We've known for quite some time
On a random page from the obscure website Science Fiction by various authors appears this prophetic beginning of a long-forgotten story:
Margaret St. Clair
Quis Custodiet . . . ?
Copyright © 1948 by Standard Magazines, Inc.
“There were thousands of human generations before the bombs, and none of them understood it the way we do. Long before the bombs our people chopped down the forests and left burned-over stumps where the trees used to stand. They plowed up the grasslands and made deserts out of them. They tore the heart out of the continents and sent it floating down in the muddy water of the rivers to lie at the bottom of the sea. The bombs only finished something that had been long ago begun.
“Earth’s done for. We destroyed it.”
1948...that's 63 years ago. So some of us at least have known for quite some time where we're headed.