Scientists Must Raise Climate Alarm: Lord Stern.

The economic impact of global warming has been grossly underestimated and scientists must warn that inaction will spell disaster, top economist and climate change expert Nicholas Stern said on Thursday.

Stern told 2,000 climate scientists that they had failed to clearly tell humanity what it faces if global temperatures reach the upper range of forecasts made by the UN's Intergovernmental Panel for Climate Change (IPCC).

"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," Stern told scientists at the Congress on Climate Change in Copenhagen".

Stern told the conference that the global recession presents an opportunity to build a more energy-efficient economy. He said; "Coming out of this we have got to lay the foundations for a low-carbon growth, which is going to be like the railways, like the electricity, like the motorcars, this is going to be over the next two, three decades the big driver in investment"