Sea levels are rising faster and higher in a 620-mile stretch of the U.S. east coast—including major cities such as Boston, New York, Philadelphia and Washington D.C. —than elsewhere around the world, federal researchers have found. For over two decades, sea levels in the area have risen at triple or quadruple the global average rate.
Most of the world will see sea levels rise by two to three feet over the next century. But seas in the aforementioned zone, labeled a “hotspot” by the U.S. Geological Survey (USGS) scientists who conducted the research, will rise an extra 8 to 11.4 inches.
These rising seas are expected to make storms more damaging and flooding more common in many areas near the coast. They also pose dangers to wetland ecosystems, the researchers found.
“Cities in the hotspot, like Norfolk, New York and Boston already experience damaging floods during relatively low intensity storms,” said Dr. Asbury Sallenger, USGS oceanographer and project lead. “Ongoing accelerated sea-level rise in the hotspot will make coastal cities and surrounding areas increasingly vulnerable to flooding by adding to the height that storm surge and breaking waves reach on the coast.”
The USGS researchers used floating sensors in the Atlantic Ocean to measure sea level changes over the past 60 years. Their study, recently published online in Nature Climate Change, confirms earlier predictions done with computer modeling, demonstrating that sea-level rise is indeed accelerating and that some spots on the globe will be more affected than others.
Scientists say that global warming is behind the sea levels rising, which is driven in part by melting glaciers and by the fact that sea water expands as it warms.
But oceans are complex, and sea-level rise isn’t a matter of simple displacement as happens when too much water is poured into a fish tank. Currents affect where waters flow, and shift as waters warm. Wind patterns also play a role. And a recent study of how the west coast will be affected by the Pacific Ocean’s rise found more serious impacts in Southern California, in part because along the northwestern U.S. coast tectonic shifting is expected to cause the land to rise.
Another study, also published in Nature Climate Change, looked at the peak sea levels that can be expected under different climate change scenarios. If global warming is limited to less than 1.5 degrees Celsius, they found, sea levels will only rise half as much over the next three centuries as they will if temperatures rise two degrees. A three-degree change could drive oceans up to 16 feet higher, the researchers found.
“Sea-level rise is a hard to quantify yet critical risk of climate change,” says Michiel Schaeffer of Climate Analytics and Wageningen University, lead author of the study. “Due to the long time it takes for the world’s ice and water masses to react to global warming, our emissions today determine sea levels for centuries to come.”
Even more moderate rises, like those expected along the east coast during this century, mean that storms will be more severe and clean-up more costly. “As an example, for New York City it has been shown that one meter of sea level rise could raise the frequency of severe flooding from once per century to once every three years,” said study co-author Stefan Rahmstorf of the Potsdam Institute for Climate Impact Research in Germany. “Coastal communities have less time to adapt if sea-levels rise faster.”
This has policymakers and insurers concerned. But some states have been slow to prepare for rising seas and storms to come. Lawmakers in North Carolina recently drew international attention for a proposed bill that would have banned state agencies from predicting how sea levels would affect the state’s coast. That bill, which local press reports said was driven by fears that property developers would shy away from coastline areas, was slightly rewritten after it was widely mocked as an attempt to legislate away reality.