NOAA — Straight Talk on Sea Level Rise

Guest Essay by Kip Hansen


North_Atlantic_RSLR_TrendsThe National Oceanic and Atmospheric Administration has some rather useful features on its web site.

One of these is the Tides and Currents which is part of its Center for Operational Oceanographic Products and Services.  Having spent most of the current century living at sea,  with my wife and occasionally a son or our daughter and granddaughter, on our venerable sailing catamaran, the Golden Dawn,   cruising the eastern coast of the United States, the Bahamas, the Turks and Caicos, Hispaniola, and the Spanish, U.S., and British Virgin Islands, I have made extensive use of its features.

For our purposes, the most used features were the predictions of the size and timing of tides in various places which often determined our sailing schedule to allow us to leave or arrive at various states of tides, often necessary to clear the bar to a harbor entrance, pass over a coral reef, or move through a pass between islands with, instead of against, the tide.   When sailing up the Hudson River in New York to our oft-times home, we must be aware of  the flow of the river, the current, which is tidal, going north on the incoming tide and south on the outgoing tide.  The current can be so strong against us that we often just anchor and fire up the barbie and put out a fishing line and wait for more favorable currents.

TurkeyPoint_Tide-StationThis is the data (excerpted) for Turkey Point on the Hudson.  The Kingston-Rhinecliff Bridge is in the background (looking south).  The tide chart shows four feet of tide, 100 miles north of New York City.

I am so familiar with the NOAA Tides and Currents site that I have tended to overlooked many features over the years.  In writing about SEA LEVEL: Rise and Fall, I have often used the Sea Level Trends portion of the site, like this one for Montauk, NY.


This graph is marked “Relative Sea level Trend”.  So, let’s start with a [hopefully] cute little “Pic-torial” (a picture-based tutorial) on the “what and how” of Relative Sea Level – it should only take 60 seconds or so to view and read:

What Exactly is Relative Sea Level (rise or fall)?

Tide stations measure Local (Relative) Sea Level, which refers to the height of the water as measured along the coast relative to a specific point on land

There are three possible combinations of relative sea level rise under current geological conditions:


This image shows Absolute Sea Level rising and its effect on Relative Sea Level at this Tide Gauge. As time goes by, the surface of the sea rises while the land remains motionless.  This results in Relative Sea Level rise.







This image shows Relative Sea Level rising but it is the land moving down, towards the center of the Earth, which is causing the sea surface to rise in relation to the land. Downward Vertical Land Movement causes Relative Sea Level rise.   Downward VLM is most often caused by movement of the Earth’s crust, compaction of the soil (which is often created by filling along the water’s edge for docks and piers) and in some cases, water and petroleum extraction.



This third image shows Relative Sea Level rising in the most usual case:  the sea surface is a rising a bit and the land is moving down a bit.  This is the case for most of the tide gauges on the US Eastern Seaboard, south of Boston.  Combined absolute sea level rise and downward VLM make Relative Sea Level rise.

NOAA pegs global absolute sea level rise at about 1.7 mm/yr.  VLM, along most of the US Eastern seaboard is of similar magnitude, in that it is measured in single-digit mm/yr, in most cases less than 5 mm/yr.


There is one more case found in the United States.  In many places in Alaska, the land is moving up at a greater rate than the sea surface is moving up (at its little 1.7 mm/yr.)  This causes the Relative Sea Level to be falling, though in reality it is the land rising faster than the surface of the sea is rising, thus the sea surface falls when measured against the shoreline.




Back to NOAA:

Now, back at the NOAA page for sea level rise in Montauk, NY.   At the bottom of that page, and all the other individual tide stations in this section of the site for Relative Sea Level Trends, there is a link to “Comparison of northern Atlantic station trends”.

The three images from that page have been made into the changing image shown below.


What this image shows are the long-term Sea Level trends for various ports along the Eastern Seaboard of the United States.  We see that they range from 1.5 mm/yr to almost 6 mm/yr.

Does this mean that the surface of the Atlantic Ocean is rising almost three times as fast in some places along the coast as in others?   That the surface of the Atlantic is rising three times as fast at the Chesapeake Bay Tunnel (5.92 mm/yr) as in Southport, N.C. (2.01 mm/yr)?

Short Answer:  No.

The fuller answer is supplied by NOAA itself, at the top of the page that displays these charts.   NOAA states clearly:

Relative Sea Level Trends for Northern Atlantic

The graphs compare the 95% confidence intervals of relative sea level trends. Trends with the narrowest confidence intervals are based on the longest data sets. Trends with the widest confidence intervals are based on only 30-40 years of data. The graphs give an indication of the differing rates of vertical land motion, given that the absolute global sea level rise is believed to be 1.7 +/- 0.3 millimeters/year during the 20th century.

These charts (and the original graphs of Sea Level change over time at individual tide gauges) do not show how much the surface of the sea is rising (or falling) — they do not show Absolute Sea Level rise or fall.  They show Relative Sea Level Trends for individual tide gauge locations and taken together simply demonstrate visually the differing rates of vertical land motion between the stations.

It is a pleasant surprise to find that NOAA, sometimes leaning towards Sea Level Rise catastrophe advocacy, not only explains this clearly, but goes on to reiterate that “global sea level rise is believed to be 1.7 +/- 0.3 millimeters/year during the 20th century” — a figure at great variance from that promulgated by NASA, which is currently claiming to show almost twice that at  3.0 +/- 0.4 mm/yr.

NOAA makes this perfectly clear:  Tide Gauges measure Local Relative Sea Level and its changes and reflect mostly the magnitude/rate of vertical land movement..  Thus, Tide Gauges, by themselves, are not fit for the purpose of determining Global Average or Regional Average Sea Level changes, rise or fall.

Bottom Line: 

  1. Tide Gauges and tide gauge-based data can only be used to measure Local Relative Sea Level and its changes. This data is the only sea level data of importance to localities.
  2. Comparing Tide Gauge sea level trends from one tide gauge to another, as the NOAA “northern Atlantic station trends” show, only gives us “an indication of the differing rates of vertical land motion”.
  3. In order for Tide Gauges and Tide Gauge data to be useful for determining actual changes in sea surface height (or rates of change in sea surface height), regionally or globally, the Tide Gauge station must have an associated GPS@TG (GPS at tide gauge) Continuously Operating [GPS] Reference Station mounted on the same structure as the tide gauge that will precisely determine vertical movement (VLM) of the tide gauge itself.

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Author’s Comment Policy:

The topic of this post is pretty narrow:  NOAA’s statement of what a comparison of tide station sea level trends shows — “an indication of the differing rates of vertical land motion” and not rates of the rising sea surface.

I have been writing a lot about Sea Level and its changes over the last couple of years, so will be happy to try to answer your questions and refer you to sources of information.

NB:  Sea Level Rise is an ongoing  Scientific Controversy.  This means that great care must be taken in reading and interpreting the past data, new studies and especially media coverage of the topic [including this essay] — bias and advocacy are rampant, opposing forces are firing repeated salvos at one another in the journals and in the press and the consensus may well simply be “an accurate measure of the prevailing bias in the field.”  (h/t John Ioannidis)

Address your comments to “Kip…” if you are specifically looking for a response – that way I’ll see it for sure.

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The Dismal Science

pretty well sums it up. is NASA claiming a greater rise because it is using satellites, which are only measuring absolute increases in sea level?

DS, covered in my essay PseudoPrecision in ebook Blowing Smoke, and in guest post here SLR, acceleration, and closure.


CO2 absorbed by water, lowers the boiling point of water. I do not see a climate model that allows for this?

Bryan A

It is a pleasant surprise to find that NOAA, sometimes leaning towards Sea Level Rise catastrophe advocacy, not only explains this clearly, but goes on to reiterate that “global sea level rise is believed to be 1.7 +/- 0.3 millimeters/year during the 20th century” — a figure at great variance from that promulgated by NASA, which is currently claiming to show almost twice that at 3.0 +/- 0.4 mm/yr.
NOAA makes this perfectly clear: Tide Gauges measure Local Relative Sea Level and its changes and reflect mostly the magnitude/rate of vertical land movement.. Thus, Tide Gauges, by themselves, are not fit for the purpose of determining Global Average or Regional Average Sea Level changes, rise or fall

It would seem to be pretty easy to verify the NASA figure by subtracting the NASA 3.0 +/- 0.4 figure from the NOAA tide gauge data which should yield the figure for the relative land height change then measure the actual land height change adjacent to the respective tide gauge locations. These two numbers should be identical +/-0.4

Great essay! I have been aware that subsidence has played a major role in ‘rising sea levels”, but never had it explained in such an articulate manner.
Great post!
Now if we could only convince Mr. Gore to read it😂

Richard G.

Another rarely mentioned variable, apart from subsidence, is sedimentation and the resultant displacement of water volume which results in an apparent sea level rise. Good luck quantifying that one.

richard verney

Maybe, but what about plate tectonics?
According to National geographic, the 2011 Japanese Tsuanmi lifted the seabed up by some 165 feet.

Japan’s devastating March 11 earthquake shifted the seabed by as much as 165 feet (50 meters)—the largest slip yet recorded, a new study says.


Research undertaken by Toshiya Fujiwara and colleagues has shown that the rupture zone (the area of the sea bed deformed by the earthquake) extended across an area measuring approximately 500km by 200 km.

I remember seeing some photos of this, but cannot quickly locate them. They are truly amazing.
Acccording to CNN

The powerful earthquake that unleashed a devastating tsunami Friday appears to have moved the main island of Japan by 8 feet (2.4 meters) and shifted the Earth on its axis.
“At this point, we know that one GPS station moved (8 feet), and we have seen a map from GSI (Geospatial Information Authority) in Japan showing the pattern of shift over a large area is consistent with about that much shift of the land mass,” said Kenneth Hudnut, a geophysicist with the U.S. Geological Survey (USGS).
Reports from the National Institute of Geophysics and Volcanology in Italy estimated the 8.9-magnitude quake shifted the planet on its axis by nearly 4 inches (10 centimeters).

The deep ocean is a mystery and we have no real handle on seabed changes. When one is only looking at mm changes, these types of events, and Tsunamis are not that uncommon, could have an impact.


Does Gore read anything except his own mind?

Andrew Hamilton

He also reads the numbers in his bank account.

I bet he has accountants for that. Lucky for him that he was born into some level of money/power.


Gore can read his own mind?
So he’s a mystic as well as a climate guru?


He’s The Goracle.


Sorry, my mistake. His reverence is not to be questioned.


If gore reads his own mind and believes any of it ….. he’s confused.

Moderately Cross of East Anglia

That shouldn’t take him very long…

Gunga Din

If so, he must be bored.


So far, I get that sea level ‘rise’ is controversial, regional, and globally indeterminate as even factors like the earth’s rotation causes centrifugal forces acting on the oceans, not to mention the moons gravitational influence. I also understand from Judith Curry that each end of the Panama canal has a different sea level. The measuring stations are themselves located on ever shifting bases, and I suspect that the vast majority of them are situated in the prosperous western world.
Even from a layman’s perspective, that’s one whopping conundrum to unravel, and I suspect I have barely scratched the surface.
And if you ever get to sail around the South coast of the UK, or are fortunate enough to enjoy the wonders of the river Clyde on the West coast of Scotland, let me know, The Royal Gourock Yacht Club is a necessary stop. If not, try The Royal Bermuda Yacht Club and I’m sure my brother in law (former Olympian) will make you welcome.

Curious George

The only economically kind of “sea level rise” is the relative kind: sea flooding the land. For that, tide gauges are most reliable. If you are afraid of a catastrophic sea level rise, don’t live in the Netherlands – but millions of people live there, more happily than alarmists.

Ron Long

Kip, it is more complicated than just the NE USA Relative Sea Level change. The entire North American Plate is tipping up in the west and down in the east. This is readily observed by the character of the shore line, ie straight with no barrier bars in the west and irregular with many barrier bars in the east. Then, some people (you know who you are) pump fresh water out of near-seashore sediments and cause sedimentary compaction and further lowering of the east coast (almost no effect for the west coast). Satellites to the rescue? The sea surface can be measured as bulging in repeating, sort of, patterns all over the earth, due to differential heating/thermal expansion or cooling, or pushing by strong wind patterns. Who said the sea bottom was stable? It changes all the time. Sea-floor volcanism anyone? Glacial cycles and inter-glacials? This is really getting complicated. Bless you for bringing up a good point re NOAA admitting something, but if you want to go for the gold (medal) you will end up crazy.


Ron Long
So, so complicated.Unknown variables, upon unknown variables, consigning the claimed catastrophic sea level rise to a case of utter bunkum. It could be falling for all we know, but human nature (well, the more pessimistic amongst us) endeavour to demonstrate that we’re all doomed, therefore sea levels are rising.
I wonder if we examined the case for falling sea levels, would that be any less disastrous. Yet the human race has probably flourished with both, and barely a scientist in sight.

Robert in Busan

Where is Donald Rumsfeld when you need him?

Geology 101. East coast of US is a sinking coast line. West coast is a rising coast line. Tectonic plates and soil/mineral composition. Erosion of the beaches is also a factor. Why do we have to replace the sand with dredges annually? Duh?

joe - the non climate scientist

SLR – Kip – you may have addressed this question –
The AGW advocates like to point out that there has been an acceleration in the rate of the increase in SLR from 3.1mm (ish) to 3.5mm (ish) in the last 5-6 years (or even the last 2-3 years). And from 2.7mm (ish) circa 1990 to 3.5mm ish today.
My two questions are – 1) it would seem to be that the increase is an artifact of the change in method of measurement for tide gauges to satellite measurement – any comments or insight?
2) My understanding is the satellite measurements are only accurate within 2.5cm (250mm), If that is true, wouldnt it take a good 10 or more years to detect any trend?


An interesting lecture by Willie Soon that discusses the various sources of error in satellite sea level measurements

Tom Halla

Good review.


Tide gauges are the best way to measure sea level, as we are concerned the sea level affect on land, the level mid ocean is little concern to most people.
But even NOAA adds a small amount to arrive at 1.7mm by calculating the ocean floors are sinking, how they arrive at that is not disclosed, the actual sea level we are concerned with is closer to 1.5 mm


Kip, I’m and engineer at a California wastewater treatment plant in the SF Bay Area. I receive an email from Water Online regularly with links to various news stories affecting our industry. This morning there was a story on researchers William & Mary’s Virginia Institute of Marine Science issuing their First-Annual Sea-Level Report Cards. The story linked to their site with the report cards, They are trying to identify acceleration of relative sea level rise over the last 30 years at several long term tidgages in the US. The east coast and gulf states show an indication of acceleration, but the west coast does not, and Alaska shows an acceleration of sea level fall. You may find it interesting reading.


MJ and Kip,
I am very confused on those projections from VIMS. John Boon, lead author, completed a study in 2012 that indicated that the year 2050 RSL for Boston would be 0.71 meters higher than the 1983-2001 MSL baseline (using 1969-2011 tide gage data for the projections). You can imagine how THAT stat got us Bostonians in a tizzy! That was an increase of 0.53m. above the 0.18m straight line linear projection he presents in this 2018 report. Six(6) years later, and using what appears to be the same methodology, he’s projecting a rise of only 0.48 m., or only about 0.30 m. higher than the straight linear projection increase, a reduction of 43% of the “accelerated rise”. This may have been because Boston RSL dropped dramatically immediately after his 2012 report. And yet his rate of acceleration has increased from 0.150mm/y2 back in 2012 to 0.186 mm/yr2 today! In effect, about 43% of the “accelerated rise” has disappeared in only 6 years, yet the rate of acceleration increased! (New York’s The Battery and Sandy Hook, NJ have even greater shifts down (about 58% and 50% reductions, respectively) since 2012, though without major changes in acceleration). Like I said, confusing, at least to me. Any inputs or clarifications on this would be welcome.


I think Dr. Boon made a mistake in choosing 1969 and 2011 as the start and end dates for his 2012 study, particularly for Boston, NY and NJ. These end points were approximate peaks in the RSL trend, with a “trough” in between, forcing the quadratic curve into a greater upward bend than, I think, was justified. The RSL’s for 1962-1968 were a lot lower than 1969’s. Including these years would have flattened out the quadratic curve and reduced the projections to 2050. Likewise, the RSL’s for 2012-2017 were a lot lower than 2011’s, flattening out the curve, which is no doubt why his 2050 numbers are already significantly lower in his 2018 report. Add in the earlier missing years and the quadratic plot flattens out even more, I’m sure, for Boston, NY and NJ. (P.S., Sewell Point was the location for the 0.62m projection. Boston’s was 0.71! And, the Boston tide gage is in an area that is subsiding 1.5mm/yr.! )

Don K

In many places in Alaska, the land is moving up at a greater rate than the sea surface is moving up

That’s also the case with reporting stations on the West Coast between Cape Mendocino ( roughly, Eureka, CA) and the Seattle area. They are on the “high side” of the Cascadia subduction zone and are being pushed upward by the subducting material. At some point, they will undoubtably “reset” by dropping a meter or two accompanied by a magnitude 9 or so earthquake. The last Cascadia quake was in 1700.

Nice post. Great ‘pictorial’. With permission, a phase I’d like to steal for future possible guest posts.

NOAA is casting no doubt whatsoever on NASA’s number.


“To the People of the State of New York:
If the water gets too high, move.”

Ed Zuiderwijk

To the people of Amsterdam:
If the water gets too high, build a dyke.

Tim Beatty

Two phenomena: “Glacial isostatic rebound” and “gyres.” This covered the vertical land motion from post glacial teeter-totter. I’d like to know how much the strength of the Atlantic Gyre affects sea level.

David J Wendt

This paper covers gyre effects on RSL
08 Feb 2010
The gyre-scale circulation of the North Atlantic and sea level at Brest
P. L. Woodworth, N. Pouvreau, and G. Wöppelmann
Ocean Sci., 6, 185-190,, 2010
I hink it is still available as a .pdf

Kip – great post! I had no idea you are a sailor (-:
What’s going on from my point of view is an endless game of bait and switch. Pick any place on earth, and apply the satellite sea level data and then scared the locals that sea level is going to go up 0.65 meters by 2100. This is particularly true in California. Sea level rise there shouldn’t be an issue, but people continue to make the rounds community by community to tell them that their coast line is going to be inundated by the ocean.
Pointing out that the scare stories of a meter or more of sea level rise by 2100 require an increase in the rate of sea level rise many times what the their tide gauges say falls on deaf ears. The people out there it seems what to believe the disaster story.


Claimed Research Findings May Often Be Simply Accurate Measures of the Prevailing Bias link

The above quote comes from a paper titled “Why Most Published Research Findings Are False” written by John P. A. Ioannidis.
Science is broken. Most of the problem is a result of perverse incentives. Bogus, but interesting, results gets published. Solid, but boring, results don’t get published.
The truly, gobsmacking, thing about Ioannidis’ paper is that there is, as far as I can tell, no push-back. Nobody is shouting from the rooftops to defend science. The replication crisis really is the elephant in the room.
This is an epic scandal. When scientists and organizations like the EPA and NOAA become activist, there is no good reason to believe them. They are demonstrably wrong most of the time.

commieBob — concerning bad science,
specifically so bad it gets retracted …
I find the Retraction Watch website interesting:
you don’t sound like a “commie”
NOAA here says sea level is rising at an increasing rate, currently about 1/8″ per yeat. Or 3.17 mm/yr. No disconnect from NASA.
And catastrophe implied! Not that the numbers support it.

Robert from oz

Just wondering about the just released claim of a massive chunk of an Antartica ice shelf was not grounded as much as previously thought , this then has the scientists predicting a one metre sea level rise by 2100 .

Robert from OZ
I wrote an article about
recent alarmism about glaciers,
which i can’t find,
but here’s a summary:
The latest huge iceberg was not the largest
KNOWN iceberg — the good articles mention that,
although they may not mention that glaciers
are moving “rivers of ice” that break off at the sea
The only known warming in Antarctica is
associated with underseas volcanoes
that mainly affect the peninsula (2% of continent)
while 98% of Antarctica is not warming.
And of course NO ONE really knows
what size icebergs were floating
out there before the satellite age
— perhaps the biggest iceberg ever
was never seen by humans,
only by penguins,
and they’re not talking !

Good presentation.
Some added graphics:
SLR from a nearby tide gauge, Battery NY:comment image?dl=0
Pulled from a rather alarmist powerpoint “Facing Higher Sea Levels and Increased Coastal Flooding in New York City
Here’s a combination of Montauk NY’s MSL on top of Montauk’s datum page defining overall tidal movement.comment image?dl=0
A clumsy attempt to relate sea level rise claims against what is daily overall water movement.

Kip, chart datum shows correction for lat, long, wgs84, etc. all this is pretty important because lives depend on nautical charts. in all your travels have you ever see a chart datum correction for global sea level rise?

Too many variables. Too much uncertainty. Rising/sinking coastlines. Ocean floor spreading/shrinking/rising/sinking. Expansion due to heat content.
Isn’t the only relevant figure the volume of water in the oceans vs surface water (Ice, lakes, rivers) at a given temperature? And can this even be measured?


From first principles , if you where to create a experiment the result of which was to produce a valid measurement of the change in status of the worlds oceans .
How many measurements would you need given the vast scale ?
How accurate would these measurements need to be , given the range of variation ?
For what period of time would you need to collect your data set for to give it meaning beyond the short term ?
Once you have answered those questions , you can then compare them to what the current reality is and see who close the two are.
In this case we can say , not close at all , for the range of measurements falls well short of what is required , the accuracy does not support the accuracy levels made within the claims and the time-line is often short to mid term even in human scale .
So how does this result offer a valid measurement of what is being claimed beyond , ‘better than nothing ‘
if you are doing science you follow the rules of it , if you cannot then you doing something else .

All cities including coastal ones rise slowly upward with time.
this is due to debris accumulation, city structures trapping and accumulating wind blown dust and leaves, human artefacts, and also flooding.
Cities themselves rise at least as fast as coastal sea level.
If sea level rise causes floods, these raise ground level from sediment deposition.
Thus the sea level rise becomes self-cancelling.
Sea level rise has happened steadily throughout the Holocene and there are no historical records of it causing flooding problems for cities. The rate is not increasing and therefore it is an utterly fictitious scare story about a problem that has never and will never happen.

March 21, 2018 at 2:32 am
Many thanks for the interesting links and your comments…I’ve often wondered about this but hadn’t realised things could grow upwards so fast.


Kip, thanks for a great post. I actually did understand it all and learned a great deal. Perfect for my beginner’s skills.

With PDO, AMO and other oscillations, these must affect the behaviour of local air pressure which must have some significant overall affect on measured sealevel changes at any point over time.

Glacial rebound plus overdrafting of aquifers makes tidal gauges unreliable in most of the US. Only tropical gauges are reliable. My favorite is Key West: no glacial rebound, no land decline issues and a long time series.


Kip. If one used a high number of tidal gauges from around the planet, wouldn’t the local affects tend to even out? They would still provide a useful measurement.


“It is a pleasant surprise to find that NOAA, sometimes leaning towards Sea Level Rise catastrophe advocacy, not only explains this clearly, but goes on to reiterate that “global sea level rise is believed to be 1.7 +/- 0.3 millimeters/year during the 20th century” — a figure at great variance from that promulgated by NASA, which is currently claiming to show almost twice that at 3.0 +/- 0.4 mm/yr.”
Confusing statement. Presupposes that “during the 20th century” equals “currently”.
NOAA makes this perfectly clear: Tide Gauges measure Local Relative Sea Level and its changes and reflect mostly the magnitude/rate of vertical land movement.. Thus, Tide Gauges, by themselves, are not fit for the purpose of determining Global Average or Regional Average Sea Level changes, rise or fall.
Confusing statement: Strawman said that “Tide Gauges, by themselves, are fit for the purpose of determining Global Average or Regional Average Sea Level changes”. As everybody knows there is a geology of Tide Gauges, measured by GPS and estimated from many other sources.


Is there a way to select tide gauges that can be representative of sea level change. I will chose to follow P. R. Thompson, B. D. Hamlington, F. W. Landerer, and S. Adhikari in the paper : Supporting Information for \Are long tide gauge records in the wrong place to measure global mean sea level rise?”
They are arguing in the following way. “The TG records that are most likely to represent 20th century GMSL rise satisfy the following criteria:
(1) long and mostly complete time series,
(2) located where solid earth models generally agree on the rate of sea level change due to GIA. (Perhaps solid earth models should be disqualified instead of TG records for 49 stations excluded by these criteria?)
(3) minimally affected by local, non-GIA vertical land motion.”
Then they come out with 15 TG stations: Honolulu, San Francisco, San Diego, Balboa, Christobal, Key West, Pensacola, New York, Cascais, Newlyn, Marseille, Trieste, Buenos Aires, Auckland II, and Freemantle. If we should use GPS measurements to estimate sea level rise from these stations, there are some additional problems. Balboa and Christobal don`t have GPS stations close enough to the tide gauge station. There has been recently local land subsidence at Buenos Aires and Freemantle stations, affecting GPS measurements. San Francisco GPS “not robust” because of tectonics. Auckland GPS “not robust” because groundwater variations.
So there are 9 stations left. What do they say? First we use PSMSL Tide Gauge Data to estimate local sea level change mm pr year for the years 1900 – 1999 (by Xuru linear regression). Then go into SONEL GPS data, and find vertical land movement. This give an estimate of relative SLR. And then compare it to CSIRO and ICE-6G adjustments
Honululu 1905 -1999: 1,50mm/year. GPS: -0,23 (SLR: 1,27).
CSIRO GIA: 0,34 (SLR: 1,84). Peltier ICE-6G: -0,23 (SLR: 1,27).
San Diego 1906 – 1999: 2,21mm/year, GPS: -0,99 (SLR: 1,22).
CSIRO GIA: -0,26 (SLR: 1,95). Peltier ICE-6G: -0,73 (SLR: 1,48)
Key West 1913 – 1999: 2,25mm/year. GPS: -1,07 (SLR: 1,18).
CSIRO GIA: -0,22 (SLR: 2,03). Peltier ICE-6G: -0,82 (SLR: 1,43)
Pensacola 1924 – 1999: 2,17mm/year. GPS: -0,42 (SLR: 1,75).
CSIRO GIA: -0,58 (SLR: 1,59). Peltier ICE-6G: -1,07 (SLR: 1,10)
New York 1900 – 1999: 3,00mm/year. GPS: -2,12 (SLR: 0,88).
CSIRO GIA: -0,88 (SLR: 2,12). Peltier ICE-6G: -1,80 (SLR: 1,20)
Cascais 1900 – 1993: 1,61mm/year. GPS: – 0,05 (SLR: 1,56).
CSIRO GIA: 0,05 (SLR: 1,66). Peltier ICE-6G: -0,34 (SLR: 1,27)
Newlyn 1915 – 1999: 1,65mm/year. GPS: -0,17 (SLR: 1,48).
CSIRO GIA: -0,40 (SLR: 1,25). Peltier ICE-6G: -0,72 (SLR: 0,93)
Marseille 1900 – 1999: 1,16mm/year. GPS: -0,18 (SLR: 0,98).
CSIRO GIA: -0,04 (SLR: 1,12). Peltier ICE-6G: -0,32 (SLR: 0,84)
Trieste 1901 – 1999: 1,14mm/year. GPS: 0,32 (SLR: 1,46).
CSIRO GIA: -0,03(Bar) (SLR:1,11). Peltier ICE-6G: -0,03 (SLR: 1,11)
This gives a mean rate of sea level rise of 1,31. Church and White (CSIRO) get a mean rate of sea level change of 1,63 for the same tide gauge stations, with their GIA corrections. Peltier GIA adjustments come out with a very low SLR on these stations, with mean rate of 1,18 (after changing and correcting models for 25 years).
With the same methods for the last 30 years you will get a sea level rise of over 3mm pr year. But I will argue that trends are not robust unless you use a timespan of over 60 years. Then natural variance is smoothed out.

The rise of sea that matters most
Is that which happens at the coast
On oceans far to west and east
Those millimetres matter least


Kip, it seems to me that tide gauge data is useful for a purpose in the same way that airport temperature measurements are: to provide valuable safety information to ships and planes respectively.
Neither system was intended to provide long term assessment for the change of climate variables, and neither system can do so due to too many confounding factors.
This to me is the great failure of climate scientists: failure to specify, design and implement a suitable monitoring network that could address these issues. Instead they expend huge effort on trying to coerce inappropriate measurement systems to divulge long term trends they were never designed to measure.

phil salmon

As the earth warms…
The real shocker here – and one with an unmistakable smoking gun of anthropogenic causation – is the above figure with SLR rates at different US coastal location. This graphic shows a correlation between rate of sea level rise and the alphabetical position of a location. Those living at locations starting with letters further up the alphabet – at no fault of their own – are imperilled by faster sea level rise and higher risk of flooding, drowning and accidental fish-swallowing.
The (we must act now) list of human activities that we now know to be linked to grievous environmental dangers and impacts just keeps on growing: now symbolic language and a written alphabet join that list of shame. Donald Trump’s persistence in sending social media tweets irresponsibly encourages people to continue and increase their use of textual communication with the Latin alphabet, which we now know to be a real risk factor for coastal flooding.
O hang on – I’m writing text in Latin alphabet now – better stop

A nice clear explanation, thanks. There is a good illustration of sinking coast according to the tide gauges all along the Gulf of Mexico to the west of the Mississippi. The land is sinking by around 6mm/year. Some suggest that it is due to water or oil abstraction, but satellite altimetry shows it is tectonic.

Thank you Kip, interesting article, down here in OZ we have the most stable continent in the world.In the 1800 hundreds the British admiralty charted our coast inscribing coastal rocks with low tide lines at a particular moon phase, these show no sea level rise. Rocks out from the coast that appeared out of the water at low tide they called dry rocks and inscribed them. They are still dry rocks at low tide.
Is it only they northern oceans that are rising? Remembering that most of the worlds ocean is down here.
Regards Wayne.

Good job on sea level rise once again.
Very good gifs, although I don’t
understand why some
of them are left centric
and others are right centric,
at least on my computer.
Your writing is getting better,
not such long sentences as usual.
Of course I have to
complain about something:
On my computer — an old Apple
MacBook Pro,
the sentences and gifs
slightly overlap.
I still think you should combine
all your sea level articles
into one article of talking points
and relevant charts.
I think you have enough good
material on sea level
to create the best article of 2018
at this website —
of course I’m assuming
short, easy to read
The more you know about a subject,
the easier it is to explain with short,
simple sentences … and you know
a lot about sea level rise.
My climate change blog
for people with common sense
— so leftists must stay away: