Sea level rising fast along American East Coast – or not

A new study published in Nature Climate Change claims there is a sea level rise “hotspot” along the East Coast of the United States.  The gullible press picked up on the story.  The lead sentence from the Arizona Daily Star reads: “From Cape Hatteras, N.C., to just north of Boston, sea levels are rising much faster than they are around the globe, putting one of the world’s most costly coasts in danger of flooding, government researchers report.”

The paper is Asbury H. Sallenger Jr, Kara S. Doran, & Peter A. Howd, 2012, Hotspot of accelerated sea-level rise on the Atlantic coast of North America, Nature Climate Change (see full paper here).

Sallenger et al. claim that during the periods 1950–1979 and 1980–2009 the rate of sea level rise in this northeast hotspot was ~ 3–4 times higher than the global average.  Their contention is based on computer modeling, statistical analysis, and extrapolation of data.  “We test the hypothesis that a statistically significant observed northeast hotspot of accelerated sea level rise exists by determining its position and dimensions and comparing them with model projections. (See my post Statistical Significance in Science – how to game the system)

The computer games of Sallenger et al. are countered by real data.  Actual readings from tidal gauges show a record of deceleration of sea level rise (dated from the early 20th Century to present) in the following cities: Annapolis, Baltimore, Bar Harbor, Boston, Charleston, Eastport, Newport, and Portland, all in or near the alleged hotspot. Some other stations in the area, such as Atlantic City, Montauk, and New London, show a small increase in the rate of sea level rise.

(Reference: Houston,  Jr.  And  Dean,  R.G.,  2011,  Sea-level  acceleration  based  on  U.S.  tide  gauges  and  extensions  of  previous global-gauge analyses. Journal of Coastal Research,  27(3), 409–417.)

Sallenger et al. are hard-pressed to come up with an explanation for the “hotspot.”  They invoke this: “Climate warming does not force sea-level rise (SLR) at the same rate everywhere. Rather, there are spatial variations of SLR superimposed on a global average rise. These variations are forced by dynamic processes, arising from circulation and variations in temperature and/or salinity, and by static equilibrium processes, arising from mass redistributions changing gravity and the Earth’s rotation and shape.”

They miss a simple explanation: sediment compaction and subsidence from varying rates of groundwater withdrawal. Relative sea level depends in part on the geology of the area. That is superimposed on a regional, long-term sinking of the East Coast caused by isostatic rebound from the last glacial epoch, i.e., as the central part of North America rebounds from the weigh of the now melted continental ice sheet, it tilts the coastal area into the ocean producing an apparent sea level rise.

For a more detailed explanation of glacial isostacy see here.

For a broader perspective of sea level rise since the last glacial epoch see my post:  Sea Level Rising?

See also:
University of Arizona dances with sea level

Sea Level Rise in the South Pacific: None

Sea Level Rise Declining says EU

Obama parts the waters, sea level drops

Size matters in sea level studies

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