He’s 93 so probably no longer compos mentis, but as it says here:

He melodramatically proclaims…that “what we do in the next few years will determine the next few thousand years.” If we don’t take action, he declares, “the collapse of our civilizations and the extinction of much of the natural world is on the horizon.”

The Walter Cronkite of climate change. Sounds plausible, inevitably wrong when it matters. And to round this out, let me add this: