Here’s an interesting presentation on North Carolina sea level that sheds light both on the long term geological history of the area and on why it’s been subjected to particular study. The author is Stanley Riggs, a veteran specialist on the geology of the North Carolina barrier islands.
The PPT nicely shows the steady rise of sea level in the North Carolina area during the Holocene with many good illustrations and pictures, including, for example, stumps in the present day surf. It illustrates how barrier islands have migrated during the process of sea level rise, showing the importance of hurricanes in the migration process. It contains some useful pictures showing the impact of sea level rise on coastal highways, sharply raising questions about the viability of settlements on a surf line that is moving on century scale. Because these settlements are important to North Carolina, it seems to have been a center of this sort of research.
They ask: “SHOULD WE ENGINEER OUR DYNAMIC COASTAL SYSTEM TO KEEP UP WITH THE ONGOING RISE IN SEA LEVEL?” or “OR SHOULD WE BEGIN ADAPTING TO THESE CHANGES NOW TO MAINTAIN A SUSTAINABLE COASTAL SYSTEM AND ASSOCIATED ECONOMY!”
Regardless of one’s position in the climate debate, this sort of question needs to be squarely faced by coastal communities.
One of Riggs’ slides contains the following information on shoreline recession for Mainland Dare County (Roanoke Island also shown is similar:
1817-1851 1700 ft 50 ft/yr
1851-1954 400 ft 4 ft/yr
1954-1997 200 ft 5 ft/yr
I was surprised by the relatively high rate of shoreline recession in the early 19th century relative to more recent recession but I’m not familiar enough with the data to comment on this.
In a supplementary slide, Riggs refers to estimates from Horton, Kemp et al on sea level rise rates as follows:
18000–11000 BP – 49 in/century
11000—8200 BP – 34 in/century
8200-3500 BP – 8 in/century
3500—200 BP – 4 in/century
1800-1900 AD – 8 in/century
1900—2000 AD – 16 in/century
1980—2000 AD – 18 in/century
The Riggs presentation is not dated, but the pdf was made in January 2010 (but it obviously might be an older PPT and merely converted to pdf at that time.)
The new Kemp et al 2011 study draws different conclusions on the past two millenia, stating:
Sea level was stable from at least BC 100 until AD 950. Sea level then increased for 400 y at a rate of 0.6 mm/y [2.3 in/century] followed by a further period of stable, or slightly falling, sea level that persisted until the late 19th century. Since then, sea level has risen at an average rate of 2.1 mm/y [8.2 in/century] representing the steepest century-scale increase of the past two millennia. This rate was initiated between AD 1865 and 1892.
and again later:
From at least BC 100 until AD 950, sea level was stable (0.0 to + 0.1 mm/y). Between AD 850 and 1080 the rate of sea-level rise increased to 0.6 mm/y (0.4 to 0.8 mm/y) for the following 400 y. A second change point at AD 1270–1480 marked a return to stable, or slightly negative, sea level (−0.2 to 0.0 mm/y), which persisted until the end of the 19th century.
Between AD 1865 and 1892 sea-level rise increased to a mean rate of 2.1 mm/y [2.3 in/century] (1.9 to 2.2 mm/y) (12). Sea-level variations in the last 2100 y did not exceed ~0.25 m until the onset of the modern rise in the late 19th century. The modern rate of sea-level rise was greater than any century-scale trend in the preceding 2100 y; a conclusion that is independent of the GIA correction applied.
What accounts for the differences? Dunno for sure, but it might be due to the Kemp et al includes an isostatic adjustment:
A constant rate of subsidence (with no error) was subtracted from the Sand Point (1.0 mm/y) [3.9 in/century] and Tump Point (0.9 mm/y) [3.5 in/century] records.
Quantitatively, the isostatic adjustment is obviously not insignificant for the past two millennia.
The desire to tease a centennial signal out of such coarse data has obviously led the academics into increasingly complicated and more problematic statistical methods. Like their decision that the “appropriate factor” for downweighting was 10. An unsavory statistical process, to say the least, almost as unappetizing as pulling a Rabett out of a hat.
For readers interested in the topic of sea level rise in North Carolina, I urge them to look at the predecessor geological literature to try to get some footing on the actual data prior to the application of obscure and mannomatic methodologies.