Climate sensitivity studies have been very popular subjects in the recent climate change science literature. Climate sensitivity (CS) means the temperature increase corresponding the doubling of CO2 concentration 280 ppm. A common feature in this research papers is that the climate sensitivity values are smaller than those of IPCC. In some cases the difference is a very big one like 0.6 degrees versus 1.75 degrees manifested by IPCC for transient climate sensitivity and 3.0 degrees for equilibrium CS..
The author has carried out his own CS calculation applying three different methods: The energy balance of the Earth, the specification of CS utilizing the spectral analysis method, and the absorption of LW radiation in the atmosphere. The author has calculated also the climate sensitivity parameter (CSP), which is an important quantity in transforming the radiative forcing values into temperatures according equation (1)
(1) dTs = CSP* RF
where dTs is the surface temperature of the Earth caused by the radiative forcing (RF) at the top of the atmosphere (TOA). For example, IPCC informs that CSP is practically constant and using the RF valur 3.71 W/m2 for CO2, and the CSP value 0.5 K/(W/m^2), the transient CS will be 1.75 °C.
The climate sensitivity (CS) values and climate sensitivity parameter (CSP) values according my studies are:
- Spectral Calculator: CS = 0.559 degrees, CSP = 0.259 K/(W/m^2)
- Modtran: CS = 0.584 degrees, CSP = 0.319 K/(W/m^2)
- Energy balance: CS = 0.576 degrees, CSP = 0.268 K/(W/m^2)
- Absorption: CS = 0.46 degrees.
The most reliable CSP value is the value calculated from the energy balance of the Earth, because the analysis is the simplest, containing only three measurement values, which are known with the high enough accuracy: solar constant, average cloudiness and the temperature corresponding to the outgoing LW radiation. It is also reassuring that the spectral analyses value carried out by Spectral Calculator is practically the same. As a summary the equilibrium CS of this study is 0.6 degrees and the CSP is 0.27 K/(W/m^2). When the right theory has been found, several approaches give the same results, and it is a common sign of the right theory.
In Figure below is depicted the graphs temperature change using different RF values of CO2 and different CSP values.
A major finding according to this Figure is that there is a simple explanation between the IPPC’s values and the values of author’s study. The starting point is the RF value of CO2 according to Myhre et al. When this values is multiplied by 0.5 and then by 0.26, the temperature increase follow the same graph as the author has calculated. In the author’s graph, the RF value is smaller based on the new relationship between radiative forcing and CO2 concentration.
The final conclusion is that the IPCC’s warming values are about 200 % too high (1.75 degrees versus 0.6 degrees) because both the CO2 radiative forcing equation, and the CS calculation include water feedback. It is well-known that IPCC uses the water feedback in doubling the GH gas effects; even though there are relative humidity measurements showing that this assumption is not justified. CO2 radiative forcing including also water feedback has not been recognized before the author’s studies. This feature explains too high contribution of CO2.