Tyndall's Experiment as Basis of CO2 Alarmism

CO2 alarmism goes back to experiments by John Tyndall reported in the Philosophical Transactions of the Royal Society as THE BAKERIAN LECTURE: On the Absorption and Radiation of Heat by Gases and Vapours,and on the Physical Connexion of Radiation, Absorption, and Conduction, February 7, 1861.

Tyndall describes the apparatus used to study the radiative power of different gases as follows:

In short, the emissivity of different heated gases were recorded by a thermopile with the following result:

• air, oxygen, nitrogen, hydrogen: 0
• carbonic oxide: 12
• carbonic acid: 18
• nitrous oxide: 29 
• olefiant gas: 53.  

The experiments thus showed a definite measurable emissivity of high concentration of CO2, but no measurable emissivity for air with low concentration of CO2 (for a closer analysis see Text of Tyndall). 

Yet the experiments by Tyndall are often presented as the first key evidence of the warming effect of atmospheric CO2 followed by On the Influence of Carbonic Acid in the Air upon the Temperature on the Ground (1896) by Swedish Nobel Laureate Svante Arrhenius (fearing a coming ice age by too little CO2).