First measurement of anthropogenic global warming

This is the 2nd episode in a series recounting the history of measurements and data related to Global Climate Change. If you’re just joining, you can read about two British scientists’ adventures with leaves and early CO2 measurements in the 1st episode.

Figure 4 from G. S. Callendar, The artificial production of carbon dioxide and its influence on temperature; Quarterly Journal of the Royal Meteorological Society 64 (1938), 223-240.

Guy Callendar, a British steam engineer and inventor, referenced Brown & Escombe’s atmospheric carbon dioxide measurements four decades later in his paper (Callendar, 1938), famous in climate science, which opened with the following sensational claim:

“Few of those familiar with the natural heat exchanges of the atmosphere, which go into the making of our climates and weather, would be prepared to admit that the activities of man could have any influence upon phenomena of so vast a scale. In the following paper I hope to show that such influence is not only possible, but is actually occurring at the present time.”

(A note of foreshadowing: As we continue in our pursuit of knowledge about climate science, it may become astounding to realize the quote above, from the year 1938, quite resembles the state of very recent “debate” that occurred on the floor of our 2015 U.S. Senate. Article about Senate absurdity. Video of Senate absurdity.)

In his peer-reviewed 1938 paper, Callendar made use of a number of other scientific studies that had taken place since around the turn of the 20th century, which he believed for the first time enabled a reasonable calculation of the effect on Earth’s temperature of CO2 increases from the burning of fossil fuels:

  • More accurate measurements of infrared absorption by CO2 (Rubens & Aschkinass, 1898);
  • The temperature-pressure-alkalinity-CO2 relation for seawater (C. J. Fox, 1909);
  • Measurements of atmospheric radiation of heat (A. Angstrom, 1918; W. H. Dines, 1927; G. C. Simpson, 1928; D. Brunt, 1932);
  • Infrared absorption measurements of water vapor (F. E. Fowle, 1918).

Callendar had the benefit of more atmospheric CO2 measurements that had been taken in the eastern U.S. between 1930 and 1936. These averaged 310 ppm, about 6% higher than the earlier measurements at the Royal Botanical Gardens around 1900. Taking into consideration better estimates of the expected absorption of CO2 by the oceans, Callendar calculated that a 6% increase was about consistent with the estimated addition of CO2 to the atmosphere by the combustion of fossil fuels (about 4,500 million tons per year at the time). Most of the added CO2 seemed to be staying airborne.

Taking account of infrared absorption by both CO2 and water vapor, downward radiation of absorbed heat from the sky, and the effect of this on surface temperature, Callendar calculated that Earth’s temperature at the surface should be increasing at the rate of about 0.003 degrees Celsius per year.

Callendar then undertook a staggering project of collecting, sorting, analyzing, and averaging measured temperatures from hundreds of global weather stations that had been collected since about 1880 (earlier standardized records did not exist). It’s frankly hard for me to imagine doing this overwhelming project, as he did, without even a calculator. He summarized his findings in the graph at the top of this post.

In all 3 major climate zones of the Earth in which temperature records existed, Callendar found the temperature variation, with respect to the 1901-1930 mean temperature, to be remarkably consistent. Everywhere on the Earth, the temperature had increased, over approximately the previous half-century, at an average rate of 0.005 degrees Celsius per year, a somewhat greater increase than he had calculated based on the CO2 increases. But he admitted the temperature record was rather short in duration, and further observation was warranted.

Interestingly, Callendar remarked at the end of his paper that he thought global warming resulting from the combustion of fossil fuels would be beneficial by preventing “the return of the deadly glaciers” (referring, it would seem, to the ice ages). Writing as he was in 1938, and only having observed the first glimmer of Global Climate Change, he can be forgiven for underestimating the future enthusiasm with which we would burn fossil fuels. By the end of it, we may find ourselves nostalgic for the glaciers we have now.

To be continued…

Continue to 3rd episode

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