CAPE TOWN, South Africa - If we don't deal with climate change decisively, "what we're talking about then is extended world war," the eminent economist said.
His audience Saturday, small and elite, had been stranded here by bad weather and were talking climate. They couldn't do much about the one, but the other was squarely in their hands. And so, Lord Nicholas Stern was telling them, was the potential for mass migrations setting off mass conflict.
"Somehow we have to explain to people just how worrying that is," the British economic thinker said.
Stern, author of a major British government report detailing the cost of climate change, was one of a select group of two dozen - environment ministers, climate negotiators and experts from 16 nations - scheduled to fly to Antarctica to learn firsthand how global warming might melt its ice into the sea, raising ocean levels worldwide.
Their midnight flight was scrubbed on Friday and Saturday because of high winds on the southernmost continent, 3,000 miles from here. While waiting at their Cape Town hotel for the gusts to ease down south, chief sponsor Erik Solheim, Norway's environment minister, improvised with group exchanges over coffee and wine about the future of the planet.
"International diplomacy is all about personal relations," Solheim said. "The more people know each other, the less likely there will be misunderstandings."
Understandings will be vital in this "year of climate," as the world's nations and their negotiators count down toward a U.N. climate conference in Copenhagen in December, target date for concluding a grand new deal to replace the Kyoto Protocol - the 1997 agreement, expiring in 2012, to reduce carbon dioxide and other global-warming emissions by industrial nations.
Solheim drew together key players for the planned brief visit to Norway's Troll Research Station in East Antarctica.
Trying on polar outfits for size on Friday were China's chief climate negotiator Xie Zhenhua, veteran U.S. climate envoy Dan Reifsnyder, and environment ministers Hilary Benn of Britain and Carlos Minc Baumfeld of Brazil.
Later, at dinner, the heavyweights heard from smaller or poorer nations about the trials they face as warming disrupts climate, turns some regions drier, threatens food production in poor African nations.
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.
After he spoke, Norwegian organizers announced that the forecast looked good for Stern and the rest to fly south on Sunday to further ponder the future while meeting with scientists in the forbidding vastness of Antarctica.