Guy Callendar was an expert on steam and combustion who found the link between fossil fuels, carbon dioxide, and temperature.

The Engineer Who Discovered Global Warming

Apr 29, 2020

by Frank Wicks

There’s likely not a more contentious science and technology issue than climate change. But 82 years ago, there wasn’t the virtually unanimous opinion of atmospheric scientists that the world is warming and that carbon dioxide added to the air by human activity was the primary cause. And there were not gangs of lobbyists and politicians lined up to discredit those scientists.

Instead, there was just one engineer who had just published his results in the Quarterly Journal of the Royal Meteorological Society. While today, climate change and its attendant fires, droughts, storms, and flooding are often inescapable subjects of the news, the April 1938 paper, “The Artificial Production of Carbon Dioxide and Its Influence on Temperature,” received scant attention at the time.

The author was Guy Callendar, a notable second-generation British combustion and steam engineer who was also an amateur climatologist. Compared to some of the other papers published in that issue (for instance, “Cloud forecasting: The daily use of the tephigram” and “Meteorological observations of the British East Greenland expedition, 1935-36, at Kangerdlugssuak, 68° 10' N., 31° 44' W.”), Callendar’s work was broad and sweeping. But to anyone who has followed the science of climate change in recent decades, his argument is familiar: The measured concentration of carbon dioxide in the atmosphere had increased in the thirty-some years since the turn of the 20th century; the mass of that increased atmospheric carbon was a considerable fraction of the fossil fuels burned in that period; and the radiation absorbed by that added CO2 closely corresponded to increases in measured mean temperature.

By collecting data from 200 meteorological stations, Callendar calculated temperature had been increasing at a rate of .005 °C per year. Separately, using the laws of radiation together with absorptivity and wavelength data, he calculated the rate of temperature change attributable to CO2 to be .003 °C per year.

Callendar’s work was unsponsored research. Indeed, it had been a laborious task for a single individual before computers and the Information Age, employing hand calculations and slide rule. Nor was Callendar an alarmist—he, in fact, saw an advantage of a warmer planet that had longer growing seasons. He was motivated not just by scientific curiosity, but also by skepticism: According to a biographer, he started out unconvinced by 19th century theories that the blanket of atmospheric gases could be thick enough to affect climate.

At the time, meteorologists and atmospheric scientists thought the link Callendar showed must be a coincidence. Today, the mechanism is known as the Callendar Effect, after the engineer who demonstrated it.

Something in the Air

The connection between burning fuel and carbon dioxide was first made in the 1750s. Joseph Black, a Scottish physician and physicist who provided financial support for James Watt’s research into steam power, was one of the first scientists to investigate thermodynamics. For instance, Black made the distinction between heat and temperature: Latent heat changes the phase from liquid to vapor while the temperature is constant; sensible heat changes the temperature while there is no phase change.

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Black also investigated the production and properties of carbon dioxide, which he called “fixed air.” He demonstrated that not only could the substance extinguish flames and suffocate animals, but also through experiments involving the bubbling of gases through a solution of lime and water, that the same material was produced by respiration, fermentation, and combustion. His work led to the later identification of other discrete substances, such as nitrogen and oxygen, and was a stepping stone to understanding the atomic nature of matter.

In the 19th century, other scientists began exploring the effect of gases in the atmosphere, such as their ability to absorb heat. For instance, in the 1820s, French physicist and mathematician Joseph Fourier calculated that without the atmosphere, the earth would be much colder. He compared the air to a glass window covering the earth, and because of that metaphor, we now refer to the phenomenon as the “greenhouse effect.”

Guy Stewart Callendar in 1934, the year of the third International Steam Table Conference. Photo: American Meteorological Society.
The specific contribution of carbon dioxide to this warming effect was quickly noticed. In 1856, the 37-year-old American physicist Eunice Newton Foote discovered that a glass bottle of CO2 placed in the sun rose to a higher temperature than a bottle of air. As a woman she was not allowed to present her research, so her paper, “Circumstances Affecting the Heat of the Sun’s Rays,” was presented by Smithsonian Secretary Joseph Henry to a conference of the American Association for Advancement of Science that was meeting in Albany.

Within a few years, the Irish physicist John Tyndall demonstrated that carbon dioxide has a much larger absorptivity for the longer wavelength radiation emitted from the Earth than for visible light, and suggested the connection between fluctuations in atmospheric CO2 and the Ice Ages. Tyndall’s discovery was followed in the 1890s by Svante Arrhenius, the Swedish physical chemist and Nobel laureate, who calculated if the level of CO2 was half its existing value, the earth would be 4 °C cooler, and if doubled, the earth would be 4 °C warmer.

According to James Rodger Fleming, a historian of science at Colby College in Waterville, Me., and author of a biography of Guy Callendar, around the turn of the 20th century, leading scientists were challenging the role of carbon dioxide as a factor in regulating climate. By the time Callendar turned his attention to the question, the prevailing theory was that water vapor was the primary absorber of infrared radiation in the atmosphere and that CO2 had little effect.

Universal Geniuses

Before investigating carbon dioxide, Guy Callendar had grown up collaborating with his better known father, the physicist Hugh Longbourne Callendar. Ernest Rutherford, the discoverer of atomic radiation, once wrote that the elder Callendar was considered a “universal genius.” Among the advances Callendar was responsible for was practical X-ray imaging and a thermometer that measured temperature via changes in electrical resistance, recording the measurement via a pen marking a line on a rolling sheet of paper.

Between the royalties from his inventions and the salary from his professorship, the elder Callendar provided his family with a degree of affluence. Guy Callendar, born in 1898 during his father’s brief tenure at McGill University in Montreal, grew up in a posh suburb of London with his three siblings in a four-story, 22-room home staffed with servants, a chauffeur, and a gardener. The mansion also had a workshop and lab to experiment with early vintage engines, gears, automobiles, and motorcycles.

Professor Callendar’s next and related initiative was measuring and publishing properties of steam.

Steam turbines were quickly replacing piston and cylinder engines that used saturated steam, but that meant that power plant design required data on steam properties at high pressure and superheated temperatures. Measured values of pressure, temperature, and volume were extended to internal energy, enthalpy, and entropy. Knowledge of absolute zero was required. Supplemental charts provided a means for better representing processes and cycles. An enthalpy-versus-entropy chart had been proposed in 1904 by Richard Mollier. It can be used to compare efficiency of an actual turbine with the ideal.

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Hugh Longbourne Callendar, armed with his electric resistance-based thermometer and recorder, was in an ideal position to produce the high-temperature measurements these charts required. The results were first collected in The Callendar Steam Tables in 1915. The young Guy Callendar collaborated with his father on later editions, and then continued the series after his father died in 1930.

Other groups were doing comparable measurements for steam properties, and there was an incentive for consistency. Guy Callendar participated in all three meetings of the International Steam Table Conference, including the third, which was co-hosted by ASME in 1934 and was held in Washington, Boston, and New York. There he mingled with Joseph Keenan and Frederick Keyes, who in 1936 would publish their own steam tables that became widely used by American students and engineers.

Pumps installed at Graveley in 1945 by the Fog Investigation and Dispersal Operation supplied petrol to pipes on either side of the main runway. Photo: Wikimedia Commons
Much like his father, Guy Callendar was a polymath. In addition to his work on steam properties, he contributed to a Royal Air Force program to clear fog from runways. At the start of the Second World War, aircraft were being lost due to weather—planes were missing the runway at foggy airfields—at nearly the same rate as losses due to enemy fire. The RAF challenged scientists to find ways to clear the fog. Callendar became a major contributor to the top-secret program, Fog Investigation and Dispersal Operation. Fog clearing was achieved by arranging burners on both sides of the runway. While it required vast amounts of the limited fuel supplies, it was credited for saving many aircraft and air crews, and for shortening the war.

Precision Measurements

Callendar’s professional base was the British Electrical and Allied Industries Research Association, a public-private organization that supported electricity producers. But at home, working essentially alone, he began an investigation of the question of what role, if any, carbon dioxide played in climate. According to Fleming, Callendar had read and took extensive notes on the literature on the atmospheric absorption of radiation, and found it wanting. He then began producing papers of his own.

His first paper, in 1938, is his most widely cited. The goal of that paper, Fleming writes, was to “establish that fuel burning had exceeded the limits of the natural carbon cycle.” Callendar showed there was a measured increase in carbon dioxide and that this build-up had led to a small but inexorable increase in the temperature of the Earth. Based on this, he predicted that the coming decades would see even greater temperature increases, which was fine in his view as it would help stave off the possibility of a new Ice Age.

Instead, a cooling period began almost immediately after Callendar published his paper. (The steady march of temperature increases he predicted would not commence until the late 1960s.) Over the span of 25 years, Callendar would publish nine more major articles on carbon dioxide. His work was admired for his quality and diligence, but not so much for the importance. Most climate specialists of the day dismissed the connection between the infrared-absorbing power of CO2 and changes in temperature.

Charles David Keeling with his carbon dioxide-measuring device. Photo: Scripps Institution of Oceanography
A major challenge for Callendar’s work was obtaining high-quality measurements of the carbon dioxide concentration in the global atmosphere. In his 1938 paper, for instance, he compared measurements from different groups on separate continents, and he worried that some of the readings must have been affected by local conditions. To conclusively demonstrate that, in fact, the combustion of fossil fuels was increasing the amount of CO2 in the atmosphere, Callendar would need a data set produced with a consistent methodology over several decades.

Working alone on his own time, Callendar had no way to produce that. The person who could was a young post-doctoral student at the California Institute of Technology, Charles David Keeling.

After completing a doctorate in geology from Northwestern University in 1953, Keeling took a post-doctoral position at Cal Tech. Bored with crushing rocks, Keeling extended his interest to geochemistry, and by combining an older design with new capabilities, he created a better, more sensitive instrument for measuring CO2. To demonstrate the power of his new instrument, he traveled up the California coast to Big Sur, where he camped and sampled the air every hour over several days.

There among the trees, Keeling discovered that CO2 concentrations followed a daily cycle. The gas decreased during the day, as trees drew in CO2 during photosynthesis, and increased at night. Keeling showed that trees can only absorb CO2 when they receive energy from the sun.

The carbon dioxide sensor Keeling built started as a hobby, but he soon found a pressing purpose for it. Keeling had been studying papers written by Guy Callendar and realized that his own equipment could fill in the gaps in Callendar’s data.

Keeling persuaded the United States Weather Bureau’s Division of Meteorology Research to provide funding to the Scripps Institution of Oceanography to initiate a series of detailed carbon dioxide measurements as part of the 18-month International Geophysical Year campaign beginning in 1957. Scripps then hired Keeling and sent him out to measure CO2 on land at various latitudes and also different altitudes by aircraft.

The CO2 measurements were surprisingly consistent: about 315 ppm in mountain, desert, and coastal areas. This indicated an unexpected high degree of mixing of CO2 in the atmosphere. That meant that to show a trend, scientists wouldn’t need to sample locations all over the world—daily measurements from a single site could confirm if a trend existed.

The Mauna Loa Observatory, atop an 11,135-foot volcanic peak in Hawaii, was chosen, and the first sample was taken in March 1958. The value was 313 parts per million. Data collection was interrupted for a few weeks due to power failure. When restored in July they were surprised to find the CO2 concentration had dropped below the March level.

It took a couple years to recognize a pattern was established. The seasonal variation was larger and more consistent than expected, and was determined to be due to the release of CO2 by biomass decay during the Northern Hemisphere fall and winter, and followed by absorption during the rapid growing of trees and plants during the spring and summer.

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On top of that annual cycle, there was an upward trend visible when comparing measurements at the same date on consecutive years. The concentration of CO2 has increased from about 310 parts per million to more than 410 ppm since 1958. It is now increasing at a rate of more than 2 parts per million per year.

Based on the estimates of the fossil fuels burned over the past 200 years and the increase in the concentration of carbon dioxide in the air, scientists calculate that roughly 55 percent of the carbon gases released by combustion since the beginning of the industrial revolution remains in the atmosphere. (The remainder has been absorbed by vegetation and ocean water.)

Keeling’s work has been widely praised, and the sampling program he began at Mauna Loa 62 years ago is now the longest-running continuous scientific experiment. It confirmed one part of Guy Callendar’s proposal, that fossil fuel combustion is increasing the fraction of carbon dioxide in the atmosphere. The rest—that additional CO2 will increase the amount of infrared radiation trapped in the atmosphere, and that this change in the radiation balance will raise the average global temperature—has also been confirmed.

It’s true that there are many mechanical engineers who are offended by the implications of climate change and object to virtually any action to halt it. But the historical record shows that it was an engineer who discovered global warming. Perhaps engineers should be the ones who rise to the occasion and stop it.

Frank Wicks is a frequent contributor to Mechanical Engineering. He is an ASME Fellow, a thermodynamicist, and Emeritus Professor at Union College in Schenectady.

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