Goldilocks and the AR6 WG1 SPM

Has anyone read the WG1 SPM yet? 

I’ve tried, I have really. It’s called “The Physical Science Basis summary for Policymakers,” but there’s hardly any science in it, and it would be incomprehensible to a policymaker who wasn’t already well versed in IPCC-speak. 

Take the first two paragraphs of the introduction:

This Summary for Policymakers presents key findings of the Working Group I contribution to the IPCC’s Sixth Assessment Report on the physical science basis of climate change. The report builds upon […] AR5 and […] incorporates subsequent new evidence from climate science. 

This SPM provides a high-level summary of the understanding of the current state of the climate, including how it is changing and the role of human influence, the state of knowledge about possible climate futures, climate information relevant to regions and sectors, and limiting human-induced climate change. 

Note that the emphasised parts can’t possibly be described as “the physical science basis of climate change.” They are respectively, predictions, and suggestions for how to limit change. In the very first few sentences the SPM has gone way off topic. 

And it gets worse, since only ten pages are devoted to “the current state of the climate,” compared with 26 pages on possible climate futures, risk assessment and regional adaptation, and limiting future climate change – subjects which are in no way part of the “physical science basis.” And even when they stick to the science, they leave out almost all the stuff that would be most useful to policy makers, like regional variations in temperature, precipitation, sea level rise etc. – stuff that you need to know if you’re in charge of a particular country in a particular place at a particular time, which the policy makers are.

The major part of the Summary is concerned with a discussion of scenarios: namely SSPs or Shared Socio-Economic Pathways which are “climate models participating in the Coupled Model Intercomparison Project Phase 6 (CMIP6) of the World Climate Research Programme.” 

Once I’d found the definitions of SSPs and CMIP6 in the footnote to a box, and in a footnote to the footnote, I was ready to tackle the rest of the report, or as ready as I’d ever be, because there was no further explanation of the terms other than the above.

I thought I’d test my understanding on a sample paragraph, and I chose the very last one, assuming the authors would want to end with a zinger. This contained a reference to an acronym I knew – GHG = greenhouse gases – and another one I wasn’t familiar with – CIDs – explained in a footnote thus:

Climatic impact-drivers (CIDs) are physical climate system conditions (e.g., means, events, extremes) that affect an element of society or ecosystems. Depending on system tolerance, CIDs and their changes can be detrimental, beneficial, neutral, or a mixture of each across interacting system elements and regions. CID types include heat and cold, wet and dry, wind, snow and ice, coastal and open ocean. 

Not very satisfactory, since apparently a driver may be a mathematical concept (a mean) an adjective (wet) an abstract noun (heat) or a thing (the ocean.) But let’s live with that and take a look at the final paragraph of AR6 WG1 SPM.

D.2.4 Scenarios with very low and low GHG emissions (SSP1-1.9 and SSP1-2.6) would lead to substantially smaller changes in a range of CIDs beyond 2040 than under high and very high GHG emissions scenarios (SSP3-7.0 and SSP5-8.5). By the end of the century, scenarios with very low and low GHG emissions would strongly limit the change of several CIDs, such as the increase in the frequency of extreme sea level events, heavy precipitation and pluvial flooding, and exceedance of dangerous heat thresholds, while limiting the number of regions where such exceedances occur, relative to higher GHG emissions scenarios (high confidence). Changes would also be smaller in very low compared to low emissions scenarios, as well as for intermediate (SSP2-4.5) compared to high or very high emissions scenarios (high confidence). {9.6, Cross-Chapter Box 11.1, 11.2, 11.3, 11.4, 11.5, 11.6, 11.9, 12.4, 12.5, TS.4.3}

Translation:

If we emit less greenhouse gases, in twenty years’ time, and even more so by the end of the century, there will be less variation in wet and dry, heat and cold etc. than if we emit lots of greenhouse gases, and these variations will occur in fewer regions – we’re very confident of that. And if we emit much less greenhouse gases, there will be less variation than if we just emitted a bit less. Likewise, if we emit a medium amount of greenhouse gases, the changes in heat and cold, wet and dry etc. will be less than if we emit lots, and even less than if we emitted a huge amount, and we’re very confident of that too.

Signed: the scientists.

If the 200 or so governments had any guts they’d send the SPM back to the authors and tell them to try again. But they won’t, because no-one likes admitting they’ve been taken for a mug. Especially when it’s for the sixth time running.

And besides, they’ve already booked their flights to Glasgow.

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August 10, 2021 at 04:26PM

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