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Preparing for Global Warming's Rising Tides

How climate change research on sea-level rise helps communities

People who live near the coast know a thing or two about environmental hazards. They know, for instance, the risks of hurricanes and those of storm-surge damage from other powerful storms. But now coastal communities are at growing risk from the effects of climate change, most notably the accelerated rise in sea levels.

Scientists' measurements show that sea levels around the globe have risen by about 1.3 inches per decade since 1990. Precise measurements from satellites as well as tide gauges indicate that this rise has accelerated over the past 20 years, up from the previous rate of  0.7 inch per decade in the last half of the twentieth century. New research suggests that if we continue pumping carbon dioxide into our atmosphere at a high rate globally, the water level along the coasts could rise another 2.6 to 5.3 feet in the next 100 years.

Rising Waters

Dr. Michael Kearney, a coastal scientist at the University of Maryland who studies climate change and coastal processes, points out that more than 100 million people around the world live within a mile of the sea. "The increased likelihood and extent of flooded areas, particularly from tropical storms, has a big impact on their livelihoods and the things they care about," he said. "Sea level has, since the middle of the nineteenth century, been rising. Anthropogenic [man-made] warming has accelerated it." Even at the current rate of increase, Kearney expects 40 to 60 centimeters (1.3 to 2 feet) of sea-level rise by 2030 to 2040."

Kearney said that wise planning based on climate research can help coastal communities adapt to rising waters. Sea levels will continue to rise no matter what, he said, but the extent of the rise will ultimately depend in large part on the emissions choices we make today. Planning for sea-level rise of 2 feet is far different from and less costly than planning for 5 feet of additional rise. Nonetheless, Kearney said, coastal communities can begin to make plans without spending very much, especially if they do so sooner rather than later. "2030 isn't that far from now," he said, adding that some leaders in coastal communities are looking at a host of responses, including steps to reduce emissions to reduce impacts and thereby the costs for detailed plans for community evacuation, and well-orchestrated plans for returning residents to their homes.

A number of government agencies, organizations, and businesses are studying and carrying out climate-related decisions. State and local governments are surveying the risks from future sea-level rise and determining the most likely types of damage to local infrastructure. They are recognizing, too, that some changes to roads and buildings can wait for a future renovation, and they may prohibit building new roads or homes close to the water because rebuilding after future storm damage will be prohibitively expensive.

Climate-change research has helped communities take steps now to prevent disasters in vulnerable coastal regions from being even worse: for example, removing large buildings that could topple during a storm surge or light poles that could block interstate traffic, one of the post-Katrina lessons learned in New Orleans.

Sea-level rise is caused by two main processes: thermal expansion of the oceans (the water expands as it heats up) and the shrinking of ice sheets and glaciers. About 80 percent of the global warming associated with carbon dioxide emissions has gone into raising the temperature of the oceans. Scientists know the oceans will continue to expand—and rise—because heat-trapping gases already in the atmosphere will continue to raise the temperature of the oceans. Ice sheets and glaciers also contribute to sea-level rise when they melt or chunks of ice break off into the sea. Recent research has shown that the major ice sheets (those of Greenland and Antarctica, which contain 23 feet and 197 feet of sea-level rise, respectively) are shrinking at a faster rate than they were a decade ago.

With tides and storms riding in on higher seas, there will be more tidal flooding and larger storm surges. Storms have already become more intense because of global warming, leading to heavier rain. All of these factors add up to increased coastal erosion. 

Sea-level rise is "going to happen to every coastal area around the world, not just here and there," Kearney said. "Some communities are drawing up plans to move forward." These plans don't have to cost much, he adds. Having long-range plans in place will help decision makers develop better ways to build more resilient infrastructure and help ecosystems that are vulnerable to rising water levels and more intense coastal storms. Economists say making such investments now is less costly than responding after the fact to storm damage made worse by inadequate building codes and out-of-date flood projection maps.

"You don't need a Ouija board to predict that sea-level rise is going to continue," Kearney said. "But the window of response is rapidly narrowing. As long as we do nothing, the worse and more costly it is going to get. It is not as if sea-level rise is going to sneak up on us, unless we allow it to." 


Miller, Laury, and Bruce C. Douglas. 2004. Mass and volume contributions to twentieth-century global sea level rise. Nature 428 (6981): 406–409.

Katsman, C., W. Hazeleger, S. Drijfhout, G. Oldenborgh, and G. Burgers. 2008. Climate scenarios of sea level rise for the northeast Atlantic Ocean: a study including the effects of ocean dynamics and gravity changes induced by ice melt. Climatic Change 91 (3–4): 351–374.

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