“Jose Endundo, environment minister of Congo, said he recently visited huge Lake Victoria in nearby Uganda, at 80,000 square kilometers (31,000 square miles) a vital source for the Nile River, and learned the lake level had dropped 3 meters (10 feet) in the past six years — a loss blamed in part on warmer temperatures and diminishing rains.

In the face of such threats, “the rich countries have to give us a helping hand,” the African minister said.

But it was Stern, former chief World Bank economist, who on Saturday laid out a case to his stranded companions in sobering PowerPoint detail.

If the world’s nations act responsibly, Stern said, they will achieve “zero-carbon” electricity production and zero-carbon road transport by 2050 — by replacing coal power plants with wind, solar or other energy sources that emit no carbon dioxide, and fossil fuel-burning vehicles with cars running on electric or other “clean” energy.

Then warming could be contained to a 2-degree-Celsius (3.4-degree-Fahrenheit) rise this century, he said.

But if negotiators falter, if emissions reductions are not made soon and deep, the severe climate shifts and sea-level rises projected by scientists would be “disastrous.”

It would “transform where people can live,” Stern said. “People would move on a massive scale. Hundreds of millions, probably billions of people would have to move if you talk about 4-, 5-, 6-degree increases” — 7 to 10 degrees Fahrenheit. And that would mean extended global conflict, “because there’s no way the world can handle that kind of population move in the time period in which it would take place.”

Melting ice, rising seas, dwindling lakes and war — the stranded ministers had a lot to consider. But many worried, too, that the current global economic crisis will keep governments from transforming carbon-dependent economies just now. For them, Stern offered a vision of working today on energy-efficient economies that would be more “sustainable” in the future.

“The unemployed builders of Europe should be insulating all the houses of Europe,” he said.”

 Charles Hanley for AP.