the Washington Post reported on July 9, 1971, quoting Dr. S. I. Rasool of NASA and Columbia University.
According to Rasool, fine dust from fossil fuel use would block out so much sunlight that the Earth’s “average temperature could drop by six degrees.” Rasool added that “such a temperature increase could be sufficient to trigger an ice age!”
Basically, pollutants from burning coal and other fuels tend to reflect solar energy back into space. Scientists were worried that such man-made aerosols would block out so much sunlight that global temperatures would drop — just like how volcanoes can cause some atmospheric cooling.