Census figures and satellite imagery tell a story of swelling populations along coastal regions that are expected to flood and experience more violent cyclones because of climate change.
Using the data, the International Institute for Environment and Development in London has released a study showing that exposed low lying coastal zones 10 meters or less above sea level contain 10 percent of all humanity, 634 million people, although they make up just two percent of the world's land area. "Coastal areas are disproportionately urban and coastal areas are disproportionately dense," said demographer Deborah Balk of the City University of New York, a co-author of the study.
"The urban areas in those coastal systems are both larger and more of the system is dedicated to urban areas than we would find in dry lands or in forests, for example," she said.
Balk says the 16 island nations are not the only places threatened by predicted sea-level rise. The study shows that nearly two-thirds of all cities with more than five million people are at least partly in the 10 meter coastal zone, including Shanghai, China; Mumbai (Bombay), India; Dhaka, Bangladesh; and Cotonou, Benin. In fact, 75 percent of people in the zone are Asians because of the nature of the continent's geography and its large population, but parts of every inhabited continent are affected.
Balk says the population in this coastal zone will continue to increase, especially in Asia. "Most of the growth we will see in Asia is not going to be in rural areas, but will be in urban areas. So that will further exacerbate this issue because the cities are already located in these low elevation coastal zones," she said.
The study appears in the April issue of the journal "Environment and Urbanization" and is unique in the way it defines coastal zones. Its focus on regions 10 meters or less above sea level contrasts with previous research that looked at areas within certain distances from the coast. The authors say their standard is a more accurate way to measure who is most at risk from rising oceans and stronger cyclones.
The study says easing climate change is the best means to deal with the problem, but adds there is not enough time for that to be the only solution. Migration away from the lowest elevation coastal zones is part of their answer. They recognize how costly, difficult, and disruptive this would be, but point out that small population shifts to higher ground can be important.
They also recommend coastal management that avoids policies, like China's, which favor coastal development to encourage exports. "This is a call to policymakers to be more active in thinking about settlement incentives or local planning to protect certain systems," she said.