Guy Callendar was a superb scientist and an expert on the physics of steam. He wrote a seminal article in 1938 on the potential for increasing levels of CO2 to warm the atmosphere:

Callendar posited a logarithmic relationship between concentration of CO2 and global temperatures, as shown in this graph:

By Callendar’s calculation, a doubling in CO2 from 300 ppm to 600 ppm would cause about a 1.7 degree C increase in atmospheric temperature. What is interesting about this is that Callender’s calculations track much more closely with actual temperatures than the formulas that are used by alarmists today. The reason is that the alarmists’ models build in hypothetical positive feedback effects in order to generate greater temperature impacts. Steve McIntyre explains:

[I]t is completely bizarre that a simple reconstruction from Callendar out-performs the CMIP5 GCMs – and, for most of them, by a lot. … Even if the Callendar parameters had been calculated using the observed temperature history, it is surely surprising that such a simple formula can out-perform the GCMs, especially given the enormous amount of time, resources and effort expended in these GCMs. And, yes, I recognize that GCMs provide much more information than GLB temperature, but GLB temperature is surely the most important single statistic yielded by these models and

it is disquieting that the GCMs have no skill relative to a reconstruction using only the Callendar 1938 formula. As Mosher observed in a comment on the predecessor post, a more complicated model ought to be able to advance beyond the simple model and, if there is a deterioration in performance, there’s something wrong with the model.

Emphasis added. The modest temperature increase suggested by Callendar, and validated so far by observation, poses no threat, and won’t bring about any of the catastrophic consequences that the alarmists are paid to predict. Callendar himself thought the effect of increasing CO2 in the atmosphere would be salutary:

It may be said that the combustion of fossil fuel, whether it be peat from the surface or oil from 10,000 feet below, is likely to prove beneficial to mankind in several ways, besides the provision of heat and power. For instance the above mentioned small increases of mean temperature would be important at the northern margin of cultivation, and the growth of favourably situated plants is directly proportional to the carbon dioxide pressure (Brown and Escombe, 1905): In any case the return of the deadly glaciers should be delayed indefinitely.

It is somewhat ironic that the “science” of global warming has regressed since 1938.