Destructive Criticism - Four Revolutions in the Earth Sciences - page 211

Destructive Criticism
The Hypothesis Evidently Fails
In the 1890s, as Arrhenius was making his onerous calculations, scientists like
Langley were just beginning to explore the absorption of the Sun's rays by atmo-
sphericgases.InSweden,aphysicistnamedKnutÅngströmandhisassistant,Herr
J. Koch, filled a 30 cm tube with CO 2 , sent heat radiation through it, and meas-
ured the fraction that came out the other end. Next Herr Koch reduced the amount
of CO 2 in the tube by one-third and repeated the measurement. But it made little
difference: barely any more heat radiation passed through the cylinder. Thus it ap-
peared that the smaller amount of CO 2 had absorbed as much infrared radiation as
CO 2 is capable of absorbing. But Arrhenius had claimed that adding CO 2 to the
atmosphere would cause more absorption and more warming. The spectroscopy of
Ångström and Koch appeared to show that he was wrong.
In1900,Ångströmpublishedthefindinginanarticletitled“ÜberdieBedeutung
des Wasserdampfes und der Kohlensaüres bei der Absorption der Erdatmosphäre”
(“On the Importance of Water Vapor and Carbon Dioxide in the Absorption of
the Atmosphere”). 1 The ink on the article had hardly dried when the widely read
Monthly Weather Review of June 1901 used Ångström's finding to debunk Arrhe-
nius's theory, writing that “A layer [of CO 2 ] so thick as to be equivalent to that
contained in the earth's atmosphere will absorb about 16 per cent of the earth's ra-
diation, and this absorption will vary very little with any changes in the proportion
of carbon dioxide gas in the air.”
The article said that Ångström's criticism had been “destructive” to Arrhenius's
theory, which had been “quite inadmissibly inferred [and based on] incorrect
premises.” The “hypothesis evidently fails,” the authors concluded. 2 Such preju-
dicial language aims not merely to cast doubt on a theory but to remove it from
further consideration.
The article identified a second alleged flaw in Arrhenius's reasoning. In the at-
mosphere, CO 2 obviously does not act alone. Tyndall had found that water vapor
absorbs more infrared radiation than CO 2 and that the atmosphere holds a lot more
water vapor. As far as anyone at the turn of the century knew, in the bands of the
spectrum where water vapor already absorbs infrared radiation, adding more CO 2
could not cause more absorption because there would be no infrared rays left to