Geoscience Reference
In-Depth Information
Callendar used the new information, particularly the absorption of radiation by
CO
2
in three wavelength bands, to calculate the effect on the “downward radiation
from the sky, usually called the 'sky radiation'” (227). He divided the atmosphere
into twelve horizontal layers of known temperature, water vapor, and carbon di-
oxide content, calculated the absorbing power of each layer, and summed them to
obtain the vertical component of the sky radiation. Echoing Arrhenius, Callendar
said: “The method . . . is simple but laborious.”
Doubling atmospheric CO
2
would cause global temperature to rise by close to
2°C, Callendar's chart showed. But his calculations did not include the effect of
the feedbacks, such as the ice-water and water-vapor feedbacks. By modern estim-
ates, these add about 2°C to the temperature effect of doubling CO
2
. Had Callen-
dar been able to include them, the feedbacks would have raised his estimate of the
effect of doubling CO
2
to close to 4°C, only slightly higher than today's estimate.
Nevertheless, he did not believe that atmospheric CO
2
could have risen and fallen
by enough to account for the ice ages because “the almost inexhaustible supply
from the oceans” would have acted as a buffer and maintained atmospheric CO
2
roughly constant. Like Tyndall, Arrhenius, and Ekholm, Callendar viewed an in-
crease in CO
2
as a good thing, “likely to prove beneficial to mankind” by expand-
ing the range of agriculture and delaying the return of the “deadly glaciers indefin-
itely” (228).
The first to rise to comment on Callendar's paper was Sir George C. Simpson,
already on record as rejecting Arrhenius's theory. Callendar's presentation had not
changed his mind. As the meeting scribe reported, Simpson “thought it not suffi-
ciently realized bynon-meteorologists whocame forthefirsttime tohelptheSoci-
ety in its study, that it was impossible to solve the problem of the temperature dis-
tribution in the atmosphere by working out the radiation. . . . The rise in CO
2
con-
tent and temperature during the last 50 years,” Simpson summed up, was “rather a
coincidence” (237).
Undaunted, Callendar replied with the irrefutable logic ofFourier,Pouillet, Tyn-
dall, and Arrhenius: “If any substance is added to the atmosphere which delays the
transfer of low temperature radiation, without interfering with the arrival or dis-
tribution of the heat supply, some rise of temperature appears to be inevitable in
those parts which are furthest from outer space” (239).
C. E. P. Brooks was more positive, having no doubt that “there had been a real
climatic change during the past thirty or forty years.” Though he did not believe
that a change in the amount of carbon dioxide was the cause, “the possibility mer-
ited discussion and he welcomed the paper as a valuable contribution” (238). But
