Humans are very good at destroying wildlife. From blackbirds to golden frogs to Tasmanian tigers, many species have succumbed to our unique mix of destruction. How many species have humans driven to extinction? Scientists don’t have a definitive answer to that question, and the number is hard to calculate. But it’s probably in the hundreds of thousands.

Let’s start with confirmed extinctions. According to the International Union for Conservation of Nature’s (IUCN) Red Book, 777 species of animals have become extinct since the beginning of the modern era (1500). Some of these extinctions may have been natural, but humans have a hand in most, if not all, extinctions, especially in the last 500 years. Humans began contributing to species extinctions thousands of years ago, long before 1500, but there were no scientists studying these extinctions at the time, and there is enough uncertainty about today’s extinction rates that we’ll focus on the last 500 years.

The IUCN estimates that only 5% of known species in the world are at risk of extinction, so there must be many more that are going unreported. A 2022 study published in the journal Biological Reviews found that between 150,000 and 260,000 of all known species may have gone extinct since around 1500.

The numbers were so large that they surprised the study’s lead author, Robert Cowie, a research professor at the University of Hawaii. “I thought, ‘Oh my God, did I make some miscalculations? ‘” Cowie told Live Science.

Cowie was right, but his assessment came with important caveats. To calculate this figure, his team took a random sample of 200 land snails and used previous scientific research and expert advice to determine how many had gone extinct. They then calculated how many species would go extinct if all known species went extinct at the same rate over the course of 500 years.

The extinction rate they calculated was 150 to 260 extinctions per million species-years (E/MSY)—in other words, 150 to 260 extinctions per year for every million species on Earth. Cowie also looked at extinction estimates for other wildlife groups, including amphibians and birds. The estimates ranged from 10 to 243 E/MSY, but there was a sweet spot.

“They are usually grouped around 100 [E/MSY]”I think it’s more reasonable, not too conservative but not too extreme either.” Cowie said.

The riddle of mathematics

Applying 100 E/MSY to the Cowie 2022 method reveals that 100,000 of the approximately 2 million known species have become extinct in the last 500 years. However, this is not the case for unknown animal species.

A 2011 study published in the journal PLOS Biology estimated that there are about 7.7 million animal species. Taking that number and assuming an E/MSY of 100 over 500 years—minus the 3,850 animals expected to go extinct naturally in 500 years and a background extinction rate of 1 E/MSY—Live Science’s final estimate for human-caused animal extinctions would be 381,150. This is a rough estimate and should be taken with a grain of salt.

A pinch of salt

John Ellroy, an associate professor in the Department of Biological Sciences at Macquarie University in Australia who works on measuring diversity and extinction, told Live Science that he thinks current extinction rates are nearly impossible to calculate.

“We have to be very careful when trying to put a number on the existing literature,” Alroy said. “I don’t think we can pinpoint the current level of extinction.”

To understand the overall rate of extinction, Alroy said, researchers first need to know how many species exist. Despite estimates, much of the world’s wildlife is not only unknown to science, but is also concentrated in poorly studied regions, such as the tropics. To make matters worse, insects have more species than any other animal group, yet we know very little about them compared to larger animal groups like mammals and birds.

Although this is difficult, Ellroy suggests estimating extinction rates for specific animal groups that represent larger groups using museum data and examining how many species have been lost over time. “If only you knew how many species you had before [і] How many species did you have after that?” Ellroy said.

Whatever the exact rate, Ellroy says humans are accelerating the rate of extinction, far exceeding the 777 recorded on the IUCN Red List. The studies’ wide range of E/MSY estimates also have one thing in common: They are all well above natural background levels. To Cowie, that’s enough to say that humans are wreaking havoc on Earth’s biodiversity.

“Whether the extinction rate is 100 E/MSY, 20 E/MSY or 200 E/MSY, it’s still too much and it’s still too bad,” he said.