Ahead of the Curve

Charles Keeling’s groundbreaking work at Mauna Loa.


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Fifty years ago — decades before terms like “greenhouse gases” and “global warming” became political buzzwords—a San Diego geochemist named Charles David Keeling set out to determine whether carbon dioxide was building up in the atmosphere. To do this, he needed to take continuous CO2 measurements at a place that was far from major pollution sources and represented a large portion of the world’s atmosphere.

Enter the Big Island’s then newly built Mauna Loa Observatory. At more than 11,000 feet above sea level, in the middle of the Pacific, its air is among the cleanest on Earth. (Although nearby Kilauea generates a large amount of CO2, it doesn’t affect the curve’s measurements. Data is obtained at night, when the down slope winds bring air from higher elevations.) Keeling and his team didn’t know it at the time, but their measurements at Mauna Loa would provide the first evidence of rapidly increasing greenhouse gases in the atmosphere due to the burning of fossil fuels.

“He recognized … that the whole planet was changing, and changing because of humans.”—Ralph Keeling on his father, Charles, pictured (above) in his laboratory in 1988.

Their data set, which became known as the “Keeling Curve,” shows a clear and steady increase in CO2 levels starting from its first measurement in 1958, at about 315 parts per million (ppm), to its February 2008 measurement, around 386 ppm.

“I think [Charles] was somewhat stunned to discover the consistency of the rise from year to year,” says Ralph Keeling, Charles’ son and a climate scientist at the Scripps Institution of Oceanography at the University of California San Diego, where his father also worked. “He recognized that there was something special about what he was seeing— evidence that the whole planet was changing, and changing because of humans.”


Carbon dioxide levels dip in the spring and summer growing seasons, when there are more plants to take in CO2 from the atmosphere.

Despite his groundbreaking discovery, Charles had to repeatedly justify the program’s importance to funding agencies as well as colleagues, who felt that he should move on since he had already proven that CO2 levels were rising. “He realized that keeping the record was going to be tremendously important because people would look back on it as the record of what was happening. He couldn’t imagine not continuing it,” says Ralph. Today, the curve is used as proof of global warming by scientists and politicians, even making a recent appearance in Al Gore’s 2006 documentary, An Inconvenient Truth.

Charles Keeling continued to monitor Mauna Loa’s measurements until his death in 2005, and Ralph continues his work today. “The challenge to humanity right now is to bend the curve,” Ralph says. “It keeps going up, and faster. Whether we succeed in slowing global warming will be measured by this curve.”
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