Callendar Connects Industry with Increased Atmospheric Carbon Dioxide

Date 1938

Guy Stewart Callendar noted the increasing level of carbon dioxide in the earth’s atmosphere and traced it to human activity.

Also known as Greenhouse effect; Callendar effect

Locale England

Key Figures

• Guy Stewart Callendar (1898-1964), English physicist
• Svante August Arrhenius (1859-1927), Swedish physicist and chemist
• Charles D. Keeling (1928-2005), American marine geochemist
• Bert R. Bolin (b. 1925), Swedish meteorologist

Summary of Event

Carbon dioxide is a colorless, tasteless, transparent gas that is present in very small quantities, about 0.03 percent by volume, in the air that humans breathe in and in larger quantities in the air that is breathed out, because it is a waste product of the process by which life is maintained. It also has the interesting property that, while it allows the electromagnetic energy of sunlight to pass through it unhindered to the surface of the earth, when the warm surface of the ground or ocean radiates heat upward at infrared frequencies, this heat is absorbed by carbon dioxide. This process by which heat is trapped near the surface of the earth is known as the greenhouse effect. It operates for other gases in the air, but, unlike other gases, the proportion of carbon dioxide in the air is increasing steadily as a result of human activity. There is no doubt that the burning of fossil fuels—coal, oil, and natural gas—releases carbon dioxide into the atmosphere.

A few decades after the beginning of the industrial age, scientists began to question the effect of increased burning of carbon-based fossil fuels on the atmosphere. Carbon-based fuels are the chief energy source for the earth’s population, and, as a result, the human impact on the global carbon cycle is far-reaching. Fossil fuels are hydrocarbon molecules whose chemical energy is released when they are burned, the principal emission from this combustion being carbon dioxide gas. The effect of carbon dioxide gas is that it heats the lower atmosphere as carbon dioxide concentrations increase. Svante August Arrhenius, a Swedish physicist and chemist, was one of the first to write about increased carbon dioxide levels in the atmosphere. In the mid-1880’s, he announced his survey of the first few decades of the Industrial Revolution and concluded that humans were burning coal at an unprecedented rate. Arrhenius knew that carbon dioxide trapped infrared radiation that would otherwise have reflected back out to space. He used measurements of infrared radiation from the full moon in his first calculations of the possible effects of anthropogenic (of human origin) carbon dioxide. His conclusions were that the average global temperature would rise as much as 9 degrees if the amount of carbon dioxide in the air doubled from its preindustrial level.

Arrhenius’s work did not gain acceptance until Guy Stewart Callendar, an English physicist, speculated in 1938 that increasing carbon dioxide levels were the probable cause for a warming of North America and Northern Europe that meteorologists had begun to observe in the 1880’s. Carbon dioxide is transparent to incoming ultraviolet but opaque to the resulting reradiation in the infrared. Because carbon dioxide also absorbs incoming infrared radiation, it is an integral part of the mechanism of global heat balance. Without compensating charges, increased levels of carbon dioxide will result in higher temperatures. The increase in the effective emissivity of infrared radiation from the earth, with resulting atmospheric heating, is responsible for the so-called greenhouse effect. Callendar was the first to assemble a large body of measurements from several scientific sources and predict significant temperature change from anthropogenic carbon dioxide.

Direct measurements of the temperature effects of carbon dioxide are difficult because the underlying natural fluctuations in temperature do not provide a stable baseline against which to reference anthropogenic disturbances. Callendar, working from this disadvantage, collected data from several scientists. They were odd, rather unsystematic, and somewhat unreliable data; however, they agreed with later, more precise observations.

Several factors worked against widespread acceptance of Callendar’s study, one of which was that a warming seemed to be replaced by a temperature decline around 1940. Another was that most scientists in the 1930’s were too busy with the exploitation of petroleum for new products and believed that the problem of excess carbon dioxide would be absorbed in the oceans, not the atmosphere. Callendar remained convinced by his 1938 study and noted in 1958, that since 1942, the carbon dioxide content had continued to rise at a rate of about 0.2 percent per year. Concern about atmospheric pollution as a direct result of humans virtually exploded in the late 1960’s, when many of the industrial nations began to promulgate laws and write regulations covering atmospheric pollution by manufacturers. The early work done by investigators such as Callendar was remarkably correct considering the fact that the work was done during a time when there were no computers to allow for the development of models to add innumerable variables and analyze them.

There are uncertainties about what has caused the increased levels of carbon dioxide in the atmosphere; for example, the rate of absorption of excess carbon dioxide by the ecosystem and oceans, the rate of production of carbon dioxide by destruction of forests, the cooling effect of increasing aerosols—both anthropogenic and from revived volcanic activity—and feedback effects of water vapor and clouds. Nevertheless, it is abundantly clear that there is a connection, as Callendar noted in 1938, between human activity and air pollution. The energy crisis in the mid-1970’s and the increasing sophistication of numerical atmospheric circulation models have led to greatly increased interest and investigation of the carbon dioxide greenhouse effect. In 1975, V. Ramanathan pointed out that the greenhouse effect is enhanced by the continued release into the atmosphere of chlorofluorocarbons, even though their combined concentration is less than a part per billion by volume.

Many physicists look to the computer models and view the steadily rising concentration of atmospheric carbon dioxide as a prelude to climatological catastrophe; at the other extreme, another group of scientists concentrates on more empirical data. Empirical data are those that rely on experience or observation alone, often without regard for system and theory. The empiricists believe that any change in the climate caused by rising levels of carbon dioxide will be indistinguishable from natural climatic fluctuations. They foresee that higher concentrations of carbon dioxide will tend to stimulate photosynthesis and so increase the productivity of crops and the efficiency with which plant life uses water. The empirical approach depends on finding some natural event that temporarily disturbs the heat balance of the atmosphere, such as the great dust storms of the 1930’s in the southern plains of the United States. By monitoring the temperature changes and flow of radiative heat during such natural events, scientists can measure the response of the real world to the perturbation.

Significance

In the several decades after Callendar first noted that humans were causing increased levels of carbon dioxide in the atmosphere, it has been found that the much more abundant constituent carbon monoxide is also increasing as a result of automobile exhausts and other combustion processes. Although carbon monoxide does not make a direct impact in enhancing the greenhouse effect, it does play an indirect role by serving as a sink for the hydroxyl radical, which acts as a catalyst in modulating the increase of nitrous oxide from combustion processes. Also contributing to carbon monoxide is the use of chemical fertilizers and the increase of methane from biogenic and industrial production.

From 1957 to 1975, the amount of carbon dioxide in the air increased from 312 to 326 parts per million, almost 5 percent. American scientists have measured this trend since 1957, initially under the leadership of marine geochemist Charles D. Keeling (until his death in 2005), and Swedish meteorologists, led by Bert R. Bolin, have taken measurements since 1963. Both groups of scientists have made their measurements in areas far away from any localized sources of carbon dioxide so that they might observe the background and thus the worldwide trends in carbon dioxide: the Americans on Mauna Loa, Hawaii, and at the South Pole, and the Swedes on the air-intake systems of commercial aircraft flying the polar route.

In addition to research in the atmosphere, considerable research has been carried out in glacial areas of the world. In 1990, two teams of European and American researchers drilled through more than two miles of ice searching for trapped air bubbles and entombed crystals in order to discover what the weather was like during the past 200,000 years. On the summit of Greenland, the highest point on the vast ice mound that almost completely covers the world’s largest island, scientists are seeking an answer to the most pressing question in climatology: Will rising levels of carbon dioxide and methane heat the earth and melt the polar ice caps? Evidence from ice cores drilled by Soviet researchers in Antarctica have indicated that rising levels of carbon dioxide in the atmosphere have resulted in warmer temperatures on the earth several times during the past 200,000 years.

Bibliography

Breuer, Georg. Air in Danger: Ecological Perspectives on the Atmosphere. New York: Cambridge University Press, 1980. Very good account of the atmosphere covers carbon dioxide increase and features a good discussion of the risks associated with higher levels of carbon dioxide in the atmosphere. Includes a few illustrations.

Callendar, Guy S. “The Artificial Production of Carbon Dioxide and Its Influence on Temperature.” Quarterly Journal of the Royal Meteorological Society 64 (1938): 223-240. Interprets and analyzes worldwide temperature measurements and the effects of production of carbon dioxide. Includes interesting temperature charts from the great cities and oceans. Valuable primarily for historical reasons.

Gore, Al. Earth in the Balance: Ecology and the Human Spirit. New York: Houghton Mifflin, 1992. Argues that only a drastic rethinking of humankind’s relationship with nature can preserve the earth for the future. Includes bibliography and index.

Goudie, Andrew. The Human Impact on the Natural Environment: Past, Present, and Future. 6th ed. Malden, Mass.: Blackwell, 2006. Excellent general reference accessible to lay readers. Chapter 7 focuses on the human impact on climate and the atmosphere. Includes glossary, bibliography, and index.

Idso, Sherwood B. “Carbon Dioxide Can Revitalize the Planet.” In The Greenhouse Effect, edited by Matthew Kraljic. New York: H. W. Wilson, 1992. Contends that the rising carbon dioxide content of the atmosphere is beneficial and that the small amount of greenhouse warming it causes may actually enhance the biosphere.

Keller, Edward A. Environmental Geology. 8th ed. Upper Saddle River, N.J.: Prentice Hall, 1999. Includes a well-illustrated chapter on urban air with diagrams showing the effects of various factors on potential air pollution: smog, future trends for urban areas, and the control of particulates in air pollution.

Lyman, Francesca. The Greenhouse Trap. Boston: Beacon Press, 1990. One of a series of books by the World Resource Institute Guides to the Environment. Discusses the basic concerns about atmosphere and climate and the steps necessary to achieve climate stability.

McKibben, Bill. The End of Nature. 10th anniversary ed. New York: Random House, 1999. Addresses the scientific evidence about the greenhouse effect, the depletion of the ozone layer, and an array of other ecological ills. Written in a narrative style accessible to the lay reader.

Revkin, Andrew. Global Warming: Understanding the Forecast. New York: Abbeville Press, 1992. Discusses Callendar’s and Arrhenius’s early studies as well as more recent developments such as the Persian Gulf War of 1990 and the effects of industrial development in emerging nations. Includes tables and color plates.

Schneider, Stephen H. Global Warming: Are We Entering the Greenhouse Century? San Francisco: Sierra Club Books, 1989. Examines the causes of world climate change and provides an authoritative, entertaining look at the science, personalities, and politics behind the problem of global warming. Explains in clear, nontechnical language what is scientifically known, what is speculative, and where major uncertainties lie.