“[This paper is] the most important climate science paper that’s come out in several years…. [It’s] really moved the game away from these questions about the physics of the climate system into questions about how are humans going to react to climate change.”
– Andrew Dessler. Quoted in “Groundbreaking Study: Earth Will Warm 4.9 to 7 Degress F.” E&E News, July 23, 2020.
“During the period of strongest greenhouse gas forcing (since 1979), the latest CMIP6 models reveal 50% more net surface warming from 1979 up to April 2020 (+1.08 deg. C) than do the observations (+0.72 deg. C).”
– Roy Spencer, “CMIP6 Climate Models …” June 25, 2020.
An alleged breakthrough, hold-the-presses moment has arrived–right during the summer heat and just in time for a Presidential election to give the problematic Green New Deal veneer.
Has mainstream climate science now solved, for practical purposes, the perennial unknown of climate sensitivity? Is the true answer a tighter, higher average bound of predicted temperature increases?
Before, the range was wide enough for the skeptics of climate alarm to declare victory at the lower end. AND the last IPCC assessment lowered the bottom end of the range to provide skeptic momentum within the mainstream.
Now, with the upper end unchanged, the lower end has jumped by 50 percent. And all in contradiction to real-world observation, as the quotation (above) from Roy Spencer indicates.
In numerical terms, the “equilibrium climate sensitivity” estimate of 1.5–4.5ºC, the range presented in the last (2013) assessment of the Intergovernmental Panel on Climate Change (IPCC) is now stated to be 2.3ºC to 4.5ºC (about 4–8ºF).
Within this range, there is a predicted two-thirds chance that the warming-to-come will be 2.6C–3.9ºC (about 4.4 – 6.6ºF). This most likely scenario is what got most of the attention, with the lower end up 73 percent and the upper end down 13 percent (a small blow against the ‘fat tails’ argument for a carbon tax).
False Certainty … Alarm!
The Washington Post climate reporters, taking the study at face value, went to the alarmists for alarm:
If the warming reaches the midpoint of this new range, it would be extremely damaging, said Kate Marvel, a physicist at NASA’s Goddard Institute of Space Studies and Columbia University, who called it the equivalent of a “five-alarm fire” for the planet.
The new range is narrower than previous studies but shows at least a 95 percent chance that a doubling of carbon dioxide, which the world is on course to reach within the next five decades or so, would result in warming greater than … the threshold beyond which scientists say the Earth will suffer dangerous effects — disruptive sea level rise, intolerable heat waves and other extreme weather and permanent damage to ecosystems.
To all this I declare–buyer beware! This is the latest in an old playbook of false certainty for alarm. Climate science, in short, is not settled toward high-sensitivity warming by any means. The fundamental physics of climate interactions with land, water, and clouds remain unsettled with the externality sign unsettled.
Déjà vu Again and Again
The script is old and repetitive. For nearly a half-century, and well before the climate alarm, Malthusian modelers have had the same confidence that mass peril was upon us.
From the MIT/Club of Rome model of 1972 to now, has an alarmist ever said ‘We are not sure…. stay tuned ….’ Of course not! The emotional and intellectual stakes have been driven far too deep in the ground for simply stating that “this is the best we can do” and “we just do not know.”
No, with confidence, they make statements such as (Donella Meadows et al., 48 years ago):
“If all the policies instituted in 1975 … are delayed until the year 2000 … population and industrial capital reach levels high enough to create food and resource shortages before the year 2000.” 
Has the mainstream media, not to mention Science and Nature magazines, ever shown humility toward the great unknowns of population, resource, or climate science? NO. And such false confidence and finality has been disproved time and again. Crying Wolf has turned into crying Wolf Packs time and again.
History and precedent matter. Humility matters. Error bars are themselves subjective when models do not know the underlying physics and are ‘tuned’ with ‘fudge factors’ to get to the ‘right’ answers. Such modeling is quite beyond controlled experiments to tease out correlations and causality.
Specifically, do we really know the physical equations of clouds, the great unknown feedback that doubles or triples the primary/initial warming. Less positive feedback effects turn the whole CO2 effect on its head with benign or positive implications for the economy and the ecosphere.
Andrew Dessler: Independent Confirmation?
The above Washington Post article quoted a familiar source:
Andrew Dessler, a climate scientist at Texas A&M University who was not involved in the study, called this “a tour de force of climate science.” He said via email that the study “really, really kills the skeptical argument that climate sensitivity is low. It would have been great if the skeptics had been correct and climate sensitivity was, say, 1.5°C, but that’s not the world we live in.
A writeup on the new study by E&E newsletter also liberally quoted Dessler:
[It’s] the most important climate science paper that’s come out in several years …. Behind the scenes, underneath the hood, our understanding of a lot of the processes was much better. And so I think that even though the range hadn’t changed, that masked a real tremendous improvement in our understanding.
The science settled, it is time to move on, Dessler states.
It’s not clear to me how much we would gain from further decreases in the uncertainty. What this has done, in my opinion, is it’s really moved the game away from these questions about the physics of the climate system into questions about how are humans going to react to climate change.
Indeed, the alarmists want to no longer question their own belief system. They want to turn to the politics, which is where their hearts have been from the start.
Uncertain Science Lurking
Dessler has long held that the true climate sensitivity lurked around 2.7ºC (April 2, 2019 tweet) for a doubling of CO2 in the atmosphere in equilibrium, well below the midpoint of the praised new study. He also tweeted April 3rd: ““There are, on the other hand, things we don’t really know about the climate system. We need to better understand how low clouds respond to changes in the climate (i.e., SST, stability, mid-trop RH).” If this is not hedging, I do not know what is….
And regarding the underlying models and physics therein, Professor Dessler elsewhere has been more frank. His textbook (with Edward Parson, The Science and Politics of Global Climate Change: A Guide to the Debate. 2000, pp. 19–20) makes these points that remain important today:
“… climate scientists cannot conduct controlled experiments on the Earth…. Instead they use … Global Climate Models, or GCMs–mathematical representations of the Earth that run on computers.”
“Processes operating at smaller scales [than 100 km], such as clouds, cannot be represented explicitly in the models but must instead be parameterized.”
“Parameterizations … [have] ad hoc constructions that are tuned so the model produces a realistic present-day climate. Consequently, parameterizations are one of the largest sources of uncertainly in GCMs.”
Climate Models: Better than Nothing?
Modeler Mototaka Nakamura takes the criticism up a notch, explaining how the computer programs “completely lack some critically important climate processes and feedbacks, and represent some other critically important climate processes and feedbacks in grossly distorted manners to the extent that makes these models totally useless for any meaningful climate prediction.” He explains:
The models are ‘tuned’ by tinkering around with values of various parameters until the best compromise is obtained. I used to do it myself. It is a necessary and unavoidable procedure and not a problem so long as the user is aware of its ramifications and is honest about it. But it is a serious and fatal flaw if it is used for climate forecasting/prediction purposes.
Clouds are the wild card:
Ad hoc representation of clouds may be the greatest source of uncertainty in climate prediction. A profound fact is that only a very small change, so small that it cannot be measured accurately…in the global cloud characteristics can completely offset the warming effect of the doubled atmospheric CO2.
Accurate simulation of cloud is simply impossible in climate models since it requires calculations of processes at scales smaller than 1mm. Instead, the modellers put in their own cloud parameters. Anyone studying real cloud formation and then the treatment in climate models would be flabbergasted by the perfunctory treatment of clouds in the models.
As a result, “I have more or less lost interest in the climate science.”
Dessler’s mentor Gerald North famously put models in their place during his active years, discussed here. And what North stated was recently explained in The Economist article, “Predicting the Climatic Future is Riddled with Uncertainty,” subtitled “But researchers are doing the best they can.” What might be ‘the best they can’ might be worse than no effort at all if false certainty is imparted.
The sudden confidence in climate models reminds me of Laurel & Hardy when Stan Laurel told Ollie, “You remember how dumb I used to be … well, I’m better now.” I also recall the story in Done In Oil when J. Howard Marshall responds to yet another peak oil narrative from a colleague, “So what makes you think you are right now?”
It’s déjà vu all over again, as Yogi would say.
 Donella Meadows et al. The Limits to Growth. New York: Universe Books, 1972, p. 169.