Since Monday, news networks and social media have been abuzz with the claim that, as The Guardian among others tweeted, “humanity has wiped out 60 percent of animals since 1970”—a stark and staggering figure based on the latest iteration of the WWF’s Living Planet report.
But that isn’t really what the report showed.
The team behind the Living Planet Index relied on previous studies in which researchers estimated the size of different animal populations, whether through direct counts, camera traps, satellites, or proxies like the presence of nests or tracks. The team collated such estimates for 16,700 populations of mammals, birds, reptiles, amphibians, and fish, across 4,000 species. (Populations here refers to pockets of individuals from a given species that live in distinct geographical areas.)
That covers just 6.4 percent of the 63,000 or so species of vertebrates—that is, back-boned animals—that are thought to exist. To work out how the entire group has fared, the team adjusted its figures to account for any biases in its data. For example, vertebrates in Europe have been more heavily studied than those in South America, and prominently endangered creatures like elephants have been more closely studied (and have been easier to count) than very common ones like pigeons.
Ultimately, they found that from 1970 to 2014, the size of vertebrate populations has declined by 60 percent on average. That is absolutely not the same as saying that humans have culled 60 percent of animals—a distinction that the report’s technical supplement explicitly states. “It is not a census of all wildlife but reports how wildlife populations have changed in size,” the authors write.
To understand the distinction, imagine you have three populations: 5,000 lions, 500 tigers, and 50 bears. Four decades later, you have just 4,500 lions, 100 tigers, and five bears (oh my). Those three populations have declined by 10 percent, 80 percent, and 90 percent, respectively—which means an average decline of 60 percent. But the total number of actual animals has gone down from 5,550 to 4,605, which is a decline of just 17 percent.
For similar reasons, it’s also not right that we have “killed more than half the world’s wildlife populations” or that we can be blamed for “wiping out 60 percent of animal species” or that “global wildlife population shrank by 60 percent between 1970 and 2014.” All of these things might well be true, but they’re all making claims about metrics that were not assessed in the Living Planet Index.
The uncertainties mount when you consider that the 63,000 species of vertebrates are vastly outnumbered by the untold millions of species of invertebrates—spineless creatures like insects, worms, jellyfish, and sponges, which make up the majority of animal life. Their fates are murkier because scientists have collectively spent less time monitoring them. They are harder to study, and draw less attention, than the allegedly more charismatic vertebrates—although plans are afoot to give them their due.
The average 60 percent decline across populations also obscures the fates of individual species. In the hypothetical scenario above, lions are still mostly fine, the tigers are in trouble, and the bears are on the brink of extinction. And of the species covered in the actual Living Planet Index, half are increasing in number, while only half are decreasing. This means that for those that are actually in decline, the outlook is even worse than it first appears.
None of this is to let humanity off the hook. Since prehistory, humans have killed off so many species of mammals that it would take 3 million to 7 million years of evolution for them to evolve an equivalent amount of diversity. At least a third of amphibians face extinction, thanks to climate change, habitat loss, and an apocalyptic killer fungus. Even invertebrates aren’t off the hook. There might be fewer data for them, but the data that exist paint an alarming picture of rapidly disappearing insects, even in supposedly pristine forests. Meanwhile, in the oceans, coral reefs are bleaching too quickly to recover: Half of the corals in the Great Barrier Reef have died since 2016. All this evidence points to a period of “biological annihilation” that some have likened to the five great mass extinctions of the past. When the reality is this sensational, there’s not much need to sensationalize it even further.
Bottom line: Things are bad. One could argue, then, that it is unnecessarily pedantic to correct the 60 percent figure. Why nitpick in the face of catastrophe? Surely what matters is waking people up, and if an inexactly communicated statistic can do that, isn’t that okay?
I don’t think it is. Especially now, in an era when conspiracy theories run rampant and lies flow readily from the highest seats of government, it’s more important than ever for those issuing warnings about the planet’s fate to be precise about what they mean. Characterizing the problem, and its scope, correctly matters. If accuracy can be ignored for the sake of a gut punch, we might as well pull random numbers out of the ether. And notably, several news organizations, such as Vox and NBC, managed to convey the alarming nature of the Living Planet Index while accurately stating its findings. The dichotomy between precision and impact is a false one.
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