Someone calling himself “Giordano Bruno” is determined to convince us sea level rise isn’t a problem, and in particular it isn’t happening at an increasing rate. He’s at it again at WUWT. I think it’s a self-flattering pseudonym for Albert/Alberto “making up stuff Parker/Boretti,” but let’s set aside his nom de plume and look at his “evidence.”



It consists of this:

For the specific of the United States, the average relative sea level rise is constant at about +1.7 mm/year mostly due to subsidence totaling on average less than 20 centimeters sea level rise by 2,100. Figure 1 – a, b) Relative sea-level rise for the United States (images from [2] downloaded May 16, 2016) over the time window of data 1930 to 1999 and 1930 to 2014. The relative rates of rise are quite similar, somewhere larger and somewhere smaller, to demonstrate they haven’t accelerated that much. Over this century, the rates of rise of sea-levels haven’t accelerated that much in the United States. Similarly, in every other area of the world where they are measured.

What he’s doing is comparing the linear rate of (local) sea level rise from 1930 through 1999, to that from 1930 to the present (basically, through 2015). He concludes that they’re “quite similar” and that establishes “the rates of rise of sea-levels haven’t accelerated that much in the United States.”

I’ve mentioned before that it’s a bad idea to compare trends from two time spans that use most of the same data. In this case the two time spans he considers have 70 out of 86 years (81%) in common, so it’s no surprise they’re “quite similar.” And he doesn’t actually show the differences between rates, he just shows a graph of each and says “quite similar.” How precise!

Here’s a better idea: let’s compare the 1930-1999 episode to the 2000-2015 episode without overlap (the 2nd section is all too brief, but we’ll humor “Bruno”). For each series, I’ll fit a continuous piecewise linear trend — piecewise linear to get a linear slope estimate for each span, continuous so we’re not fitting a “broken” trend. Then I’ll compute the difference between the rates of sea level change during the two separate time spans. I’ll also omit inland stations; I’m not really interested in what’s going on along the St. Lawrence River. I’ll plot the results as dots, using red for rate increases and blue for rate decreases. Here it is:

It’s easy to see that most stations have shown an increase in the rate of sea level rise, especially on the eastern seabord. The largest rate increases (the biggest red dots) are from Cape Hatteras to Cape Cod, part of the “northeast hotspot” identified by Sallenger et al., which “Bruno” doesn’t seem to believe in.

At these stations, the rate of sea level rise has increased from an average of 1.38 mm/yr during the 1930-1999 span, to 2.16 mm/yr during the 2000-2015 span. That’s an acceleration — an additional 0.78 mm/yr. Much of the reason for the low average rate is the local fall of sea level at stations in the far northwest, due to glacial isostatic rebound; here are the actual rates (not rate differences):

If we restrict our attention the the Eastern U.S., the rate of sea level rise has increased from an average of 2.89 mm/yr during the 1930-1999 span, to 4.75 mm/yr during the 2000-2015 span. That’s a sizeable acceleration — an additional 1.86 mm/yr.

As an aside, I wonder why local sea level appears to be decelerating in the far northwest, especially Alaska. It makes me wonder: is it possible that the shrinking of Alaska’s glaciers has increased the rate of glacial isostatic rebound, thereby increasing the rate of sea level fall? I don’t know nearly enough about glacial rebound even to know whether or not such an idea is plausible — but it’s interesting to consider.

Despite “Bruno’s” efforts, not only does the ocean continue to rise, that rise is accelerating. Not only does it threaten coastal areas in the U.S. (especially the east coast), the rate of increase along the eastern seaboard has accelerate even more than in other areas. And despite the ease with which he garners praise from the readers of the WUWT blog, when it comes to his understanding and his analysis of sea level rise, we are not impressed.

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