An incendiary new report from two major conservation groups predicts dire circumstances for the world's wild animals, warning that two-thirds of vertebrate populations could be wiped out by 2020, based on 1970 population levels.
The new report, called the Living Planet Index, was prepared by the World Wildlife Fund and the Zoological Society of London. The index found that animal populations dropped by 58 percent between 1970 and 2012, largely as a result of human activities, from poaching to habitat loss and pollution.
The team then extrapolated those trends forward to 2020. They based their analysis on data collected in the field on more than 14,000 populations of vertebrates, from 3,700 different species. The data came from many sources, from all around the world.
The researchers concluded that lakes and rivers saw the steepest declines in resident animals. Groups that have fared particularly badly include marine mammals, fish, and some birds (especially vultures).
We must "act now to reform our food and energy systems and meet global commitments on addressing climate change, protecting biodiversity and supporting sustainable development," the report begins.
"Global biodiversity is declining at an alarming rate, putting the survival of other species and our own future at risk," the index warns.
But hang on, says National Geographic explorer and conservation scientist Stuart Pimm of Duke University, who was not involved with the report.
"Trying to take all those different data sets, from all over the world, and putting that in a blender and trying to break that down into one number is irresponsible," Pimm says. "That's disingenuous and not helpful."
Pimm says there is far too much variability across different regions, from the land to the sea, and too much uncertainty to predict a dire crash of all species. Further, the report "depresses people to no end, and suggests there is no hope," he says.
"But there is a lot of hope around the world," Pimm adds.
He points to the recent successes in stemming the decline of lions, tigers, and other big cats across Africa and Asia, some of which has been spearheaded by National Geographic's Big Cats Initiative, which Pimm works on.
As another example, a recent study found that coral reefs are actually doing better, and are more resilient in the face of warming seas and acidification, than scientists had thought.
Although conservationists face many challenges in protecting endangered species and their habitat, the actual issues they face are more varied and subtle than a single number of index can convey, says Pimm.
Such reports may be more about trying to grab attention and raise money than sound science, he says.
Conservation biologist Luke Dollar, who leads National Geographic's Big Cats Initiative, says he agrees with Pimm's assessment of the Living Planet Index. "That said, there's no question that a great number of populations of myriad species are in substantial decline, and will continue to demand ever-increasing efforts to stem their loss and protect the systems of which they are a part," says Dollar.
"The need for self-awareness and proactive measures to mitigate our ever-increasing impact on wildlife has also never been greater," says Dollar.
This story was updated at 6:30 pm ET with comments from Luke Dollar.