I'm pretty sure we were taught exactly that in elementary school back in the late-60's, while studying the Vikings. Because I've grown up always believing (knowing) that Greenland was once green.
I haven't read the collected works of Al Gore or seen his fictomentaries, has he been asserting that Greenland was always and forever covered with ice?
Seems like the kind of statement that even a 6th grader might find odd. "Then why is it called Greenland, Mr. Gore?"