The Callendar Effect: The Life and Work of Guy Stewart Callendar (1898–1964), the Scientist who Established the Carbon Dioxide Theory of Climate Change
- James Rodger Fleming
With so much written on the subject of carbon dioxide as a cause of climate change, it seems to have a settled history. But the word 'established' in this book's subtitle moved me to ask who actually came up with this now well-accepted theory, and what the basis is for James Rodger Fleming's claim that the subject of his biography holds this honour.
There seems to be little doubt that in 1827 Jean Baptiste Joseph Fourier first articulated the idea that “light finds less resistance in penetrating the air, than in repassing into the air when converted to non-luminous heat”. In the 1860s, John Tyndall showed that CO2 and water vapour both absorb and emit infrared radiation. Then, in 1896, Svante Arrhenius performed the first calculations of the sensitivity of Earth's temperature to changes in atmospheric CO2. He went on to calculate (incorrectly) that it would take some 3,000 years for a 50% increase of its atmospheric content at the prevailing rate of coal consumption. He further calculated, on the basis of the measured infrared transmission of the atmosphere by Samuel Langley, that a 50% increase of CO2 would warm Earth's surface by 3.4 °C.
So how did author Fleming come to state that the CO2 theory was established by Callendar? It seems that this credit should be given to Fourier, Tyndall and Arrhenius.
Callendar's seminal paper, 'The Artificial Production of Carbon Dioxide and its Influence on Temperature', was published in 1938, nearly half a century after these nineteenth-century works. During the intervening period, serious doubts had developed about the importance of changing atmospheric CO2 as a factor in Earth's climate and a cause of ice ages. Competing theories — changes in Earth's orbital geometry or in solar output, the role of the oceans, the attenuation of sunlight by volcanic dust, and spectroscopic considerations such as water vapour and CO2 absorbing infrared light in the same spectral regions — had seemingly brought the CO2-climate field into a 'deep eclipse'.
Callendar's 1938 paper did not include a citation of Arrhenius's 1896 paper, although there are many parallels between the two. Callendar analysed just one set of data on atmospheric CO2 content taken at Kew, near London, between 1898 and 1900. These data were taken near a source of CO2 and were analytically very uncertain. From this analysis, he concluded that at around 1900 the free atmosphere over the North Atlantic region contained 274 ± 5 parts per million (p.p.m.) of CO2. Then, after arguing that only a small fraction of the CO2 from combustion of fossil fuels would dissolve in the ocean, he calculated from an estimated global production rate of CO2 the amount that he thought would be there in 1936 (290 p.p.m.), 2000 (314–317), 2100 (346–358) and 2200 (373–396).
With a simple model of the absorption of infrared radiation, he worked out the amount of global warming to be expected from his predicted CO2 levels, concluding that temperature would then have been increasing at a rate of about 0.03 °C per decade. Callendar's 1938 attribution of early twentieth-century warming to CO2 increase might have been believable if global cooling had not ensued in the 1960s and 1970s.
His result was based on many assumptions and he used no contemporary CO2 data on which to base his estimates. Nonetheless, his prediction was almost correct and, along with his 1958 paper — which included large amounts of CO2 data (albeit of dubious quality) — his 1938 publication did rejuvenate the CO2 theory of climate change. I doubt that this amounts to establishing the theory, but it came at a time when the fields of geochemistry and climate dynamics were ripe for stimulation, especially during the International Geophysical Year (1957–58). Shortly thereafter, Charles David Keeling presented accurate data, and the rest of the story is history.
Callendar's work on climate change is just part of the story Fleming tells about Callendar's life in this well written and especially well documented book.
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Charlson, R. A lone voice in the greenhouse. Nature 448, 254 (2007). https://doi.org/10.1038/448254a