An odd new theory: Stratospheric cooling increases the surface temperature
The so called Anthropogenic Global Warming (AGW) theory has based on the absorption of longwave (LW) radiation emitted by the Earth’s surface. The major absorber is carbon dioxide (CO2) besides other greenhouses (GH) gases and clouds. In this story, the impacts of CO2 will be analyzed.
It is not generally known how quickly the absorption process happens in the atmosphere (Fig. 1): 0,01 km 34 %, 0,1 km 67 %, 1 km 90 %, 2 km 95 %, 11 km 98 %, 50 km 100 %, Ref. 1. Because absorption has a key role in the AGW theory, you could except that the warming effects happen in the same way. But you wrong. A new theory has been introduced by well-known climate scientists during the latest 4-5 year with astonishing results.
Figure. 1. The total absorption in the atmosphere according to the altitude.
The Concepts of Instantaneous Forcing and Rapid Adjustments
The warming effect of enhanced GH effect is based on the mechanism where GH drivers increase LW absorption in the atmosphere and this causes unbalance to the Earth’s energy balance by decreasing the LW radiation into space. Since the cooling rate of the surface has decreased, the surface’s temperature starts to increase, which causes an increase in the emitted LW radiation. Finally, the LW radiation at the TOA (top of the atmosphere) will reach its original value before a perturbation.
It should be noticed that the Earth's energy balance reacts on the SW and LW radiation changes and not for example on temperature changes in different parts of the atmosphere. The energy balance can be achieved with different temperature profiles in the atmosphere if the energy balance can be satisfied.
The IPCC has used the Radiative Forcing (RF) equation of Myhre et al. (henceforth MHSS98, Ref. 1) for CO2 in the three latest Assessment Reports 2001, 2007, and 2011 for calculating RF at the top of the atmosphere (TOA). The RF equation of Ollila (henceforth Ollila14, Ref. 2) has the same form
RF = k * ln(C/208) (1)
where k is 5.35 (Ref. 1) or 3.12 (Ref. 2), and C is the concentration of CO2 (ppm). MHSS98 has used the term “Instantaneous Radiative Forcing” (IRF) meaning the RF value calculated by the means of Line-By-Line (LBL) spectral analysis method or by a narrow or broadband method at the tropopause. MHSS98 introduced two adjustment terms for the IRF and they were negative shortwave RF in the stratosphere -0.11 Wm-2 and positive stratospheric cooling +0.05 Wm^2 totaling -0.06 Wm^2 for the CO2 concentration change from 280 ppm to 363 ppm.
IPCC has defined RF at the tropopause or the top of the atmosphere due to a change in an external driver of climate change. Since RF values can be calculated at two different places of the atmosphere a new term has been introduced. The IPCC has used the term Effective Radiative Forcing (ERF) to mean the final RF after stratospheric adjustments (marked As here) to IRF and the ERF happens always at the TOA and it is simply ERF = IRF + As.
In the case of MHSS98, the ERF of CO2 concentration 560 ppm (henceforth 2*CO2) is the sum of these three entities ERF = 3.86 – 0.29 + 0.13 = 3.71 Wm^2. The adjustment terms have been estimated from the reported values for CO2 the concentration of 363 ppm versus 560 ppm.
Etminan et al. (henceforth EMHS16, Ref. 3) has updated the original calculations of MHSS98 using the latest HITRAN databases and atmospheric data and the calculated value of 3.82 Wm^2 for 2*CO2 is remarkably close to the value of MHSS98.
After the last IPCC’s report in 2013, researchers have introduced more adjustments in addition to the stratospheric cooling. A comprehensive presentation comes from Chung & Soden (Ref. 4) with six different adjustments
ERF = IRF + AT + AS + ATS + AW + Aa + Ac +E (2)
where Ax is a rapid adjustment due to tropospheric temperature (T), stratospheric temperature (S), surface temperature (TS), water vapor (W), surface albedo (A), and clouds (C), and E is a residual that accounts for nonlinearities. According to the analyses of Smith et al. (henceforth S&al18, Ref. 5) the critical adjustment in equation (2) is the stratospheric temperature adjustment because the sum of other adjustments is practically zero. ERF value of 2*CO2 is thus ERF = IRF + AS = 2.6 + 1.1 = 3.7 Wm^2 (estimated from a graphical presentation).
In Figure 2 has been depicted the instantaneous RF values, stratospheric adjustments, and ERF values according to the studies of MHSS98 and S&al18 for 2*CO2. The ERF value of Ollila (Ollila14, Ref. 1) for 2*CO2 is 2.16 Wm^2.
Figure 2. The instantaneous RF, stratospheric adjustments, and ERF values according to different studies for CO2 is 560 ppm (2*CO2). The RF values are in Wm^2.
The ERF values of MSHH98, EMHS16, and S&al18 are close to each other. There is a big difference between the value IRF value of 2.6 Wm^2 of S&al18 and 3.86 Wm^2 of MHSS98. There are essential differences in calculation methods. The IRF of MHSS98 is based on the spectral calculations at the tropopause, the ERF of EMHS16 is based on the spectral calculations at the TOA, and S&al18 values are based on the average IRF values of 11 Global Climate Models (GCM). The researchers of S&al18 have carried out simulations with these models applying 2*CO2 concentration of 280 ppm and 560 ppm. They call simulation runs “experiments” as if they had been carried out in the real climate conditions.
There is a straightforward method for calculating ERF values. The ERF values of Ollila14 and EMHS16 have been calculated by spectral analysis from the surface to the TOA. The spectral analysis applications have no theoretical or practical problems to include the atmosphere above the tropopause. The ERF value of EMHS16 is practically the same as S&al18.
At the tropopause already more than 98 % of the total absorption has happened. The enhanced GH effect is based on the absorption impact. It is very contradictory to think that something happening in the stratosphere would have a contribution of about 30 % in the total ERF thinking the fact that only 2 % of total absorption happens there.
The magnitude of stratospheric cooling impact for 2*CO2 is -0.13 Wm^2 by MHSS98 and the same by S&al18 is +1.1 Wm^2. There are no comments about these striking differences in the latter paper of S&al18 – even the cooling has changed into warming effect – and Myhre is an author in both papers. Therefore, a separate analysis is needed about stratospheric cooling and it is one of the objectives of this study.
The absorption areas of GH gases have been depicted in Figure 3 according to wavelengths and it is useful information for understanding the stratospheric cooling phenomenon. According to the spectral analysis calculations of Ref. 2, in the stratosphere ozone absorbs 66 %, water 32.5 %, and methane & nitrogen oxide 1.5% in the present-day climate. The absorption of ozone happens in the so-called “atmospheric window” wave zone from 9 to 10 µm. In Fig. 3 it can be noticed that the ozone’s absorption peak is much greater in the stratosphere than in the troposphere. The reason is that water is the only GH gas capable to absorb in the absorption zone of ozone, but its concentration is extremely low in the stratosphere. CO2 is so strong absorber is its wavelength zone from 12 to 19 µm that its absorption does not increase after 1 km altitude. Strong absorption of O3 in the stratosphere and non-existing absorption of CO2 are decisive features in stratospheric cooling.
Figure 3. Absorption bands and areas of GH gases being alone in the atmosphere. The total absorption curve (a purple line) illustrates the average global climate conditions.
When CO2 absorption increases, the lower part of the atmosphere warms, less upwelling radiation in the non-window part reaches the higher altitudes and therefore these altitudes cool. The stratosphere is warmer than the troposphere and it is caused mainly by shortwave absorption of O3 and partially by LW radiation absorption of O3 in the region from 9 µm to 10 µm and these absorptions remain practically the same regardless of CO2 concentration changes. When the absorption by CO2 increases in the troposphere, it reduces the absorption of water (the main competitor with the CO2 absorption) also in the stratosphere in the wavelength zone from 12 to 14 µm, Table 1.
Table 1. The absorptions (Wm^2) by GH gases in the stratosphere for CO2 concentrations of 280 ppm and 560 ppm applying the atmospheric GH gas profiles of the year 2015. B. LW radiation upward (LWup) values and changes at the tropopause and at the TOA (70 km). Both calculations have been carried out in clear sky conditions.
The results summarized in Table 1 show that the stratospheric absorption decreases when the CO2 concentration increases from 280 ppm to 560 ppm. Table 1 shows that the IRF value of 3.196 Wm^2 is 0.507 Wm^2 greater than the ERF value of 2.689 Wm^2. It means that the stratospheric cooling decreases the final ERF value and the term “stratospheric cooling” is justified: less absorption means lower forcing and lower temperature. This result is univocal, and it contradicts the results of references 4 and 5. This result is in line with Figure 1 showing that at the tropopause the absorption value is already about 98 % of the total absorption in the atmosphere indicating that the stratospheric cooling has an insignificant role in the ERF value anyway.
The conclusion about the stratospheric cooling is that it is a real phenomenon, but its impact does not increase RF but decreases it. In this respect, the stratosphere does not differ from the troposphere. The earth’s energy balance reacts to LW radiation changes at the TOA and it does not matter if the absorption changes happen in the troposphere or in the stratosphere.
It is now an interesting issue what is the decision of the IPCC in the coming Assessment Report A6 which is in the second review step. The level of confidence for the CO2 forcing concept was “very high” in the AR5. It should be embarrassing to the IPCC to change the calculation basis of Myhre et al. to the Smith et al. It is even more embarrassing because now the concept would be against the physical laws. We have seen these kinds of changes and the IPCC does not explain the groundings of changes.
One more observation about the references 3-5: They do not mention the term “Greenhouse effect” at all. For me, it means a paradigm change. It means also that they know that definition of the GH effect of the IPCC is against the physical laws and that is why the climate establishment must fade out this term.
1. Myhre G, Highwood EJ, Shine KP, Stordal F. New estimates of radiative forcing due to well mixed greenhouse gases. Geophys Res Lett 1998;25:2715-2718.
2. Ollila A. The Greenhouse Effect Calculations by An Iteration Method and The Issue of Stratospheric Cooling. Phys Sci Int J 2020;24(7)):1-18.
3. Etminan E, Myhre G, Highwood EJ, Shine KP. Radiative forcing of carbon dioxide, methane, and nitrous oxide: A significant revision of methane radiative forcing. Geophys Res Lett 2016;43:12614-12636.
4. Chung ES, Soden BJ. An assessment of direct radiative forcing, radiative adjustments and radiative feedbacks in coupled ocean–atmosphere models. J Clim. 2015;28(10):4152–4170. 5. Smith CJ, Kramer RJ, Myhre G, Forster PM, Soden BJ, Andrews T, Boucher O, Faluvegi G, Fläschner D, Hodnebrog Ø, Kasoar OM, Kharin V, Kirkevåg VA, Lamarque J-F, Mülmenstädt J, Olivié D, Richardson T, Samset BH, Shindell D, Stier P, Takemura T , Voulgarakis A, Watson-Parris D. Understanding rapid adjustments to diverse forcing agents. Geophys Res Lett 2018;45:12023–12031.