More proof that human beings are party to our own demise, but will we act?

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 mass extinction, the huge loss of species that is under way right now. It has been discussed in public before, of course, but what Ehrlich and other scientists have done is to document it statistically.

Animals and plants are always going extinct, usually to be replaced by rival species. But the normal turnover rate is quite slow, according to the fossil record. Ehrlich and his colleagues deliberately raised the bar, assuming that the normal rate is twice as high - 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.

"We are now entering the sixth great mass extinction event," said Gerardo Ceballos of the National Autonomous University of Mexico, lead author of the 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, biologist E. O. 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 7½ 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. And still our population continues to grow and our appetite for meat causes more land to be cleared. All this even before global warming really gets under way. We are on the Highway to Hell, and it's hard to see how we get off.

In a way, climate change is the easiest part of the problem to fix; we just have to stop burning fossil fuels and reform the way we farm to cut carbon dioxide emissions.

Maintaining the diversity of species that provides 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.

Gwynne Dyer is an independent journalist