The 2022 Living Planet Index Is Out. Here’s How to Understand It.

It’s clear that wildlife on our planet is suffering mightily, but scientists don’t know exactly how much. A comprehensive number is extremely difficult to ascertain. Counting wild animals — on land and at sea, from mosquitoes to whales — is no small feat. Most countries lack national monitoring systems.

One of the most ambitious efforts to fill this gap is published every two years. Known as the Living Planet Index, the index is a collaboration between two major conservation organizations, the World Wide Fund for Nature and the Zoological Society of London. However, the report has repeatedly generated inaccurate headlines when journalists have misinterpreted or overstated the findings.

The latest figure from the assessment, released Wednesday by 89 authors from around the world, is the most alarming yet: From 1970 to 2018, monitored vertebrate populations declined by an average of 69 percent. That’s more than two-thirds in just 48 years. It’s a staggering number with dire implications as nations prepare to gather in Montreal this December to agree on a new global plan to protect biodiversity. But does it mean what you think?

What the data means and what doesn’t

Remember that this number is only about vertebrates: mammals, birds, reptiles, amphibians and fish. Creatures without spines are absent, although they make up the vast majority of animal species (scientists have even less data on them).

Have wild vertebrates plummeted 69 percent since 1970?

no

The study tracks select populations of 5,320 species, absorbing all relevant published research and adding more each year as new data allows. It includes, for example, a population of whale sharks in the Gulf of Mexico, counted from small planes flying low over the water, and birds counted by the number of nests on cliffs. Depending on the species, tools like camera traps and evidence like trace feces help scientists estimate the population at a given location.

This year’s update includes nearly 32,000 such populations.

One is tempted to think that an average 69 percent decline in these populations means that this is the proportion of monitored wildlife that has been wiped out. But that’s not true. An addendum to the report provides an example of this.

Imagine, the authors wrote, that we start with three populations: birds, bears, and sharks. Birds go down from 25 to 5, an 80 percent drop. The bears drop to 50 with 45 animals, i.e. 10 percent. And the sharks go down from 20 to 8 or 60 percent.

That works out to an average drop of 50 percent. But the total number of animals fell from 150 to 92, a drop of about 39 percent.

The Index is designed this way because it attempts to understand how populations change over time. It does not measure how many people are present.

“The Living Planet Index is truly a contemporary view of population health that underpins the functioning of nature across the planet,” said Rebecca Shaw, senior scientist at WWF and author of the report.

Another important factor is the way the monitored populations are included in the index. They do not represent a broad, randomized sample. Rather, they reflect the available data. So there’s quite likely a bias where species are tracked.

A controversy has been whether a small number of populations with drastic declines casts doubt on the overall results. Two years ago, a study in Nature found that just 3 percent of the population caused a drastic decline. When these were removed, the global trend switched to an increase.

The paper prompted a flurry of reactions in Nature, as well as additional explanations and stress tests for this year’s update. On the plus side, the authors note that about half of the populations in the Living Planet Index are stable or increasing. However, when they tried to exclude populations with the most drastic changes in both directions, down and up, the mean descent remained steep.

“Even after removing 10 percent of the entire data set, we’re still seeing drops of about 65 percent,” said Robin Freeman, head of indicators and assessments at the Zoological Society of London and author of the report.

Yes. Some scientists believe the report actually underestimates the global biodiversity crisis, in part because the data may underrepresent the devastating decline in amphibians.

And over time, the trend does not reverse.

“Year after year we fail to improve the situation, despite important measures,” said Henrique M. Pereira, professor of conservation biology at the German Center for Integrative Biodiversity Research, who was not involved in this year’s report. “At most we were able to slow down the decline somehow.”

Latin America and the Caribbean experienced the worst regional decline, down 94 percent from 1970. The pattern was most pronounced in freshwater fish, reptiles, and amphibians. Africa followed with 66 percent; Asia and the Pacific saw 55 percent. The region defined as Europe-Central Asia saw a smaller decline at 18 percent, as did North America at 20 percent. Scientists emphasized that much steeper biodiversity losses in these two areas likely occurred well before 1970 and are not reflected in these data.

Scientists know what causes biodiversity loss. On land, agriculture is the main driver as humans convert forests and other ecosystems into farmland for cattle or palm oil. At sea it’s fishing. There are ways to do both more sustainably.

Unless climate change is limited to 2 degrees Celsius, and preferably 1.5 degrees, its impacts are expected to become the leading cause of biodiversity loss in the coming decades, the report says.

In December, the nations of the world will gather to try to reach a new deal to protect the planet’s biodiversity. The latter mostly missed its targets. The Living Planet report offers evidence of how to succeed this time around, said Dr. Shaw. A crucial lesson is that conservation does not work without the support of local communities.

“If we get really focused conservation efforts that involve the community, where the communities drive the outcomes because they benefit, we see that it’s possible to increase the population,” she said. “That’s really the bright spot.”