So why did David Rose put a forgery of a Time Magazine cover in the Mail on Sunday? Well, the simple answer is that there weren't any real Time covers which supported his point, otherwise I'm sure he would have used one of them. His point was, to quote Michael Crichton, "in the 1970′s (sic) all the climate scientists believed an ice age was coming.”
The subtext being that climate scientists are slightly hysterical doom-mongers who were wrong then and so can be wrong now. I'm sure you can guess who really has the monopoly on wrongness in this debate.