Mass extinction 'already triggered'
Humans have already triggered the start of Earth's sixth mass extinction, thereby threatening their own future as a species, a hard-hitting new study has claimed.
The window of opportunity to prevent the worst diversity disaster since dinosaurs were swept from the planet 65 million years ago is "rapidly closing", warn the authors.
In the last century vertebrates have been disappearing at a rate 114 times higher than would normally be expected without the destructive influence of humans, according to the scientists, who insist their analysis is "extremely conservative".
If the current pace of extinction is allowed to continue, species loss will have a significant effect on human populations in as little as three generations, it is claimed.
Once the damage is done, it could take millions of years for nature to recover, said the researchers.
They pointed out that since 1900, over 400 more vertebrates than expected had vanished. The lost animals included 69 mammal, 80 bird, 24 reptile, 146 amphibian and 158 fish species.
Today, the spectre of extinction hung over 26% of all mammalian species and 41% of all amphibians.
Professor Paul Ehrlich, from Stanford University in California, a leading member of the team, said: "Without any significant doubt ... we are now entering the sixth great mass extinction event.
"There are examples of species all over the world that are essentially the walking dead. We are sawing off the limb that we are sitting on."
Loss of species disrupts ecosystems, leading to serious knock-effects felt by humans, the scientists stressed. Crop pollination by bees and the water purification of wetlands were two examples of biodiversity benefits which could be lost in three human lifetimes.
Mexican lead researcher Dr Gerardo Ceballos, from the Universidad Autonoma de Mexico, warned that humans could one day follow in the footsteps of the dinosaurs.
"If it is allowed to continue, life would take many millions of years to recover, and our species itself would likely disappear early on," he said.
Mass extinctions have occurred on five occasions throughout the history of life on Earth. The last event happened 65 million years ago when a giant meteor smashed into the planet, altered the climate, and wiped out the dinosaurs.
The scientists used a conservative approach to calculate a natural "background rate" of two mammal extinctions per 10,000 species per century.
This was the rate of diversity loss that should be expected between mass extinctions.
Given the number of species that had vanished over the last 100 years, it would have taken between 800 and 10,000 years for so many creatures to disappear if the background rate had applied.
Writing in the journal Science Advances, the researchers concluded: "Our analysis emphasises that our global society has started to destroy species of other organisms at an accelerating rate, initiating a mass extinction episode unparalleled for 65 million years."
The authors said it was still - just - possible to avert a "dramatic decay of biodiversity" through intensive conservation, but time was running out.
They wrote: " 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.
"All of these are related to human population size and growth, which increases consumption (especially among the rich), and economic inequity."