In the movie Avatar, so many magnificent animals have gone extinct that scientists can only study them virtually. This environmentally ravaged Earth is set in the near future, in the year 2154, but according to University of Florida biologist Todd Palmer and his colleagues, the Earth in 2015 is already undergoing an accelerated mass extinction.
In a study published today in the journal Science Advances, Palmer and his colleagues say there no longer is any doubt: We are entering a mass extinction that threatens humanity’s existence.
“The Earth’s biodiversity plays a really critical role in sustaining the human species, from the pollination of our crops, to the purification of our water supply to the amelioration of climate change. We simply cannot afford to continue losing species at the rate they are currently disappearing,” Palmer said.
There is general agreement among scientists that extinction rates have reached levels unparalleled since the dinosaurs died out 66 million years ago. However, some have challenged the theory, believing earlier estimates rested on assumptions that overestimated the crisis.
The new study shows that even with extremely conservative estimates, species are disappearing up to about 100 times faster than the normal rate between mass extinctions, known as the background rate.
“If it is allowed to continue, life would take many millions of years to recover, and our species itself would likely disappear early on,” said lead author Gerardo Ceballos of the Universidad Autónoma de México.
Using fossil records and extinction counts from a range of records, the researchers compared a highly conservative estimate of current extinctions with a background rate estimate twice as high as those widely used in previous analyses. This way, they brought the two estimates – current extinction rate and average background or going-on-all-the-time extinction rate – as close to each other as possible.
Focusing on vertebrates, the group for which the most reliable modern and fossil data exist, the researchers asked whether even the lowest estimates of the difference between background and contemporary extinction rates still justify the conclusion that people are precipitating “a global spasm of biodiversity loss.” The answer: a definitive yes.
“We emphasize that our calculations very likely underestimate the severity of the extinction crisis, because our aim was to place a realistic lower bound on humanity’s impact on biodiversity,” the researchers write.
To history’s steady drumbeat, a human population growing in numbers, per capita consumption and economic inequity has altered or destroyed natural habitats. The long list of impacts includes:
- Land clearing for farming, logging and settlement
- Introduction of invasive species
- Carbon emissions that drive climate change and ocean acidification
- Toxins that alter and poison ecosystems
Now, the specter of extinction hangs over about 41 percent of all amphibian species and 26 percent of all mammals, according to the International Union for Conservation of Nature, which maintains an authoritative list of threatened and extinct species.
“There are currently over 2,400 animal and 2,000 plant species that are critically endangered, and some of those are essentially the walking dead, whose populations have been so drastically reduced that there’s little hope for their recovery,” Palmer said.
As species disappear, so do crucial ecosystem services such as honeybees’ crop pollination and wetlands’ water purification. At the current rate of species loss, people will lose many biodiversity benefits within three generations, the study’s authors write.
“We are responsible for the current extinction crisis. There is no question about it. We simply cannot continue to treat nature like a bottomless checking account,” Palmer said.
Hope for the future
Despite the gloomy outlook, there is a meaningful way forward, according to Palmer and his colleagues. “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,” the study’s authors write.
In the meantime, the researchers hope their work will inform conservation efforts, the maintenance of ecosystem services and public policy.
Co-authors on the paper include Gerardo Ceballos of Universidad Autónoma de México, Paul R. Ehrlich of Stanford University, Anthony D. Barnosky of the University of California at Berkeley, Andrés García of Universidad Autónoma de México, Robert M. Pringle of Princeton University.