In this era of post-truth media and politics, it is often difficult to hold on to long held beliefs and understandings. The very reality that seemingly existed yesterday slips away and is replaced by something quite different, perhaps based on cherry picked data or assertions that have little or no factual basis. This is happening all around us and the subject of climate change has had its fair share of post-truth assertions thrown at it.
Therefore, the opportunity to reach back in time and bring reality to the fore should be encouraged and valued. I was fortunate to have such an experience over Christmas, with the gift from my wife of the original 1896 publication that presented the detailed calculations behind the change in global temperature that would be observed should the level of carbon dioxide in the atmosphere change. The work in question is the well-known article by Swedish chemist Svante Arrhenius, On the Influence of Carbonic Acid in the Air upon the Temperature of the Ground published in The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science. I am now the very proud owner of Vol. XLI – Fifth Series, January-June 1896, which also contains dozens of articles on subjects ranging from glacial geology of Arctic Europe to temperature correction of barometers.
Arrhenius was actually looking for an explanation for the occurrence of Ice Ages, which were known about from the geological record but could not be explained in terms of expected cooling due to orbital fluctuations of the Earth around the Sun. It was clear that another factor was at work, accelerating and amplifying the impact of the small changes in solar radiation. He established that carbon dioxide in the atmosphere could do this. During each of the periodic ice ages over the last million years, the amount of solar energy reaching the planet dips due to the orbital variations and, consequently, the ocean / atmosphere system cools slightly. This allows the amount of carbon dioxide dissolved in the ocean to increase and therefore the atmospheric carbon dioxide level drops. That drop results in further cooling, causing the much bigger shift in temperature than would be expected from a straight radiation balance calculation.
In his paper Arrhenius established a methodology for linking the change in surface temperature with the change in the level of carbon dioxide (carbonic acid as he referred to it as) in the atmosphere. Table VII of the paper showed the results of his calculation for different levels of carbon dioxide ranging from K=0.67 (where K=1 for the level in the atmosphere at the time or ~280 ppm) to K=3.0 (which would equate to 840 ppm) . At the equator he derived the following results;
The Arrhenius paper also discusses the work of a Professor Högblom, another Swedish scientist of the day, who had even calculated how much the burning of coal at that time (500 million tonnes per annum) might change the surface temperature of the planet. The number was very small, but today annual fossil carbon extraction is some twenty to thirty times greater than this and more importantly the cumulative extraction (which we now know is what actually matters) since the late 19th century is hundreds of times this level. It may well have been this calculation that led to a 1912 story in Popular Mechanics on the impact coal use would have on the climate.
In this post-truth world, let us not forget that there is reality to hold on to. Happy New Year.