A polar bear stands on an ice floe near Manitoba, Canada, in 2012. Polar bears depend on sea ice, which is forming later in the fall and disappearing earlier in the spring. (photo: Paul Souders/Corbis)
20 June 15
Study reveals rate of extinction for species in the 20th century has been up to 100 times higher than would have been normal without human impact
he modern world is experiencing a “sixth great extinction” of animal species even when the lowest estimates of extinction rates are considered, scientists have warned.
The rate of extinction for species in the 20th century was up to 100 times higher than it would have been without man’s impact, they said.
Many conservationists have been warning for years that a mass extinction event akin to the one that wiped out the dinosaurs is occurring as humans degrade and destroy habitats.
But the authors of a study published on Friday said that even when they analysed the most conservative extinction rates, the rate at which vertebrates were being lost forever was far higher than in the last five mass extinctions.
“We were very surprised to see how bad it is,” said Dr Gerardo Ceballos of the National Autonomous University of Mexico. “This is very depressing because we used the most conservative rates, and even then they are much higher than the normal extinction rate, really indicating we are having a massive loss of the species.”
Previous studies have warned that the impact of humans taking land for buildings, farming and timber has been to make species extinct at speeds unprecedented in Earth’s 4.5bn-year history.
Ceballos said that his study, co-authored by Paul R Ehrlich who famously warned of the impact of humanity’s “population bomb”, employed better knowledge of natural or so-called background extinction rates. He said it was conservative because it looked only at species that had been declared extinct, which due to stringent rules can sometimes take many years after a species has actually gone extinct.
Under a “natural” rate of extinction, the study said that two species go extinct per 10,000 species per 100 years, rather than the one species that previous work has assumed.
Modern rates of extinction were eight to 100 times higher , the authors found. For example, 477 vertebrates have gone extinct since 1900, rather than the nine that would be expected at natural rates.
“It’s really signalling we’ve entered a sixth extinction and it’s driven by man,” said Ceballos.
Noah’s Ark and the General Deluge – a colour lithograph. (photo: Corbis)
However, Prof Henrique Miguel Pereira, the chair of the Group on Earth Observations Biodiversity Observation Network, said that the new paper did not add anything revolutionarily new.
“They argue that recent extinction rates are up to 100 times higher than in the past. I think it improves our documentation of the process but it does not yet confirm a sixth mass extinction. I tend to think we have a major biodiversity crisis, but it would take either a fast acceleration of current extinction rates or a couple of centuries at current extinction rates, for the current process to become a sixth mass extinction.”
The team behind the new analysis said “rapid, greatly intensified efforts” would be needed to stop or slow the extinctions currently underway.
Ceballos pointed to the Pope Francis’s encyclical on the environment, which was published on Thursday and lamented the loss of the world’s biodiversity, and interventions by Barack Obama, as signs of hope. “These important figures are starting to really grasp the problem,” he said.
On why people should be worried about the rate of extinctions, he said: “People say that’s really sad, but why does it affect me? There are many reasons we should care. We are the species that are causing the loss of all these other species.”
But the most important reason, he said, was that by losing species humanity was losing what enabled us to have a “good standard of living”.
The paper, Accelerated modern human–induced species losses: Entering the sixth mass extinction, was published in the journal Science Advances.