Today, skeptics of global warming sometimes point to what they call the 'global-cooling scare' of the 1970s as a reason to discount what they hear now. If the news media 30 years ago hyped 'global cooling' and were wrong, skeptics say, doesn't it follow that 'global warming' coverage might prove equally wrong?
But those who have looked closely at the two eras or have been part of the scientific community then and now say the comparison is unfair. William Connolley, a sort of self-appointed historian of the global-cooling theory, says that although global cooling was briefly but prominently covered in some speculative news articles,
the idea never got much traction within the scientific community. New data and research over the decades has convinced the vast majority of scientists that global warming is real and under way.
Dr. Connolley's full-time job is climate modeler for the British Antarctic Survey. But on his personal website, and as a contributor to RealClimate.org (a website written and edited by working climate scientists), he's authored a number of articles that try to clarify the place of global cooling in the history of science.
In the mid-1970s, scientists were researching the possibility that the nearly three decades of cooling experienced in the Northern Hemisphere since World War II might be the beginning of a new ice age. Data suggested that perhaps the huge increase in dust and aerosols (tiny airborne particles that reflect sunlight back into space) from pollution and human development might be stepping up the cooling process.
The investigation didn't last long. Temperatures began to rise. Improving climate methodologies revealed that, although aerosols did indeed have a cooling effect, CO2 and other greenhouse gases were more potent in bringing about atmospheric change on a global scale. Once this became known, scientists moved on to other things.
Scientists change their minds as data change
Today's global-warming contrarians have resurrected the short-lived theory as a reason to doubt what the recent Intergovernmental Panel on Climate Change (IPCC) assessment report calls 'unequivocal' evidence that global warming is happening.
'Scientists are criticized by global-warming skeptics for making new claims and revising theories, as if we are required to stay politically consistent,' says Stephen Schneider. As a young scientist, Dr. Schneider served as second author of a 1971 paper in the journal Science that discussed the cooling effects of aerosols.
'But that goes against science,' Schneider says now. 'We must allow for new evidence to influence us.' His 1971 paper, called 'Atmospheric Carbon Dioxide and Aerosols: Effects of Large Increases on Global Climate,' was one of the first studies on the issue and was soon overtaken by further research.
'For some, the original speculation was that dust and aerosols would increase at a rate far beyond CO2 and lead to global cooling,' says Schneider, now a professor in the Department of Biological Sciences at Stanford University and a senior fellow at the Center for Environment Science and Policy of the Institute for International Studies there. 'We didn't know yet that such effects were so regionally located. By the mid-1970s, it was realized that greenhouse gases were perhaps more likely to be shifting climate on a global scale.'
Adds climate-modeler Connolley: 'Climate science was far less advanced [in the 1970s], only beginning in a way, and ideas were explored in a tentative way that have later been abandoned.'
Theory never embraced by scientists
Today some global-warming skeptics portray the news media of the 1970s as 'hysterical' over the prospect of global cooling, publishing stories warning of growing glaciers and widespread famine.
The article perhaps most often cited by skeptics was in an April 28, 1975, issue of Newsweek magazine. The author wrote that a dramatic climatic shift to cooler temperatures would bring about massive crop failures and famine - 'perhaps only 10 years from now.'
Although the Newsweek article exhibited some journalistic caution - 'meteorologists disagree about the cause and extent of the cooling trend...' - it ultimately sounds a grave warning. '[Meteorologists] are almost unanimous that the trend will reduce the agricultural productivity for the rest of the century,' the 1975 story says. 'If the climatic change is as profound as some of the pessimists fear, the resulting famines could be catastrophic.'
The Newsweek article hardly made a splash (it appeared on page 64), however, and while a few other mainstream publications also ran global-cooling articles, the subject never became a major topic in the popular media. Nor did it ever achieve the kind of scientific consensus that now surrounds global warming, as noted in the IPCC report.
Connolley and Schneider say that if the public had looked directly at the peer-reviewed scientific papers, and not at the popular media coverage, they would not have found any basis for a global-cooling scare.
Even Richard Lindzen, professor of meteorology at the Massachusetts Institute of Technology and a prominent global-warming skeptic, wrote in a paper published by the conservative Cato Institute that 'the scientific community never took the issue [of global cooling] to heart, governments ignored it, and with rising global temperatures in the late 1970s the issue more or less died.'
By contrast, an abundance of scientific articles today point to evidence of human-induced global warming. Unlike the 1970s, Schneider says, a true scientific consensus now exists on global warming. 'Global warming was a good theory [even in the 1970s], and now it's good fact backed by empirical evidence,' he concludes.