dynamic evaluation:

“Each finding is grounded in an evaluation of underlying evidence and agreement. A level of confidence is expressed using five qualifiers: very low, low, medium, high and very high, and typeset in italics, for example, medium confidence. The following terms have been used to indicate the assessed likelihood of an outcome or a result: virtually certain 99–100% probability, very likely 90– 100%, likely 66–100%, about as likely as not 33–66%, unlikely 0–33%, very unlikely 0–10%, exceptionally unlikely 0–1%. Additional terms (extremely likely 95–100%, more likely than not >50–100%, and extremely unlikely 0–5%) may also be used when appropriate. Assessed likelihood is typeset in italics, for example, very likely. This is consistent with AR5. In this Report, unless stated otherwise, square brackets [x to y] are used to provide the assessed very likely range, or 90% interval. “

If this method can be valid for retrospective studies, it is probably about as likely as not (33%–66%) that prospective judgements have no basis other than intimate sentiments reinforced by confirmation biases among peers.

So, I will need to study how theses scientific assessments have been reached, with a particular interest on how models have been validated as fit for making projections into the future. It is more likely than not that my curiosity will not be satisfied (see https://blog.mr-int.ch/?p=6696).

The bulk of the SPM is prospective: it deals w6ith estimates of future emission scenarios and their potential impacts on temperature, frequency and intensity of meteorological events, precipitations and soil moisture, sea level and acidity. Climatic impact-drivers (CID, physical climate system conditions that affect an element of society or ecosystems) are addressed at global, regional, and local scale.

Thus, all conceivable extrapolations have been made possible, including the worst case being taken as a kind of ‘business as usual’, albeit the IPCC reckons that its likelihood is low. But the contrary is already spelled in printed press headlines and media breaking news: if the worst could happen, it will and the sooner the better for the prophecies of doom to be confirmed. However, as the social cost of warming may be acceptable for a temperature higher than the arbitrary limit of 1.5°C or 2°C, a more sober assessment of the figures as presented does not provide an argument for a state of emergency. This is important because it leaves room for an ordered decarbonization instead of panic.

Let’s recall that such prospective studies are in no way a scientific job, but mere speculation driven by the choice of interplaying parameters. Doing so has its merits… as long as conclusions are not drawn in such a biased way as the knee jerk reactions of the media and political circles already show.

Finally, carbon budgets are calculated. These are the remaining quantities of anthropogenic greenhouse gases to be emitted before trespassing a given global temperature threshold (1.5 °C, 2 °C, or more). Not unexpected, a low emission scenario leaves more time to attain such limits. Nevertheless, “discernible differences in trends of global surface temperature would begin to emerge from natural variability within around 20 years”. This means that all efforts undertaken now, even the strongest and fastest decarbonization actions if successful, would not produce any result before the next generation will be in charge. For the time being, this will be a pill hard to swallow for developing and emerging countries, which are home to the vast majority of the World’s population and have a great many other priorities than the threat of a too warm climate. The COP26 (next November in Glasgow?) will not be a smooth and flowery ride; rationality could at last be brought back to the agenda in a much less consensual spirit.

This will have been my last grain of salt in that matter, the penultimate as always. At first glance, this new report does not bring new insights. Its speculative orientation will contribute to fostering the current alarmist dogma.

A plea to readers and email correspondents: As no breaking news is brought forward, please refrain from sending me links or copies of long videos, boring articles, ‘in-depth’ reports, or meaningful and meaningless reviews. I don’t need to waste my time pointing out misuses and prejudices surrounding this matter, because I know well enough that this is abundantly the case.

What really becomes urgent is to savour and enjoy anything else that is more joyful.

Original article published on the author’s blog:  MR’s Blog