Eric Post has observed seasons at the same location on the West Greenland tundra for 26 years. Over that time, he’s seen profound changes. When he first started working there, hundreds of caribou covered the hills. Now, he says, the herd is down to around 90.

“You find yourself thinking they’ll be back next spring; numbers will go up again,” Post says, “but year after year goes by and the big groups just aren’t there the way they used to be.”

As Earth trudges steadily toward a dangerously warm future, a new report on the outlook for the polar regions says the Arctic is already there—with consequences on the horizon for everyone.

“There is a real possibility that we will be entering a