The reasons to disbelieve that humans are causing global warming are many and varied, skeptics say. For example: Natural factors such as long-term variations in solar radiation are causing the rise in worldwide average temperature. The urban heat island effect is skewing modern weather data, so the warming observed in recent decades isn’t real. And besides, not long ago experts all believed the Earth was cooling, not warming.
Actually, research has shown that many such ideas are bogus. While changes in solar output have slightly increased global average temperature since the beginning of the Industrial Revolution, the planet-warming effect of man-made greenhouse gases is about 20 times larger (“Heated dispute” letter, SN: 10/27/07, p. 271). And although cities are warmer than neighboring rural areas, that phenomenon doesn’t mask recent warming trends in long-established cities (“Don’t blame the cities,” SN Online: 9/5/08).
Now, new research also skewers the global warming skeptics’ claim that, in the 1970s, scientists believed that an ice age was imminent. Researchers of the day had discovered that Earth had been cooling since the 1940s. Some believed that continued increases in the amount of planet-cooling aerosols kicked up or emitted by human activity — dust and smog, for example —could easily tip the planet into an ever-deepening cycle of cooling, skeptics have repeatedly pointed out. That wave of concern was obviously a false alarm, the skeptics note, so maybe today’s scientists are equally mistaken about global warming.
Not true, climatologist Thomas C. Peterson of the National Climatic Data Center in Asheville, N.C., and his colleagues report in the September Bulletin of the American Meteorological Society. The team’s survey of major journal papers published between 1965 and 1979 found that only seven articles predicted that global average temperature would continue to cool. During the same period, 44 journal papers indicated that the average temperature would rise and 20 were neutral or made no climate predictions.
The findings were “a surprise to us,” Peterson says. For decades the “skeptics had repeated their argument so often and so strongly that we misremembered the tenor of the times.”
When these skeptics mention previous concerns about global cooling, they typically cite media reports from the 1970s rather than journal papers —“a part of their tremendous smoke screen on this issue,” says Peterson. Among major magazines, Time and Newsweek ran articles expressing concern about the previous decades’ cooling trend, juxtaposing the specter of decreased food production with rising global population.
But even a cursory review of 1970s media accounts shows that there was no consensus about global cooling among journalists, either, Peterson says. In May 1975, the headline of a New York Times article warned that “major cooling may be ahead.” Three months later, another headline in the same paper—atop a feature written by the same reporter—stated that two recent journal articles “counter [the] view that [a] cold period is due.”
