Greenhouse effect
In developing a theory to explain the
ice ages, Arrhenius, in 1896, was the first to use basic principles of physical chemistry to calculate estimates of the extent to which increases in atmospheric carbon dioxide (CO
2) will increase Earth's surface temperature through the
greenhouse effect.
[3][22][23] These calculations led him to conclude that human-caused CO
2 emissions, from fossil-fuel burning and other combustion processes, are large enough to cause global warming. This conclusion has been extensively tested, winning a place at the core of modern climate science.
[24][25] Arrhenius, in this work, built upon the prior work of other famous scientists, including
Joseph Fourier,
John Tyndall and
Claude Pouillet. Arrhenius wanted to determine whether greenhouse gases could contribute to the explanation of the temperature variation between glacial and inter-glacial periods.
[26] Arrhenius used infrared observations of the moon – by
Frank Washington Very and
Samuel Pierpont Langley at the
Allegheny Observatory in
Pittsburgh — to calculate how much of infrared (heat) radiation is captured by CO
2 and water (H
2O) vapour in Earth's atmosphere. Using 'Stefan's law' (better known as the
Stefan–Boltzmann law), he formulated what he referred to as a 'rule'. In its original form, Arrhenius's rule reads as follows:
if the quantity of carbonic acid increases in geometric progression, the augmentation of the temperature will increase nearly in arithmetic progression.
Here, Arrhenius refers to CO
2 as carbonic acid (which refers only to the aqueous form H
2CO
3 in modern usage). The following formulation of Arrhenius's rule is still in use today:
[27]
where
is the concentration of CO
2 at the beginning (time-zero) of the period being studied (if the same concentration unit is used for both
, then it doesn't matter which concentration unit is used);
is the CO
2 concentration at end of the period being studied;
ln is the natural logarithm (= log base e (log
e)); and
is the augmentation of the temperature, in other words the change in the rate of heating Earth's surface (
radiative forcing), which is measured in
Watts per square
meter.
[27] Derivations from atmospheric radiative transfer models have found that
for CO
2 is 5.35 (± 10%) W/m
2 for Earth's atmosphere.
[28]
Based on information from his colleague
Arvid Högbom, Arrhenius was the first person to predict that emissions of carbon dioxide from the burning of fossil fuels and other combustion processes were large enough to cause global warming. In his calculation Arrhenius included the feedback from changes in water vapor as well as latitudinal effects, but he omitted clouds, convection of heat upward in the atmosphere, and other essential factors. His work is currently seen less as an accurate quantification of global warming than as the first demonstration that increases in atmospheric CO
2 will cause global warming, everything else being equal.
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