The Search for Acceleration, part 2: East Coast of North AmericaJune 24, 2013
The original detrended sea level rise rate graphs for this post was off by a factor of 12!. This greatly changes my conclusion. Incorrect information is now crossed out and is followed by corrected information in red.
This is part 2 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.
East Coast of North America
Conclusion: There is no sign of an acceleration in the sea level rise rate in the tide gauge data from the East Coast of North America.
Conclusion: The tide gauge data for the East Coast of North America that covers that satellite sea level data era (1993 to present) does show a rise rate that is significantly higher than the tide gauge data rise rate for the 20th century. But the sea level rise rate in the 1930s through 1940s and around 1970 was as high or higher.Whether or not this data reconciles the difference between the 20th century tide gauge rise rate average and the satellite rise rate average is still ambiguous.
I have selected the East Coast of North America, for no particular reason, as the first region to analyse. I looked for tide gauge data along the coast such that it covered at least the period from 1960 to 2008 with 90% of all monthly data accounted for. Usable sites ranged from Nova Scotia to Georgia.
The following plot shows the qualifying data spread out for easy comparison. The key at the right shows the associate RLR data files.
As I mentioned above, I am not concerned with finding the sea level rise rate, but rather the change in sea level rise rate. However the following data for the East Coast of North America is interesting because it shows an averaged sea level rise rate for the 20th century that is close to the satellite derived sea rate for the end of the 20th century. This is will not be the case for most regions around the world. If you squint the right way you can also see the change in rise rate around 1930 that shows up in the various iterations of Church and White’s derivations of 20th century sea levels.
The last frame of the detrended data animation is worth repeating (see below). Notice that there is no evidence of an extreme or consistent increase in the sea level rise rate in the last two decades. The rise rates were as great or greater in the 1940s, 1950s and 1970s than they were in the 1980s, 1990s and 2000s. However, at least part of the satellite era (1993 to present) tide gauge data may be more than 2 mm/year greater than the average for the 20th century. It is safe to say that the tide gauge data from the East Coast of the North America does not reconcile the difference between the 20th century rise rate average (about 1.8 mm/year) and the satellite measured average (about 3 mm/year) Whether or not this data reconciles the difference between the 20th century tide gauge rise rate average and the satellite rise rate average is still ambiguous.