6 things to know about Earth's 6th mass extinction | MNN - Mother Nature Network - 0 views
-
Natural disasters have triggered at least five mass extinctions in the past 500 million years, each of which wiped out between 50 and 90 percent of all species on the planet
-
it's happening again. A 2015 study reported the long-suspected sixth mass extinction of Earth's wildlife is "already underway." And a 2017 study calls the loss of that wildlife a “biological annihilation” and a “frightening assault on the foundations of human civilization.
-
And while previous extinctions were often linked to asteroids or volcanoes, this one is an inside job. It's caused mainly by one species — a mammal,
- ...18 more annotations...
-
Many scientists have been warning us for years, citing a pace of extinctions far beyond the historical "background" rate. Yet critics have argued that's based on inadequate data, preserving doubt about the scope of modern wildlife declines. To see if such doubt is justified, the 2015 study compared a conservatively low estimate of current extinctions with an estimated background rate twice as high as those used in previous studies. Despite the extra caution, it still found species are disappearing up to 114 times more quickly than they normally do in between mass extinctions
-
"Even under our assumptions, which would tend to minimize evidence of an incipient mass extinction, the average rate of vertebrate species loss over the last century is up to 114 times higher than the background rate," the study's authors write. "Under the 2 E/MSY background rate, the number of species that have gone extinct in the last century would have taken, depending on the vertebrate taxon, between 800 and 10,000 years to disappear.
-
The No. 1 cause of modern wildlife declines is habitat loss and fragmentation, representing the primary threat for 85 percent of all species on the IUCN Red List. That includes deforestation for farming, logging and settlement, but also the less obvious threat of fragmentation by roads and other infrastructure.
-
Even under the most conservative estimates, the extinction rates for mammals, birds, amphibians and fish have all been at least 20 times their expected rates since 1900, the researchers note (the rate for reptiles ranges from 8 to 24 times above expected). Earth's entire vertebrate population has reportedly fallen 52 percent in the last 45 years alone
-
he threat of extinction still looms for many — including an estimated 41 percent of all amphibian species and 26 percent of mammals.
-
The 2015 study was intentionally conservative, so the actual rate of extinctions is almost certainly more extreme than it suggests
-
The study also focuses on vertebrates, which are typically easier to count than smaller or subtler wildlife like mollusks, insects and plants. As another recent study pointed out, this leaves much of the crisis unexamined. "Mammals and birds provide the most robust data, because the status of almost all has been assessed," the authors of that study write. "Invertebrates constitute over 99 percent of species diversity, but the status of only a tiny fraction has been assessed, thereby dramatically underestimating overall levels of extinction.
-
"If it is allowed to continue, life would take many millions of years to recover, and our species itself would likely disappear early on," says Gerardo Ceballos of the Universidad Autónoma de México, lead author of the 2015 study. "We are sawing off the limb that we are sitting on,"