NORWICH, England (Reuters)
Global warming over the coming century could mean a return of temperatures last seen in the age of the dinosaur and lead to the extinction of up to half of all species, a scientist said on Thursday.
Not only will carbon dioxide levels be at the highest levels for 24 million years, but global average temperatures will be higher than for up to 10 million years, said Chris Thomas of the University of York.
Between 10 and 99 percent of species will be faced with atmospheric conditions that last existed before they evolved, and as a result from 10-50 percent of them could disappear.
"We may very well already be on the breaking edge of a wave of mass extinctions," Thomas told the annual meeting of the British Association for the Advancement of Science.
Scientists predict average global temperatures will rise by between two and six degrees centigrade by 2100, mainly as a result of the heat-trapping carbon dioxide being pumped into the air from burning fossil fuels for transport and power.
"If the most extreme warming predicted takes place we will be going back to global temperatures not seen since the age of the dinosaur," Thomas said.
"We are starting to put these things into a historical perspective. These are conditions not seen for millions of years, so none of the species will have been subjected to them before," he added.
Thomas said scientific observations had already found that -- as predicted by the climate models -- 80 percent of species had already begun moving their traditional territorial ranges in response to the changing climatic conditions.
"That is an amazingly high correlation. It is a clear signature of climate change," he said.
Not only had the animals, birds and insects started to react, but there was evidence vegetation was also on the move.
For example, climate-triggered fungal pathogen outbreaks had already led to the extinction of more than one percent of the planet's amphibian species, Thomas said.
Not only would some species simply find no suitable space to live anymore, but there would be confrontations with invasive species being forced to move their territory. This would produce not just wipe-outs but species' mixtures never seen before.
And the changes would all happen at a faster rate than ever before in evolution.
"In geological terms 100 years is effectively instantaneous," Thomas noted.
