I was asked:
Q: How did you get into something as interesting as sea-level data?
A: Short answer: I don't really enjoy watching other kids play ball.☺
Long answer:
It was really the fault of the Climategate anonymous whistleblower, and of James Hansen.
I don't watch much television, but one night I had a TV turned on, back in 2009, and I happened to channel-surf by the Late Night Show with David Letterman, and his guest was James Hansen. I heard Hansen tell Letterman that sea-level had long been rising at a rate of about 1½ mm per year, but that the rate had recently doubled to about 3 mm per year.
I thought that seemed odd, because I remembered having stumbled upon a NOAA web page with a list of sea-level trends at various places, and I didn't remember most of the numbers being that large. I recalled that some were even negative. So, out of curiosity, I searched for that web page, and found it again. This is it, though it has been updated:
https://tidesandcurrents.noaa.gov/sltrends/MSL_global_trendtable.html
This is probably the version I found:
I scrolled to the bottom, expecting to find an average... but it wasn't there.
It seemed strange to me that someone would go to the trouble of doing regression analyses of all those measurement records, yet not bother to calculate an average of them!
But I let it go, and didn't think about it again... until Climategate happened.
Climategate deeply shocked me. I'd always suspected that, like most problems, the climate problem was probably exaggerated. But I'd not dreamed that scientists would commit such brazen fraud.
Then I remembered James Hansen's claim, on Letterman, that the rate of sea-level rise had recently doubled to 3 mm/year, and I wondered whether it was true. I thought about all the lies revealed by Climategate, and wondered: if they had lied about those things, then what other things might they have also lied about? Like sea-level?
So I went back to that NOAA web page, and the first thing I did was calculate the missing "average" line from that list of GLOSS-LTT tide gauges:
https://tidesandcurrents.noaa.gov/sltrends/MSL_global_trendtable.html
It turned out that page is an exported Excel spreadsheet, so it was trivial to import it back into Excel and calculate the average... which was less than 1 mm/year. The median was slightly larger, but still much less than the numbers Hansen had claimed, and most of the sites showed nothing resembling a doubling in rate of sea-level rise.
I joined a climate skeptics email list, and posted my results. Someone promptly pointed out the very uneven global coverage, and how many sites are close together, and so are really measuring almost the same thing. That led me to calculate weighted averages, according to sites' distances from one another. I still found an average of only +1.133 mm/year (4½ inches per century).
Then came the 2010-2012 NC sea-level kerfuffle.
More recently I used a different approach to calculate a "global average" rate of coastal sea-level rise, and I found it to be about 1½ mm/year (6 inches per century):
https://sealevel.info/avgslr.html
And so forth, and onward, gee whiz!
Dave Burton
1/24/2023