sea level rise

Why all the angst over sea level rise?

Coastal flooding as sea level rises with future greenhouse gas emissions will rapidly get worse over the coming decades, according to the National Oceanic and Atmospheric Administration

In the past, powerful storms caused coastal flooding. But sea level rise will mean common wind events and high tides will more frequently cause ocean waters to spill into communities. Rising sea levels will make more and more cities progressively vulnerable to high tide flooding, which is rapidly increasing in frequency, depth and extent along many U.S. coastlines.

Rising sea level also will increase the salinity of coastal aquifers and impair water quality for coastal communities around the world, most of which depend on groundwater. Exacerbating matters, many coastal regions will face the double threat of sea level rise and sinking land.  

“One thing that always goes unrecognized is that sea level rise alone is not as dangerous as when it’s combined with vertical land motion, or land subsidence,” said Manoochehr Shirzaei, a geophysicist at Virginia Tech who studies the impacts of subsidence and sea level rise on coastal areas.

And that difference between the change in land elevation and the change in the sea surface level, called relative sea level rise, Shirzaei said, “can be really devastating.” 

With sea level rise alone, people living along vulnerable coastal areas could probably elevate their house by a meter and stop worrying. But land can sink rapidly, by four or five centimeters a year in some coastal regions, he explained. 

Under the worst case climate models, where nothing is done to curtail greenhouse gas emissions, sea level is projected to rise about 10 millimeters (0.4 inches) per year by the end of the century, Shirzaei said. In contrast, the rate of land subsidence could approach hundreds of millimeters in some places.

“That’s something that has to be paid attention to, if you care about the risk and hazard associated with sea level rise and flooding,” Shirzaei said. “But unfortunately, it doesn’t get as much attention as sea level rise itself.”

By the end of the 21st century, more than 1 billion people will live by the coast, he added. “As sea level rises and the land erodes, we will have less space for these people to live.”

Exactly how these climate impacts will affect people and the economy isn’t known, he said, because scientists haven’t yet figured out how to link socioeconomic and physical models. One thing is clear, though, Shirzaei said: “We have to take measures to reduce carbon emissions and slow down the warming of the climate.”

And those measures have to be coordinated at the international level, he said. “The problem is at a state that is past individual action.”

For more information on sea level rise, and relative sea level rise, see NASA’s Rising Waters

—Liza Gross

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