CMIP6 ECS – does it work?

From Rud Istvan

This post was motivated by May’s second topic on paleoclimate, through comments on Bradley Jrs. All are linked below. This post summarizes some of the most important climate fundamentals on a simple, high level while also summarizing the myriad of underlying specifics through linked references to many things that have been published at WUWT over the years. Hopefully this will be helpful to the many recent WUWT commentators on both levels. It also indirectly scientifically targets some of the extreme skeptics voicing out here as well, such as those who deny that the greenhouse effect exists or that ECS cannot be significantly positive.

First, the greenhouse effect (GHE) is real, although it is often misunderstood. Unlike a real greenhouse (which inhibits convective surface cooling), the GHE works by inhibiting radiant cooling in the troposphere. “Greenhouse gases” (GHG) absorb and emit infrared radiation (IR) in all directions, which prevents (delays) the cooling of IR into space. Greenhouse gases (including their “reflection”) cannot heat up – the incident solar radiation is solely responsible for this. But as was first shown experimentally by Tyndall in 1859, greenhouse gases can inhibit radiation cooling. The level in the troposphere at which the GHE no longer plays a role is known as the effective radiation level (ERL). The ERL is also the reason the GHE can never be saturated. More greenhouse gases only increase the ERL, which means that the ERL emission temperature is cooler and therefore less efficient thanks to the rate of temperature drop in the troposphere. For this reason, Guy Callendar recognized in his 1938 paper that an increase in CO2 has a decreasing logarithmic effect. For the following, this also means that the ECS per CO2 doubling remains roughly constant over a much broader concentration range, regardless of its level.

Second, the notion that there must be some positive ECS when CO2 is doubled is logically valid. With constant solar radiation but reduced compensatory radiation cooling, the earth’s surface temperature must rise until the resulting rise in IR compensates for the GHE, so that the TOA radiation “equilibrium” is restored. ECS can be set up in two basic ways. Firstly through problematic climate models that have predicted around 3 ° C in AR4 (CMIP3), around 3.4 ° C in AR5 (CMIP5) and now around 3.7-4.5 ° C in the upcoming AR6 (CMIP6, details to follow) . Second, through various observation methods, all of which point to around 1.7 ° C. This 2x discrepancy was so large that AR5 therefore explicitly rejected a central ECS estimate.

Third, the climate models ARE problematic for an inevitable reason. Thanks to the arithmetic unwieldiness of the size scales of important climate phenomena (e.g. Willis Eschenbach’s many TStorm articles here), you are forced to parameterize them. The parameterization lengthens the attribution problem, both on long time scales, as Andy May has just shown, and on the short time scales of the last century. The attribution is very simple, how much of the observed temperature change was natural in the past and how much CO2 was “driven”. The IPCC assumes (by statute!) All forced forces and ignores the natural variability. In 1999 MBH attempted to (mistakenly) eliminate the natural variability of the millennial timescale over its infamous hockey stick grip – by erasing the historically well-documented but only natural MWP.

The latest and ‘best’ CMIP6 climate models are coming soon for AR6. Even if their results have not yet been finalized, it is already apparent that there is still a gap between the climate and reality. The preliminary CMIIP6 ECS results are as follows.

The high ECS of the 40 models reported is 5.6 ° C, the low one at 1.8 ° C (INM CM5, the Russian model that comes close to the observation methods). The mean value is now 4.5 (yellow / blue), far removed from observation methods. The median has risen to 3.7 ° C. So CMIP6 significantly INCREASED the ECS uncertainty (the opposite of what current science is supposed to do) while further increasing its modeled central tendencies (now with greater deviation from the observations that caused AR5 heartburn). As the text around the linked carbonbrief.org graphic above shows, the Warmunists find this both plausible and a reason to celebrate easily!?!

It is evident that those who believe in anthropogenic global warming do not understand the persistent underlying problem with their climate modeling approach. They dig a deeper hole. The army’s first rule about holes is that if you’re in one and you want to get out, the first thing to do is stop digging.

Or to paraphrase a very famous summary of the Feynman lecture:

“It doesn’t matter how beautiful your theory is. If it doesn’t agree with observations (theory-based experiments), IT IS WRONG. ‘

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