Nobel scientist warns on climate change

By Tom Brown

MIAMI (Reuters) - The Nobel Prize-winning scientist who rang the first alarm bells over the ozone hole issued a warming about climate change on Saturday, saying there could be "almost irreversible consequences" if the Earth warmed 2.5 degrees Celsius (4.5 degrees F) above what it ought to be.

"Things are changing and there's no doubt that it's as a result of human activities," said Mario Molina, a Mexican who shared a Nobel prize in chemistry in 1995 for groundbreaking work on chlorofluorocarbon gases and their threat to the Earth's ozone layer.

"Long before we run out of oil, we will run out of atmosphere," he said.

Molina told a panel discussion on climate change at an annual Inter-American Development Bank meeting in Miami that the increasing intensity of hurricanes was among the worrisome changes that scientists had linked to a rapid global warming trend over the past 30 years.

Molina did not elaborate on specific effects so far from the Earth's temperature rise, which has been slightly less than 1 degree Celsius (1.8 F) over the last century.

But he said certain "tipping points" would be reached if temperatures continue increasing, including unmanageable changes to the Earth's environment.

Molina later told Reuters there was considerable uncertainty about how much further warming the planet can sustain before it reaches critical levels.

"You keep changing the temperature gradually but then suddenly things change dramatically," he said.

"Trying to keep it (warming) below two degrees (Celsius) means we want to keep the change at most twice or three times what it has changed already. And that's because it's unrealistic to change it by less, because of what we have already done," Molina said.

"The idea to keep the temperature change not above 2.5 (degrees Celsius) is precisely to reduce the possibility of these tipping points happening," he added.

He said warming beyond that would pose "a risk that is not acceptable to society."

(Editing by Michael Christie and Peter Cooney)