Scientists have been aware of global warming for decades, it turns out (via Matt Stoller):
It is a bit eerie to see that the problem was known about so clearly way back then. It's also a reminder of the production values of educational movies in the 1950s, which really was the golden age of the genre. St. John's alumni reading this, for example, will recall the infamous frog video set to Stravinsky's "Rite of Spring." Sadly, I can't find it on YouTube.