The first modern theoretical estimates of ECS, the equilibrium climate sensitivity to carbon dioxide, were reported in 1979 in the so-called “Charney Report” (Charney, et al., 1979). They reported, on page 2, a theoretical ECS of 1.5°C to 4.5°C per doubling of the CO2 atmospheric concentration. This estimate included an estimate of water vapor feedbacks, the effect of ice and their assumed uncertainties. Absent any water vapor feedback their computed value was 1°C per doubling of CO2. They also supply a likely value of 2.4°C on page 9, although on page 2 they offer a value “near 3.0.” The page 9 value is not far off from the empirical estimate of 2°C made by Guy Callendar in 1938, but significantly higher than the 1.2°C to 1.95°C (17% to 83% range, best estimate 1.5°C) given by Nic Lewis and Judith Curry (Lewis & Curry, 2018).
The IPCC, in their AR5 report (Bindoff & Stott, 2013), estimate ECS as lying between 1.5°C and 4.5°C and provide no best estimate. This range is precisely the same as the Charney Report made 34 years earlier. While the empirical, observation-based, estimates have narrowed significantly, the theoretical range has not changed, despite thousands of government-funded scientists spending billions of dollars trying to do so. The data is very much the same today and churning it faster with more powerful computers and billions of dollars doesn’t seem to matter. It works the same way with manure.
Digging deeply into the AR5 internals, as Monckton, et al. did in MSLB15, a paper entitled, “Why Models run hot: results from an irreducibly simple climate model” (Monckton, Soon, Legates, & Briggs, 2015), we see that the elements of the AR5 theoretical calculations suggest that the range is narrowing in a downward direction. Given the political environment at the IPCC, one can easily suspect that the politicians do not want to admit the theoretical risks of CO2-caused climate change are lessening. As more empirical estimates of the CO2 effect appear and more theoretical work is done, one wonders how long the politicians can support the clearly inflated range of 1.5°C to 4.5°C?
Estimates of ECS have been declining for a long time, as shown in 2017 by Nicola Scafetta and colleagues. Figure 1 is from their paper:
The 1980s was when the catastrophic man-made (or anthropogenic) global warming catastrophe (CAGW) idea was developed. The alarmists have been beating the drum year-after-year ever since. In the United States, a Senate committee meeting, hosted by Senator Tim Wirth, on CAGW took place in the Washington, DC Dirksen Senate Office Building on June 23, 1988. It was a hot and humid day in swampy Washington, DC. The meeting was a watershed moment, in no small part due to Dr. James Hansen of NASA. In his presentation to the Congressional committee, he said:
“It is warmer in 1988 than at any time in the history of instrumental measurements.”
“Altogether the evidence that the earth is warming by an amount which is too large to be a chance fluctuation and the similarity of the warming to that expected from the greenhouse effect represents a very strong case. In my opinion, … the greenhouse effect has been detected, and it is changing our climate now.”
“The present observed global warming is close to 0.4 degrees C, relative to ‘climatology,’ which is defined as the thirty-year (1951 – 1980) mean. … we can state with about 99 percent confidence that current temperatures represent a real warming trend rather than a chance fluctuation over the 30-year period.” (Hansen, 1988)
ExxonMobil believed that natural variability was ±0.5°C. They thought that a change had to be larger than that to be significant. Obviously, Hansen somehow narrowed this natural range. The world cooled globally from 1944 to 1977, then began warming in 1978. An increase of 0.4°C is not much, so using that to determine that the “greenhouse effect” has been detected after a long period of cooling should have raised eyebrows and questions. Notice Hansen says, “greenhouse effect,” when he means “human-caused greenhouse effect” or “enhanced greenhouse effect.” There is a natural greenhouse effect, caused by natural CO2 and other greenhouse gases, especially water vapor. This is the beginning of a deceptive tactic commonly used by the alarmists. To ignore natural causes of climate change, they equate “greenhouse effect” with “human-caused greenhouse effect.” Also, they use “global warming” as synonymous to “human-caused global warming” and “climate change” is synonymous with “human-caused climate change.” This sort of deceptive and manipulative language is still used today.
The IPCC Reports
The first IPCC report (FAR), chaired by Bert Bolin, determined that global warming to 1992, when the report was published, fell within the range of “natural climate variability” and was not necessarily due to human activities (IPCC, 1990, p. XII). They thought the unequivocal detection of a human influence was “not likely for a decade or more.” Bert Bolin thought James Hansen’s congressional testimony in 1988 had exaggerated the significance of recent global warming.
The second report, SAR, published in 1996, found that “The balance of evidence suggests a discernable human influence on global climate.” (IPCC, 1996, p. 4). But this was based upon unpublished and unreviewed work by Benjamin Santer and colleagues. His study suggested that climate model predictions about warming in the troposphere and cooling in the stratosphere, were like what was occurring. He called this a “fingerprint” of human influence on climate (Santer, et al., 1996a). After the paper was published, it was found that Santer had cherry-picked his fingerprint (Michaels & Knappenberger, 1996). The study was dismissed, and the IPCC humiliated. This humiliation was compounded by the fact that the politicians in charge of the IPCC were caught changing the scientific reports within SAR to match their political Summary for Policymakers (Seitz, 1996).
The third report, TAR, published in 2001, found that “most of the observed warming over the last 50 years is likely to have been due to the increase in greenhouse gas concentrations.” (IPCC, 2001, p. 10). They based this decision on the “hockey stick,” which was later shown to be flawed. By the time the fourth report (AR4) was published in 2007, numerous investigations of the hockey stick showed it was incorrect and showed too little variability. This was acknowledged in the fourth report, AR4, by Keith Briffa, who wrote, somewhat euphemistically, that the hockey stick was too sensitive to particular proxies (tree rings) and the statistical methods (principal components) used to construct it (IPCC, 2007b, p. 436). Willie Soon and Sallie Baliunas demonstrated that the hockey stick did not reflect the data used to build it (Soon & Baliunas, 2003). The hockey stick turned out to be an elaborate fiction created solely from a flawed statistical procedure and a poorly selected set of temperature proxies (National Research Council, 2006, pp. 112-116) and (Wegman, Scott, & Said, 2010, pp. 4-5, 48-50).
By the time AR4 was published in 2007, the leadership of the IPCC had given up on finding any direct evidence that humans dominate climate change. They had tried Santer’s “fingerprint” and Michael Mann’s “hockey stick” and failed to convince the public with either. So, in AR4, they tried to use climate models to convince the public that, “Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations.” (IPCC, 2007b, p. 10). They present no observational evidence, just model results. The fifth report, AR5, was just a repeat of AR4. Same two models, same result. As already mentioned, deep in the AR5 internals, MSLB15 (Monckton, Soon, Legates, & Briggs, 2015) showed that the newer AR5 model results suggested IPCC headlines are overstating the sensitivity of the climate to CO2, but this result was not explained or acknowledged in the report.
So, while empirical calculations of the climate sensitivity to CO2 now show ECS to be between 1.1°C and 2.45°C (see Table 1), the theoretical estimates have remained 1.5 to 4.5, except for AR4 when it was changed to 2.0 to 4.5. The ranges in Table 1 are all 5% to 95% ranges as far as I can tell.
Table 1. Various estimates of ECS. All are theoretical calculations except for Lewis and Curry, their estimate is based on observations.
Thus, thousands of scientists and billions of dollars later, we still have the same theoretical uncertainty about the impact of CO2 on climate. The one empirical estimate of ECS shown is about 1.5°C. Most such empirical estimates are less than 2°C and cluster around 1.5°C to 1.6°C (Lewis & Curry, 2018). Guy Callendar’s empirical estimate was 2°C (Callendar, 1938) and Arrhenius’ theoretical estimate (Arrhenius, 1908) was 4°C, so it can be said all the work and money spent since 1938 to attribute climate change to humans was wasted.
Is it getting any better? What about the latest generation of theoretical models, CMIP6? Early indications are that the results are getting worse, not better, as reported by Ron Clutz and John Christy. While most of the new models show absurdly inflated values for ECS, it is interesting that the latest version of the Russian model, INM-CM4, referred to in my previous post, now predicts an ECS of 1.83. So, except for INM-CM4, we’ve seen no progress since 1938. As my late Grandmother Marie McCartney would say, “now isn’t that just dandy.”
This is a condensed excerpt, with minor modifications, from my new book, Politics and Climate Change: A History.
To download the bibliography, click here.