There’s no doubt any longer. The Earth has entered the sixth great extinction in its 4.5-billion-year history.
Species are disappearing 100 times faster than the background rate — normal rate between mass extinctions — a pace unparalleled since the dinosaurs died out 66 million years ago. And the reason is not asteroids, volcanic eruptions, or massive tectonic movements. It is us — human beings.
Five mass extinctions have thus far been recorded in the Earth’s geological history. Proof that a sixth is upon us lies in showing that current rates of extinction are above the ‘background’ rate prevailing in the previous five extinctions. New research by biologists at multiple North American universities, published last week in Science Advances, shows that even assuming a highly conservative background rate of 2 mammal extinctions per 10,000 species per 100 years (2E/MSY), the average rate of vertebrate species loss over the last century has been up to 114 times higher than the background rate. By the 2E/MSY rate, it should have taken, depending on the vertebrate taxon, 800-10,000 years for the same number of species to go extinct.
Growing human populations, consumption and economic inequity that has destroyed natural habitats. In the list: land clearing for farming, settlement; introduction of invasive species; carbon emissions driving climate change; toxins that alter ecosystems. About 41% of amphibians and 26% mammals are on the brink, says the International Union for Conservation of Nature, which lists threatened and extinct species. As species disappear, so do ecosystem services such as honeybees’ crop pollination and wetlands’ water purification. At the current rate of species loss, we will lose many biodiversity benefits within three generations. “We are sawing off the limb we are sitting on,” says the study.
COULD IT BE WORSE?
Past mass extinctions took thousands of years. At current dieoff rates, the sixth could reach Big 5 proportions in just 240 to 540 years. Even this is based on a very conservative approach. Researchers estimated current extinctions highly conservatively, and a background rate double that used in previous analyses, and asked if even the lowest estimates of the difference between background and contemporary extinction rates justified assuming “a global spasm of biodiversity loss”. The answer: a definitive Yes. “Our calculations very likely underestimate the severity of the extinction crisis,” says the study.
Is There No Hope?
A very slim one. “Avoiding a true sixth mass extinction will require rapid, greatly intensified efforts to conserve already threatened species, and to alleviate pressures on their populations — notably habitat loss, over-exploitation for economic gain and climate change,” says the study.