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Carbon Dioxide and the Climate

A 1956 American Scientist article explores climate change; two contemporary commentaries illuminate its relevance to the present

Gilbert N. Plass, James Rodger Fleming, Gavin Schmidt

Gilbert N. Plass: Climate Science in Perspective

James Rodger Fleming

Gilbert Plass was a scientist on the cutting edge of climate research in 1956. His article in American Scientist, on the recently revived carbon dioxide theory of climate change, and the role that the combustion of fossil fuel was playing in it, was aimed at a broadly educated scientific readership; it was one of six related articles he published that year and one of about a dozen he published that decade. In a 1997 interview, Plass told me, “all sorts of things came together” that placed him at the scientific forefront: new detailed laboratory measurements of the absorption bands of water vapor, carbon dioxide and ozone; theoretical developments involving the influence of temperature and pressure on infrared absorption; new information about the carbon cycle and industrial emissions; and access to a new high-speed electronic computer to facilitate complex calculations of radiative transfer that replaced the older, graphical approximations.

Gilbert Norman Plass was born in Toronto, Ontario, Canada, on March 22, 1920. He was a physicist who developed an early computer model of infrared radiative transfer and published a number of articles on carbon dioxide and climate between 1953 and 1959. He received a B.S. from Harvard University in 1941, where he recalled that his courses on geology, chemistry and physics provided an interdisciplinary foundation for his later work. He was particularly impressed by the experimental techniques of John Strong, one of his physics professors. Plass received his Ph.D. from Princeton University in 1947 and worked as an associate physicist at the Metallurgical Laboratory (Manhattan District) of the University of Chicago from 1942 to 1945. He became an instructor of physics at Johns Hopkins University in 1946 and was subsequently promoted to assistant and then associate professor. At Hopkins he conducted research on infrared radiation with funds provided by the Office of Naval Research. During his sabbatical year, at Michigan State University in 1954–55, he gained access to a large computer and realized it offered the perfect way to construct a better model of radiative transfer. In 1955 Plass moved out of academics, serving for a year as a staff scientist with Lockheed Aircraft Corporation. He then joined the advanced research staff of the Aeronutronic division of the Ford Motor Company. Ford provided him with excellent laboratory facilities where he could continue his experimental work on infrared physics. In 1960, he became manager of the research lab at Ford’s theoretical physics department and a consulting editor of the journal Infrared Physics. In 1963, he accepted a position as the first professor of atmospheric and space science at the Southwest Center for Advanced Studies (now the University of Texas, Arlington) where he remained for five years. In 1968, he arrived at Texas A&M University, where he served as professor of physics and head of the department. He is the author of six books, including Infrared Physics and Engineering (1963) and more than 100 articles on radiative transfer and climate change, nuclear fission and neutron physics, electromagnetic and gravitational action at a distance, electron emission, and electrostatic electron lenses. Plass and his spouse were active supporters of the arts, helping to establish and direct arts societies and producing a radio program in Texas. He passed away in Bryan, Texas, on March 1, 2004.

In 1956 Gilbert Plass was heir to a century of work that identified variations in the trace amounts of carbon dioxide in the atmosphere as a possible cause of ice ages and interglacial periods. John Tyndall wrote in 1861 that slight changes in the amount of any of the radiatively active constituents of the atmosphere—water vapor, carbon dioxide, ozone or hydrocarbons—may have produced “all the mutations of climate which the researches of geologists reveal … they constitute true causes, the extent alone of the operation remaining doubtful.” Thirty-five years later Svante Arrhenius published a landmark paper examining the effect of different concentrations of atmospheric CO2 on the temperature of Earth. His energy budget model, which he calculated by hand, contained estimates of the absorption and emission of terrestrial radiation by water vapor and carbon dioxide, but since infrared research was in its infancy then, Arrhenius had access to only very limited spectroscopic data.

Because of these limitations, the carbon dioxide theory of climate change was in deep eclipse in 1938 when British scientist and engineer Guy Stewart Callendar revived it and placed it on a firm scientific basis. Callendar documented a significant upward trend in temperatures for the first four decades of the 20th century and noted the systematic retreat of glaciers. He compiled estimates of rising concentrations of atmospheric CO2 since pre-industrial times and linked the rise of CO2 to the combustion of fossil fuel. Finally, he synthesized information newly available concerning the infrared absorption bands of trace atmospheric constituents and linked increased sky radiation from increased CO2 concentrations to the rising temperature trend. Today this is called The Callendar Effect.

Building on such foundations, Plass was able to take the next steps in research and provide his masterful overview of the carbon dioxide theory and its implications for the future. He established connections between the physics of infrared absorption by gases, the geochemistry of the carbon cycle, feedback loops in the climate system and computer modeling. Using recent measurements of the influence of the 15-micrometer CO2 absorption band, Plass calculated a 3.6 degrees Celsius surface temperature increase for doubling of atmospheric carbon dioxide and a 3.8 degree decrease if the concentration were halved. Contrary to the assumptions of many scientists at the time, the effect of water vapor absorption did not mask the carbon dioxide effect by any means. He used these results to argue for the applicability of the carbon dioxide theory of climate change for geological epochs and in recent decades.

Stressing the intrinsic role carbon dioxide plays in our atmosphere, Plass discussed the danger of fossil fuel burning and deforestation. The six billion tons of CO2 being added to the atmosphere each year was sufficient to cause noticeable changes in the Earth’s radiation balance and thus the climate. He noted that the observed 1.1 degree rate of climate warming per century was in agreement with the predictions of the carbon dioxide theory.

Waxing prophetic, Plass wrote that the oceans would be able to sequester only a small amount of the anthropogenic carbon, leaving the majority in the atmosphere. Accumulating atmospheric CO2 content from fossil fuel-based industrial activities would eventually result in a temperature rise of at least 7 degrees. Plass held out little hope for nuclear power—expressing an opinion that would not be widespread for several more decades. Presaging the work of Charles David Keeling, which began two years later, Plass called for new accurate measurements of the increasing CO2 concentration in the atmosphere, which he rightly estimated should be on the order of 0.3 percent per year. Plass pointed out that humanity was conducting a large-scale experiment on the atmosphere, the results of which would not be available for several generations: “If at the end of this century, the average temperature has continued to rise and in addition measurement shows that the atmospheric carbon dioxide amount has also increased, it will be firmly established that carbon dioxide is a determining factor in causing climatic change.”

There have been two interruptions (pauses, if you will) in the rise of global average temperature since 1956, and of course, Earth’s climate is influenced by more than just CO2. Other trace gases and black carbon warm the climate, and aerosols cool it. On a larger scale, the astronomical theory of orbital influences was revived circa 1976, and climate variation attributed to such factors as ENSO, the Pacific Decadal Oscillation, and solar activity (or the lack thereof) are now being widely discussed. Still, more than 50 years later, scientists agree that the uncontrolled experiment pointed out by Plass in 1956 has been verified, and a warmer future caused by the radiative effects of CO2 is in store. The cutting edge question now is, What to do about it?


  • Arrhenius, Svante. 1896. On the influence of carbonic acid in the air upon the temperature of the ground. Philosophical Magazine, series 5, 4:237–276.
  • Callendar, G. S. 1938. The artificial production of carbon dioxide and its influence on temperature. Quarterly Journal of the Royal Meteorological Society 64:223–240.
  • Callendar, G. S. 1949. Can carbon dioxide influence climate? Weather 4:310–314.
  • Fleming, James Rodger. 1998, 2005. Historical perspectives on climate change. New York: Oxford Univeristy Press.
  • Fleming, James Rodger. 2007. 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.
  • Plass, Gilbert N. 1953. The carbon dioxide theory of climatic change. Bulletin of the American Meteorological Society 34:80.
  • Plass, Gilbert N. 1956a. Carbon dioxide and the climate. American Scientist 44:302–316.
  • Plass, Gilbert N. 1956b. The influence of the 9.6 micron ozone band on the atmospheric infra-red cooling rate. Quarterly Journal of the Royal Meteorological Society 82:30–44.
  • Plass, Gilbert N. 1956c. The influence of the 15µ carbon-dioxide band on the atmospheric infra-red cooling rate. Quarterly Journal of the Royal Meteorological Society 82:310–324.
  • Plass, Gilbert N. 1956d. The carbon dioxide theory of climatic change. Tellus 8:140–154.
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  • Plass, Gilbert N. 1956f. Effect of carbon dioxide variations on climate. American Journal of Physics 24:376–387.
  • Plass, Gilbert N. 1959. Carbon dioxide and climate. Scientific American, July, 41–47.
  • Plass, Gilbert N., and D. I. Fivel. 1955a. A method for the integration of the radiative-transfer equation. Journal of Meteorology 12:191–200.
  • Plass, Gilbert N., and D. I. Fivel 1955b. The influence of variable mixing ratio and temperature on the radiation flux. Quarterly Journal of the Royal Meteorological Society (81)48–62.
  • Tyndall, John. 1861. On the absorption and radiation of heat by gases and vapours, and on the physical connection of radiation, absorption, and conduction. Philosophical Magazine, series 4, 22:169–194, 273–285.

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