As much as 10 percent of the world's population lives in costal areas that might sink as ocean levels rise, shows a study conducted by the Earth Institute at Columbia University and the International Institute for Environment and Development.

Researchers point out that the problem is largely overlooked because many people think this problem concerns only small island countries such as the Tuvalu Islands in the South Pacific. In Tuvalu the highest point of land is only 5 meters above sea level and tidal floods occasionally cover their crops in seawater.

However, the authors found that many large cities on costal areas face risks posed by rising sea level and increased storm intensity.

"Urban areas have traditionally been studied in a way that separates them from their physical surroundings," says Deborah Balk, a demographer with the Center for International Earth Science Information Network (CIESIN), a member of The Earth Institute at Columbia University. "We talk about urban issues as if they occur in a spatial vacuum, but you can't address these questions without understanding the spatial dimensions."

Balk and her colleagues report that 10 percent of world's population lives in coastal areas that are less than 10 meters above sea level - low-elevation coastal zones (LECZs). Although these areas comprise only about 2.2 percent of the world's land area, they are inhabited by 600 million people. Moreover, 60 percent of them live in urban areas and thus face more dangers as sea-level rises and storms get more powerful - phenomena that are expected to worsen as a result of global warming.

Among the most affected countries are Vietnam and Bangladesh that both have a high percentage of their total area as well as major metropolitan areas situated inside the LECZ. Bangladesh already faces periodic floods that are much worse than in the past.

Researchers show that even wealthier countries with access to economic and technical resources often face insurmountable challenges. More than 60 percent of the population and land area of The Netherlands is located in the LECZ, and the country has expended vast resources over decades on flood prevention projects. However, the results were mixed and some efforts have been abandoned as ineffective or not cost-effective. The U.S. also faces significant risks as it has more urban areas in the LECZ than any other country.

"These results illustrate the importance of looking beyond the small island states to recognize how wide-spread the risks truly are," concludes the study. Researchers underline that the different types of cities and coastal zones must be examined in more detail in order to assess the vulnerabilities to climate change faced by various countries.