It is hard to pinpoint exactly when we all started hearing about the polar bears. There is an important moment in “An Inconvenient Truth,” from 2006, when Al Gore recounts a trip he took to the North Pole with scientists measuring sea ice. “It has diminished by forty per cent in forty years,” he explains. “And there are now two major studies showing that, within the next fifty to seventy years, in summertime it will be completely gone.” A C.G.I.-animated bear appears onscreen, panting and wading through water before reaching a piece of ice that breaks under its paws. “A new scientific study shows that, for the first time, they’re finding polar bears that have actually drowned swimming long distances,” Gore says. “Up to sixty miles to find the ice.”

Imagery of death and extinction has done much to emotionally invest people in the climate problem and in environmentalism broadly speaking. Charts and numbers lack the immediacy of an image of a big-game hunter grinning in front of a poached kill, or bleached coral marking another dead zone in the ocean. But the unarrested progress of climate change and environmental degradation are forcing us to stretch our imaginations beyond specific narratives of loss. We face not just the collapse of particular habitats or particular ecosystems but, as Elizabeth Kolbert documented five years ago, in “The Sixth Extinction,” a vast, general collapse. Last week, the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (I.P.B.E.S.), a research arm of the United Nations, told the world that we may be on our way to losing as many as a million plant and animal species. It is thought that scientists have catalogued only about 1.8 million of the eight million species extant on earth—a mass extinction means that many of them may now never be known to us.

The report is the latest in a wave of efforts, by scientists, officials, journalists, and activists, to speak more frankly than ever before about what we have done and are doing to our planet, including the Intergovernmental Panel on Climate Change’s report last year, which highlighted the risk of dire effects of climate change emerging as soon as 2040. David Wallace-Wells, the author of the recent best-seller “The Uninhabitable Earth,” said that the I.P.B.E.S. and I.P.C.C. reports are “built on science that people who had been following the story would know but seemed to be organized in a much more systematic, big picture kind of a way.” He noted that last week’s report was “really strategically organized in order to deliver a particular narrative impact. In both cases, the authors of the reports seemed very conscious about moving away from any particular data point and wanting to impress upon the public a broader-canvas story.”

The authors of the I.P.B.E.S. report also want to impress upon us that a mass extinction will profoundly affect the living things likely to survive it, including us. Grasping the way some of climate change’s more dramatic assumed impacts—rising seas, oppressive heat waves, extreme-weather events—might hurt human beings is easy. The consequences of losing obscure insects and plant life—uncharismatic microflora and fauna, not polar bear or Bengal tigers—are harder to conceptualize. The report’s authors have taken pains to insure we try anyway. “Nature, through its ecological and evolutionary processes, sustains the quality of the air, fresh water and soils on which humanity depends, distributes fresh water, regulates the climate, provides pollination and pest control and reduces the impact of natural hazards,” they write, in their summary for policymakers. The group has previously estimated that, in the Americas, nature itself—animals, plants, soil, water, all of it—is worth about twenty-four trillion dollars to us, an implausibly specific figure that makes the costs of degradation both more and less concrete. As a price tag on the inherently invaluable, it’s a number at once too large to grasp and ultimately too small, but one can’t exactly blame them for writing one up.

“I think a lot of people are like, ‘Oh, you know, a million species, what does that really mean?’ ” Varshini Prakash, a co-founder of the Sunrise Movement, which has been advocating for the Green New Deal, told me. “I think fundamentally we’ve got to get the message across that this is a crisis for humanity that could signal the end of human civilization as we know it. It’s not about animals somewhere off in the Arctic. It’s about the life that we lead, and whether we can keep leading it, and the chaos and violence that could ensue if we don’t do something immediately.”

A group calling itself Extinction Rebellion has been making that case in the U.K. Last month, they took to the streets of London by the hundreds, stopping traffic in multiple locations in an effort to get Parliament to declare a climate emergency. Parliament did so earlier this month, approving a nonbinding motion that urges Britain to zero out carbon emissions by 2050. “Even as someone who is basically an alarmist, it seemed really up in your face,” Wallace-Wells said of the group’s name and messaging. “But I also think, like, you kind of can’t argue with the results.”

Extinction Rebellion considers climate change and looming mass extinctions as intersecting but separate and potentially competing issues. In a statement last week, in response to the I.P.B.E.S. report, the group said that “too much of the focus has been on greenhouse gases and climate change. We also face an ecological crisis—the sixth mass extinction—which is as dangerous for our planet as climate change.” Jonathan Franzen said much the same, in this magazine, in 2015, describing climate change as a “usefully imponderable” problem compared to the threat of mass extinctions. “To prevent extinctions in the future, it’s not enough to curb our carbon emissions,” he wrote. “We also have to keep a whole lot of wild birds alive right now.”

Franzen was right that addressing extinctions will require much more of us than reducing emissions.“There’s places where you’re losing habitat because temperatures are increasing, climate ranges are shifting north,” Collin O’Mara, the C.E.O. of the National Wildlife Federation, told me. “But a lot of it is because we’re paving hundreds of millions of miles of roads. One third of the planet right now is in production of agriculture, and only about half of that is actually agriculture that has any kind of mind for the wildlife-habitat benefits that could be provided by just doing things slightly differently.”

“We’re trying to convince folks that, like, if we save nature, we save ourselves,” he continued. “If you have healthy habitats, we have healthy wildlife populations with clean water—all of that can help reduce emissions.”

The National Wildlife Federation is among the groups involved in a classic conservation fight, in which big business is pitted against the defenders of the sage grouse, a spiky-looking bird that ranges across the American West and has been on the verge of endangerment for some time. In March, the Trump Administration directed the Bureau of Land Management to ease protections on thirteen thousand square miles of the sage grouse’s habitat, to facilitate oil-and-gas drilling on protected lands. Environmental groups insist that the sage grouse, just one of the countless bird species now thought to be at risk, really matters, and not only because undermining protections for it would be a boon for the fossil-fuel industries.