Here’s What a Shocking New Number on Wildlife Declines Really Means

Wildlife populations around the world continue dropping precipitously, according to an important but limited and often misinterpreted assessment that’s issued every two years.

The declines reported by the Living Planet Index, a collaboration between two large conservation organizations, have been so steep as to feel disorienting. This year is no exception: A reduction of 73% in the average size of monitored wildlife populations in a mere 50 years, from 1970 to 2020. The previous figure was similar, a 69% decline through 2018.

But the findings do not mean that wildlife in general has dropped by that much. This year’s index was based on evidence from 34,836 local populations of 5,495 species, all of them vertebrates: mammals, birds, fish, amphibians and reptiles. Changes in tiny populations can have outsized effects on the global count because they are averaged together with much larger ones. But beyond that, the data is too varied and inconsistent to make confident estimates, some researchers say.

These limitations mean the index’s figures should not be used as an overall measure of biodiversity loss, said Walter Jetz, a professor of ecology at Yale who studies changes in global biodiversity and is not affiliated with the effort. Still, he said, the underlying database provides a valuable contribution, especially in identifying populations in need of further attention. And the bigger problem it points to is very real.

“There is no doubt that species populations are declining at alarming rates,” Jetz said. David Murrell, a biology professor at University College London who focuses on quantitative approaches, partnered with the authors of the Living Planet Index on an assessment of its reliability. They found that the index would need more data to increase confidence in the estimates, especially for amphibians and reptiles, and more generally in the global south. Nonetheless, the index is “one of our best guesstimates for the trends in animal groups,” Murrell said. “It is not perfect, but no perfect methods exist.”

A recent study raised issues with the way the index is calculated, saying it overrepresented declines. The Living Planet authors have defended their approach and are preparing a rebuttal. “What would be wonderful is if people could help us make this a better estimate,” said Robin Freeman, head of the indicators and assessment unit at the Zoological Society of London, which manages the index in collaboration with the World Wildlife Fund. “We’ve tried to make the code open-source, the data opensource, we’re using peer-reviewed methods.”

While the magnitude of declines remains unknown, there is widespread scientific consensus that the planet is facing a crisis of biodiversity loss with dangerous implications for humanity. “Wildlife population declines can lead to the loss of ecosystem function and ecosystem services to people such as carbon storage, water storage, clean air, clean water, pollination services and protection against storm surge and flooding, just to name a few,” said Rebecca Shaw, chief scientist at WWF and the lead author of a report that accompanies the new figures.

The drivers of biodiversity decline are habitat loss, typically from farming, logging, building, producing energy and mining; hunting and fishing animals directly for food or other reasons; climate change; pollution; invasive species; and disease.

Coral reefs, battered by climate change, pollution and overfishing, are experiencing the widest global bleaching event on record. The Amazon, pummeled by deforestation and climate change, is facing a drought that has dried up stretches of its great river. Some areas are releasing more planet-warming carbon than they store.

While Latin America and Africa saw far greater declines than North America or Europe and Central Asia, the authors pointed out that the discrepancy comes from the magnitude of biodiversity loss suffered in the northern regions before 1970, when the index started.

“The impacts have been experienced far earlier in history,” said Andrew Terry, director of conservation and policy at the Zoological Society of London. In less than two weeks, representatives from countries around the world will gather in Cali, Colombia, for the first United Nations biodiversity negotiations since a sweeping agreement in Montreal two years ago.

Countries are supposed to submit plans to show how they will implement the targets, and negotiations will tackle questions over how poorer countries will pay for it.