There’s a feeling you get in Grizzly country when you’re passing too close to what looks like a perfect location for a bear’s day bed. Maybe a thicket of huckleberries, maybe an island grove of cottonwood with plenty of downed limbs and new undergrowth. But whatever it is, you stop in your tracks. Silent alarms are triggered, your hackles rise to attention, you forget to breathe.

That’s how it feels to come to the end of Doug Peacock’s latest book, In the Shadow of the Sabertooth: A Renegade Naturalist Considers Global Warming, the First Americans and the Terrible Beasts of the Pleistocene. The challenge he presents, vividly and unapologetically, of just how to respond to the effects of our long and brutal war against our own climate commands our focus and demands a decision.

Peacock’s writings, in one way or another, always elicit such a response. The difference is, in his earlier books, Grizzly Years and Walking It Off, the alarm is vicarious. One reacts to his harrowing experiences in Vietnam and close-calls with charging bears, or to his memories of walking the fine line between life and death in a southwestern desert or Himalayan snowfield. In this new book, the danger is not in his past, rather it’s in our collective future. And it’s a future so looming and imminent, that if we are to survive at all, we had better accept the idea that it is our present.

In the Shadow of the Sabertooth lays out the story of the great adventure of the first Americans in a visceral way that only a true American adventurer could. But more than that, it gives us the profound and desperately needed hope that we, today, can learn from our ancestors. That we can choose to preserve the one thing that can possibly sustain us through this current upheaval: wilderness, that primordial memory of our evolutionary success that Thoreau rightly addressed when he wrote, “In wildness is the preservation of the world.” And finally, that we can heed the threat of the sabertooth lurking in the shadows, and once again rise to the challenge.