Still, wherever Lopez goes, he is never far from a disquisition on humanity’s merciless ways. Rising from his bed one night in the tropical heat of Isla Santa Cruz, in the Galápagos, he walks alone (a frequent habit that makes for some of the book’s best bits) to the beach and watches a group of brown pelicans asleep on the bay. The birds’ vulnerability — “oblivious just now to all that is hidden and potentially threatening in the lightless world we share” — leads his train of thought to Spanish conquistadores releasing vicious dogs on Indians, and from there to the European bankers who underwrote the slave trade in West Africa, and on to the present horrors of Boko Haram. It’s all, ultimately, in the service of pondering the roots of barbarism, and how we ignore the barbarism unfolding in our own society at our peril.

Image Clearcutting near Highway 30 in Oregon. Credit... Leah Nash for The New York Times

[ Read our round-up of recent books about climate change. ]

Strangely, though, these relentless reminders of egregious acts don’t diminish the appeal of seeing the world through Lopez’s eyes. His reverence for exploring every corner of the world, even the sites of its most shameful histories, is infectious. Rarely does Lopez decline an offer of adventure, no matter how potentially grueling the trip might be. Traveling, he writes, “turns the mind toward a consideration of context and releases it from the dictatorship of absolute truths about humanity. It helps one understand that all people do not want to be on the same road.”

Lopez’s journeys often start in ways that make you shake your head. (More than a few trips begin with a banal sentence like: “In the austral fall of 1987 I was traveling through Namibia with a few people.” You know, as one does.) One night he reads a paper in the scientific journal Nature about the discovery of some 4.27-billion-year-old zircon crystals in remote Western Australia. He immediately emails the researchers about visiting the field site — because he just happens to be headed to Perth soon, “en route from Zimbabwe to the Northern Territory.”

The scientists initially ignore his request. But he persists, and several years later he’s finally on his way to the Jack Hills. He flies from the United States to Sydney, and then goes by train to Perth, persuading the engineers to let him ride in the locomotive. One day, crossing the vast Nullarbor Plain, “the train suddenly ran into a wall of water,” a drenching rainstorm. When the weather clears, a double rainbow appears. And then a mob of kangaroos arrives, over a hundred of them, leaping across the plain. “The sight of it was so exhilarating the three of us in the cab nodded an affirmation to one another. Whatever was wild and lyrical in the timeless world, we were in the middle of it now.”

Lopez proceeds in a rented four-wheel drive to a sheep-ranching outpost where a geologist has arranged lodging, 120 miles from the nearest town “on an unsigned dirt track.” When he arrives, the rancher and his daughter have “a meat pie in the oven, and he wanted to know whether I took milk with my tea.” One day, as Lopez is heading out to the geology site, the rancher offers him a rifle and asks if he’d mind shooting any wild goats he encounters. Lopez declines. But through evening chats on the veranda, the two men form a bond; the rancher ultimately visits Lopez at home in Oregon. This knack for making friends in the most unlikely places resonates long after you turn the last page. “Are we not bound,” he asks, “to learn how to speak with each other?”

Had we mastered that skill 30-odd years ago, would we be where we find ourselves today, grappling with violent xenophobia while forests incinerate, oceans rise and acidify, magnificent organisms everywhere fade away? Where will we be three decades on, if we don’t take heed? There is still time, though not as much as there once was, to shape what’s coming.