Callendar, Guy Stewart

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(b. Montreal, Canada, 9 February 1898;

d. Horsham, Sussex, United Kingdom, 3 October 1964), steam and combustion engineering, climatology, glaciology, anthropogenic climate change.

Callendar is noted for identifying, in 1938, the link between the artificial production of carbon dioxide and global warming, later called the “Callendar Effect.” He was one of Britain’s leading engineers, author of the standard reference book of tables and charts on the properties of steam at high temperatures and pressures, and designer of key components of the famous World War II airfield fog dispersal system, FIDO. He was keenly interested in weather and climate, taking measurements so accurate that they were used to correct the official temperature records of central England and collecting a series of worldwide weather data that showed an unprecedented warming trend in the first four decades of the twentieth century. He formulated a coherent theory of infrared absorption and emission by trace gases, established the nineteenth-century background concentration of carbon dioxide, and argued that its atmospheric concentration was rising due to human activities, which was causing the climate to warm.

Background and Education . Callendar was the third of four children and second son of Victoria Mary Stewart and the noted physicist Hugh Longbourne Callendar. When Guy was two, the family moved from Montreal to London. He received his primary education at Durston House, secondary education at St. Paul’s School, and, after the war, attended City and Guilds Engineering College (part of Imperial College), where his father was chair of the physics department. His home life provided a rich creative and technical environment where he was introduced to the scientific elite of England and was able to pursue his interests in science and engineering, competitive tennis, and motor sports.

The loss of an eye in childhood rendered him unsuitable for frontline service during World War I. From 1915 to 1917, he worked in his father’s laboratory at Imperial College as an assistant to the X-ray Committee of the Air Ministry, testing a variety of apparatus, including aircraft engines at the Royal Aircraft Factory (later Establishment) in Farnborough. Later he enlisted in the Royal Naval Volunteer Reserves, attaining the rank of sublieutenant. He served as a hydrophones officer and gained experience with electrical apparatus developed by his father for sound ranging and detection of submarines. Both father and son chose to work on defense projects that improved the efficiency of the military but avoided working on weapons systems. Callendar entered college in 1919, earned a certificate in mechanics and mathematics in 1922, and immediately went to work in the Physics Department at Imperial College where he assisted his father’s experiments on steam at high temperatures and pressures.

After his father’s death in 1930, Callendar continued his steam research at Imperial College, collaborating with the Oxford physicist Alfred Charles Glyn Egerton, under the patronage of the British Electrical and Allied Industries Research Association. Callendar participated in the International Steam Conferences in London (1929), Berlin (1930), and the United States (1934). He and Egerton led the British effort, working to reduce errors and inconsistencies in the thermodynamic properties of steam as measured by different techniques, taking measurements at ever higher temperatures and pressures, and striving to define international standard units. They published frequent updates of the famous Callendar Steam Tables,

and their joint articles appeared in the Philosophical Transactions from 1933 until just after Egerton’s death in 1959.

In 1930, Callendar married Phyllis Burdon Pentreath. Identical twin daughters were born the following year. The family moved from Ealing to Worthing and finally to Horsham in 1942 to a bungalow named “Redwoods” where Callendar resided the rest of his life. This final move placed him in close proximity to Langhurst, a secret research facility in West Sussex, where he worked on defense engineering projects until his retirement in 1958. His hobbies included tennis (he won a local tournament at age forty-nine), bicycling (20–40 mile trips), gardening (primarily fruit trees and conifers), and keeping an accurate and unbroken series of weather records from 1942 to 1964 at his home station, which he named “Percuil.”

Wartime Research . During World War II, Callendar worked in research and development for the Petroleum Warfare Department and the Ministry of Supply. He was a key engineer and shared a patent in FIDO, an airfield fog dispersal system that provided Royal Air Force and Allied aviators with safe takeoff and landing facilities in marginal weather conditions. The FIDO system burned massive quantities of petrol to heat the fog, clear the air, and light the airfield. It used 3,000 to 5,000 gallons of fuel to land just one aircraft. Yet it was deemed worth the cost, since it allowed for flying in marginal weather conditions. FIDO was favored by pilots returning to foggy England after a mission, since they could see the airfield glowing in the distance, beckoning them home to a lighted, fog-free airport. They could also save valuable time getting their damaged planes and exhausted (and possibly wounded) crews on the ground.

During the war Callendar also examined the efficiencies of different types of electrochemical storage and generating devices. This work required that he devise tests to record and compare the efficiencies of different types of batteries and fuel cells. The challenge was immense, since the problem of providing powerful, reliable, and long-lived sources of electricity in the field was a perennial one.

In another project, Callendar collaborated with the Cambridge physicist Gordon Brims Black McIvor Sutherland, on delineating the absorption and emission characteristics of the infrared spectra of hydrocarbons and atmospheric trace gases. Captured German fuel was burned and subjected to spectroscopic analysis to determine its composition and likely place of origin, yielding strategically important knowledge. The research also resulted in fundamental new insights into the spectra of water vapor, carbon dioxide, and ozone at low concentrations and low temperatures in the atmosphere, of critical importance to studies of the Earth’s heat budget.

Callendar was deeply engaged in research for the Petroleum Warfare Department that emphasized the development of flamethrowers. Thus it was impossible not to contribute to their use as offensive weapons. Nevertheless, by emphasizing FIDO and other projects involving the efficiency of fuel propellant systems and the application of thermal technology to war-related problems, Callendar attempted to isolate his work as much as possible from the killing fields. He designed internal baffles for fuel tanks, experimental devices for forest clearing, and new fuel propellant systems.

After the war, Callendar’s work for the Ministry of Supply involved experimental methods for generating high-speed air currents and testing space heaters for military applications in cold climates. Throughout his years of government service, Callendar remained steadfast in his resolve to contribute to improvements in efficiency rather than weapons systems. In this he was following the pattern inculcated by his father.

Climate Research . Callendar’s most significant and original scientific contribution was in climatology, specifically anthropogenic climate change. In the first half of the twentieth century, the carbon dioxide theory of climate change, established by John Tyndall (1859) and Svante Arrhenius (1896) had fallen out of favor with most scientists. This was due mainly to the lack of detailed understanding of the infrared spectra of atmospheric trace gases. The dominant opinion was that, at current atmospheric concentrations, carbon dioxide already absorbed all the available long-wave radiation; thus any increases would not change the radiative heat balance of the planet but might augment plant growth. Other physical mechanisms of climatic change, although highly speculative, were given more credence, especially changes in solar luminosity, atmospheric transparency, and the Earth’s orbital elements. Callendar acknowledged the “chequered history” of the CO2 theory: “[I]t was abandoned for many years when the prepondering influence of water vapour radiation in the lower atmosphere was first discovered, but was revived again a few years ago when more accurate measurements of the water vapour spectrum became available” (Callendar, 1949).

Beginning in 1938, Callendar revived and reformulated the carbon dioxide theory by arguing that rising global temperatures and increased fossil fuel burning were closely linked. Callendar, working on his own time and from home, compiled weather data from stations around the world that clearly indicated a global warming trend of about 0.5 C in the early decades of the twentieth century. Callendar investigated the carbon cycle, including natural and anthropogenic sources and sinks, and the role of glaciers in the Earth’s heat budget. From his review of earlier measurements, Callendar established what would become the standard number of 290 parts per million (ppm) as the nineteenth-century background concentration of carbon dioxide in the atmosphere. He documented an increase of ten percent in this figure between 1900 and 1935, which closely matched the amount of fuel burned. Callendar pointed out that humans had long been able to intervene in and accelerate natural processes, and that humanity was now intervening heavily in the slow-moving carbon cycle by “throwing some 9,000 tons of carbon dioxide into the air each minute” (Callendar, 1939a). In an era before computer climate modeling, Callendar compiled all the newly available information on the detailed infrared absorption and emission spectra of atmospheric trace gases into a coherent picture of interest and relevance to meteorologists. He argued that the rising carbon dioxide content of the atmosphere and the rising temperature were due to human activities, thus establishing the carbon dioxide theory of climate change in its recognizably modern form and reviving it from its earlier, physically unrealistic and moribund status.

By the 1950s, as temperatures around the Northern Hemisphere reached early-twentieth-century peaks, global warming first found its way onto the public agenda. Concerns were expressed in both the scientific and popular press about rising sea levels, loss of habitat, and shifting agricultural zones. Amid the myriad mechanisms that could possibly account for climatic changes, G. S. Callendar was the first of many to document connections between rising surface temperatures, increasing anthropogenic CO2 emissions, infrared radiation, and global climate warming. His writings revived the theme of human agency, which had been dormant since the age of Jefferson, by pointing out that humanity had become an agent of global change by interfering with the natural carbon cycle. In the early 2000s, the theory that global climate change can be attributed to an enhanced greenhouse effect due to elevated levels of carbon dioxide in the atmosphere from anthropogenic sources, primarily from the combustion of fossil fuels, is called the “Callendar Effect” (Fleming, 2007).

Although Callendar was in declining health for the last six months of his life, he did not discuss it openly. His weather journal ended in September 1964, with a note indicating: “The sunniest September since 1911.” He died suddenly on 3 October 1964 of coronary thrombosis.

Callendar was a quiet, family-oriented man, an avid sportsman, and a modest and unassuming contributor at the leading edge of research. He was a Fellow of the Royal Meteorological Society and served on its council. He was also a Fellow of the Glaciological Society. He counted many, many distinguished scientists as his friends, colleagues, and coworkers. In his early years he was deeply influenced by his famous physicist father. He received a first-rate technical education and entered into collaborations with Britain’s technical elite on steam research and the infrared spectra of complex molecules.

His work on the thermodynamics of steam was foundational for steam-plant design calculations in Great Britain for over three decades. His papers on the infrared properties of trace gases drew rave reviews from leading meteorologists and climatologists and influenced the later development of the field. His work in defense-related research in two world wars and the Cold War was directed, wherever possible, toward nonviolent ends. Among many, many other accomplishments, he established the “Callendar Effect,” the link between anthropogenic CO2 and global warming.


Callendar’s unpublished papers (3 linear ft.) are in the library of the Climatic Research Unit at the University of East Anglia. The collection, including scientific correspondence, charts, research notebooks on climate and carbon dioxide, and a box of family documents and scanned photographs, has been published in digital format on DVD as The Papers of Guy Stewart Callendar, edited by James Rodger Fleming and Jason Thomas Fleming, Boston, American Meteorological Society, 2007.


“The Artificial Production of Carbon Dioxide and Its Influence on Temperature.” Quarterly Journal of the Royal Meteorological Society 64 (1938): 223–240.

“The Composition of the Atmosphere through the Ages.” Meteorological Magazine74 (March 1939a): 33–39.

With Hugh L. Callendar and Sir Alfred Egerton. The 1939 Callendar Steam Tables. London: Published for the British Electrical and Allied Industries Research Association by Edward Arnold, 1939b. 2nd ed. 1944, 1949, and 1957.

With Gordon Brims Black McIvor Sutherland. “The Infra-red Spectra of Atmospheric Gases other than Water Vapour.” Reports on Progress in Physics9 (1942–1943): 18–28.

“Can Carbon Dioxide Influence Climate?” Weather 4 (1949): 310-314.

“On the Amount of Carbon Dioxide in the Atmosphere.” Tellus 10 (1958): 243–248.

With Sir Alfred Egerton. “An Experimental Study of the Enthalpy of Steam.” Philosophical Transactions of the Royal Society of London, Series A, 252 (1960): 133–164.

“Temperature Fluctuations and Trends over the Earth.” Quarterly Journal of the Royal Meteorological Society 87 (1961): 1–11.


Bowen, Mark. Thin Ice. New York: Henry Holt, 2005.

Fleming, James Rodger. Historical Perspectives on Climate Change. New York: Oxford University Press, 1998.

———. The Callendar Effect: The Life and Work of Guy Stewart Callendar (1898–1964), the Scientist Who Established the Carbon Dioxide Theory of Climate Change. Boston, American Meteorological Society, 2007. This book contains Callendar’s complete annotated bibliography, many family photographs, and an inventory of his study at the time of his death.

James Rodger Fleming

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