Rising oil prices, global food shortages and the economic crisis are proof for many survivalists that society is on the brink of meltdown. But are their predictions all gloom and doom - or a chance to create new communities?

As many as one billion people could lose their homes by 2050 because of the devastating impact of global warming, scientists and political leaders will be warned today.

They will hear that the steady rise in temperatures across the planet could trigger mass migration on unprecedented levels.

Hundreds of millions could be forced to go on the move because of water shortages and crop failures in most of Africa, as well as in central and southern Asia and South America, the conference in London will be told.

“Don’t look now, but the good times may have just stopped rolling,” the economist Paul Krugman wrote in his New York Times column. The Economist was more strident: “The era of cheap food is over,” it declared. World Bank President Robert Zoellick, reaching back to policies created during the Great Depression for inspiration to address food inflation, is pushing a “New Deal” for global food policy, aimed at aiding impoverished countries with income support and help in producing crops.

I don’t want to alarm anybody, but maybe it’s time for Americans to start stockpiling food.

No, this is not a drill.

You’ve seen the TV footage of food riots in parts of the developing world. Yes, they’re a long way away from the U.S. But most foodstuffs operate in a global market. When the cost of wheat soars in Asia, it will do the same here.

Many parts of America, long considered the breadbasket of the world, are now confronting a once unthinkable phenomenon: food rationing. Major retailers in New York, in areas of New England, and on the West Coast are limiting purchases of flour, rice, and cooking oil as demand outstrips supply. There are also anecdotal reports that some consumers are hoarding grain stocks.

At a Costco Warehouse in Mountain View, Calif., yesterday, shoppers grew frustrated and occasionally uttered expletives as they searched in vain for the large sacks of rice they usually buy.