"If you were faced with the threat of the disappearance of your nation, what would you do?"

That's the question Enele Sopoaga, the prime minister of the tiny Pacific Island nation of Tuvalu, asked fellow world leaders at the United Nations climate summit in Lima, Peru, in December.

It's a question that leaders of Pacific Island states have been asking for decades. As a warming climate drives sea levels upward, low-lying island nations face an uncertain future—or no future at all, say these leaders, who warn of their nations' imminent disappearance.

Officials in Tuvalu, 600 miles (965 kilometers) north of Fiji, have been some of the most vocal critics of the world's large greenhouse gas emitters—industrialized nations such as