Could Flooding Finally Wake Americans Up to the Climate Crisis? - by David Roberts

One of the perennial discussions in climate circles is about which impacts will break through the noise and apathy to finally galvanize people to do something about the problem.  The usual suspects are droughts and food shortages, since they’re expected to bite first.

My own dark-horse candidate has been sea level rise.  As I wrote last year, the carbon in the atmosphere today has already “locked in” enough sea level rise to swamp hundreds of coastal cities and towns around the world.  Some 316 settlements in the lower 48 states, with a cumulative 3.6 million residents, are already doomed.  If we continue on our current trajectory, 1,400 American towns and cities will eventually, inevitably be lost to the ocean.

But when?  Problem is, we don’t know.  It’s likely in the next several hundred years, but it could be a thousand.  The science is maddeningly difficult to nail down.  It’s not exactly enough to get people fired up.

But! It turns out rising sea levels don’t have to rise very much before they get annoying, and then burdensome, and then overwhelming.  This fact is well-captured in some interesting new research from NOAA scientists William Sweet and Joseph Park. (Over on Mashable, reporter Andrew Freedman has a great write-up.)

Rather than focus on average sea level, researchers focused on the frequency of “nuisance-level” flooding events, defined as water one or two feet higher than local high-tide level.  (The name is deceptive — it’s expensive to clean up and repair after such events, especially if they reach vulnerable infrastructure.)  Two important insights emerged.

First, the frequency of nuisance-level flooding is rising faster than average sea level, and on a non-linear trajectory.  Such floods are already five to 10 times more common than they were 50 years ago.  Long before the sea rises far enough to literally swamp coastal towns and cities, it will rise enough to bedevil them with frequent floods.

Second, lots of American cities and towns are on the verge of serious trouble.  The researchers identified 30 or more days of nuisance-level flooding a year as a “tipping point,” the level at which flooding goes from burdensome to overwhelming.  The tipping point has already passed in some places and it’s rapidly approaching in others.

In addition to [Washington] D.C. and Annapolis, Maryland, other cities that will soon exceed their tipping points include Baltimore, Maryland; Charleston, South Carolina; and Atlantic City, New Jersey.  These locations should pass the 30-day flood-frequency benchmark within the next five years, the study found.

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