Global Extinction Rates: Why Do Estimates Vary So Wildly?
Is it 150 species a day or 24 a day or far less than that? Prominent scientists cite dramatically different numbers when estimating the rate at which species are going extinct. Why is that?
Most ecologists believe that we are in the midst of the sixth mass extinction. Humanity’s impact on nature, they say, is now comparable to the five previous catastrophic events over the past 600 million years, during which up to 95 percent of the planet’s species disappeared. We may very well be. But recent studies have cited extinction rates that are extremely fuzzy and vary wildly.
The Millennium Ecosystem Assessment, which involved more than a thousand experts, estimated an extinction rate that was later calculated at up to 8,700 species a year, or 24 a day. More recently, scientists at the U.N. Convention on Biological Diversity concluded that: “Every day, up to 150 species are lost.” That could be as much as 10 percent a decade.
But nobody knows whether such estimates are anywhere close to reality. They are based on computer modeling, and documented losses are tiny by comparison. Only about 800 extinctions have been documented in the past 400 years, according to data held by the International Union for the Conservation of Nature (IUCN). Out of some 1.9 million recorded current or recent species on the planet, that represents less than a tenth of one percent.
Nor is there much documented evidence of accelerating loss. In its latest update, released in June, the IUCN reported “no new extinctions,” although last year it reported the loss of an earwig on the island of St Helena and a Malaysian snail. And some species once thought extinct have turned out to be still around, like the Guadalupe fur seal, which “died out” a century ago, but now numbers over 20,000.
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