The 150 year sea level record is tied to the dutch ordnance survey level. The linear trend is 14.4 cm/century (relative sea level change). The Netherlands ordnance survey datum is tied to underground benchmarks. A recent study shows that these underground benchmarks have a subsidence in the Den Helder area of approximately 5 cm/century. Fitting well with the subsidence models: Henk Kooi et al, Geological causes of Recent (~100 yr) vertical land movement in the Netherlands, Tectonophysics 299 (1998) 297-316 Here is a subsidence map. see also: http://www.ncg.knaw.nl/SubBZ/BeginSubBZ.htm This gives for the eustatic sea level change a value of 9 cm/century.
Comparison with New York
In the course of the observed time series in Den Helder some deviations of the linear trend are observed. The deviations can be attributed to the varying strength of the westerly winds due to the North Atlantic Oscillation. It is clear that a stronger westerly raises the level in Den Helder and lowers at the same time the level in New York on the opposite side of the Atlantic. Finally: Is the rise unprecedented? Here is a paleosealevel graph for Holland Hans Erren
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