New mapping techniques show how much land would be lost and how many people affected by rapid sea level rises that are often triggered by storms and earthquakes, a U.S. Geological Survey-led team determined.
E. Lynn Usery, who led the team, said nearly one-quarter of the world's population lives below 100 feet above sea level -- the size of the biggest surge during the 2004 tsunami that pulverized villages along the Indian Ocean and killed 230,000 people.
"What we are suggesting is what kind of areas are at risk (in) a catastrophic event," Usery told a meeting of the Association of American Geographers.
"The fact that there are that many people living at that sea level means there are probably a lot of people potentially in harm's way."
The team also found that a 100-foot rise in sea level would cover 3.7 million square miles of land worldwide.
A rise of just 16 feet would affect 669 million people and 2 million square miles of land would be lost.
Sea levels are currently rising about 0.04 to 0.08 inches each year, making it unlikely such a scenario would suddenly occur across the globe, Usery said.
But he said 10,000 years ago sea levels rose 20 meters in 500 years -- a relatively short span -- after the collapse of the continental ice sheets.
"It can happen in a short period of time if we look at the historical data," Usery said.
More importantly, he said, the new mapping technique provides detail that was previously unavailable and gives policymakers better tools to prepare for potential disasters. With just a mouse click on the computer, researchers can gauge how much land would be lost at various sea levels, and where.