Climate sensitivity to CO2 lower than UN models project

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A new research approach has found a very low value for CO2 climate sensitivity, on the order of just one half degree C. This is in stark contrast to the latest IPCC computer modeling results, many of which give sensitivity results over five degrees. Sensitivity is a standard benchmark, the warming that might be expected when the atmospheric concentration of CO2 is doubled.

This result is especially interesting because the journal that has published it conducted two separate reviews before doing so. They did this because of strong resistance from alarmists. While this double review does not guarantee the truth of the findings it certainly strengthens their credibility.

The article is “The Impact of CO2, H2O and Other Greenhouse Gaseson Equilibrium Earth Temperatures” by Coe, Fabinski and Weigleb, in the International Journal of Atmospheric and Oceanic Sciences.

The article is open access so not paywalled. Take a look here:

Lead author David Coe explains the paper this way:

The concept of this paper is to reduce the complexity of the problem of climate sensitivity determination by the separation of variables, a common technique. We conclude that The atmosphere, mainly due to the beneficial characteristics and impact of H2O absorption spectra, proves to be a highly stable moderator of global temperatures. There is no impending climate emergency and CO2 is not the control parameter of global temperatures, that accolade falls to H2O. CO2 is simply the supporter of life on this planet as a result of the miracle of photosynthesis.

As with the Happer and van Wijngaarden work I wrote about earlier, Coe et al use line by line spectral analysis the explore the potential forcing from increasing greenhouse gases. They do this by estimating the relative contributions of the most common GHGs to the widely accepted natural greenhouse effect of 33 degrees C.

Their abstract puts their approach and results very well:

The aim of this paper is to simplify the method of achieving a figure for climate sensitivity not only for CO2, but also CH4 and N2O, which are also considered to be strong greenhouse gases, by determining just how atmospheric absorption has resulted in the current 33K warming and then extrapolating that result to calculate the expected warming due to future increases of greenhouse gas concentrations. The HITRAN database of gaseous absorption spectra enables the absorption of earth radiation at its current temperature of 288K to be accurately determined for each individual atmospheric constituent and also for the combined absorption of the atmosphere as a whole. From this data it is concluded that H2O is responsible for 29.4K of the 33K warming, with CO2 contributing 3.3K and CH4 and N2O combined just 0.3K. Climate sensitivity to future increases in CO2 concentration is calculated to be 0.50K, including the positive feedback effects of H2O, while climate sensitivities to CH4 and N2O are almost undetectable at 0.06K and 0.08K respectively. This result strongly suggests that increasing levels of CO2 will not lead to significant changes in earth temperature and that increases in CH4 and N2O will have very little discernible impact.

Other researchers have found observation based sensitivity estimates of as little as 0.3 degrees. These give credence to Coe et al’s 0.5 degrees. Given that we are almost half way to a doubling of atmospheric CO2, and seeing maybe one degree of warming from all causes, the projections of dangerous CO2 induced warming look extremely implausible.

Many of the climate models are now giving sensitivities greater than 5 degrees, which is truly absurd. Coe et al are far more likely to be on target.

The double review is also interesting. The paper was originally published online in August. The journal then received a pointed technical criticism, presumably from a leading alarmist scientist. So the journal pulled the article, asked the authors to respond to the criticism, then conducted a review of this dispute. In the journal world this is called post-publication review and several journals are experimenting with it.

The journal concluded that the authors were correct and has now republished the paper, keeping the original publication dates for the official record. Who publishes what, when can be very important. The journal’s integrity in this matter is commendable. It certainly suggests that the results are robust.

Coe et al’s physics aligns very well with the growing body of observation based studies that indicate a CO2 sensitivity of less than one degree C. This growing body of evidence makes the increasingly hot climate models look completely unrealistic. Thus that there is no climate emergency now looks very likely.

  • David Wojick, Ph.D. is an independent analyst working at the intersection of science, technology and policy. For origins see For over 100 prior articles for CFACT see Available for confidential research and consulting.

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