Killing the sources that keep us alive

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 Mr 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. Mr 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 (animals with internal skeletons made of bone or cartilage — mammals, birds, reptiles and fish) 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 1,000 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 EO Wilson has estimated that at the current rate of loss, half of earth’s higher life forms 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 one billion of us in 1800. We are now seven and a half billion, on our way to 10 or 11 billion. We have appropriated the most biologically productive 40 per cent 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, because all we have to do is stop burning fossil fuels and reform the way we farm to cut carbon dioxide emissions. More easily said than done, as the history of the past 30 years amply demonstrates, but certainly not impossible if we take the task seriously.

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.