(CBS) -- A huge iceberg -- said to be the size of Delaware -- broke off from the Antarctic Peninsula. It's one of the largest ever recorded. But scientists differ on whether it can be blamed directly on climate change. Still, former Vice-President Al Gore called the floating giant "a jarring reminder of why we must solve the climate crisis." Gore has been a crusader on that issue for years now, and took Lee Cowan back to Tennessee to take stock of the battle in our "Sunday Morning" Cover Story:

Meandering through the rolling green hills of Carthage, Tennessee, is the Caney Fork River -- a place where Al Gore seems right at home.

"This place down here is where, when I was a boy, my family used to come down here and go swimming," he showed Cowan.

Yes, he's the man who was almost President, and yes, that is a pretty tough act to follow.

And yet, Al Gore has still made his voice heard -- and not just echoing off those limestone cliffs on the Gore family farm.

"One time when Winston Churchill lost an election as a young man, one of his friends said, 'Winston, this is a blessing in disguise.' And he said, 'Damn good disguise!' So that's sort of the way I feel about it.

"When I went through that experience in the election of 2000 and the Supreme Court decision, I knew I was going to be fine. And I hated the result, obviously, but I just started looking for other ways I could be of service."

So he dusted off an old slideshow that he had once used to convince his colleagues in the House and the Senate that global warming was a provable environmental threat. And in 2006, that wonky slideshow became an Oscar-winning documentary.

"An Inconvenient Truth" made him the face of the climate debate. It helped him win a Nobel Peace Prize -- and it put him right back in the political crosshairs.

Cowan said, "You faced some pretty stiff criticism from people that called you everything from a fanatic to a fraud."

"Yeah. When I spoke at my father's funeral, I quoted a passage from scripture, 'Woe unto him about whom all men say good things,'" Gore laughed. "If everybody's just completely happy with what you're doing, you may not be working hard enough to bring about the kind of change that we need!"

He's still fighting for change, and he's still giving that slideshow … over 100 times a year, if you can believe that.

"16 of the 17 hottest years ever measured with instruments have been since the year 2001."

It's enough to discourage anyone living anywhere on the planet. But Gore also sounds a hopeful note -- he's even humorous at times.

MORE: Read/watch the full interview at CBSNEWS.com