R I RI S I S SI I U T I O O C E A N O G R A P H Y
S C S C P P P P S NI N T T T T U T IOONN O FF O C E A N O G R A P H Y
expl rations T h e
T h e M a g a zz i i nn ee
M a g a oo f f OO c c e e a an n a an nd d r
E Ea a tr h
t h S S c e e n c e
c i i n c e s s
DEC. 2007/JAN. 2008
After two decades in recent
In March, one of the Most sIgnIfIcant research efforts
science history will celebrate its 50th anniversary. The
watching atmospheric record of rising carbon dioxide levels in the atmosphere
oxygen levels drop, known as the Keeling Curve marks for many people the
a Scripps researcher’s point when society became aware that human activities
can cause long-term changes to climate.
conclusions about The Keeling Curve, named for the late Charles
climate could leave one David Keeling, a geochemist at Scripps Institution of
feeling light-headed Oceanography at UC San Diego, has resolved a number
of debates in its 50-year history. It had established by
the early 1960s that fossil fuel burning would lead to greater concentrations of
atmospheric CO2. That early warning helped make clear to climate scientists that
that rise in carbon dioxide would trigger large climate changes.
But the Keeling Curve only describes what happens to a portion of the carbon
dioxide produced by natural and human activities. Other parts of the story are now
being told by a number of researchers, including Keeling’s own son Ralph. Some
20 years after he entered the family business, Ralph Keeling has produced a record
of atmospheric levels of oxygen, yin to the yang of CO2, that is helping scientists
understand what to expect from climate in the future. This part of the story started
with a conversation between a father and a son at the kitchen table.
(Ralph) Keeling CuRve
At lonely outposts like By Robert Monroe
this one at Palmer Sta-
tion, Antarctica, Ralph
Keeling’s research group
has watched oxygen
levels drop. Top, Charles
David (left) and Ralph
Keeling in 1989.
S C R IP P S IN S T IT U T IO N O F O C E A N O G R A P HY/U C SAN D IEGO
Left, Ralph Keeling
demonstrates the use of an
evacuated flask to former
Vice President Al Gore
during Gore’s May 2007
visit to Scripps. Right, A
near mirror image of the
famous Keeling Curve
named for his father (lower
right), Ralph Keeling’s
curve of oxygen levels
It took the Keeling Curve to prove false shows a scientifically sig-
the explanation by early twentieth nificant but environmentally
century scientists for where all the safe drop in atmospheric
emissions of a new industrial era were oxygen levels. Below, Alert
going. As the age of the automobile station, Canada, part of
ramped up, researchers at the time Ralph Keeling’s oxygen
understood that human activities measurement network.
were producing extra carbon dioxide
beyond the amount created by nature.
They assumed, however, that the vast
oceans would have the capacity to
absorb that extra amount with little
consequence to people.
The curve showed that was far
from the case. Beginning in March
1958 with an hourly measurement
of CO2 taken at a National Weather
Bureau station atop Hawaii’s
Mauna Loa, Charles David Keeling’s
measurements revealed a sharp
increase in the concentration of carbon
dioxide in the atmosphere. It has risen
from roughly 315 parts per million
(ppm) for that month to 383 ppm in
the most recent measurement. The
upward trajectory of the last century
is nearly perpendicular to the flat line
that existed in the centuries prior to doesn’t account for all the CO2 that people have produced through fossil
the industrial age. As dramatized by fuel burning, a quantity relatively easy to calculate from energy industry
former Vice President Al Gore in his records from the past century. Where is the rest going?
film “An Inconvenient Truth,” present- Scripps marine chemist Andrew Dickson has helped chip away at the
day levels are, in fact, a wild departure answer from one angle. Since 1990, he has taken part in efforts to make
from anything seen in the last 480,000 ultraprecise measurements of concentrations of carbon levels in the oceans
years. Through several ice ages and that show an upward trend consistent with uptake of carbon dioxide from
interglacial periods, ice core records the atmosphere.
show that those concentrations have That uptake is part of a natural exchange of gases between the
never risen above 300 ppm until ocean and sky; the oceans are a carbon “sink” or repository, absorbing it
now. through a direct mixing of gases that takes place through the actions of
But the measurement of rapid winds and waves at the surface and through the photosynthetic activity of
increase of CO2 in the atmosphere still phytoplankton in the surface ocean.
S C R I P P S I N S T I T U T I O N O F O C E A N O G R A P H Y / U C S A N D I E G O
Clockwise from left, The Keeling group measures oxygen
at nine stations around the world, including ones at the
Atmospheric Research Observatory at the South Pole (far
left and left); a NOAA observatory in American Samoa;
the Alert station in Canada’s Ellesmere Island, located
within the Arctic Circle; and Kumukahi, Hawaii.
But even though there was more
carbon dioxide in the air and extra being
taken up by the oceans, scientists have
found these quantities in the two spheres
still aren’t sufficient to account for all that
is produced by fossil fuel burning.
Where dOes CO2 GO?
A kitchen table conversation with his
father, a man whose work Ralph Keeling
didn’t fully appreciate until he was in
college, set the younger Keeling to begin
making a measurement of oxygen levels
in the atmosphere. At the time, in the late
1970s, a debate was brewing between
oceanographers and terrestrial ecologists
who estimated that people were emitting
even more CO2 on land through activities
such as urbanization and increased timber
use than oceanographers could account stretching north from Antarctica to points in and around the Pacific
for. The gap between what people and Atlantic oceans, showed what Ralph Keeling expected to see in
produced and what scientists measured a world filled with an ever-growing number of internal combustion
was even greater than previously thought, engines that take in oxygen and emit greenhouse gases: Just as carbon
said the ecologists. dioxide levels were going up, oxygen levels were going down about
Ralph Keeling recalls that during his 400 ppm from 1989 to the present day, a loss of 20 out of every
father’s account of what was happening million oxygen molecules per year.
with his research, the elder Keeling The downward trend in oxygen levels was no surprise but the
mentioned how an accurate measure of rate of decline was. It is not declining as fast as it should be. With the
oxygen in the atmosphere could provide amounts of carbon dioxide in the oceans and the air well-estimated,
an answer to the discrepancy because Ralph Keeling postulates that increased photosynthesis on land must
CO2 uptake in the oceans is discernibly account for the rest of the CO2 produced by society.
different from how land plants take up Exactly how all the terrestrial trees and plants in the world
carbon dioxide. achieve this is an open topic, however. In an era of clear-cut forests
With that seed planted in his mind, and the replacement of wilderness with human development, it
the younger Keeling devised methods for would seem at first glance that there would be fewer plants available
measuring extremely minute variations to somehow do more work. The act of chopping down trees and
in atmospheric oxygen. His first readings burning them releases the carbon dioxide stored in the trees, making
were taken in 1989, about the same time extra absorption all the more unlikely.
that Dickson began his ocean carbon There are a variety of theories out there about why there must
work. The O2 readings, taken at stations be more plant biomass on land, said Keeling and Dickson, and each
S C R I P P S I N S T I T U T I O N O F O C E A N O G R A P H Y / U C S A N D I E G O
Right, A family photo shows Charles David
Keeling with sons Ralph (center) and
Drew at California’s Mt. Whitney in 1967.
A chance conversation helped draw Ralph
into the family business. Below, Air intake
valves at Alert station in Canada.
“instability will be the norm.” have made the nature of the solution
“What we’re talking about isn’t equally clear. Nature’s own fate
a world that’s a little bit warmer but will essentially be beyond its own
a world that’s constantly warming,” control, leaving society only two
of them probably accounts for part said Keeling. “The period of options. It can keep on expanding
of the answer. One basic premise instability plays out for centuries. fossil fuel use at current rates and
is that there is available to plants That’s why it’s so important to almost certainly face catastrophic
more carbon dioxide and nitrogen, stabilize carbon dioxide.” climate change. Its other option is to
two natural fertilizers produced The younger Keeling points out drastically curtail fossil fuel use and
through fossil fuel burning. that the use of remaining fossil fuel learn to adapt to a new world in
Additionally, Dickson notes, there reserves on the planet will create a which climate changes significantly
is a body of evidence suggesting store of carbon dioxide at least five but hopefully not as severely.
that, as farming practices in the last times that of the store of carbon stored “We are seeing the beginnings of
century have become more efficient in the atmosphere or on land. If all what will almost certainly be a rapidly
and less land-intensive, places such those reserves are used, his father’s changing planet,” Keeling said.
as the northeastern United States famous curve could register CO2
have become reforested. Such new readings as high as 1,500 ppm within View the complete multimedia presentation of
Photo credits: Page 2 Al Gore photo, Bob Ross Photography. Page 3 upper left, Stephanie Koes/NOAA; upper right, Brian Vasel/NOAA.
growth creates temporary surges in a few hundred years. Concentrations this story at explorations.ucsd.edu.
CO2 uptake before plateauing as of CO2 will remain inflated for T I O N O F OC
ITU E A
forests mature. thousands of years, overwhelming
SCR I PPS
RAP H Y
natural controls over climate.
Ou t O f MO t h e r N atu re’ s ha N d s
“Ralph’s work with oxygen
But however Mother Nature is is taking us to the next depth of U C S D
working to mitigate the effects of understanding,” said Dickson. “We
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rising CO2 levels on land and in the need to know that to make plausible Scripps Institution of Oceanography
oceans, Ralph Keeling is quick to assertions about what likely future UC San Diego
point out that the apparent ability of we have.” 9500 Gilman Dr., # 0210
La Jolla, CA 92093-0210
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