Why was the concern of global warming replaced with the concern of global cooling?

The idea of global cooling gained popularity about during the 1970s, “There are ominous signs that the earth’s weather patterns have begun to change dramatically,” Newsweek reported in 1975. At the time the highly influential source convinced “drastic decline in food production.”, at that time climate scientists were convinced that a ice age was coming. Global temperatures falling between 1940 to 1975 drove the concern of global cooling, little did they know it was only a temporary fall of temperature. 
That's as much as I know, hope it helped! :)

H=   2(area/a+b)h= 2(144/a+b)h= 2(144/18+18)h= 2(144/36)h= 2(4)h=8

Answer (d) the greenhouse effect is primarily caused by car and trucks;