PBzeer-
"Global cooling in general can refer to a cooling of the Earth. More specifically, it refers to a
conjecture during the 1970s of imminent cooling of the Earth's surface and atmosphere along with a posited commencement of glaciation. This hypothesis
never had significant scientific support, but gained temporary popular attention due to press reports following a better understanding of ice age cycles and a slight downward trend of temperatures from the 1940s to the early 1970s."
See more:
http://en.wikipedia.org/wiki/Global_cooling
There have been numerous studies looking at non man made contributions to global warming and their significance which are easily accesible if you are interested.