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makes it possible to discover dynamic patterns in the behavior of the condition in question as
it changes over time. This type of discovery is what happened in a surprising way for a geo-
chemical researcher named Charles David Keeling, starting in the mid-20th century.
David Keeling was a postdoc beginning a research project to study the balance between car-
bonate in the air, surface waters, and limestone when his attention was drawn to a very signi-
ficant pattern in data he was collecting in Pasadena, California. He was using a very precise
instrument to measure atmospheric CO
2
levels on different days. He found a lot of variation,
mostly because of the influence of industrial exhaust in the area. So he moved to a less
built-up location, the Big Sur region of the California coast near Monterrey, and repeated
these measurements day and night. By observing atmospheric CO
2
levels as a function of
time for a short time interval, he discovered a regular pattern of difference between day and
night, with CO
2
levels higher at night.
This observation piqued Keeling's interest. He continued his measurements at a variety of
locations and finally found funding to support a long-term project to measure CO
2
levels in
the air at an altitude of 3,000 meters. He did this by setting up a measuring station at the top
of the volcanic peak in Hawaii called Mauna Loa. As his time series for atmospheric CO
2
concentrations grew, he was able to discern another pattern of regular variation: seasonal
changes. Keeling's data showed the CO
2
level was higher in the winter than the summer,
which made sense given that there is more plant growth in the summer. But the most signi-
ficant discovery was yet to come.
Keeling continued building his CO
2
time series dataset for many years, and the work has
been carried on by others from the Scripps Institute of Oceanography and a much larger, sep-
arate observation being made by the US National Ocean and Atmospheric Administration
(NOAA). The dataset includes measurements from 1958 to the present. Measured over half a
century, this valuable scientific time series is the longest continuous measurement of atmo-
spheric CO
2
levels ever made. As a result of collecting precise measurements as a function
of time for so long, researchers have data that reveals a long-term and very disturbing trend:
the levels of atmospheric CO
2
are increasing dramatically. From the time of Keeling's first
observations to the present, CO
2
has increased from 313 ppm to over 400 ppm. That's an in-
crease of 28% in just 56 years as compared to an increase of only 12% from 400,000 years
ago to the start of the Keeling study (based on data from polar ice cores).
Figure 1-4
shows a
portion of the Keeling Curve and NOAA data.
