The walking dead

“There are examples of species all over the world that are essentially the walking dead,” said Stanford University Professor Paul Ehrlich. “We are sawing off the limb that we are sitting on.”

He was talking about the Sixth Extinction, the huge loss of species that is underway right now. It has been discussed in public before, of course, but what Ehrlich and other scientists from Stanford and Princeton universities and the University of California Berkeley have done is to document it statistically.

Animals and plants are always going extinct, usually to be replaced by rival species that exploit the same ecological niche more efficiently. But the normal turnover rate is quite slow, according to the fossil record: about one species of vertebrate per 10,000 species goes extinct each century. Ehrlich and his colleagues deliberately raised the bar, assuming that the normal extinction rate is twice as high as that – and still got an alarming result.

In a study published this month in Science Advances, they report that vertebrates are going extinct at a rate 114 times faster than normal. In a separate study last year, Professor Stuart Pimm of Duke University estimated that the loss rate may be as much as a thousand times higher than normal – and that includes plants as well as animals.

“We are now entering the sixth great mass extinction event,” said Gerardo Ceballos of the Universidad Autonoma de Mexico, lead author of the Science Advances study. “If it is allowed to continue, life would take many millions of years to recover and our species itself would likely disappear early on.” Indeed, Harvard biologist E.O. Wilson has estimated that at the current rate of loss, half of Earth’s higher lifeforms will be extinct by 2100.

It’s fair to say that we are the victims of our own success, but so is the entire biosphere. There were 1 billion of us in 1800. We are now 7.5 billion, on our way to 10 billion or 11 billion. We have appropriated the most biologically productive 40 percent of the planet’s land surface for our cities, farms and pastures, and there’s not much room left for the other species.

They have been crowded out, hunted out, or poisoned by our chemical wastes. Their habitats have been destroyed. Even the oceans are being devastated as one commercial fish species after another is fished out.

And still our population continues to grow, and our appetite for meat causes more land to be cleared to grow grain not for people, but for livestock.

All this even before global warming really gets underway and starts to take huge bites out of the ecosphere. We are on the Highway to Hell, and it’s hard to see how we get off it.

In a way, climate change is the easiest part of the problem to fix, but maintaining the diversity of species (some of which we haven’t even identified yet) that provide essential “ecosystem services” is going to be far harder, because the web of interdependence among apparently unrelated species is very complex. At the very least, however, it is clear that we must restore around a quarter of our agricultural land to its original “wild” state and cut back drastically on fishing.

It’s far from clear that we can do that in time and still go on feeding all of the human population, but the alternative is worse. James Lovelock put it very bluntly in his book “The Revenge of Gaia.”

“If we continue business as usual, our species may never again enjoy the lush and verdant world we had only a hundred years ago,” he wrote. “What is most in danger is civilization; humans are tough enough for breeding pairs to survive....but if these huge changes do occur it seems likely that few of the teeming billions now alive will survive.”