Updated: The Shrinking
CO2 Climate Sensitivity
A recently highlighted paper published by atmospheric scientists Scafetta et al., (2017) featured a graph (above) documenting post-2000 trends in the published estimates of the Earth’s climate sensitivity to a doubling of CO2 concentrations (from 280 parts per million to 560 ppm).
The trajectory for the published estimates of transient climate response (TCR, the average temperature response centered around the time of CO2 doubling) and equilibrium climate sensitivity (ECS, the temperature response upon reaching an equilibrium state after doubling) are shown to be declining from an average of about 3°C earlier in the century to below 2°C and edging towards 1°C for the more recent years.
This visual evidence would appear to indicate that past climate model determinations of very high climate sensitivity (4°C, 5°C, 6°C and up) have increasingly been determined to be in error. The anthropogenic influence on the Earth’s surface temperature has likely been significantly exaggerated.
Scafetta et al., 2017 “Since 2000 there has been a systematic tendency to find lower climate sensitivity values. The most recent studies suggest a transient climate response (TCR) of about 1.0 °C, an ECS less than 2.0 °C and an effective climate sensitivity (EfCS) in the neighborhood of 1.0 °C.”
“Thus, all evidences suggest that the IPCC GCMs at least increase twofold or even triple the real anthropogenic warming. The GHG theory might even require a deep re-examination.”
An Update On The Gradually Declining Climate Sensitivity
The graph shown in Scafetta et al. (2017) ends in 2014, which means that papers published in the last 3 years are not included. Also, there were several other published climate sensitivity papers from the last decade that were excluded from the analysis, possibly because they did not include and/or specify TCR and/or ECS estimates in isolation, but instead just used a generic doubled-CO2 climate sensitivity value (shown in purple here).
Below is a new, updated graph that (1) includes some of the previously unidentified papers and (2) adds the 10 – 12 climate sensitivity papers published in the last 3 years. Notice, again, that the trend found in published papers has continued downwards, gradually heading towards zero. The reference list for the over 20 additional papers used for the updated analysis is also included below.
For a more comprehensive list of over 60 papers with very low (<1°C) climate sensitivity estimates, see here.
Smirnov, 2017 (~0.4°C)
It is shown that infrared emission of the atmosphere is determined mostly by atmospheric water. One can separate the flux of outgoing infrared radiation of the atmosphere from that towards the Earth. The fluxes due to rotation-vibration transitions of atmospheric CO2 molecules are evaluated. Doubling of the concentration of CO2 molecules in the atmosphere that is expected over 130 years leads to an increase of the average Earth temperature by (0.4±0.2) K mostly due to the flux towards the Earth if other atmospheric parameters are not varied.
[W]e take into account that CO2 molecules give a small contribution to the heat Earth balance and, therefore, one can use the altitude distribution of the temperature for the standard atmosphere model , and a variation of the CO2 concentration does not influence this distribution. … [I]njection of CO2 molecules into the atmosphere leads to a decrease of the outgoing radiation flux that causes a decrease of the average Earth temperature. But this decrease is below 0.1K that is the accuracy of determination of this value. Thus, the presence of carbon dioxide in the atmosphere decreases the outgoing atmospheric radiative flux that leads to a decrease of the Earth temperature by approximately (1.8 ± 0.1) K. The change of the average temperature at the double of the concentration of atmospheric CO2 molecules is determined by the transition at 667cm−1 only and is lower than 0.1K.
In particular, doubling of the concentration of CO2 molecules compared to the contemporary content increases the global Earth temperature by ΔT = 0.4 ± 0.2K. … From this we have that the average temperature variation ΔT = 0.8 ◦C from 1880 up to now according to NASA data may be attained by the variation of the water concentration by 200ppm or Δu/u ≈ 0.07, Δu = 0.2. Note that according to formula (2) the variation of an accumulated concentration of CO2 molecules from 1959 (from 316ppm up to 402ppm) leads to the temperature variation ΔT = 0.15°C. One can see that the absorption of a water molecule in infrared spectrum is stronger than that of the CO2 molecule because of their structures, and the injection of water molecules in the atmosphere influences its heat balance more strongly than the injection of CO2 molecules.