The Search for Acceleration, part 5, The NetherlandsJuly 6, 2013
This is part 5 of a series of posts in which I am searching for a large acceleration in sea level rise rate in the latter part of the 20th century that could reconcile the 1.8 mm per year average rise rate for the century attributed to tide gauge data and the approximately 3 mm per year rise rate for the tail end of the century attributed to the satellite data.
The global sea level rise rate is swamped by other effects. In most locations the yearly rise and fall of the oceans is greater than the 18 cm of sea level rise during the entire 20th century. Geologic effects (e.g. glacial isostatic adjustment or plate tectonics) add to local and regional rise rates, making them deviate greatly from the global rise rate.
I am working under the theory that by detrending sea level data from individual (local) sites and averaging with other regional sites it should be possible to extract changes in regional sea level rise rates while bypassing the question of what the “true” sea level rise rate is in that region.
Nobody cares more about sea level rise than the folks in The Netherlands. They have been dealing with the issue long before anybody was worried about global warming, since 20% of the country’s area is below sea level. They have excellent sea level data spanning nearly 150 years. This map shows land elevations in the Netherlands as well as the location of seven high quality tide gauge stations.
Here is the PSMSL data for those seven locations…
As I have mentioned before, I am not concerned with finding the sea level rise rate, but rather the change in sea level rise rate. But this set of data averages out to have a 20th century rise rate very close to the commonly reported tide gauge derived average of 1.8 mm/year. (Click on image if animation does not advance.)
These seven stations also have very coherent yearly signals, created from the 2, 3, 4, 6 & 12 month Fourier components. Note that the magnitude of the yearly signal is nearly the same as the entire average sea level rise for the entire 20th century.
Now, lets consider the weighted, detrended data to derive the relative acceleration. (Click on image if animation does not work.)
The Netherlands tide gauge data if of the highest quality and long duration. All seven stations cover 1870 to the present. The detrended sea level rise rate does indicate that the overall sea level rise rate for last two decades of the 20th century was a few mm per year greater than the century’s average. However, this very reliable data also indicates that the sea level rise rate at the beginning of the century was just as high as the end of the century.
20th century rise rate average of 1.8 mm/year
Satellite data (about 3 mm/year)
RLR tide gauge data