The complacent view that CO2 from human activity could never become a problem was overturned during the 1950s by a series of costly observations. This was a consequence of the Second World War and the Cold War, which brought a new urgency to many fields of research. American scientists enjoyed massively increased government funding, notably from military agencies. The officials were not aiming to answer academic questions about future climates, but to provide for pressing military needs. Almost anything that happened in the atmosphere and oceans could be important for national security. Among the first products were new data for the absorption of infrared radiation, a topic of more interest to weapons engineers than meteorologists.(23)
The early studies sending radiation through gases in a tube had an unsuspected logical flaw — they were measuring bands of the spectrum at sea-level pressure and temperature. Fundamental physics theory, and a few measurements made at low pressure in the 1930s, showed that in the frigid and rarified upper atmosphere, the nature of the absorption would change. The bands seen at sea level were actually made up of overlapping spectral lines, all smeared together. Improved physics theory, developed by Walter Elsasser during the Second World War, and laboratory studies during the war and after confirmed the point. At low pressure each band resolved into a cluster of sharply defined lines, like a picket fence, with gaps between the lines where radiation would get through.(24)
These measurements inspired the theoretical physicist Lewis D. Kaplan to grind through some extensive numerical computations. In 1952, he showed that in the upper atmosphere the saturation of CO2 lines should be weak. Thus adding more of the gas would make a difference in the high layers, changing the overall balance of the atmosphere. Meanwhile, precise laboratory measurements found that the most important CO2 absorption lines did not lie exactly on top of water vapor lines. Instead of two overlapping bands, there were two sets of narrow lines with spaces for radiation to slip through.(25)
Nobody could say anything more specific without far more extensive computations. By 1956, these could be carried out thanks to the increasingly powerful new digital computers. The physicist Gilbert N. Plass took up the challenge of calculating the transmission of radiation through the atmosphere, nailing down the likelihood that adding more CO2 would increase the interference with infrared radiation.(26) Going beyond this qualitative result, Plass announced that human activity would raise the average global temperature “at the rate of 1.1 degree C per century.” The computation, like Callendar’s, paid no attention to possible changes in water vapor and clouds, and overall was too crude to convince scientists. “It is almost certain,” one authority scolded, “that these figures will be subject to many strong revisions.”(27) Yet Plass had proved one central point: it was a mistake to dismiss the greenhouse effect with spectroscopic arguments. He warned that climate change could be “a serious problem to future generations” — although not for several centuries. Following the usual pattern, Plass was mainly interested in the way variations in CO2 might solve the mystery of the ice ages. “If at the end of this century the average temperature has continued to rise,” he wrote, then it would be “firmly established” that CO2 could cause climate change.(28)
None of this work met the argument that the oceans would promptly absorb nearly all the CO2 humanity might emit. Plass had estimated that gas added to the atmosphere would stay there for a thousand years. Equally plausible estimates suggested that the surface waters of the oceans would absorb it in a matter of days.(29) Fortunately, scientists could now track the movements of carbon with a new tool — the radioactive isotope carbon-14. This isotope is created by cosmic rays in the upper atmosphere and then decays over millennia. The carbon in ancient coal and oil is so old that it entirely lacks the radioactive isotope. In 1955, the chemist Hans Suess reported that he had detected this fossil carbon in the atmosphere.
The amount that Suess measured in the atmosphere was barely one percent, a fraction so low that he concluded that the oceans were indeed taking up most of the carbon that came from burning fossil fuels. A decade would pass before he reported more accurate studies, which showed a far higher fraction of fossil carbon. Yet already in 1955 it was evident that Suess’s data were preliminary and insecure. The important thing he had demonstrated was that fossil carbon really was showing up in the atmosphere. More work on carbon-14 should tell just what was happening to the fossil carbon.(30)
Suess took up the problem in collaboration with Roger Revelle at the Scripps Institution of Oceanography. (Some other carbon-14 experts attacked the topic independently, all reaching much the same conclusions.) From measurements of how much of the isotope was found in the air and how much in sea water, they calculated the movements of CO2 (link from below). It turned out that the ocean surface waters took up a typical molecule of CO2 from the atmosphere within a decade or so. Radiocarbon data also showed that the oceans turned over completely in several hundred years, an estimate soon confirmed by evidence from other studies.(31) At first sight that seemed fast enough to sweep any extra CO2 into the depths.
But Revelle had been studying the chemistry of the oceans through his entire career, and he knew that the seas are not just salt water but a complex stew of chemicals. These chemicals create a peculiar buffering mechanism that stabilizes the acidity of sea water. The mechanism had been known for decades, but Revelle now realized that it would prevent the water from retaining all the extra CO2 it took up. A careful look showed that the surface layer could not really absorb much gas — barely one-tenth the amount a naïve calculation would have predicted.
A supplementary essay on Revelle’s Discovery tells this crucial story in full, as a detailed example of the complex interactions often found in geophysical research.
Revelle did not at first recognize the full significance of his work. He made a calculation in which he assumed that industry would emit CO2 at a constant rate (like most people at the time, he scarcely grasped how explosively population and industry were rising). This gave a prediction that the concentration in the air would level off after a few centuries, with an increase of no more than 40%. Revelle did note that greenhouse effect warming “may become significant during future decades if industrial fuel combustion continues to rise exponentially.” He also wrote that “Human beings are now carrying out a large scale geophysical experiment of a kind that could not have happened in the past nor be reproduced in the future.”(32)
As sometimes happens with landmark scientific papers, written in haste while understanding just begins to dawn, Revelle’s explanation was hard to grasp. Other scientists failed to see the point that was obscurely buried in the calculations, and continued to deny there was a greenhouse effect problem. In 1958, when Callendar published a paper to insist once again that CO2 observations showed a steady rise from the 19th century, he noted Revelle’s paper but still confessed that he did not understand why “the oceans have not been accepting additional CO2 on anything like the accepted scale.”(33) Finally in 1959 two meteorologists in Sweden, Bert Bolin and Erik Eriksson, caught on. They explained the sea water buffering clearly — so clearly that during the next few years, some scientists cited Bolin and Eriksson’s paper for this decisive insight rather than Revelle and Suess’s (only in later years was Revelle always cited for the discovery).(34) The central insight was that although sea water did rapidly absorb CO2, most of the added gas would promptly evaporate back into the air before the slow oceanic circulation swept it into the abyss. To be sure, the chemistry of air and sea water would eventually reach an equilibrium — but that could take thousands of years. Arrhenius had not concerned himself with timescales shorter than that, but geoscientists in the 1950s did.
In the late 1950s a few American scientists, starting with Plass, tentatively began to inform the public that greenhouse gases might become a problem within the next few centuries. Revelle in particular warned journalists and government officials that greenhouse warming might come within the foreseeable future, and deserved serious attention. The stakes were revealed when Bolin and Eriksson pursued the consequences of their calculation to the end. They assumed industrial production would climb exponentially, and figured that atmospheric CO2 would rise some 25% by the end of the century. That was a far swifter rise than anyone before had suggested. In 1962, a still stronger (although not widely heeded) warning was sounded by the Russian climate expert Mikhail Budyko. His calculations of the exponential growth of industrial civilization suggested a drastic global warming within the next century or so.
Once meteorologists understood that ocean uptake was slow, they found it possible that CO2 levels had been rising, just as Callendar insisted.(35) Yet it was only a possibility, for the measurements were all dubious. By the mid 1950s, researchers were saying that it was important to measure, much more accurately, the concentration of CO2 in the atmosphere.(36) A Scandinavian group accordingly set up a network of 15 measuring stations in their countries. Their only finding, however, was a high noise level. Their measurements apparently fluctuated from day to day as different air masses passed through, with differences between stations as high as a factor of two. Only much later was it recognized that their methods of analyzing the air had been inadequate, and responsible for much of the noise.(37) A leading authority summarized the scientific opinion of the late 1950s: “it seems almost hopeless to arrive at reliable estimates [of CO2]… by such measurements in limited areas.” To find if the gas level was changing, measurements would have to “be made concurrently and during a great number of years” at many locations.(38)
Charles David (Dave) Keeling held a different view. As he pursued local measurements of the gas in California, he saw that it might be possible to hunt down and remove the sources of noise. Technical advances in infrared instrumentation allowed an order of magnitude improvement over previous techniques for measuring gases like CO2. Taking advantage of that, however, would require many costly and exceedingly meticulous measurements, carried out someplace far from disturbances. Most scientists, looking at the large and apparently unavoidable fluctuations in the raw data, thought such precision irrelevant and the instrumentation too expensive. But Revelle and Suess had enough funds, provided by the International Geophysical Year, to hire Keeling to measure CO2 with precision around the world.
A supplementary essay tells the precarious story of Keeling’s funding and monitoring of CO2 levels as a detailed example of how essential research and measurements might be fed — or starved.
Revelle’s simple aim was to establish a baseline “snapshot” of CO2 values around the world, averaging over the large variations he expected to see from place to place and from time to time. After a couple of decades, somebody could come back, take another snapshot, and see if the average CO2 concentration had risen. Keeling did much better than that with his new instruments. With painstaking series of measurements in the pristine air of Antarctica and high atop the Mauna Loa volcano in Hawaii, he nailed down precisely a stable baseline level of CO2 in the atmosphere. In 1960, with only two full years of Antarctic data in hand, Keeling reported that this baseline level had risen. The rate of the rise was approximately what would be expected if the oceans were not swallowing up most industrial emissions.(39*)
Lack of funds soon closed down the Antarctic station, but Keeling managed to keep the Mauna Loa measurements going with only a short hiatus. As the CO2 record extended it became increasingly impressive, each year noticeably higher. Soon Keeling’s curve, jagged but inexorably rising, was widely cited by scientific review panels and science journalists.(40) For both scientists and the public it became the primary icon of the greenhouse effect.
getting more funding can also be explained for the fact that indeed many governments want to be sure of what is going on, and I can say now that some governments were expecting that there would be nothing to worry about.