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.
Read: It’s a mistake to focus just on animal extinctions.
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.