On a stormy night in 1987, an American herpetologist named Marty Crump was getting ready for bed when she heard a tapping at her door. This was in the mountains of northwest Costa Rica, where evening callers were rare. The visitor had braved the downpour to give Crump what counted, in field-biology circles, as a hot tip: the golden toads had emerged.

Golden toads had been formally described only two decades earlier, by another American herpetologist, named Jay Savage. In the paper Savage had written assigning the species its Latin name—Bufo periglenes—he noted that the toads exhibited “the most startling coloration.”

“I must confess that my initial response when I saw them was one of disbelief,” he wrote in an otherwise staid scientific tract. He wondered briefly whether someone had tricked him by dipping “the examples in enamel paint.”

Golden toads had been seen only in rugged terrain, near the crest of a mountain range known as the Cordillera de Tilarán, which forms part of the Continental Divide. They seemed to live mostly underground, surfacing only long enough to reproduce, an M.O. that made them difficult to study. The morning after the knock on her door, Crump trekked up the cordillera, through a soup of fog, mud, and drizzle. When she finally spotted the golden toads, she was so astonished that she forgot how miserable she felt. The toads, she later wrote, were “dazzling,” like jewels scattered on the forest floor.

That spring, Crump watched golden toads mate, a process that sometimes took as long as twenty-five hours. Males outnumbered females by as much as ten to one, and when a guy managed to find a single lady he would tackle her from behind. Carrying him piggyback, she would hop to the nearest puddle, while he fended off competitors. Sometimes so many males were trying to crawl on top of the same female that they formed an orange ball, studded with writhing orange limbs.

Crump returned to Costa Rica the following May to continue her research on golden-toad reproduction. By the end of July, she had spotted just one toad at the site where, the previous year, she’d seen dozens.

In 1989, Crump arrived in Costa Rica in early April. She hiked up the mountain: no toads. She made the trip again—same result. After a month, a family emergency compelled her to return home to Florida, and one of her graduate students took over. He eventually found a lone toad, a male. Crump spent 1990 on sabbatical in Argentina. A colleague monitored her research site and was to alert her if any toads appeared. None did.

By 1990, it was no secret that many populations of wild animals were in trouble. Still, Crump’s experience represented something new under the cloud cover. A biologist could now choose a species to study and watch it disappear, all within the course of a few field seasons.

Crump chronicled the loss of the golden toad in a book titled, for complicated reasons, “In Search of the Golden Frog.” (The golden frog, which is native to Panama, is only very distantly related to the golden toad. Neon yellow in color, it, too, has vanished from the rain forest.) She followed this with a second book, “Extinction in Our Times,” co-written with a colleague. Meanwhile, naturalists with similar experiences were weighing in with similarly mournful titles: “Requiem for Nature,” “Silence of the Songbirds,” “The Last Rhinos,” “Planet Without Apes.” In 2006, Samuel Turvey, a researcher with the Zoological Society of London, participated in a survey aimed at locating the last remaining Yangtze River dolphins, or baiji. Six weeks of intensive monitoring failed to turn up a single baiji. When the survey results were made public, in the journal Biology Letters, Turvey was deluged with interview requests. In one twenty-four-hour period, he spoke to more than three dozen news outlets around the globe.

“It turned out it was possible to galvanize the world’s media on behalf of the baiji,” he observes in his book “Witness to Extinction.” But only after the dolphin was gone for good: “That’s what would sell. That’s what constituted a story.”

The losses on our human-dominated planet keep coming, and so, too, do the stories. These days, it’s not just species that are vanishing. Entire features of the earth are disappearing—thus, the latest batch of “witness-to” books, written by geologists.

Peter Wadhams, the author of “A Farewell to Ice: A Report from the Arctic” (Oxford), is the head of the Polar Ocean Physics Group, at the University of Cambridge. He first visited the polar north in 1970, when, as an undergraduate, he got a job on a Canadian research vessel, the Hudson, which was attempting to circumnavigate the Americas. Although the Hudson was built for travel through sea ice, on the last leg of the journey it got stuck in the Northwest Passage and had to be rescued by an icebreaker. Evidently, Wadhams enjoyed the experience—in the stiff-upper-lip tradition of British adventurers, he’s largely mum on the topic of emotion—because he returned to northern Canada a few years later to work on his Ph.D. This involved flying over the ice cap in a sort of aeronautical jalopy—a Second World War-era DC-4 with the cockpit bubble of a Sabre fighter jet welded to the fuselage. The flights left from Gander, and Wadhams recalls a bar in town, called the Flyers’ Club, where a band played topless.

At the time, Wadhams imagined himself part of a glaciological tradition stretching back to the Napoleonic Wars. The idea was to map the extent of the Arctic sea ice and then, basically, forget about it. (Many died trying.) The ice cap’s size varied, expanding in winter, when the polar darkness descended, and then contracting in summer. But this cycle, like the seasons themselves, was supposed to be unchanging. The assumption, Wadhams writes, was that “everything in the ocean is constant.”

In the nineteen-eighties, satellites replaced scientists eyeballing the Arctic from DC-4s. The satellite data revealed that the ice was shrinking. By this point, the earliest climate models had been assembled, using I.B.M. punch cards, and they predicted that global warming would be felt first and foremost at the poles. In 1990, Wadhams compared surveys of the sea ice north of Greenland that had been conducted from British submarines, using upward-looking sonar. The comparison showed that the ice cap, in addition to contracting, was thinning; during the previous decade, its thickness had declined by fifteen per cent.

By the end of the summer of 2007, the ice cap was about half the size it had been at the start of the satellite era, and the Arctic sea ice had entered what an American scientist, Mark Serreze, has dubbed its “death spiral.” Today, a decade deeper into the spiral, older Arctic sea ice has mostly melted away. What’s left, in large part, is first-year ice, which forms over the winter and, since it’s thinner, is that much more prone to melt the following spring. The most recent climate models predict that within a few decades the Arctic Ocean will be entirely ice-free in summer. Based on his own observations, Wadhams believes that the time frame is more like the next few years. “It is clear that the summer Arctic sea ice does not have long to live,” he writes.