One wondered whether the faster sea level rise in the Mid-Atlantic North (MAN) region might be somewhat due to the choice of starting point, the year 1950. As I said, I am particularly interested in sea level change since then, but the choice can certainly affect how one perceives the trend. Let me do the same analysis as before (regional estimate for each of the four regions) but starting earlier in time. I’ll insist that each region cover only years with at least two stations reporting, which limits us to years after 1920 except for the Mid-Atlantic North (MAN), which I’ll cut off at 1920 anyway to match the other regions. Here’s what I got:
It’s easier to see how their trends compare by plotting the smoothed versions:
This makes it pretty clear that yes, the sea level along the MAN is rising faster than in the other regions, while along New England (NE) it’s rising slowest. This is in the long term, there are recent upturns of sea level rise in the Mid-Atlantic South (MAS) and Florida (FL).
I did the same analysis, but by a method I devised to adjust for vertical land movement. This doesn’t compute sea level, but something I call sea level excess, which is the amount above or below constant sea level rise at the same rate as the 1950-1989 average. If sea level is rising at a constant rate, then the sea level excess won’t be rising at all.
Here’s what I got:
Here are the smoothed values:
Sea level has tended to rise faster than the 1950-1990 rate, both during the early part of the century, and since around 1990. The exception might be Florida (FL) but there are years with insufficient data so such a conclusion is not warranted. This is yet another illustration of sea level (in this case, regional) showing a complex pattern of both acceleration and deceleration through the 20th century.
Quite fascinating is that although New England (NE) and Mid-Atlantic North (MAN) have very different overall rates (slowest and fastest, due to glacial isostatic adjustment), they have quite similar short-term fluctuations. So too do Mid-Atlantic South and Florida. This is easier to see if we plot their yearly values, but with the MAS/FL pair offset from the NE/MAN pair:
By using 1950-1990 to define a “reference trend”, we’ve shown how well their fast fluctuations match.
I’ll probably return to the previous plan, looking at sea level since 1950 for the other regions of the U.S. east coast. But who knows what might catch my interest? In any case, more to come …
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