One of the hallmarks of a past generation’s nature documentaries was the animal-in-peril scene: the cub hunted by the jungle cat, the fledgling teetering at the edge of its nest.

It was like the terror of a thrill-park ride, one that usually came with the implicit knowledge of safeguards and constraints. In the end, the adorable creature would survive. This was the compact. The animal that you liked would be O.K. After all, this was TV.

There is one of those scenes in the second episode of “Our Planet,” the remarkable docu-series on Netflix. But now the compact is gone. A teeming colony of walruses is crammed at the edge of eighty-meter cliffs along the coast of Russia, where climate change has melted away the sea ice. Not evolved to navigating the precarious surfaces, one walrus falls, and another, and another, their massive bodies slamming onto the rocky beach.

They do not, most of them, get up and shake it off. Their broken bodies litter the shore. This is the resounding message of “Our Planet”: It will not, necessarily, be O.K. And humans — the unpictured but omnipresent part of “our” in “Our Planet” — are the reason.