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.