Yesterday I posted a critique of Lord Christopher Monckton’s latest explanation of why he believes climate sensitivity is low. At issue is his claim that researchers have somehow neglected that the feedback response to a climate perturbation (e.g. how much warming occurs from adding CO2 to the atmosphere) needs to include the feedback response to the total emission temperature of the system, which he claims then greatly reduces the system “gain factor” and thus calculated climate sensitivity. I maintain that this is not how climate sensitivity in climate models is determined — only actual physical processes are modeled — and I used clouds as an example of why the system response to small perturbations cannot be determined by including the response of a cold (e.g. 2.7 Kelvin) Earth to solar heating (this is what I claim his argument amounts to when he includes the total system temperature in his system gain calculation). While he and I agree sensitivity to increasing CO2 is likely to be low, I laid out my explanation of why his reasoning is faulty. I invited him to respond, and I present that response, below, without comment. At a minimum this exchange might help us better understand exactly what Christopher is saying from a physical process standpoint, rather than a “system gain” standpoint.
I am most grateful to my friend Dr. Roy Spencer, one of the world’s foremost and most expert meteorological researchers and commentators, for the attention he has kindly devoted to our conclusion that official climatology has an insufficient understanding of control theory and has, therefore, led itself into a persistent and grave error.
I am still more grateful to him for this opportunity to reply to his latest posting on this topic, so as to set the record straight. Roy talks of my “feedback arguments suggesting a very low climate sensitivity”. Let me begin my response to that posting by clearing up the misconceptions that are evident in that thought. First, the arguments we make are not my arguments alone. My team includes many experts more than usually competent in both theoretical and applied control theory.
Secondly, our arguments do not “suggest a very low climate sensitivity”. Consider the position at the temperature equilibrium in 1850. The reference temperature that year was the 267.1 K sum of the 259.6 K sunshine or emission temperature and the 7.5 K directly-forced warming by, or reference sensitivity to, preindustrial noncondensing greenhouse gases; and the observed HadCRUT equilibrium global mean surface temperature was the 287.5 K sum of 259.6 K and the 27.9 K total natural greenhouse effect, which itself comprises the 7.5 K reference greenhouse-gas sensitivity and 20.4 K total feedback response.
Early papers on equilibrium doubled-CO2 sensitivity (ECS) based on explicitly quantifying feedback response, from Hansen (1984) onwards, show that the original reason why climatology imagined ECS to be of order 4 K was that the system-gain factor (the ratio of equilibrium sensitivity after feedback response and reference sensitivity before accounting for feedback response) was 27.9 / 7.5, or 3.7 (or, using the round numbers in vogue at the time, 32 / 8, or 4). Since midrange reference doubled-CO2 sensitivity (RCS) is 1.05 K, it was thus imagined that midrange ECS was 3.7 times 1.05, or about 4 K.
Once Hansen and others after him had repeated that midrange estimate often enough, it became impossible for the climatological community to move away from it. They were stuck with it. The whole shoddy house of cards would collapse if they revised it significantly.
The correct system-gain factor for 1850 was not 27.9 / 7.5, or 3.7. It was (259.6 + 27.9) / (259.6 + 7.5), or 1.08. In effect, climatologists had forgotten the Sun was shining and had, therefore, forgotten that there is a feedback response to emission temperature. They had overlooked that large emission-temperature feedback response, and had added all of it to the actually small feedback response to preindustrial greenhouse-gas reference sensitivity. They had thus reached their high midrange ECS of about 4 K by imagining, incorrectly, that the feedback response to emission temperature was zero, which is nonsense.
In reality, such feedback processes as subsist in the climate system at any given moment (such as 1850) must, at that moment, necessarily respond equally to each Kelvin of the entire reference temperature. Feedbacks do not, repeat not, respond solely to perturbation signals, the reference sensitivities. They also respond to the base signal, the emission temperature that would prevail even if there were no greenhouse gases in the air, because the Sun is shining.
Roy says that the underlined words are not true. [“Feedbacks do not, repeat not, respond solely to perturbation signals, the reference sensitivities. They also respond to the base signal, the emission temperature that would prevail even if there were no greenhouse gases in the air, because the Sun is shining.”] When I first realized that climatologists — on both sides of the debate — simply did not understand enough control theory to appreciate the truth of the underlined words, I discovered that a control theorist who was a friend of one of my distinguished co-authors did not realize they were true either. But he had his own lab. So he built a feedback amplifier circuit and tested the matter for himself. That was not easy, because so small is the true unit feedback response that he had to run wires into the next room so that his body temperature did not affect the readings. To his surprise, he found that the underlined words are correct.
Another control theorist, also a co-author, suggested that we should consult a national laboratory of physical engineering to put the point beyond doubt. So we did, and the lab came to exactly the same conclusion, after months of delay because the operator’s body temperature again interfered with the readings, and he had not thought to run wires into an adjacent room. So the matter is not in doubt.
Next, Roy incorrectly assumes that we maintain that “the climate system’s response to a small perturbation from its current state might be discerned from its response to the presence of solar heating assuming an initial cold Earth”.
In reality, we start not with “an initial cold Earth” but with the climate of 1850. We do not need to know what might have happened at 2.73 K ambient temperature. In 1850, when the equilibrium temperature was measured to a respectable precision, the system-gain factor — the ratio of equilibrium to reference temperature — was 287.5 / 267.1, or somewhat below 1.08. All we say, therefore, in relation to 1850 (we go back no further than that) is that ECS based on climatology’s original method adjusted to take account of the fact that in 1850 the feedback processes then extant had to respond equally to each Kelvin of reference temperature regardless of its origin is 1.08 times the 1.05 K RCS, or about 1.1 K.
We then demonstrate via a detailed energy-budget calculation that using mainstream midrange initial conditions it is perfectly possible that the system-gain factor following a CO2 doubling compared with 1850 remains somewhat below 1.08 and that, therefore, ECS is about 1.1 K.
However, we also draw explicit attention to the fact that, precisely because feedbacks respond to the entire reference temperature, and precisely because the base signal, emission temperature, is 30 times larger than the perturbation signal, reference sensitivity to natural and anthropogenic greenhouse gases, even a very small change in the feedback regime compared with the equilibrium in 1850 would exert a disproportionately large influence on ECS. In fact, a mere 1% increase in the system-gain factor at a new moment of equilibrium compared with 1850 would push ECS up by 300% to the 4 K that is the CMIP6 models’ current midrange projection. Therefore, our method does not prove that ECS is low: instead, it shows that it may be low, but proves that ECS is not reliably constrainable.
We draw the conclusion, applying standard feedback analysis, that it is simply not possible to derive ECS as climatologists now do, by diagnosing feedback strengths from the outputs of the general-circulation models and then deriving ECS therefrom. Or, to put it another way, the interval of system-gain factors implicit in IPCC’s current 3 [2, 5] K ECS interval is only 1.10 [1.09, 1.13], an interval so tiny as to fall well within the published uncertainty envelope of feedback strengths, rendering any attempt to predict ECS no better than guesswork.
Albeit by an entirely different method, we reach the same conclusion as Pat Frank in his important paper of 2019, in which he demonstrated that the envelope of uncertainty in ECS arising from propagation of the published uncertainty in a single climatic variable — the low-cloud fraction — was so large that all projections of ECS that have ever made fall within that envelope and are, therefore, mere guesswork. They have no predictive validity at all.
Roy devotes much of his article to the question of clouds. However, in the entire posting by my to which his piece is a response, the word “clouds” occurs only once, and in a context peripheral to the central argument. We point out, in common with Professor Lindzen, that at emission temperature, when by definition there are no greenhouse gases in the air, there would be no clouds either, wherefore, by the Professor’s calculation, emission temperature would not be 259.6 K but more like 271 K, which would of course reduce ECS still further. However, we explicitly point out that we take no account of that fact at all. Our analysis does not depend on the value of the cloud or any individual feedback. Roy says our analysis implies that further warming will not be mitigated by an increase in cloud cover. But our method carries no such implication, for it takes no view on ECS, other than to point out that on the basis of mainstream, midrange data it is possible that ECS may be as little as 1.1 K.
Roy then says climate sensitivity does not depend upon feedback analysis. Indeed, models do not implement feedback formulism directly. Instead, feedback strengths are diagnosed from the models’ outputs (see e.g. Soden & Held 2006 or Vial et al. 2013 for the method). However, the climate is a feedback-moderated dynamical system. Therefore, feedback formulism in control theory is applicable to it and we may, as we have done, apply feedback formulism to the published ECS interval. We may, as we have done, show that in this as in any system where the base signal exceeds the perturbation signal by orders of magnitude it is not possible reliably to predict the output signal in response to a given small perturbation in the total input signal where, as in the climate, the envelope of uncertainty in feedback strength grossly exceeds the interval of uncertainty in the absolute system-gain factor.
It is for this reason that it matters that climatologists had, in effect, forgotten that the Sun is shining and that, therefore, at any time in the industrial era, in the presence of the greenhouse gases, some 29/30ths of total feedback response is feedback response to the emission temperature — i.e., to the surprising fact that the Sun is shining.
It is simple to deduce, again from mainstream, midrange data, that each $1 billion spent on attempting to reach global net-zero CO2 emissions by 2050 would abate between one five-millionth and one millionth of a Kelvin of future global warming, at a total cost potentially exceeding total global corporate profits over the next 30 years (and indefinitely thereafter). Even if there were a real “climate emergency”, the expenditure would not be justifiable, because it would purchase an abatement amounting to only 3/8 K (if you believe IPCC’s midrange ECS estimate) or 1/7 K (if instead we note that since 1990 the world has warmed at little more than a third of the originally-predicted rate). In short, there is nothing we can do to abate future global warming other than reverting to the Stone Age — the decision that the UK Government under the unlamented Boris Johnson had in effect taken.
But there is no rational or legitimate excuse for doing anything about global warming on the basis of any current predictions, because, as Pat Frank has already demonstrated in his way and as we have demonstrated in ours, all predictions of global warming are mere guesswork. Would you trash the Western economies, and continue the inexorable transfer of industries, jobs, profits, wealth and global economic and political hegemony from the democratic, Judaeo-Christian, freedom-loving West to the grim oligarchs of Communist-led China and Russia on the basis of forecasts that are proven guesswork and are not borne out by events? We wouldn’t. I do hope that this has cleared up some misconceptions about our result.
— Christopher Monckton (4 October 2022)
Home/Blog
The 36 models are those catalogued at the KNMI Climate Explorer website, using Tas (surface air temperature), one member per model, for the ssp245 radiative forcing scenario. (The website says there are 40 models, but I found that four of the models have double entries). The surface temperature observations come from NOAA/NCEI.
