"Colder Winters Held Dawn of New Ice Age" screamed a front page Washington Post headline on January 11, 1970. The Post writer David R. Boldt reported that some climatologists were arguing that Earth had entered a cold period in 1950 and it could last for hundreds of years. In support of this argument, the climatologists noted that the global temperature had dropped 0.6°F (0.33°C) since 1950. If the current rate of decline continued, in 240 years Earth's temperature would be 7.2°F (4°C) lower and gripped by an ice age climate—more snow in winter, less snow melting in summer. As far as the University of Wisconsin meteorologist Reid A. Bryson (1920- ) was concerned, "There's no relief in sight."
Not everyone in the scientific community agreed. Bryson contended that human-created pollution was cutting off solar radiation and causing the cooling. The National Weather Service's J. Murray Mitchell strongly disagreed. He maintained that volcanoes produced more dust than people. Volcanic activity had increased significantly since 1940, about the time the global temperature started dropping. Mitchell also argued that any possible ice age might be postponed by thermal pollution from factories and home heating. Another prominent meteorologist, MIT's Hurd
C. Willett, presented evidence that the cooling trend was due to changes in solar radiation. In terms of past solar behavior the Sun was emitting less radiation, but it would be back to full strength before the occurrence of an ice age. Willett thought that after a short period of cooling, Earth would heat up even more than it had 6,000 years before.
Some scholars disputed the cooling trend. Britain's Lord Peter Ritchie-Calder (1906-82) pointed to increases of greenhouse gases in the atmosphere and argued that global temperatures might increase 6.5°F (3.6°C) by 2020. Comparing the claims of scientists supporting global cooling with those supporting global warming, an editorial in the April 7, 1970, Christian Science Monitor pleaded, "Physicists, please coordinate!"
The arguments in favor of cooling were mainly based on the amount of atmospheric dust. A Smithsonian study had shown a 16 percent decrease in sunlight in the Washington, D.C., area over the previous 50 years. Other scientific groups had reported that the amount of dust in the air over the North Atlantic and Indian Oceans was twice as great as 1900s levels and was due entirely to human-made pollutants. Using computer models to project the impact of increasing atmospheric dust on future climate, the NASA atmospheric scientists S. Ichtiaque Rasool (1933- ) and Stephen Schneider (1945- ) concluded that dust created by burning fossil fuels could screen out enough sunlight to drop the global temperature by 10.8°F (6°C). If this temperature decrease continued over five to 10 years, it could trigger a new ice age. Rasool recommended that people stop burning fossil fuels and use nuclear energy instead. Other scientists were less concerned about the aerosols from burning fossil fuels than they were about the release of sulfates, nitrates, and hydrocarbons. They were convinced that those combustion by-products were more likely to alter the global climate by raising temperatures than the aerosols were to cool it.
In the summer of 1971, MIT sponsored a conference called Study of Man's Impact on Climate. Hosted by the Royal Swedish Academy of Sciences in Stockholm, the participants tried to reach a consensus on how human actions were currently changing or could in the future change Earth's climate. Briefing the press, the scientists acknowledged that atmospheric dust could lead to cooling, but they could find no evidence of the global effects of dust. The participants thought that naturally occurring events such as volcanic eruptions influenced atmospheric behavior more than human activity. They were concerned that jet contrails in the stratosphere could upset climatic conditions and recommended more study.
Despite the apparent disagreements, the global cooling argument was more prominent in the first half of the decade. Reid Bryson, in particular, pressed his theory of global cooling. He pointed to declining temperatures, the southward shift of the Gulf Stream, worsening Arctic conditions, and the failure of the summer monsoons as evidence for a profound shift in the climate. Early 20th-century weather, Bryson said, had been extremely abnormal. Between 1918 and 1960, the Indian subcontinent had experienced many fewer droughts than would have been expected on the basis of past records. This period, with its excellent growing conditions, had lulled people into thinking that the climate was always hospitable. Now that it was changing, people were getting worried.
Concerns over climate change led the National Science Foundation to establish its Office of Climate Dynamics, and extensive climate research began at NOAA and the National Center for Atmospheric Research in Boulder, Colorado. Scientists tried to determine the lengths of past warm and cold climates. Some meteorologists, most notably B. J. Mason, director of the British Meteorological Office, argued that Earth's climate was "robust" and "inherently stable," and not likely to change any time soon. There was plenty of time to determine what could be done about problems related to climate change. Other scientists were not so sure.
One scientist who doubted that Earth was cooling was Wallace S. Broecker (1931- ) of the Lamont-Doherty Geological Observatory— part of Columbia University. Broeker had been examining past weather records and concluded that Earth naturally warmed approximately every 80 years. He predicted that it would warm again in the 1990s, only this time there would be much more carbon dioxide in the atmosphere. The excess carbon dioxide would enhance the warming effect and lead to warmer global temperatures than in the previous 1,000 years. With 10 times more carbon dioxide being spewed into the atmosphere in 1970 than in 1900, Broeker was convinced that the warming effect of the carbon dioxide had been masked by the periodic cooling trend. NOAA's J. Murray Mitchell, Jr., concurred. He pointed out that there could be some serious consequences of global warming: the melting of Arctic ice, the melting of ice caps on Greenland and Antarctica, and changing storm tracks and rainfall patterns.
Additional evidence disputing the cooling trend appeared in 1975. A team of British scientists reported that between 1970 and 1974, sea ice— which had been advancing—had begun retreating, cold northerly winds had weakened, and temperatures in the North Atlantic were warmer. At about the same time, two scientists from New Zealand, M. James Salinger and J. M. Gunn, reported that while the Northern Hemisphere may have been cooling, the Southern Hemisphere had actually been warming. This finding was backed up two years later when the National Academy of Sciences (NAS) concluded a 30-month study of climate change. In the first major federally funded report that provided specific figures and a position on greenhouse gases, the 23-member scientific team concluded that the continued burning of fossil fuels could lead to a 10.8°F (6°C) temperature increase in 200 years.
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