Dave Burton writes:
Those NASA guys are tricky.
Click the “Update: Sea level change / Ocean rising at 3.42 mm per year” link in their latest Newsletter and you’ll see the big, bold “3.42 mm/yr” near the top of the web page, and two very similar-looking graphs of sea-level: one from satellites, and one from tide stations.
Since only one rate of sea-level rise is shown, the casual observer is likely to think that the same 3.42 mm/yr rate applies to both graphs. Here’s a screenshot:
But the 3.42 mm/yr rate does not apply to both graphs. Look closer at the scales, and do the arithmetic, and you’ll realize that the 2nd graph is actually showing a slope of only about half that claimed 3.42 mm/yr.
Since the late 1920s it shows a slope of about 1.8 mm/yr, with no evidence of acceleration. But those tricky NASA guys scaled it to look like the slope is about the same as the first graph. It’s pretty obvious why they didn’t show a rate of sea-level rise for that graph.
What’s more, the second graph is not really just from tide gauge data; it’s from tide gauge data inflated by a +0.3 mm/yr GIA “adjustment,” to subtract off the rate by which the sinking ocean floor is hypothesized to reduce sea-level rise. The real rate of coastal sea-level rise from averaged tide gauge measurements is only about 1.4-1.5 mm/yr (under six inches per century), and that rate hasn’t increased since the late 1920s.
What’s more, even NASA’s first graph, of satellite altimetry measurements, is deceptive. Like the second graph, it shows a rate which has been inflated by the addition of model-derived GIA, plus by combining the various satellite measurements it also hides the wide variations in rates measured by different satellites.
AVISO has a much more informative graph of satellite altimetry measurements, showing a rate of +2.87 mm/yr, without GIA adjustment, here: