Guy Callendar, 1934.
Nearly everybody likes to be right, and scientists perhaps more so than the rest of us. Their professional lives, after all, are dedicated to uncovering the truth, which they do in part by quantifying and minimizing error. The interesting thing, though, is that in science there is more than one way to be right.
Consider the case of Guy Stewart Callendar. He should be famous. Scholar James Fleming writes flatly that “Callendar established the CO2 theory of climate change in its recognizably modern form.” It was Callendar who first used meteorological data to construct a global temperature time series; who first established the background concentration level of atmospheric CO2 and identified an anthropogenic increase; and who was instrumental in bringing thirty years of advances in spectroscopy to bear on climate studies. All of these types of studies are crucial to the modern understanding of CO2 and climate.
So why is Callender not better known today? Partly because he worked, not as an academic, but as a defense researcher. He not only lacked the “bully pulpit” of a professorial chair, but was expected to maintain discreet silence about his job-related research. Perhaps worse, he was—in terms of employment, though not of technical skill—an “amateur.” (In the auctorial heading of his 1938 paper on CO2-induced warming he is “G.S. Callendar, steam technologist.”) And partly it is because he did not anticipate the temperature declines experienced in the 1950s and 1960s. Thus, at the end of his life, he was wrong about the most central of his conclusions: that he had actually detected the human fingerprint on Earth’s climate.
One of the first surprises about Callendar is that this quintessentially English man was born, not in London or some leafy corner of Sussex, but in Montreal. His father, Hugh Longbourne Callendar, had since 1893 held a chair in Physics at McGill University. Among his many accomplishments there, he had in 1896 created the first Canadian x-ray images, and had helped to pioneer their use in clinical medical diagnosis. But after Guy Callendar’s birth on February 9, 1898, Professor Callendar accepted the Quain Chair of Physics, University College, London. He would be succeeded at McGill by no less than Ernest Rutherford, who wrote:
Callendar here was considered a universal genius and I gain a sort of reflected glory by carrying on with things Callendar alone was able to do. The trouble is that Callendar left such a reputation behind him that I have to keep rather in the background at present.
The elder Callendar’s career advanced again with a move to the Royal College of Science (later part of Imperial College) in 1902, and in 1905 the Callendar family—now including a fourth child, with Guy’s younger brother Max—was able to move into a fine home in the London suburb of Ealing. 49 Grange Road had 22 rooms, and—in addition to the greenhouse, tennis lawn, and putting green—boasted two garages equipped with “pit, crane, lathe and all tools” necessary to maintain the family car. The household was supported by a staff of four to six servants, plus a chauffeur and a gardener.
The amenities reflect the family’s pastimes: tennis was a lifelong avocation for Guy, and all three Callendar brothers contended for the local club singles championships at various times—though only Max would win it. (Guy’s best result came in 1928 when he was runner-up.) Motoring was a favorite recreation for the family, too, and Hugh Callendar himself spent time modifying their Stanley Steamer to make it a practical touring vehicle.
We hear little about Guy at first—apart from an unfortunate accident in 1903, in which he was permanently blinded in his left eye by his pin-wielding elder brother, Leslie. But his education was evidently the first-class affair that one might expect. He began by attending the Durston House School, which was followed by St. Paul’s School, Hammersmith. Though St. Paul’s lacks an historic campus, having moved several times over its history, it has been in existence since 1509, and boasts among its distinguished alumni the poet John Milton, the astronomer Edmund Halley, and the diarist Samuel Pepys.
But 1914 was to be the year in which this comfortable upper middle-class life was to be darkened considerably by two tragedies, one historic and one familial. Guy’s sister, Cecil—whose beautiful pen drawing of 49 Grange Road can be seen in James Fleming’s account of Callendar’s life and work—died of pneumonia at 19. And in September came the outbreak of the Great War, as it soon became known.
Hugh Callendar was appalled by the events of the unfolding bloodbath. Leslie Callender, then a student in one of his father’s classes, wrote in May 1915:
. . .the morning after the Lusitania had been sunk by a submarine with the loss of many men, women, and children. . . my father opened his lecture by expressing his horror with the deepest emotion I have ever heard in his voice. He then looked slowly round the students as if these young men too would soon be lost in the war, and with difficulty went on with his lecture.
Guy, too, was affected. Like many young men, he left school early to contribute to the war effort. Barred from active service by his partial blindness, he assisted in his father’s laboratory at Imperial College, using x-ray technology to improve military aero engines. In 1917, with manpower needs ever more critical as the slaughter continued on the battlefields of Europe, he joined the Royal Navy Volunteer Reserves, serving as a hydrophone (sonar) officer and reaching the rank of sublieutenant.
“Demobilised” in 1919, Guy returned to school at City & Guilds College—which had not yet been subsumed into his father’s institution, Imperial College—earning a certificate in Mechanics and Mathematics in 1922.
This would mark the end of Guy’s formal education, but not the end of his learning. Hired by his father as a research assistant working on the physics of steam, Guy would serve an eight-year apprenticeship marked by publication—Guy’s first article, on the total heat of steam, came out in 1926—and participation in the First International Steam Tables Conference in 1929. (Steam tables listed steam properties under varying conditions, including very high temperatures, and were critical for a number of engineering applications.)
This period ended in 1930, a highly eventful year for Guy. Hugh Longbourne Callendar died at home on January 21, 1930, a victim to the same disease that had claimed Cecil sixteen years before. Guy was bequeathed ‘“the copy right of and all income royalties and other benefits which may accrue” from the Steam Tables and Diagrams, as well as all manuscripts, papers, and illustrations that are connected to them.’ The steam research funded by the British Electrical and Allied Industries Research Association (BEIRA) continued, and Guy’s salary was increased to 450 pounds yearly—commensurate, one supposes, with his increased responsibilities as lead researcher.
In June Guy attended his first important event as a principal: the Second International Steam Table Conference in Berlin. This must have been something of a milestone for the young researcher. But on August 30, 1930, he took a step personally much more portentious still, marrying Phyllis Burdon Pontreath in Upper St. Leonards-on-sea. Interestingly—in light of what would soon be Guy’s research focus—their wedding day marked the breaking of a record-setting heat wave.
Following the birth of twin daughters, Bridget and Ann on November 19, 1931, Guy’s family settled in a new home in Worthing. Their life together was happy; the parents were both active in the Ealing Tennis Club, and the family particularly enjoyed vacations to Shanklin on the Isle of Wight in 1937 and 1938.
Of course, Guy’s professional life had its claims, too. The 1934 Third International Steam Conference was the first to be held in the United States, with sessions in Washington, Boston and New York. Guy sailed for New York aboard the Britannic—ironically, given the purpose of his visit, a motorship and not a steam liner.
Guy’s letters to Phyllis following the conclusion of the conference provide a rare glimpse into Callendar’s personal life:
Now that all the rush & work of the conference is over I feel frightfully homesick, and long to be back at our quiet little home where I really belong. Once the boat starts moving I shall be all right. I see the Britannic started back this morning, I wish I was on her. Many people would think I must be mad to wish to quit living like a lord free of charge, in the center of New York, but I want to get home to you and the twins. The air here is like thick warm soup, there is no movement, and it tastes & smells very secondhand. I have a huge fan in my room, but the air in the streets (canyons) is awful. I long for the glorious fresh breezes of Worthing.
Indeed, the very uniqueness of the letters is a testament to the sincerity of their content: following his return home aboard Mauretania, Guy would never again spend such an extended time away from home and “his girls.”
Perhaps these images of air like “warm soup” reflect something of Guy’s growing interest in weather and climate. During these years he was collecting information. He read the papers of Fourier, Tyndall, Arrhenius, Ekholm and others, recording information and comments in voluminous notebooks. He saw that the work, though then not held in high regard, had merit—but was badly in need of updating. He was familiar with new developments in spectroscopy, for instance, which would put the ideas of Arrhenius and Ekholm on much surer footing. His first paper, “The Artificial Production of Carbon Dioxide and Its Influence on Temperature,” would be published in 1938. It would prove to be the most-cited of all of his papers.
He begins with a startlingly bold statement:
Few of those familiar with the natural heat exchanges of the atmosphere, which go into the making of our climates and weather, would be prepared to admit that the activities of man could have any influence upon phenomena of so vast a scale.
In the following paper I hope to show that such influence is not only possible, but is actually happening at the present time.
His demonstration is carried out in six sections. The first examines atmospheric concentrations of carbon dioxide, concluding that the nineteenth century “background level” was 274-292 ppm—still considered a valid estimate—and that the increase to the date of writing was about 6 per cent. (Interestingly, he projected for 2000 a concentration of 335 ppm—in very reasonable agreement with the 2000 369.4 ppm annual mean value measured at the Mauna Loa Observatory, if one considers the increase in the rate of CO2 emission over that of Callendar’s day.) The biggest unknown in 1938 was the rate at which the ocean would absorb increased amounts of CO2.
Callendar then examines the absorption of infrared radiation by water vapor and carbon dioxide, and—using the advances in spectrography since Arrhenius’ day—shows absorption by both to be significant.
The third section examines observational data on downwelling infrared radiation in the atmosphere. The term in use in Callendar’s day was “sky radiation,” defined as “The downward radiation from the sky, excluding the direct and scattered short wave radiation from the sun.” (Italics mine.) Callendar cites studies by Angstrom (1918), Dines (1927), Simpson (1928), and Brunt (1932.)
(It is noteworthy that today there are those arguing against the reality of this phenomenon from first principles of physics—without acknowledging that it has repeatedly been measured.)
Callendar summarizes the results in this way: “For normal conditions near the earth’s surface, with a clear sky the downward radiation varies between three and four fifths of that from the surface, the proportion being greatest when the air is warm and carries much water vapour.” He then calculates natural sky radiation for varying Terrestrial conditions, varying from the Antarctic plateau (high elevation, low temperature, humidity and pressure) to the tropics (high humidity).
The fourth section then uses the information from sections 2 and 3 to calculate how CO2 might contribute to sky radiation. Callendar wrote that “For temperate conditions at vapour pressure 7.5 mm Hg. I calculate that 95 per cent of the radiation comes from the water vapour; for arctic conditions the carbon dioxide may supply as much as 15 per cent of the total.”
Callendar describes how CO2 changes sky radiation:
When radiation takes place from a thick layer of gas, the average depth within that layer from which the radiation comes will depend upon the density of the gas. Thus if the density of the atmospheric carbon dioxide is altered it will alter the altitude from which the sky radiation of this gas originates. An increase of carbon dioxide will lower the mean radiation focus, and because the temperature is higher near the surface the radiation is increased, without allowing for any increased absorption by a greater total thickness of the gas.
This interpretation is essentially the converse of the point (made years earlier by Nils Ekholm) that radiation escaping the atmosphere is controlled by the effective altitude of the radiating layer. In both interpretations, the increased infrared optical thickness moves the effective radiative focus along a temperature gradient: warmer near the surface in Callendar’s formulation, colder near the top of the atmosphere in the case of Ekholm’s.
Moving on to the effect on global temperature, Callendar began:
If the whole surface of the earth is considered as a unit upon which a certain amount of heat falls each day, it is obvious that the mean temperature will depend upon the rate at which this heat can escape by radiation, because no other type of heat exchange is possible.
(Evidently by “the whole surface of the earth,” he means to include the whole thickness of the atmosphere.) Callendar calculates that for temperate conditions, a doubling of CO2 should increase surface temperature by about 1.5 C. Looking back, this stands as a reasonable estimate.
The final section is again a milestone. Unquestionably the most novel feature of Callendar’s work is his effort to link observed temperature change to the influence of CO2—a field of study referred to today as the problem of “attribution.”
To investigate whether CO2-induced warming might be happening required a great deal of data—data that had not been collected with a view to investigating long-term temperature trends. Callendar showed the way. He collected weather records for over 200 locations, painstakingly checking and cross-checking them for consistency and accuracy. He used area weighting to compile regional trends. He compared various groupings of data against one another to detect inaccuracies.
Those acquainted with current controversies around the measurement of global temperature may be amused, surprised or even angered to learn that Callendar discussed, and compensated for, what is now known as the “urban heat island effect”:
It is well known that temperatures, especially the night minimum, are a little higher near the centre of a large town than they are in the surrounding country districts; if, therefore, a large number of buildings have accumulated in the vicinity of a station during the period under consideration, the departures at that station would be influenced thereby and a rising trend would be expected.
To examine this point I have divided the observations into three classes, as follows:—
(i) First class exposures, small ocean islands or exposed land regions without a material accumulation of buildings.
(ii) Small towns, which have not materially increased in size.
(iii) Large towns, most of which have increased considerably during the last half century.
Callendar briefly examines Arrhenius’s research question, can CO2 variation account for the ice ages? His conclusion is cautiously negative. On the one hand, “I find it almost impossible to account for movements of the gas of the required order. . .” but “if the effect of carbon dioxide on temperatures was considerably greater than supposed, glacial periods might well be accounted for in this way.” (The modern view has glaciation initiated by cyclical orbital changes and amplified by a strong CO2 feedback.)
Though Callendar was a strong advocate for CO2-induced global warming, he was no “climate alarmist.” His paper concludes:
. . . the combustion of fossil fuel, whether it be peat from the surface or oil from 10,000 feet below, is likely to prove beneficial to mankind in several ways, besides the provision of heat and power. For instance the above mentioned small increases of mean temperature would be important at the northern margin of cultivation, and the growth of favourably situated plants is directly proportional to the carbon dioxide pressure (Brown and Escombe, 1905). In any case the return of the deadly glaciers should be delayed indefinitely.
As regards the reserves of fuel these would be sufficient to give at least ten times as much carbon dioxide as there is in the air at present.
1939, like 1914, would prove a portentious year. The steam research culminated with the publication of “The 1939 Callendar Steam Tables.” (Further editions would follow in ’44, ’49 and ’57.) It also marked renewed hostilities in Europe; once again, Britain was at war. Following the Nazi’s September conquest of Poland, the war settled into a period of inactivity dubbed ‘the phony war.’ But soon enough blitzkrieg warfare rolled over a thoroughly out-manoeuvered France, and the British Expeditionary Force narrowly escaped annihilation on the beaches of Dunkirk.
On September 15, 1940, the Callendars experienced battle at just a slight remove. They were moving into their third home in Worthing—a house which would have enough space for them to take in Phyllis’s aged father. Above them, one of the major engagements of the Battle of Britain was taking place. Bridget Callendar—not yet 9—later recalled seeing planes in the air and, perhaps more frightening, cartridge casings on the ground. Later there would be “blackouts. . . night patrols, and searchlights beaming across the sky.” As the Luftwaffe turned from RAF airfields to the city centers of southern England, Guy would volunteer again, this time as a “fire-watcher.”
Images of the Battle of Britain.
The war naturally shifted research priorities, and this changed Guy’s life, too. On July 11, 1941, the BEIRA steam research formally concluded, and the next year Guy began defence research work at Langhurst, “a secret research facility” operated by the Ministry of Supply. Even today, information about the facility is not easy to come by.
Ironically, it made the Callendar’s life yet more idyllic in a way: the family moved to 44 Parsonage Road, Horsham, about 2 miles away from the lab. Guy would bicycle to work in good weather. There was a cow pasture behind the house, and from trees in their new yard the Callendars had surplus apples to give away. Here Guy set up a weather station; he would log daily observations nearly until his death.
Guy’s most important work at Langhurst was his first project. In June of 1942 he joined the team researching FIDO, the “Fog Investigation and Dispersal Operation.” As had been true since Victorian times, British weather was marked by dense fogs—most inconvenient for air operations! Instrument landings and take-offs were still years in the future, and Britain badly needed her air forces in her fight for survival. German bombers could not be allowed to pound London with impunity on every foggy night. Prime Minister Churchill himself authorized intense efforts to deal with the problem.