A mass global extinction, rivalling that which wiped out the dinosaurs, is already under way and little can be done about it. Without doubt, human activity caused this extinction, founded as it was in the destruction of the world's rain forests, said Irish scientist, Prof John Halley of St Andrew's University. And even if the destruction ended tomorrow, we have already condemned to death great numbers of organisms which will eventually disappear for ever.
Prof Halley, from Waterford and a graduate of University College Dublin, is attached to the Mathematical Institute at St Andrew's and specialises in analysing and modelling the ecology of extinction. He studies mass extinctions to understand disasters to come.
He believes the world's sixth-greatest extinction is already upon us. "We are currently dealing with a mass extinction and the current slow known rate of species extinction is an underestimate of the numbers already committed to extinction," he said.
His assumptions are based on the continuing destruction of the world's rain forests, particularly in the Amazon, one of the world's areas of greatest biological diversity, he said. Its destruction, likely by 2025-2050 if it continued at its present rate, would wipe out a large proportion of the globe's total species population of insects, birds and mammals.
Mass species extinctions are nothing new, but none of the "big five" - including the Permian collapse 230 million years ago in which 95 per cent of all marine species were killed off, or the dinosaur extinction 65 million years ago when 76 per cent of species disappeared - were attributable to human activity.
This latest, however, was of human origin and most recent smaller extinctions could also be linked to man. The flightless Dodo bird of Mauritius disappeared by about 1680 because of man, he said.
Australia lost about 86 per cent of its mammal species when man arrived between 30,000 BC and 20,000 BC and North America lost 33 per cent of its mammal variety when humans reached it in about 9000 BC, he said.
He also linked the demise of the great woolly mammoth to human depredation. The creature had survived earlier periods of climate change so this was an unlikely cause. "I am inclined to believe the human impact myself."
But such extinctions are a part of life on Earth. The highly successful sea creatures, ammonites and trilobites lived for 300 million years before succumbing to extinction. "You could say the carnage continues," Prof Halley said.
Human activity had already brought to an end 1.3 per cent of all recorded mammal and 1.2 per cent of all recorded bird species, with another 13 per cent and 12 per cent, respectively, on the brink of extinction. The rain forest losses provided a focus for the current extinction, but the process itself was highly complex. There was a connection between the size of habitat and the total numbers of a species living there.
"We are committing to extinction about 0.8 per cent of total species per year," said Prof Halley. Survival of low numbers of a given species did not guarantee future survival, he said, "even living in a friendly environment". A series of bad winters or a viral attack could be enough to push a species already under pressure into extinction.
While the species might struggle on at low numbers for centuries, the randomness of climate, illness and birth rates dictated eventual collapse if there was an insufficiently large population.
There were also interconnections between otherwise unrelated species, with the disappearance of one causing the extinction of another. "Current losses are not yet in the ball park of the big five," he said, but rain forest loss continued and prospects for stopping it were limited.
Continuing clearance could push total species extinction up into the big five, he said. What was not clear was the possible impact on our own species should the sixth great mass extinction continue unchecked.
