Page 22 - James Rodger Fleming - Fixing the sky

Age.” In this scenario, climate warming by enhanced coal burning would be pit-
ted against the natural changes in the Earth’s orbital elements, recently identified
by James Croll, or the secular cooling of the Sun, as pointed out by Lord Kelvin
(William Thomson). Ekholm concluded, “It is too early to judge of how far Man
might be capable of thus regulating the future climate. But already the view of
such a possibility seems to me so grand that I cannot help thinking that it will
afford Mankind hitherto unforeseen means of evolution.” 7
Arrhenius popularized Ekholm’s observations in his book Worlds in the Mak-
ing, noting that “the slight percentage of carbonic acid in the atmosphere may
by the advances of industry be changed to a noticeable degree in the course of a
few centuries.” Arrhenius considered it likely that in future geological ages, the
Earth would be “visited by a new ice period that will drive us from our temper-
ate countries into the hotter climates of Africa.” on the timescale of hundreds
to thousands of years, however, Arrhenius agreed with Ekholm that a “virtuous
circle” could be defined in which the burning of fossil fuels could help prevent a
rapid return to the conditions of an ice age and could perhaps inaugurate a new
carboniferous age of enormous plant growth.
Yet in the early decades of the twentieth century, the carbon dioxide theory
of climate change, along with the human influence theory, fell out of favor with
most scientists. Most scientists believed that at current atmospheric concentra-
tions, carbon dioxide already absorbed all the available long-wave radiation;
thus any increases would not change the radiative heat balance of the planet.
The person responsible for reviving the ideas of Arrhenius and Ekholm and plac-
ing them on a revised scientific basis was Guy Stewart Callendar (1898–1964),
a British steam and defense engineer. In 1938 Callendar reformulated the car-
bon dioxide theory by arguing that rising global temperatures and increased
fossil fuel burning were closely linked. He compiled weather data from stations
o
o
around the world that clearly indicated a climate warming trend of 0.5 C (0.9 F)
in the early decades of the twentieth century. His estimate of 290 parts per mil-
lion for the nineteenth-century background concentration of Co is still a valid
2
estimate, and he documented an increase of 10 percent between 1900 and 1935,
which closely matched the amount of fuel burned. on the basis of new under-
standing of the infrared spectrum and calculations of the absorption and emis-
sion of radiation by trace gases in the atmosphere, Callendar established the car-
bon dioxide theory of climate change in its recognizably modern form, reviving
it from its earlier, physically unrealistic and moribund status. Today the theory
that global climate change can be attributed to an enhanced greenhouse effect
resulting from elevated levels of carbon dioxide in the atmosphere from anthro-
pogenic sources and activities is called the Callendar effect. 8

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