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At next month’s American Geophysical Union (AGU) Fall Meeting in New Orleans (US), an independent researcher named Trevor Underwood will be presenting an equation-rich analysis that thoughtfully undermines the perspective that increases in CO2 concentrations are a fundamental variable affecting climate.

Instead, Underwood argues that the absorption band where CO2 emissivity could have an effect is likely already saturated, precluding the capacity of increased CO2 concentrations to produce atmospheric warming.

He also advances the position that solar irradiance changes can explain modern temperature variations, which is consistent with other recent analyses.

It seems that more and more of these papers questioning the “consensus” view on the efficacy of the CO2 within the greenhouse effect are being considered in scientific circles. Several previous examples are listed below.

The volume of contrarian analyses would seem to suggest that the climate’s specific sensitivity to CO2 concentration changes is not yet settled.

And so the debate rages on.

No Increase in Earth’s Surface Temperature From Increase in Carbon Dioxide

A critical look at these different in situ measures of the Earth’s surface temperature identified a divergence between land and marine surface temperatures, with land surface air temperatures showing a significant and increasing rate of warming of around 0.5°C between 1880 and 1981, and 0.7°C between 1982 and 2010, whilst marine air temperatures show little if any change between 1880 and 2010 (Underwood (1) 2017). Recent academic literature is also beginning to question the accuracy of the adjusted in situ data (Kent et al. 2017).

In order for an increase in carbon dioxide or other greenhouse gas concentration in the atmosphere to result in an increase in the surface temperature of the Earth, it must be able to increase the absorption of infrared radiation emitted from the surface. This would result in an increase in the absorption factor, f. However, as seen above f is currently around 0.9444. Absorption of infrared radiation by molecules of greenhouse gases, involves increasing the internal energy of the molecule by changing the quantum state of the molecules, which can only occur at particular wavelengths, known as absorption bands.

These absorption bands can be extended by what is referred to as pressure broadening (Strong and Plass 1950; Kaplan 1952), but when all of the emitted infrared radiation within these absorption bands has been absorbed by greenhouse gas molecules in the atmosphere, no further absorption of the terrestrial radiation is possible. The radiation with wavelengths falling outside of the absorption bands passes through the atmosphere and escapes into space.

Absorption of solar radiation in in the stratosphere is almost 100% efficient in the ultraviolet due to electronic transitions of oxygen (O2) and ozone (O3) and a significant amount of solar radiation is absorbed by water vapor (H2O) in the lower atmosphere. It is primarily the visible radiation that is absorbed at the Earth’s surface. In the infrared, absorption is again almost 100% efficient because of the greenhouse gases, but there is a window between 8 and 13 mm, near the peak of terrestrial emission, where the atmosphere is only a weak absorber except for a strong ozone feature at 9.6 mm. This atmospheric window allows direct escape of radiation from the surface of the Earth to space and is of importance in determining the temperature of the Earth’s surface (Jacob 1999).

Additional leakage could occur if the greenhouse gas concentration in the atmosphere were insufficient to absorb all of the infrared radiation in the absorption bands emitted by the Earth’s surface, but due to the extent of the atmosphere and its known unsaturated state, it is more likely that the current leakage corresponds to radiation in the part of the infrared spectrum that does not fall in the greenhouse gas absorption and emission bands, referred to as the “infrared window”. As a consequence, even in the case where there is leakage of infrared radiation from the Earth’s surface directly into space, as long as the atmosphere is able to absorb all of the upwelling infrared radiation in the greenhouse gas absorption bands, neither the amount of this leakage nor the amount of the absorption will depend on concentration of greenhouse gases in the atmosphere. From the emission spectra (a) and absorption percentages (b) in the diagram above (Fig. 2.6, Yang 2016), where the 255°K blackbody curve represents the terrestrial radiation, it appears that at the current surface temperature and absorption factor of 0.9444 all of the radiation within the emission bands is fully absorbed, and that the remaining 5.56 percent of the infrared emission represents radiation with wavelengths within the atmospheric window. If this is true, there can be no further increase in f [absorption] , and no increase in the surface temperature with an increase in carbon dioxide .

Increase In Solar Forcing Explains Recent Warming

The difference between the minima showed an increase of 0.2812 W/m-2 for VIRGO; 0.4701 W/m-2 for ACRIM; and 0.2650 W/m-2 for ACRIM + TIM over the 11.6 year solar cycle 23 beginning in May 1996 and ending in January 2008; or 0.24 W/m-2 per decade for VIRGO, 0.40 W/m-2 per decade for ACRIM, and 0.23 W/m-2 per decade for ACRIM + TIM (pmodwrc website

2016).

These decadal increases in TSI [Total Solar Irradiance] from ACRIM, SARR, VIRGO and ACRIM + TIM are sufficient to explain the whole of the increase in surface temperature estimated from in situ data during the last 100 years. They compare with the six published model-based estimates of forcing examined in Schwartz (2012) that showed forcing by incremental greenhouse gases and aerosols over the twentieth century ranging between 0.11 and 0.21 W/m-2 per decade.

Summary

Solution of the Greenhouse Effect equations based on a more realistic atmospheric model that includes absorption of solar radiation by the atmosphere, thermals and evaporation, and an examination of the fraction of terrestrial infrared radiation absorbed whilst passing through the atmosphere, suggests that the contribution of greenhouse gases to the surface temperature is close to its upper limit. Any further contribution would depend on an increase in the infrared absorption factor of the atmosphere from its current level of around 0.9444, which seems unlikely. As this appears to correspond to total absorption of all black body infrared emission from the Earth’s surface at wavelengths at which there are greenhouse gas absorption bands, including for water vapor, it seems likely that we are close to the thermodynamic limit of greenhouse warming for the current luminosity of the sun, and that any further increase in carbon dioxide concentration in the atmosphere will have little or no effect on the surface temperature of the Earth . Questions about the reliability of in situ measurements of surface temperatures also raise questions about current estimates of global warming. Moreover, recent evidence from satellite measurements of solar irradiance, indicate that any recent warming could be due to increasing solar irradiance.

A conference paper with a similar conclusion regarding the emissive/warming limitations of increased CO2 concentrations was presented by a molecular physicist, Dr. N. Doustimotlagh, at the World Conference On Climate Change in October, 2016.

So because of the limited values of electromagnetic waves that come from Earth and limitation of absorption of greenhouse gasses, the greenhouse effect of greenhouse gasses should be limited. In other words, after absorbing of all the IR waves that come from Earth by greenhouse gasses in the atmosphere, there are no IR wa ves to cause greenhouse effect. It means that “two things that cause greenhouse effect are greenhouse gasses and IR waves in absorption spectrum of these gasses, so if greenhouse gasses increases but there are no IR waves, it is natural that there is no gr eenhouse effect”. If the concentration of CO 2 in atmosphere increases until absorbs all the values of electromagnetic waves that are absorbable for CO 2 , additional values of CO 2 should not have greenhouse effect .