Geoscience Reference
In-Depth Information
CO
2
by ancient plant carbon was then and remains today dispositive evidence that
humans are the cause of the observed temperature rise.
Suess and others soon realized that radiocarbon provided a way to trace the
movement of CO
2
between the atmosphere and the oceans—and even the move-
ment of water masses between the shallow and deeper parts of the ocean. Within
a few years, at the invitation of its dynamic director, Roger Revelle, Suess had
moved to the Scripps Institute of Oceanography in La Jolla, California.
No End in Sight
Following the lead of Callendar and Plass, Revelle (1909-1991) had become inter-
ested in the role of CO
2
in climate. In 1957, he and Suess published a classic paper
in which they concluded that
the average lifetime of a CO
2
molecule in the atmosphere before it is dissolved into the sea is
of the order of 10 years. This means that most of the CO
2
released by artificial fuel combustion
since the beginning of the industrial revolution the oceans must have absorbed. The increase of
atmospheric CO
2
from this cause is at present small but may become significant during future
decades if industrial fuel combustion continues to rise exponentially.
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The carbon chemistry of seawater is extraordinarily complex, but the upshot is
that seawater is “buffered” against changes. When seawater absorbs CO
2
from the
atmosphere, the pH (acidity) of the water changes, which causes other changes,
and so on, the effect rippling through a chain of reactions whose result is to move
the pH partway back toward where it started. Seawater absorbs CO
2
, yes, but it
alsoexpelsCO
2
backintotheatmosphere.Asanincomingmoleculeofatmospher-
ic CO
2
dissolves in the oceans, we might say that it meets another molecule on the
way out, traveling back into the atmosphere. The net effect is to cause much more
of the carbon emitted from fossil fuel combustion to wind up in the atmosphere
than the ten-year average lifetime would indicate.
At the end of their article, Revelle and Suess wrote that “the probably large in-
crease in CO
2
production by fossil fuel combustion in coming decades” would
assumed “a constant rate of addition of industrial CO
2
” of about 0.8 ppm per year.
This turned out to be a serious underestimate.
The import of research on the chemistry of CO
2
in seawater was that humanity
could not depend on the oceans to absorb an unlimited amount of added carbon
dioxide. Revelle summed up: “Human beings are now carrying out a large scale
geophysical experiment of a kind that could not have happened in the past nor be
reproduced in the future.”
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