U.S. coasts — California faces fast sea level rise: “hot spot” already in Atlantic

Much of California could suffer sea level will rise of about a meter (39 inches) this century — faster than the global average — while there is already a “hot spot” of sea level rise on a densely populated 1,000 km (600 mile) strip of the east coast, studies show.

The separate reports are new evidence that city planners, governments, engineers etc will have a tangle of priorities and competing claims for money if sea level rise accelerates since the effects won’t be the same everywhere.

The west coast projections, in a report by the U.S. National Research Council, are bad news for low-lying areas such as San Francisco airport or Venice Beach (below) in Los Angeles, which might look ever more like the flood-prone Italian city of the same name.

And a recent acceleration of sea level rise along a strip of the east coast, to 3 to 4 times the global average (of about 3 mm a year), is affecting cities including New York and Boston, according to scientists writing separately in Nature Climate Change.

A slowdown of the Gulf Stream system that sweeps warm water northwards in the Atlantic seems to be the cause. (…of course that doesn’t mean that seas off the east coast can keep on rising at such fast rates throughout the century).

 

The west coast report also says that seas will rise by less than the world average in Northern California, Oregon and Washington. Yet other worries are that a big earthquake could cause subsidence that lowers the coastline by a meter in one gigantic jolt.

“Sea-level rise is uneven and varies from place to place. Along the U.S. west coast it depends on the global mean sea-level rise and regional factors, such as ocean and atmospheric circulation patterns, melting of modern and ancient ice sheets, and tectonic plate movements,” the council said.

For the California coast south of Cape Mendocino — a spot north of San Francisco — the committee projects that sea level will rise by 42 to 167 centimeters by 2100 (so a meter is about the middle of the range). For Washington, Oregon, and California north of Cape Mendocino, sea level is projected to rise by 10 to 143 centimeters by 2100, it said.

On the east coast, scientists write that “Our analyses support a recent acceleration of sea level rise on about 1,000‚ÄČkm of the east coast of North America north of Cape Hatteras. It said the hotspot was “consistent” with sea level rise expected by a slowdown of the Gulf Stream.

The report about California projects that world sea level will rise by 50 to 140 centimeters by 2100, a lot more than the estimate of 18 to 59 cms by the U.N. panel of climate scientists in 2007, which also said there was a possible extra of up to 20 cms if there are big changes in ice sheets in Greenland or Antarctica.