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Is The Rate Of Sea Level Rise Accelerating?

June 29, 2017

By Paul Homewood




Sea level alarmists often claim that the rate of sea level rise is increasing. They need to do this to convince the public that the innocuous 7” or so of sea level rise experienced in the 20thC is suddenly going to turn into meters by 2100.

They use two tricks to back up this claim:

1) They splice the satellite record, which only started in 1993, onto the tidal gauge records.

According to satellites, sea levels have been rising at 3.4mm/yr. Whether this figure is right or not, no half competent scientist would dream of splicing two totally different sets of data together in such a way.

Worse still, their banner figure of 3.4mm includes what is known as glacial isostatic adjustment (GIA), which accounts for the fact that the ocean basins are getting slightly larger since the end of the last glacial cycle.

In other words, if the basins were not getting larger, sea levels would rise more. To account for this, they add 0.3mm a year to their sea level figures.

This is all well and good, if it were not for the fact that tidal gauges do not include such an adjustment, so the comparison of satellites and gauges becomes incompatible.


2) They compare recent sea level rise with the 20thC average.

However, sea levels were not rising at an even pace during the last century. There were times when it was rising at rates similar to today, and others, notably between 1950 and 1980 when global temperatures were falling, which saw a lower rate of rise.

As the IPCC stated in its 2013 AR5 report:

It is very likely that the mean rate of global averaged sea level rise was 1.7 [1.5 to 1.9] mm/yr between 1901 and 2010 and 3.2 [2.8 to 3.6] mm/yr between 1993 and 2010. Tide gauge and satellite altimeter data are consistent regarding the higher rate during the latter period. It is likely that similarly high rates occurred between 1920 and 1950

So, the current rate of rise is not unprecedented, and does not “prove” that the rise will continue to accelerate. Indeed, if the 20thC record is anything to go by, it could well slow down again, as part of a natural cycle.

The year 1993 is also not a very reliable place to start from, because it was just after the Pinatubo eruption in 1991. This lowered global temperatures, leaving sea levels also lower than they would otherwise have been, consequently increasing the subsequent upward trend.

Interestingly, University of Colorado sea level page refers to this, in a paper by John Fasullo:


Global mean sea level rise estimated from satellite altimetry provides a strong constraint on climate variability and change and is expected to accelerate as the rates of both ocean warming and cryospheric mass loss increase over time. In stark contrast to this expectation however, current altimeter products show the rate of sea level rise to have decreased from the first to second decades of the altimeter era. Here, a combined analysis of altimeter data and specially designed climate model simulations shows the 1991 eruption of Mt Pinatubo to likely have masked the acceleration that would have otherwise occurred. This masking arose largely from a recovery in ocean heat content through the mid to late 1990 s subsequent to major heat content reductions in the years following the eruption. A consequence of this finding is that barring another major volcanic eruption, a detectable acceleration is likely to emerge from the noise of internal climate variability in the coming decade.


So we learn two things:

a) The rate of sea level rise has actually slowed down in the last decade.

b) The rate of rise in the first decade of satellite data was artificially high, because of the recovery in ocean heat content in the mid 1990s, when the effects of Pinatubo had disappeared.

A 2013 paper by Chen et al also found a similar slowdown in sea level rise:

It is found that the GMSL rises with the rate of 3.2 ± 0.4 mm/yr during 1993–2003 and started decelerating since 2004 to a rate of 1.8 ± 0.9 mm/yr in 2012.


In any event, expert oceanographers know full well that measuring trends over just a decade or two is meaningless. Top ocean scientist, Bruce Douglas, wrote a paper, “Global Sea Rise: a Redetermination”, in 1996, with the Abstract stating:

It is well established that sea level trends obtained from tide gauge records shorter than about 50-60 years are corrupted by interdecadal sea level variation.


In particular, sea levels are particularly influenced by ENSO changes, as CU show.

During El Ninos sea levels rise:



One more complication is groundwater depletion, via irrigation, water use etc. A study by Yoshide Wada in 2012 estimated that this had added 0.44mm/yr to sea levels since 1993.

So, far from the scary headlines put about, the rate of recent sea level rise has not been unprecedented, is not accelerating, and shows no sign doing so in years to come.

  1. Curious George permalink
    June 29, 2017 6:56 pm

    I don’t believe that the satellite altimetry can measure the sea level, with all its waves up to 29 m tall, with a precision under a millimeter. I don’t believe that the satellite altimetry can measure the elevation of the coast with all its vertical relief with a precision under 1 mm. The practical level of sea level rise is the difference of the two – doubling the uncertainty.

  2. MikeW permalink
    June 29, 2017 7:03 pm

    Global mean sea level is meaningless. The sea level at any given location is dominated by land movements, not by global sea level. And the satellite-based Deltares Aqua Monitor has measured that coastal land areas have actually increased over the past 30 years more than they have decreased. Sea level alarmism is a manufactured hysteria from the Global Warming of Doom cult

  3. John F. Hultquist permalink
    June 29, 2017 7:17 pm

    About once each year, I trot this out:
    My(?) “Easy Ice” hypothesis: The low latitude and low elevation ice melted. Charts like this one document the post-glacial melt and show the typical curve for this sort of event:

    Remaining ice is high latitude and or high elevation. Such ice will not melt as easily as the ice that was in Puget Sound or in the central mid-west of the USA.

  4. Brian Vaux permalink
    June 29, 2017 7:40 pm

    Of course it is all measured at Standard, Temperature and Pressure. I remember it all now!

  5. Broadlands permalink
    June 29, 2017 8:08 pm

    Haven’t we been over this sea-level-rise topic before?

    “Another study related to sea-level rise (Webb and Kench 2010) appears to contradict the general anticipation that the impacts of climate change will eventually make low-lying reef islands unable to support human occupation. It uses aerial and satellite images taken over the past 60 years, a time during which there is evidence that sea levels have risen, to compare the landform dynamics of 27 atoll islands in the central Pacific Ocean. The study found that as a whole, instead of declining, the islands grew in land area by a total of 63 ha or seven percent. The research findings show that although sea level in the central Pacific Ocean rose by about 2.0 mm/yr over the study period and that all 27 islands changed physically during that time, there is considerable variation in the amount and style of change between and among the islands, with an overall net increase in land area; 86 percent of the islands remained relatively stable or their outline or shape increased in size. Twelve of the 27 islands increased in size by more than three percent but only four islands reduced in area by more than three percent.”

    2.0 mm/yr for 60 years… 4.75 inches.

    The IPCC focused on the decrease…?

    • M E Emberson permalink
      June 29, 2017 10:47 pm

      What is an island? Is an atoll an island? My vague memories of Physical Geography Edinburgh University one year course for non geologists in 1960s makes me think atolls can grow or almost disappear in storms when sand and rocky debris and broken coral wash up or scour out?

      Has the definition changed since then?

      • Athelstan permalink
        June 29, 2017 11:23 pm

        “Has the definition changed since then?”

        Not really, some nomenclature……………… atolls are usually island arcs, thus are only [Geologically speaking] temporary structures, volcanic island arcs at any rate and thus subject to tectonic ie plate movements and severe upheaval at that, readings of SL alterations are of little value.

      • Broadlands permalink
        June 30, 2017 12:07 pm

        The reference was to “27 atoll islands”, inhabited by humans. No human inhabited location has suffered complete submergence from sea level rise.

  6. June 29, 2017 8:32 pm

    Reblogged this on Climate Collections.

  7. June 29, 2017 8:34 pm

    I was repeatedly informed by widely acclaimed experts on the topic that the city I lived in would be under three feet of water in a century. That the science was settled and only ignoramuses could possibly doubt it. A quarter of a century after having been so advised, sea levels in this area have risen less than two inches.

    Now these same experts and their acolytes have informed me that only a complete ignoramus would deny that the settled science proves that the city will be under water a hundred years from _now._

    Now they say that while I was skeptical back then, I was right for the wrong reasons and that they were wrong for the right reasons so I was still an ignoramus then and an even worse one now since they have shown how much they understand the true nature of the problem by seeing how wrong they were and how easily influenced I am by having been right all along.

    I admit I am unable to find a way to argue with that line of reasoning. .

  8. tom0mason permalink
    June 29, 2017 9:40 pm

    The current method of ‘scientific’ methods say the sea is rising —

    Here is the method —


    • John of Cloverdale, WA, Australia permalink
      June 30, 2017 2:16 am

      Should be hypothesis becomes theory, in the bottom part of the figure, unless I am confused.

      • tom0mason permalink
        June 30, 2017 10:17 am

        I understand that modern science has no need for hypotheses as they impose unacceptable levels of uncertainty on progress, and thus impedes rapid development to setting new standards upon which evermore restrictive statues can be based.
        (see EPA progress under Obama as an example)

  9. AndyG55 permalink
    June 29, 2017 10:43 pm

    “Adjustments to the satellite data on sea levels started somewhere between 2000 and 2003.

    • Athelstan permalink
      June 29, 2017 11:24 pm

      how convenient.

  10. John of Cloverdale, WA, Australia permalink
    June 30, 2017 1:24 am

    I’ve looked at the sea level plots of many historical long tide stations on the NOAA website and cannot see any acceleration at all. An example is Fort Denison (Sydney Harbor) on the east coast of Australia. Sydney is geologically stable (sitting on Permo-Triassic rocks) with no isostatic rebound and very little subsidence to account for. According to NOAA:
    “The mean sea level trend is 0.65 millimeters/year with a 95% confidence
    interval of +/- 0.10 mm/yr based on monthly mean sea level data from
    1886 to 2010 which is equivalent to a change of 0.21 feet in 100 years.”
    In fact, if you look at the plot, there has been little change for 60 years.
    I then looked at similar plots with long records on each continent and came to a similar conclusion that there is little, if any, acceleration in sea level from the late 1880’s to today.
    This is Sydney’s plot from NOAA:

  11. johchi7 permalink
    June 30, 2017 1:43 am

    That the Expanding Earth theory is still disputed, when evidence says the sea basins are increasing and coastal areas are increasing since the last glacial period is beyond rational thought. Repeatedly there are expansions of the trenches in our life time that have been recorded. Data from samples of the ocean floors give their approximate age that coincide with the geographic Geological and biological timeline of the changes in Earths day increasing going back to over 3 billion year’s when it took Earth to revolve less than half of what it takes today. If the ocean’s have expanded the water on land would fill it and lower it from the land surface leaving fossils of aquatic life behind. A smaller Earth where water covered most of the Earth during a Glacial Period would show a Snowball Earth to the Equator. More expansion of the ocean’s leave more dry land exposed. Some Subduction has occurred and Orogeny too, but not to the extent that the Pangea Theory can explain, especially for the Pacific and Indian Oceans. These are disputable because there is not enough evidence of our ocean floors history. We know more about what we can see, than what we cannot see.

  12. Tim Hammond permalink
    June 30, 2017 8:09 am

    “In other words, if the basins were not getting larger, sea levels would rise more. To account for this, they add 0.3mm a year to their sea level figures.”

    That is fine for an abstract view of what would be happening to sea-levels if there was not increase in basin-size.

    However, it utterly WRONG to use that extrapolate what will happen in the future. You have to use the original data, not the adjusted data.

  13. Max Stavros permalink
    June 30, 2017 8:17 am

    Claims to have detected a 3 mm sea level rise from Ku band satellite radar altimitery can be safely filed away with claims to have heard subliminal messages in music recordings.

    According to basic radar physics, radar range resolution is a function of bandwidth. A 3 millimeter range resolution would require a bandwidth of at least 50 Ghz, clearly impossible with a Ku band carrier frequency of just 13.65 Ghz. A 3 centimeter resolution would need a 5 Ghz bandwidth, which is feasible, but would never be licensed as it would blot out most satellite communications and broadcasting with every pass.

    The Jason/Posiden altimeter is allocated a bandwidth of just 320 Mhz, centred on a 13.65 Ku band carrier, giving a best range resolution for perfectly flat water and ideal conditions of 0.47 metres. However, the backscatter equation includes a significant wave height term. Thus, a typical 2 metre significant wave height reduces the resolution to just under a metre. This is the very best theoretical altimeter range accuracy that can be achieved.

    Incidentally, the Ku band (13.45 GHz) is also used by US law enforcement for radar speed detection, so if you have a copy of the Jason ephemeris and can prove it happens to be passing overhead you might have a novel defence. Worth a try.

    • July 1, 2017 1:30 pm

      Excellent point. Something I hadn’t even thought of. I’m sure someone has worked out an algorithm for all the climate scientists that allows them to adjust and therefore ignore all those laws of basic physics.

  14. dennisambler permalink
    June 30, 2017 8:54 am

    “They splice the satellite record, which only started in 1993, onto the tidal gauge records.”

    Isn’t this reminiscent of “Mike’s Nature Trick”?

    John Daly on satellites:

    “T/P cannot measure sea level when there is any land within the footprint because T/P cannot tell the land echoes from the sea echoes and gives a false result. This means that all sea areas within 3 to 5 kilometres of continental coasts, islands, even atolls, are not covered.

    Also not covered is all oceanic area north of 66°N or south of 66°S, due to the angled track of the satellite. This results in the Arctic Ocean and the high-latitude part of the North Atlantic being excluded.

    Also excluded is much of the oceanic area surrounding Antarctica. In areas with a large density of islands such as the Indonesian archipelago or the West Indies, the `no-go’ area several kilometres around each island will result in a substantial area of ocean being excluded from sea level measurement altogether.”

  15. Ben Vorlich permalink
    June 30, 2017 9:00 am

    Looking at the the GMSL v ENSO chart it looks like the heat content of the (Pacific) Ocean has been fairly constant apart from the ENSO element, if you see what I mean. Which means the heat hiding in the deep oceans is fairly minimal?

  16. tom0mason permalink
    June 30, 2017 10:36 am


    Evidence of an accelerating sea level rate of increase is crucial to the man-made CO2 climate change theory. It is a smoking gun piece of evidence and would be extremely important in bolstering the case of the Alarmists. The theory goes man-made CO2 is increasing at an increasing rate, Atmospheric CO2 has reached levels not seen over the entire ice core record spanning 800k years, the rapidly increasing CO2 had been absorbing outgoing IR radiation at an increasing rate, this increasing rate of absorbing outgoing IR Radiation has CAUSED global temperatures to increase at an increasing rate, global temperatures increasing at an increasing rate would CAUSE glaciers to melt at an increasing rate, the increasing glacier melt rate would CAUSE the sea levels to increase at an increasing rate. The “increasing rate” is critical to proving the man-made CO2 driven warming theory. Warming isn’t enough, what is needed is an “increasing rate,” for calculus fans, this is a second derivative model.

  17. Green Sand permalink
    June 30, 2017 12:15 pm

    Ole Humlum has some interesting info on sea level (a section that’s new to me), on both tide-gauges and satellite altimetry.

    Under ‘Oceans’ here:-

  18. stinkerp permalink
    July 3, 2017 5:45 am

    The important question is what do the tide gauges tell us the current global average rate of sea level rise is? The tide gauges didn’t stop recording when they started using satellites to guess global sea levels. Why doesn’t anyone publish the latest globally-averaged tide gauge data? I suspect the reason is because it refutes the popular myth of “accelerating” and “unprecedented” sea level rise and illustrates how badly the satellite calculations differ from tide gauge data. At the very least it should be analyzed and published to calibrate the accuracy of the satellite calculations. If anyone knows a source for the latest globally-averaged tide gauge data, I’d love to see it.

  19. July 7, 2017 12:15 pm

    Did you see this paper on the CU site?
    Presumably the question implies that acceleration has not been detected.
    Of course there is always an excuse.
    From the abstract:
    “Global mean sea level rise estimated from satellite altimetry provides a strong constraint on climate variability and change and is expected to accelerate as the rates of both ocean warming and cryospheric mass loss increase over time.
    In stark contrast to this expectation however, current altimeter products show the rate of sea level rise to have decreased from the first to second decades of the altimeter era.
    Here, a combined analysis of altimeter data and specially designed climate model simulations shows the 1991 eruption of Mt Pinatubo to likely have masked the acceleration that would have otherwise occurred. “

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