I have always believed that the hysteria over global warming has been caused by academics who get research grants to study alleged phenomena like this.
In the 1980's and into the early 1990's, these guys were telling us about the coming ice age which was being caused by man-made pollution.
All this cooling/warming stuff is just to bilk more tax dollars out of us to support their jobs. Volocano activity probably plays more of a role than man made pollution is my hubby's theory.