Head for high ground: Bangladesh is about the size of Wisconsin but bursts with a population nearly half that of the United States. On average, about 2,600 people are crammed into each square mile of the country. Monsoons already seasonally flood more than 200 rivers that crisscross the countryside. Rising ocean levels would compound this problem, forcing more Bangladeshis into an even tighter living space.

In 1970 the deadliest tropical cyclone in recorded history swept the coast of what was then known as East Pakistan, now Bangladesh, killing 500,000 people -- most drowned in the 20-foot tidal surge. Disaster struck again in 1991 when another cyclone took 13,000 lives. With one-tenth of this crowded country barely a meter above sea level, the dangers of flooding from storms and sea level rise are severe.

Now experts say warmer global temperatures could increase the intensity of cyclones that form over the Bay of Bengal, sending more violent storms crashing into the coast. As the oceans rise, the saltwater front will crawl farther inland, rendering farmland unusable and polluting much of the country's drinking water. The Sundarbans National Forest, the largest remaining mangrove ecosystem in the world and home to the Royal Bengal tiger, could be obliterated. "A global sea level rise of about half a meter -- the average expected over this century -- could cause an area of Bangladesh where about 10 million people now live to be permanently submerged," says Princeton climatologist Michael Oppenheimer. "If even a modest chunk of the Greenland ice sheet or the west Antarctic ice sheet goes, the sea level would rise past the capital of Dhaka -- which is in the center of the country. Untold tens of millions of people live between Dhaka and the sea right now."

Bangladeshi officials are scrambling to prepare for the inevitable flooding, but adaptation, rather than relocation, has been their focus so far. Some Bangladeshi farmers rely on gardens that float on water, planted on beds of water hyacinth --expanding this farming method to other flood-prone areas is one approach. Others say the dikes and levees built along the southern coast in the 1960s could be upgraded and built higher.

But climate scientists outside Bangladesh are far less hopeful. "The picture for Bangladesh, if nothing is done to limit greenhouse gas emissions, is very bleak," says Oppenheimer. "They can protect their citizens from an out-and-out, day-to-day disaster, but in the long term the land is going, going, gone for a good chunk of the country."