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Editor's note: Climate change will wreak havoc on the world's most famous garden of biodiversity. Three writers travelled to the Galapagos Islands to show us just what we stand to lose. Read Terry Tempest Williams' take here. Read Rick Bass' take here.

We cross the equator by boat on March 14, 2014, off the northwest tip of Isabela Island in the Ecuadorian Galápagos—the first time for me. A couple of bottlenose dolphins race the bow of the ship, and the ocean below shimmers with perceptible energy as if a leviathan hovers just below the surface.

Boobies, pelicans, and hundreds of other seabirds dive-bomb the anchovies leaping free of the sea, driven from below by bonito and albacore tuna. Phalaropes float on mats of insects. Noddies follow the , and soar above, swooping down to steal scraps of baitfish from the diving birds. A surge of gulls and storm-petrels breaks in front of the boat, following the anchovies, rolling from one patch of frothing ocean to another upwelling, where bloody chunks of bait litter the surface. Far ahead I can see giant fins cutting the waves. A number of my boat mates jump off to swim across the invisible equatorial line. They say the water is freezing.

I am riding on a 78-foot-long, steel-hulled, refitted fishing boat named the Samba. This ship is plush, with hot water and air-conditioning. Onboard are a crew of six, a naturalist, and 13 fellow travelers, half of whom I have never met before. When we go ashore to visit the wildlife, we're not supposed to touch anything. It is exactly the kind of cruise I have carefully avoided for the past three decades.

Nonetheless, as an old soldier with a foot in the grave, I'm working on my bucket list, and this cushy, indulgent-seeming journey to these well-tended islands—planned with close friends and family—is number one. This isn't exactly a vacation, though. For more than four decades I have done my best to protect wild places, grizzly bears, and other top predators. After this trip, I will head to the North Slope of the Yukon, where polar bears are interbreeding with grizzlies. The summer sea ice in the Arctic's Beaufort Sea will be gone in a couple of years, and the permafrost is already heaving, releasing heavy gasps of methane into the atmosphere. It's possible a worldwide warming of 8 to 11 degrees Fahrenheit and six feet of sea-level rise could arrive by the end of a century, estimates I personally believe are too conservative. The rate of change is mind-boggling. I am seeking clarity from this madness. The isolated Galápagos, as yet largely untouched by climatic changes, seems something sane I can wrap my mind around.

After a sleepless night on pitching seas, we aim for Darwin Bay, a volcanic caldera cookie-cut into the edge of Genovesa Island, where Charles Darwin never ventured. The best thing about the northern and western Galápagos is that the smaller islands, including this one, are uninhabited by humans. The Samba's Zodiacs unload us on a flat beach swarming with Red-footed Boobies. Male frigatebirds puff out their red throats, trying to attract females, Swallow-tailed Gulls regurgitate mushed-up squid for their chicks, and mated boobies preen each other. A sea lion pup plays in a tide pool. Everywhere float the smells and sounds of reproduction, the cries and squawks of birds mingling in raucous chorus.

We strap on snorkels and dive into Darwin Bay. Sea lions loop around us. There are balls of wrasses, schools of angelfish, snappers, parrotfish, and grunts—a hundred times more species than I could name and more fish than anyone could ever count. My daughter, Laurel, grabs me and points to a sizeable fleeing hammerhead shark. Winging their way over the ocean bottom are dozens of golden cownose rays. These schools, flocks, swarms of life—fish, birds, mammals, or insects; it doesn't seem to matter what the species or size is—constitute the tip of an ancient iceberg of animal craving for me, like watching a herd of 10 million bison cross the Iowa River or a mass of Passenger Pigeons that black out the sun for three days while it passes. I wouldn't care to live in a world without such possibility.

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Back on Genovesa, we climb up steps carved out of the basalt to an arid, mesa-like plateau ruled by Nazca Boobies. Frigatebirds roost in the deciduous low trees. Short-eared Owls squat in shallow lava tubes. Down on the shoreline, we see turnstones rolling big pumice rocks and Whimbrels, amid a shifting tide of plovers, dodging the breaking surf. Flocks of Red-billed Tropicbirds squawk but soar gracefully above. These tern-like flyers nest in the cliffs and make clumsy landings, thanks to graceful tails that can grow twice as long as their bodies. A testosterone-aggressive Nazca Booby blocks the return trail and snaps at each of us as we pass.

Our boat guide, Juan Salcedo, discourses at length on bird mating patterns, testosterone levels in Nazca Boobies, and the reproductive advantages of aggression and social monogamy. My wife, Andrea, whispers, "Maybe it's been a long time since he had a girlfriend." Our two local guides are well read, biologically literate, and, best of all, versed in solid evolutionary theory (recently Galápagos fundamentalist churches have produced a plague of creationist guides). But even the best of guides is reluctant to go too far, to paint a less than rosy picture of a human history where land tortoises have been slaughtered into extinction and the Galápagos Hawk, historically the islands' top predator, pushed to dangerously low numbers. Juan tells me there are no Galápagos Hawks on Genovesa because the island is too young to produce land reptiles, the lizards the hawk likes to feed on.

The next day, I see a Galápagos Hawk off Marchena Island. We are watching a lava lizard, as black and crenulated as the basalt it lies upon; it turns to look up at us. As if on cue, a brown raptor curls overhead. Like the Harris's Hawks of my own low desert country, these social birds hunt in groups of two or three and feed together in larger numbers. They sometimes roost on the ground, though the ones we saw were on high tree branches. With human tolerance, the hawk could probably live in nearly any Galápagos habitat, feeding on insects, lizards, smaller iguanas, rats, carrion, and even birds. It has no fear of people: Charles Darwin once ". . . pushed off a branch, with the end of [his] gun, a large hawk."

Buteo galapagoensis was once common on most of the main islands of the Galápagos but suffered a serious population decline with the influx of immigrants from the mainland. It is now extinct on five islands, and the adult population is about 300 birds. Chicken-ranching immigrants perceived the Galápagos Hawk as a threat to their chicks and, by some accounts, solved the problem by eliminating the "tame" bird. More recently, the raptors have been forced to compete for food with introduced feral cats.

The guides use the phrase "ecological naïveté" to explain the apparent tameness of hawks, tortoises, and other Galápagos creatures that evolved in habitats without predators or other threats. David Quammen coined that particular expression in Song of the Dodo, his classic 1996 book on island biogeography. The corollary of that naïveté in these animals, however, is that the evolutionary loss of defensive behaviors, or the failure to acquire new ones, may render them vulnerable to new or introduced predators like mongooses, tree snakes, or feral cats. Evolution prepared the islands' creatures for a simpler, more innocent world.

We, meanwhile, evolved to deal with saber-toothed cats in the bush, bears in the night, or, especially, other humans. But a new danger has arrived, a relatively fresh enemy, the beast of our time: . How do we respond to a dimly perceived, deadly worldwide threat, one that will require a collective human resolve? Did evolution not provide us with the wit to face the rising oceans, the melting ice, and the warming earth that will greatly shrink the habitats 7 billion people depend on? Ecological naïveté will not serve us well either.

These troubling thoughts ebb as we take a swim in a warm lagoon filled with life. Andrea briskly paddles over to Laurel and me and pushes up her mask. She has found a colorful castle of coral, spirals surrounded by blue-phased sergeant majors busy snacking off the green algae growing like lawn around it. My bucket list again: For the past three years we have unsuccessfully searched for unbleached coral off Costa Rica and the Florida Keys. The castle is her gift to me.

The Galápagos were discovered by accident in 1535 by a Spanish cleric from Panama who found himself becalmed in the doldrums north of these equatorial waters and then drifted southward into the islands. My visit to the Galápagos constitutes, in part, an attempt to escape my own doldrums: I touch the collar of my shirt and feel the top of a long vertical scar covering my steel-wired sternum.

The Samba swings around the western nose of seahorse-shaped Isabela Island and into a broad cove east of Punta Vicente Roca. We pull on wetsuits and slip into the water. Juan says, "Find your own turtle." The waves rock us back and forth against a sheer cliff where a penguin perches. Green sea turtles seem to be everywhere—big ones, little ones. Something leans against my flipper, and I lurch sideways to let a 300-pound turtle pass. Suddenly I find myself within a squadron of swimming turtles. I spot my daughter, noticeable with only one flipper due to an injured knee. Next to her swims my best friend, , conspicuous in her rainbow wetsuit. They grab my hands, and we join the broad flotilla.

Riding back in the Zodiac, two of the people I most respect in the world are privately weeping. I feel a knot loosen in my chest, a shared magic with the women who make my life.

Read Terry Tempest Williams' take here. Read Rick Bass' take here.