Sea level rise and NASA
As mentioned in last month's blog, I now started to look into the Global Warming controversy.
Most of the issues are extremely complex and hard to judge for outsiders. But when reading discussions, I stumbled on a comprehensive overview of global sea tide gauges which measure directly the rise and fall of sea water with respect to the coast:
Please do click on the link and hover your mouse over each graph to see its location. It's very neat: with one mouse click you get a full page plot and with one more click you can see the most recent update directly on the data source site.
What was surprising to me, is that overall the tendencies look quite steady over the last hundred years [edit: even over 150 years], including the last decades.
When combined with GPS data, we can also estimate the net sea level rise; however I found that that isn't yet very robust. Here follow two examples (available for some stations, from "Nearby GNSS Stations from SONEL"):
- Warnemunde2: Sea level relative to land ca. +1.25 mm/year and GPS Land height ca. +0.65 mm/yr. Thus "absolute" sea level rise ca. 1.9 mm/yr.
- Marseille: Sea level relative to land ca. 1.28 mm/yr, GPS Land height very messy signal from two detectors, but apparently ca. 0 mm/yr. "absolute" seal level rise ca. 1.3 mm/yr.
I think that in principle such outcomes should be approximately the same, but overall it appears to be around 1.5 mm/yr over the last decades. That's not far off from what I also saw stated in several video presentations on Internet such as by Thomas Wysmuller, who found 1.1 mm/yr from such data.
Now compare that information with some NASA news from last year (sorry to pick on NASA again, it just happened to catch my attention!):
'Global sea level rise has been accelerating in recent decades, rather than increasing steadily, according to a new study based on 25 years of NASA and European satellite data. [..] If the rate of ocean rise continues to change at this pace, sea level will rise 26 inches (65 centimeters) by 2100 -- enough to cause significant problems for coastal cities, according to the new assessment by Nerem and colleagues.' The paper by Nerem et al in 2018 is not hyperlinked there.
The News commentary by Weeman and Lynch says further:
' "The tide gauge measurements are essential for determining the uncertainty in the global mean sea level acceleration estimate,” said co-author Gary Mitchum, University of South Florida College of Marine Science. “They provide the only assessments of the satellite instruments from the ground.” Others have used tide gauge data to measure sea level acceleration, but scientists have struggled to pull out other important details from tide-gauge data, such as changes in the last couple of decades due to more active ice sheet melt. ' (emphasis mine).
It's no doubt open for discussion if in turn they reliably extracted such information out of the satellite data. Especially as their suggestion of an [alarming] accelerating trend since the last decade of the 20th century seems hard to reconcile with the expressed opinion in an article by Holgate in 2007:
' Although the mean rate of change of global mean sea level is found to be greater in the first half of the twentieth century, the two rates are consistent with being the same at the 95% confidence level, given their individual standard errors. However, a greater rate of rise in the early part of the record is consistent with previous analyses of tide gauge records which suggested a general deceleration in sea level rise during the 20th century. ' (again emphasis mine)
The Holgate article which also shows the cyclical nature of sea level rise - periods of acceleration followed by periods of deceleration - is not referenced in the Nerem paper. And strikingly, according to Nerem and colleagues 'The rate of sea level rise in the satellite era has risen from about 0.1 inch (2.5 millimeters) per year in the 1990s to about 0.13 inches (3.4 millimeters) per year today' - which is about double from what appears from the tide gauge data combined with GPS!
I should perhaps make clear what my first take is on this matter. In my humble non-expert opinion it's very tricky to establish a clear trend change from the data, be it noisy gauge data or imprecise satellite data. And while Nerem may well be "right" simply because the faster melting land ice should have gone somewhere, it's probably at least in part due to natural causes. I don't doubt that such an acceleration is consistent with the start of catastrophic climate change but I'm pretty sure that it's also consistent with natural, cyclical variation.
The NASA webpage doesn't permit discussion but the corresponding Facebook page does; and it should not surprise that it led to serious scientific discussion, as we can ... not see! For, regretfully, the most pertinent comments were the victim of stealthy censorship as shown here: http://sealevel.info/nasa_shadowbans/
Indeed, https://www.facebook.com/NASA/videos/10156020865631772/ now has more than 1000 comments, with "David Burton" at the top of the list. But when clicking on comments, I see only 436 comments displayed (after some work), and I can find none of David Burton. The visible remainder of comments is a mixture of opinions with little scientific content.
I find that really not OK. And it enhances the bad impression that I got earlier, as discussed in last month's blog. Should their Facebook post with suppressed pertinent comments be marked as "Fake News"? That would be a bit exaggerated I think. But it's certainly "Borderline" in view of their discussion manipulation as well as the overly sensational headline and video. The accompanying short video clip states as an unusual scientific fact:
' For the past 25 years, sea level is not only rising, but the rate of that rise is getting faster. '
and the headline states:
' This acceleration is driven mainly by increased melting in Greenland and Antarctica, having the potential to double the total sea level rise projected by 2100. '
I'm afraid that many young Facebook users will swallow those statements as established scientific facts that prove beyond doubt that nature is spinning out of control.
Loosely adopting the Washington Post's Pinocchio rating system, I herewith award the NASA department that is responsible for this communication 3 (three) Pinocchios for this news item of last year. The maximum number of 5 corresponds to outright lies, and "all judgments are subject to debate and criticism from our readers and interested parties, and can be revised if fresh evidence emerges." [- revised to only 2 Pinocchios for the overly sensational presentation and their unfair, misleading discussion thread; see Afterword hereunder.]
Comments (including corrections) are welcome here below. :-)
PS. Little bug: if commenting does not work, try refreshing the page - but copy your comment first!
Afterword February 2020. With InfoCheckers' own independent analysis here (and in consideration of the additional analysis here), it is found that the statement "For the past 25 years, sea level is not only rising, but the rate of that rise is getting faster" is maybe a bit incomplete, but essentially correct.