Sea Level Rise: U.S. East Coast (I)

A new paper by Piecuch et al. looks at how sea level rise has differed from place to place along the east coast of the U.S. There’s a nice write-up about it in Science Magazine.

They divide the U.S. east coast into three regions, with the separation points being Cape Cod (in Massachussetts) and Cape Hattaras (in North Carolina), and conclude different rates of sea level rise for each, with the space between the capes (which they call the “Mid-Atlantic Bight”) showing the fastest increase:

Rates of change along the eastern coast of the USA (the US East Coast) during the past century were spatially variable, and relative sea level rose faster along the Mid-Atlantic Bight than along the South Atlantic Bight and the Gulf of Maine.

They not only attribute the bulk of the difference to glacial isostatic rebound, they get more specific about where it’s strongest:

Rates of coastal subsidence caused by ongoing relaxation of the peripheral forebulge associated with the last deglaciation are strongest near North Carolina, Maryland and Virginia.

To get an idea how sea level is affecting different regions of the U.S. east coast, I calculated the trend rate (the rate of sea level rise) during the period from 1980 to the present for each station with enough data to get a decent estimate. I then compared each individual station’s rate to the overall average rate, plotting dots for each, blue for those where sea level is rising faster than average, red where it’s rising slower than average:

On this basis I divide the coast into four regions. The one with the fastest sea level rise is the one I call “Mid-Atlantic North” (MAN for short), and extends from New York City down to about Cape Hatteras, about the same as the “Mid-Atlantic Bight” region of Piecuch et al. The slowest sea level rise turns out to be what I’ve called “New England” (NE), similar to their region “Gulf of Maine”. What they call “South Atlantic Bight” I’ve split into two regions, the “Mid-Atlantic South” (MAS) and Florida (FL).

Having defined my regions, I can form a composite for each based on its tide gauge data. I’m particularly interested in what has happened since 1950 (after all, a lot of people seem interested in recent sea level acceleration). I took my monthly values for each region and computed yearly averages, which gave me this (different regions in different colors using different symbols):

Clearly they all see sea level rise. Clearly they all share some fluctuations (they are, after all, part of a larger region called the U.S. east coast). But just as clearly they don’t all seem to be changing at the same rate. This is perhaps easier to see if I smooth the data (using a lowess smooth):

Now we can see that region 1 (New England) is rising slowest, region 2 (Mid-Atlantic North) fastest.

More to come …

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One response to “Sea Level Rise: U.S. East Coast (I)

  1. A quick comment. You said, “we can see that region 1 (New England) is rising slowest, region 2 (Mid-Atlantic North) fastest” but that ordering seems to be true of the amount of rise and the overall rate of rise since 1950 but not of the current rate of rise. At the right of the graph, Florida and Mid Atlantic South seem to be currently rising at the highest rate.