Keeling measured the carbon
dioxide level at the station regularly,
and discovered three things.
First, there was a daily variation
locally. The concentration was at
a minimum midafternoon, when
green plants were at their most
active in soaking up CO 2. Second,
there was annual variation globally.
The northern hemisphere had more
land for plants to grow, and the
level of CO 2 rose slowly during the
northern winter when plants were
not growing. It reached a peak in
May before plants started to grow
and began soaking up CO 2 again.
The level dropped to a minimum in
October, when northern plants died
back for winter. Third, crucially,
the concentration was increasing
inexorably. Cores of polar ice
contained bubbles of air, which
showed that during most of
the time since 9000 BCE, the CO 2
concentration varied from 275 to
285 ppm by volume. In 1958,
Keeling measured 315 ppm; by
May 2013, the average concentration
exceeded 400 ppm for the first time.
The increase from 1958 to 2013
was 85 ppm, meaning that the
concentration had increased by
27 percent in 55 years. This
was the first concrete evidence
that the concentration of CO 2 in
Earth’s atmosphere is increasing.CO 2 is a greenhouse gas, helping
to trap heat from the Sun, so
increasing CO 2 concentration is
likely to lead to global warming.
Keeling found the following:
“At the South Pole the concentration
has increased at the rate of about
1.3 ppm per year...the observed
rate of increase is nearly that to
be expected from the combustion
of fossil fuel (1.4 ppm).” In other
words, humans are at least part
of the cause. ■295
See also: Jan Ingenhousz 85 ■ Joseph Fourier 122–23 ■ Robert FitzRoy 150–55
FUNDAMENTAL BUILDING BLOCKS
Charles Keeling Born in Scranton, Pennsylvania,
Charles Keeling was an
accomplished pianist as well
as a scientist. In 1954, as
a postdoctoral fellow in
geochemistry at the California
Institute of Technology (Caltech),
he developed a new instrument
to measure carbon dioxide in
atmospheric samples. He found
that the concentration varied
hour by hour at Caltech, probably
because of all the traffic, so he
went camping in the wilderness
at Big Sur and found small but
significant variations there, too.
This inspired him to begin whatwas to be a lifetime’s work.
In 1956, he joined the Scripps
Institution of Oceanography in
La Jolla, California, where he
worked for 43 years.
In 2002, Keeling received
the National Medal of Science,
America’s highest award for
lifetime achievement in science.
Since his death, his son Ralph
has taken over his work
monitoring the atmosphere.Key work1997 Climate Change and
Carbon Dioxide: An IntroductionThe demand for energy is
certain to increase...as
an ever larger population
strives to improve its
standard of living.
Charles KeelingKeeling’s graph
plots the rising
levels of CO 2 in the
atmosphere year
after year. The
small annual
fluctuation (shown
by the blue line) is
due to seasonal
changes in CO 2
uptake by plants.390
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1960 1970 1980 1990 2000 2010Carbon Dioxide ConcentrationParts per million