On 18 May 1955, Charles David Keeling – Dave to most – set up camp near a footbridge over a river in Big Sur State Park in California. Armed with a set of five litre flasks containing nothing but vacuum, he planned to suck up air samples regularly over the 24 hours. At the time it may have seemed the latest uncertain step of a young man unsure how best to combine his interest in science and love of the outdoors. But instead it became the start of a lifelong quest to accurately measure the main gas that man is changing the world’s climate with: CO2.
“At the age of 27, the prospect of spending more time at Big Sur State Park to take suites of air and water samples instead of just a few didn’t seem objectionable, even if I had to get out of a sleeping bag several times in the night,” Dave wrote in his autobiography. “I did not anticipate that the procedures established in this first experiment would be the basis for much of the research that I would pursue over the next forty-odd years.”
Growing up in the midwest US near Chicago, Dave’s interest in science was kindled at age five, when his economist father introduced him to the wonders of astronomy. To show Dave how the seasons came about, together in their living room they circled a globe around a lamp, serving as the sun. Going through school during the Second World War, Dave took a special class in preflight aeronautics as well as the conventional sciences.
He then enrolled in the University of Illinois early, during the summer, to fit in a year of study before he reached the conscription age of 17. With limited science options available at this time of year, he chose to major in chemistry. “I didn’t particularly like chemistry and repeatedly doubted that I had made the right choice,” he recalled. But before the year – 1945 – was out, the war was over, and so Dave could continue his course. Chemistry students were expected to study economics, but Dave felt that he’d had enough economics at home. So he opted out of chemistry, ultimately getting a general liberal arts degree.
Yet he was still offered a place to study for a chemistry PhD at nearby Northwestern University with a friend of his mother’s. He took it without applying for any others, but later realised his previous studies had left him unprepared. “Accepting so soon was probably a mistake,” he wrote. Required to take a minor subject as part of his studies, Dave chose geology. His supervisor even suggested he might like to make this his major, though Dave declined, graduating in chemistry after a gruelling five years. And while his skills were in great demand from the post-war chemical industry Dave wanted a job that would let him work outside. So he applied for geology roles at universities, managing to find one at the California Institute of Technology.
‘Evidently not correct’
There Dave’s new boss asked him to study the level of carbonate salts dissolved in water sat on limestone landscapes. That involved looking at CO2 movement between the water and air, meaning Dave needed a way to measure the gas. He therefore built a maze of interconnected glass tubes that would let him separate the CO2 from his five litre flasks, and work out how much there was.
Pumps would create vacuum in some sections of the maze and stopcocks would direct the gases and control whether or not they got sucked into a neighbouring vacuum. Dave could use this to freeze CO2 out of the air with liquid nitrogen, which had just become commercially available, and is cold enough to turn CO2 gas to dry ice. After thawing it again, he could then measure how much there was using a tube filled with mercury, known as a manometer. He directed the CO2 through his glass maze to sit above the mercury, exerting a force that pushed the liquid downwards. He would use gases to apply pressure at the other end, to keep the mercury at a fixed height. Reading off the pressure gave Dave the most accurate CO2 measurements of the time in around two hours, with an imprecision of just 0.1%
Dave started planning his Big Sur trip, but when practising with the air above his building’s roof he found big variations. “It was obvious that Pasadena’s air was often affected by CO2 emissions from industry, car exhaust, and backyard incinerators,” he explained. That made him worry about how easy it would be to get a good value even in the clean air of Big Sur, and so decided on his day-long experiment to take as many measurements as possible.
Those results quickly showed that his boss’s idea was wrong. But Dave saw an interesting pattern in the measurements: there was more CO2 in the air at night than during the day. He therefore spent the rest of the summer doing similar tests in various mountain and National Park locations, and found that in the afternoon they always seemed to have nearly the same amount of CO2, about 310 parts per million (ppm) parts of air.
This was surprising, as existing research didn’t suggest that daytime concentrations should be so similar from place to place. So Dave took ever wider measurements, gradually realising that the outcome depended on how well mixed the air was. “The highly variable literature values for CO2 in the free atmosphere were evidently not correct,” he pronounced. “Rather, a concentration of 310 ppm of CO2 appeared to prevail over large regions of the northern hemisphere.”
A possible rise
When Dave reported these findings in 1956, they quickly gained him attention and job offers, from the US Weather Bureau in Washington DC and Scripps Institution of Oceanography in San Diego. Both were involved in an exciting global science project, called the International Geophysical Year (IGY), set to take place from 1957-1958. Roger Revelle and Hans Suess at Scripps had proposed a modest program to measure CO2 during IGY. Meanwhile, the Weather Bureau was adding sites where they could do CO2 measurements including one on top of a volcano called Mauna Loa, in Hawaii.
Dave encouraged both potential employers to let him take continuous measurements of CO2 levels in air, worried that the existing plans would just lead to more unreliable data. But he also took a big risk: He recommended using expensive new infra-red spectrophotometers to collect data. These tools exploit the same heat-absorbing properties that make CO2 a greenhouse gas to identify it, but Dave had only used one for a few days. But Scripps took him on and agreed to buy them, with support from the Weather Bureau, which wasn’t sure how to spend its IGY funds for atmospheric chemistry otherwise.
Roger wanted Dave to monitor CO2 partly because he didn’t trust earlier research done by British engineer Guy Callendar. Using the unreliable data at the time, Guy had found a rise in CO2 equivalent to all the gas produced by burning fossil fuels until then to stay in the atmosphere. Roger expected some to dissolve in the sea. So he hoped to compare the IGY measurement ‘snapshot’ with another later snapshot, and work out if the changes between these times fit his idea.
The results from the Mauna Loa spectrophotometer were intriguing from the very start. The first measurement was strikingly just 1 ppm away from the 313 ppm Dave predicted from his manometer work. And amid power failures and early erratic results, a steady cycle of rising and falling CO2 appeared across the year. As in the daytime cycle, it was like the Earth was breathing in and out as plants grew and declined. “We were witnessing for the first time nature’s withdrawing CO2 from the air for plant growth during the summer and returning it each succeeding winter,” Dave wrote.
By 1960, they could publish their early results, showing this cycle, and “possibly a worldwide rise in CO2 from year to year”. Though the increase was close to suggesting all CO2 from fossil fuel burning staying in the air, Dave hoped that more data would settle the matter one way or the other. By 1962 the ‘snapshot’ was complete and Keeling’s measurement program would seemingly face its end for the first time of many. And though it was slowly realised, the creeping CO2 increase it revealed had an importance that drives continuing Mauna Loa measurements today. It provided confirmation of Guy Callendar’s earlier CO2 claims, making his other findings – that the world was warming – much more credible.
- This is the first blog entry of two on Dave Keeling’s contributions to climate science. You can read part two here.
Spencer Weart’s book, ‘The Discovery of Global Warming’ has been the starting point for this series of blog posts on scientists who played leading roles in climate science.
Charles D. Keeling (1958). The concentration and isotopic abundances of atmospheric carbon dioxide in rural areas Geochimica et Cosmochimica Acta DOI: 10.1016/0016-7037(58)90033-4
Charles D. Keeling (1960). The Concentration and Isotopic Abundances of Carbon Dioxide in the Atmosphere Tellus DOI: 10.1111/j.2153-3490.1960.tb01300.x
Charles D. Keeling (1998). REWARDS AND PENALTIES OF MONITORING THE EARTH Annual Review of Energy and the Environment DOI: 10.1146/annurev.energy.23.1.25
This year I’ve already written about the following pivotal climate scientists who came before Dave Keeling, or were around at the same time: Svante Arrhenius, Milutin Milanković, Guy Callendar part I, Guy Callendar part II, Hans Suess, Willi Dansgaard.