User:Rchlanne00/History of climate change science

Increasing concern, 1950s – 1960s

Charles Keeling, receiving the National Medal of Science from George W. Bush, in 2001

Better spectrography in the 1950s showed that CO₂ and water vapor absorption lines did not overlap completely. Climatologists also realized that little water vapor was present in the upper atmosphere. Both developments showed that the CO₂ greenhouse effect would not be overwhelmed by water vapor.

In 1955 Hans Suess's carbon-14 isotope analysis showed that CO₂ released from fossil fuels was not immediately absorbed by the ocean. In 1957, better understanding of ocean chemistry led Roger Revelle to a realization that the ocean surface layer had limited ability to absorb carbon dioxide, also predicting the rise in levels of CO₂ and later being proven by Charles David Keeling. By the late 1950s, more scientists were arguing that carbon dioxide emissions could be a problem, with some projecting in 1959 that CO₂ would rise 25% by the year 2000, with potentially "radical" effects on climate. In the centennial of the American oil industry in 1959, organized by the American Petroleum Institute and the Columbia Graduate School of Business, Edward Teller said "It has been calculated that a temperature rise corresponding to a 10 per cent increase in carbon dioxide will be sufficient to melt the icecap and submerge New York. [....] At present the carbon dioxide in the atmosphere has risen by 2 per cent over normal. By 1970, it will be perhaps 4 per cent, by 1980, 8 per cent, by 1990, 16 per cent if we keep on with our exponential rise in the use of purely conventional fuels.". In 1960 Charles David Keeling demonstrated that the level of CO₂ in the atmosphere was in fact rising. Concern mounted year by year along with the rise of the "Keeling Curve" of atmospheric CO₂.

Another clue to the nature of climate change came in the mid-1960s from analysis of deep-sea cores by Cesare Emiliani and analysis of ancient corals by Wallace Broecker and collaborators. Rather than four long ice ages, they found a large number of shorter ones in a regular sequence. It appeared that the timing of ice ages was set by the small orbital shifts of the Milankovitch cycles. While the matter remained controversial, some began to suggest that the climate system is sensitive to small changes and can readily be flipped from a stable state into a different one.

Scientists meanwhile began using computers to develop more sophisticated versions of Arrhenius's calculations. In 1967, taking advantage of the ability of digital computers to integrate absorption curves numerically, Syukuro Manabe and Richard Wetherald made the first detailed calculation of the greenhouse effect incorporating convection (the "Manabe-Wetherald one-dimensional radiative-convective model"). They found that, in the absence of unknown feedbacks such as changes in clouds, a doubling of carbon dioxide from the current level would result in approximately 2 °C increase in global temperature.

By the 1960s, aerosol pollution ("smog") had become a serious local problem in many cities, and some scientists began to consider whether the cooling effect of particulate pollution could affect global temperatures. Scientists were unsure whether the cooling effect of particulate pollution or warming effect of greenhouse gas emissions would predominate, but regardless, began to suspect that human emissions could be disruptive to climate in the 21st century if not sooner. In his 1968 book The Population Bomb, Paul R. Ehrlich wrote, "the greenhouse effect is being enhanced now by the greatly increased level of carbon dioxide... [this] is being countered by low-level clouds generated by contrails, dust, and other contaminants... At the moment we cannot predict what the overall climatic results will be of our using the atmosphere as a garbage dump."

Efforts to establish a global temperature record that began in 1938 culminated in 1963, when J. Murray Mitchell presented one the first up-to-date temperature reconstructions. His study involved data from over 200 weather stations, collected by the World Weather Records, which was used to calculate latitudinal average temperature. In his presentation, Murray showed that, beginning in 1880, global temperatures increased steadily until 1940. After that, a multi-decade cooling trend emerged. Murray’s work contributed to the overall acceptance of a possible global cooling trend.

In 1965, the landmark report, "Restoring the Quality of Our Environment" by U.S. President Lyndon B. Johnson’s Science Advisory Committee warned of the harmful effects of fossil fuel emissions:

The part that remains in the atmosphere may have a significant effect on climate; carbon dioxide is nearly transparent to visible light, but it is a strong absorber and back radiator of infrared radiation, particularly in the wave lengths from 12 to 18 microns; consequently, an increase of atmospheric carbon dioxide could act, much like the glass in a greenhouse, to raise the temperature of the lower air.

The committee used the recently available global temperature reconstructions and carbon dioxide data from Charles David Keeling and colleagues to reach their conclusions. They declared the rise of atmospheric carbon dioxide levels to be the direct result of fossil fuel burning. The committee concluded that human activities were sufficiently large to have significant, global impact—beyond the area the activities take place. “Man is unwittingly conducting a vast geophysical experiment,” the committee wrote.

Nobel Prize winner Glenn T. Seaborg, Chairperson of the United States Atomic Energy Commission warned of the climate crisis in 1966: "At the rate we are currently adding carbon dioxide to our atmosphere (six billion tons a year), within the next few decades the heat balance of the atmosphere could be altered enough to produce marked changes in the climate--changes which we might have no means of controlling even if by that time we have made great advances in our programs of weather modification."

A 1968 study by the Stanford Research Institute for the American Petroleum Institute noted:

If the earth's temperature increases significantly, a number of events might be expected to occur, including the melting of the Antarctic ice cap, a rise in sea levels, warming of the oceans, and an increase in photosynthesis. [..] Revelle makes the point that man is now engaged in a vast geophysical experiment with his environment, the earth. Significant temperature changes are almost certain to occur by the year 2000 and these could bring about climatic changes.

In 1969, NATO was the first candidate to deal with climate change on an international level. It was planned then to establish a hub of research and initiatives of the organization in the civil area, dealing with environmental topics as acid rain and the greenhouse effect. The suggestion of US President Richard Nixon was not very successful with the administration of German Chancellor Kurt Georg Kiesinger. But the topics and the preparation work done on the NATO proposal by the German authorities gained international momentum, (see e.g. the Stockholm United Nations Conference on the Human Environment 1970) as the government of Willy Brandt started to apply them on the civil sphere instead.

Also in 1969, Mikhail Budyko published a theory on the ice-albedo feedback, a foundational element of what is today known as Arctic amplification. The same year a similar model was published by William D. Sellers. Both studies attracted significant attention, since they hinted at the possibility for a runaway positive feedback within the global climate system.

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Scientists increasingly predict warming, 1970s

Mean temperature anomalies during the period 1965 to 1975 with respect to the average temperatures from 1937 to 1946. This dataset was not available at the time.

In the early 1970s, evidence that aerosols were increasing worldwide and that the global temperature series showed cooling encouraged Reid Bryson and some others to warn of the possibility of severe cooling. The questions and concerns put forth by Bryson and others launched a new wave of research into the factors of such global cooling. Meanwhile, the new evidence that the timing of ice ages was set by predictable orbital cycles suggested that the climate would gradually cool, over thousands of years. Several scientific panels from this time period concluded that more research was needed to determine whether warming or cooling was likely, indicating that the trend in the scientific literature had not yet become a consensus. For the century ahead, however, a survey of the scientific literature from 1965 to 1979 found 7 articles predicting cooling and 44 predicting warming (many other articles on climate made no prediction); the warming articles were cited much more often in subsequent scientific literature. Research into warming and greenhouse gases held the greater emphasis, with nearly 6 times more studies predicting warming than predicting cooling, suggesting concern among scientists was largely over warming as they turned their attention toward the greenhouse effect.

John Sawyer published the study Man-made Carbon Dioxide and the “Greenhouse” Effect in 1972. He summarized the knowledge of the science at the time, the anthropogenic attribution of the carbon dioxide greenhouse gas, distribution and exponential rise, findings which still hold today. Additionally he accurately predicted the rate of global warming for the period between 1972 and 2000.

The increase of 25% CO2 expected by the end of the century therefore corresponds to an increase of 0.6°C in the world temperature – an amount somewhat greater than the climatic variation of recent centuries. – John Sawyer, 1972

The first satellite records compiled in the early 1970s showed snow and ice cover over the Northern Hemisphere to be increasing, prompting further scrutiny into the possibility of global cooling. J. Murray Mitchell updated his global temperature reconstruction in 1972, which continued to show cooling. However, scientists determined that the cooling observed by Mitchell was not a global phenomenon. Global averages were changing, largely in part due to unusually severe winters experienced by Asia and some parts of North America in 1972 and 1973, but these changes were mostly constrained to the Northern Hemisphere. In the Southern Hemisphere, the opposite trend was observed. The severe winters, however, pushed the issue of global cooling into the public eye.

The mainstream news media at the time exaggerated the warnings of the minority who expected imminent cooling. For example, in 1975, Newsweek magazine published a story titled “The Cooling World” that warned of "ominous signs that the Earth's weather patterns have begun to change." The article drew on studies documenting the increasing snow and ice in regions of the Northern Hemisphere and concerns and claims by Reid Bryson that global cooling by aerosols would dominate carbon dioxide warming. The article continued by stating that evidence of global cooling was so strong that meteorologists were having "a hard time keeping up with it." On 23 October 2006, Newsweek issued an update stating that it had been "spectacularly wrong about the near-term future". Nevertheless, this article and others like it had long-lasting effects on public perception of climate science.

Such media coverage heralding the coming of a new ice age resulted in beliefs that this was the consensus among scientists, despite this is not being reflected by the scientific literature. As it became apparent that scientific opinion was in favor of global warming, the public began to express doubt over how trustworthy the science was. The argument that scientists were wrong about global cooling, so therefore may be wrong about global warming has been called “the “Ice Age Fallacy” by TIME author Bryan Walsh.

In the first two "Reports for the Club of Rome" in 1972 and 1974, the anthropogenic climate changes by CO₂ increase as well as by waste heat were mentioned. About the latter John Holdren wrote in a study cited in the 1st report, “… that global thermal pollution is hardly our most immediate environmental threat. It could prove to be the most inexorable, however, if we are fortunate enough to evade all the rest.” Simple global-scale estimates that recently have been actualized and confirmed by more refined model calculations show noticeable contributions from waste heat to global warming after the year 2100, if its growth rates are not strongly reduced (below the averaged 2% p.a. which occurred since 1973).

Evidence for warming accumulated. By 1975, Manabe and Wetherald had developed a three-dimensional Global climate model that gave a roughly accurate representation of the current climate. Doubling CO₂ in the model's atmosphere gave a roughly 2 °C rise in global temperature. Several other kinds of computer models gave similar results: it was impossible to make a model that gave something resembling the actual climate and not have the temperature rise when the CO₂ concentration was increased.

In a separate development, an analysis of deep-sea cores published in 1976 by Nicholas Shackleton and colleagues showed that the dominating influence on ice age timing came from a 100,000-year Milankovitch orbital change. This was unexpected, since the change in sunlight in that cycle was slight. The result emphasized that the climate system is driven by feedbacks, and thus is strongly susceptible to small changes in conditions.

The 1979 World Climate Conference (12 to 23 February) of the World Meteorological Organization concluded "it appears plausible that an increased amount of carbon dioxide in the atmosphere can contribute to a gradual warming of the lower atmosphere, especially at higher latitudes....It is possible that some effects on a regional and global scale may be detectable before the end of this century and become significant before the middle of the next century."

In July 1979 the United States National Research Council published a report, concluding (in part):

When it is assumed that the CO₂ content of the atmosphere is doubled and statistical thermal equilibrium is achieved, the more realistic of the modeling efforts predict a global surface warming of between 2°C and 3.5°C, with greater increases at high latitudes. ... we have tried but have been unable to find any overlooked or underestimated physical effects that could reduce the currently estimated global warmings due to a doubling of atmospheric CO₂ to negligible proportions or reverse them altogether.

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