Make clear dire scenarios to prod climate action: Stern

By Gelu Sulugiuc

COPENHAGEN (Reuters) - Scientists must make clear the disastrous effects of climate change so the world takes action now to cut carbon emissions, leading economist Nicholas Stern said on Thursday.

"You have to tell people very clearly and strongly just how difficult (a temperature rise of) four, five, six or seven degrees Celsius is," he said.

"Billions of people would have to move and there would be very severe conflict," said Stern, a professor at the London School of Economics and a former British Treasury economist.

"That's a story that must be told to persuade people it's a very bad idea to go anywhere near five degrees. This is not a black swan, this is a big probability of a devastating outcome," he told a gathering of 2,000 scientists at the Congress on Climate Change in Copenhagen.

"The costs of delay are very big," he said.

Stern, in a 2006 report, warned inaction on greenhouse gas emissions could cause economic pain equal to that of the Great Depression of the 1930s.

Above two degrees warming, hundreds of millions of people would face reduced water supplies, and above three degrees food production worldwide would be very likely to decrease, a U.N. panel of climate scientists said in 2007.

Professor John Schellnhuber of the Potsdam Institute for Climate Impact Research, speaking before Stern, said a warming of five degrees would mean the planet could support less than 1 billion people.