Reader “TLM” submitted a comment to this post about sea level rise. Let’s look at some of his (her?) statements.
It starts thus:
Not wishing to defend the original post too much, but I think you have slightly missed the point of the WUWT article. He is not saying that you should measure SLR on the basis of 6 years of data, …
“Measure SLR on the basis of 6 years of data” is exactly what he did. He fit a straight line, treated us to a graph showing it, and reported the trend rate. I quote: “Since December 2009, the sea levels have declined in both Washington DC and The Battery NY, -3.3 mm/year in Washington DC and -10.7 mm/year in The Battery NY.” But you tell us “He is not saying that you should measure SLR on the basis of 6 years of data“?
… he is questioning Sallenger’s method of comparing the first and second halves of periods of 60, 50 and 40 years when there is an apparent sinusoidal periodicity of 30 – 60 years, which is a reasonable point to investigate, but not proved in his article (or even addressed properly to be frank!).
To do so he chooses to “measure SLR on the basis of 6 years of data.” He doesn’t establish any purported “sinusoidal periodicity.” He certainly doesn’t test Sallenger’s result with sea level, but with sea level rate which he gets from 6 years’ data.
If he had compared sea level to what’s expected from Sallenger’s method, say, the 2nd half of the 60-year split interval at New York, we’d be looking at this:
The red dotted line is the extrapolation of the 1980-2009 trend, the big blue dot is the average sea level since 2010. Since then, mean sea level at New York (the Battery) has been 12.7 mm higher than what would have been expected based on Sallenger’s 2nd-half-of-60-year-period analysis.
His 6 years of decline is simply looking at what has happened since the end of the data analysed by Sallenger in 2009. Which is, of course, far too short a period to determine anything!
I have to say, looking at the actual data there does not seem to be any noticeable acceleration in the Tide Gauge data nor the satellite data in any record I have seen. …
The most trusted global sea level record based on tide gauges is that from Church & White. The monthly data look like this:
Annual averages, together with a straight-line fit, look like this:
If we subtract the linear fit to compute residuals, we’ll get a much clearer picture of its departures from linear increase at a constant rate. It’s this:
That’s “noticeable acceleration.”
Taking individual tide gauge records from PSMSL (the Permanent Service for Mean Sea Level), you needn’t look any further than the very first one they list (for Brest, France) to see this:
That too is “noticeable acceleration.”
What should we conclude? That you feel qualified to lecture us on sea level rise, but when it comes to the most reliable global data based on tide gauges or the very first tide gauge data set listed by PSMSL, you haven’t seen them?
They gauges all seem to show a pretty monotonic rise – and usually less than the satellite data seems to show. …
Perhaps you meant something other than “monotonic.”
If we apply changepoint analysis to the Church & White data set, it indicates its most recent slope change about 1999:
The slope of the most recent segment is +4.1 mm/yr. Taking the two data sets used by “Bruno,” the rate at New York over the last 50 years is +3.4 mm/yr, that at Washington DC is +3.3 mm/yr. All of which belies your claim of “less than the satellite data seems to show.”
… Some researchers have tried to infer acceleration based on estimations from proxies for pre-gauge data, but splicing proxy data and direct measurements has a rather dodgy history and probably best avoided!
“Dodgy” describes the strategy of dismissing evidence you don’t want with nothing more that the insult “dodgy.”
Read the literature, conclusions of acceleration based on proxy data don’t rely on combining them with recent direct measurements anyway.
I think it is better to rely on the actual measurements we do have, which globally do not show any significant increase in the rate of rise.
Your saying they do not, don’t make it so.
Sallenger chose to concentrate on a “dynamic hotspot” of acceleration in north east USA but that just seems to be cherry picking locations rather than time periods! I don’t think you can prove “dynamic sea level rise acceleration” from just that data, although it might be consistent with dynamic rise acceleration if it is actually occurring.
Have you even read Sallenger et al? They make it clear at the outset (in the abstract even) that they’re not “looking for a hotspot” — they’re seeking to “verify predicted patterns” which are “forced by dynamic processes, arising from circulation and variations in temperature and/or salinity, and by static equilibrium processes, arising from mass redistributions changing gravity and the Earth’s rotation and shape.”
The intimation that they’re “cherry picking locations” is both false, and a cheap shot.
I been running my own analysis of SLR based on the CU Satellite Data and discussed it in a brief email exchange with Dallas Masters. The trend rate of rise is a very consistent 3.4mm per year +/- 0.4mm. Most of the excursions from this are associated with ENSO and the rate is currently a bit higher than the past because of the end point in the recent El Nino. This is, of course, with an isostatic adjustment of 0.3mm per year (making it more akin to a rate of growth in sea level volume rather than height).
The average rate of rise in the apparent sea level (what you would actually see at the coast) is 3.1mm +/- 0.4mm per year. Looking at start and end points in ENSO neutral periods, the trend rate is between 2.8mm and 3.0mm a year. The rate of growth has been higher in the west Pacific and Indian Oceans, where tide gauge data is very poor, which probably explains the difference between satellite data and the tide gauges.
Considering your false statements, your mischaracterization of the WUWT post by “Bruno,” and your apparent unfamiliarity the most basic data sets, perhaps you’ll understand that we’ll seek elsewhere for insight about sea level rise.
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