Issue 10.5: October/November 2007

Behind the Inconvenient Truth

story by Rose Kahele
photo by Peter French


Before it was an inconvenient truth, it was an indisputable fact.

In 1958, a young chemist named Charles Keeling theorized that the Earth’s oceans, once thought to be inexhaustible sponges absorbing excess carbon, were in fact saturated—and that CO2 had been accumulating in the atmosphere. To test that hypothesis, Keeling came to the Big Island’s then-new Mauna Loa Observatory. Mauna Loa was an ideal location to collect air samples, because the mountain it sat upon in the middle of the Pacific Ocean was a world away from large industrial centers, which could contaminate samples. The air at Mauna Loa’s 11,000-foot summit is among the cleanest in the world.

Twice daily for nearly fifty years since, scientists at the National Oceanic and Atmospheric Administration’s Mauna Loa Observatory have been measuring atmospheric concentrations of carbon dioxide, a by-product of fossil fuel combustion and the chief greenhouse gas responsible for global warming. Beginning in 1958, their continuous record, known as the Keeling Curve, documents an average annual increase in atmospheric carbon dioxide of 0.44 percent.

For the first couple of years, it seemed that Keeling’s hypothesis might be mistaken; his data initially produced a graph with a serrated pattern, showing wide yearly fluctuations in the levels of CO2. “He immediately saw that there was an annual biological cycle,” says Dr. John Barnes, director of NOAA’s Earth System Research Laboratory, Mauna Loa Observatory. “Plants grow in the spring and summer, so CO2 gets sucked out of the air and then returned in the fall and winter. That in itself was a significant discovery.” But it turned out that these serrations are only small variations in CO2 levels; the more troubling long-term increase is starkly represented by a steadily rising curve, proving Keeling’s theory true.

Because of its longevity and accuracy, the Keeling Curve is the most important data set in climate science. It is the foundation on which the theory of global warming is based. It is also credited with the eventual creation of the Kyoto Protocol, an agreement by a majority of nations to cap CO2 emissions. More recently, the curve played a starring role in the 2006 Academy Award-winning documentary An Inconvenient Truth.

However, not all the readings from Mauna Loa are discouraging. According to Barnes, levels of ozone-depleting chlorofluorocarbons (CFCs) have been steadily declining over the last several years. These artificial gases, which had a number of commercial uses, were phased out in 1995, and the ozone layer has begun to repair itself since. A most welcome and convenient truth. —Rose Kahele

To tour NOAA’s Mauna Loa Observatory, call
Dr. John Barnes at (808) 933-6965, ext. 222 or e-mail