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Holocene Sea Level Trends

August 22, 2018

By Paul Homewood

 

postglacial_sea_level_thumb

https://commons.wikimedia.org/wiki/File:Holocene_Sea_Level.png

 

There seems to be a general acceptance about overall sea level trends during the Holocene.

There was naturally a very rapid rise in sea levels at the end of the ice age, until 6000 years ago, since when the rise has been much more gradual. Some research puts the rate of rise in the last 2000 years at 0.07mm/yr, and this reflects the fact that ice caps left over from the ice age are still melting, rather than that the world is warmer than before.

However, the impression is often given that, until the 20thC, this rate of rise has been pretty steady. This is despite the fact some of the authors of the above studies have warned of the existence of significant short-term fluctuations in sea level such that the sea level curve might oscillate up and down about this ~1 kyr mean state. [The above graph is based around 1000 year averages].

 

HH Lamb looked carefully at many expert studies in his day, and wrote about the very significant fluctuations they found. The following excerpts come from “Climate, History and the Modern World”:

1) The most rapid phases [of sea level rise] were between 8000 and 5000 BC, and that the rise of general water level was effectively over by about 2000 BC, when it may have stood a metre or two higher than today.

2) The water level may have dropped by 2 metres or more between 2000 and 500 BC. What does seem certain is that there was a tendency for world sea level to rise progressively during the time of the Roman Empire, finally reaching a high stand around 400 AD comparable with, or slightly above, present.

3) The slow rise of world sea level, amounting in all probably to one metre or less, that seems to have been going on over the warmer centuries in Roman times, not only submerged the earlier harbour installations in the Mediterranean, but by 400 AD produced a notable incursion of the sea from the Wash into the English fenland, and maintained estuaries and inlets that were navigable by small craft on the continental shore of the North Sea from Flanders to Jutland.

4) The existence of pre-Norman conquest salterns – saltpans over which the tide washed and from which salt-saturated sand was taken – outside the later sea dykes on the Lincolnshire coast may point to a period of slightly lowered sea level between the late Roman and the medieval high water periods.

5) Our survey of the European scene during the warmer centuries of the Middle Ages would not be complete without mention of the things that suggest a higher stand of the sea level, which may have been rising globally during that warm time as glaciers melted .

Fig 60 [not shown] draws attention to the greater intrusions of the sea in Belgium, where Bruges was a major port, and in East Anglia where a shallow fjord with several branches led inland toward Norwich. [Bear in mind that the land here has been sinking due to isostatic forces since the ice age. If relative sea levels were as high then as now, it would mean absolute levels were higher than.]

6) Close study by Sylvia Hallam over many years of the history of human settlement near the coast of the Wash in eastern England has indicated has indicated that sea level was rising for some centuries before up to a maximum attained in the last century BC. There was then some recession of the water until about 200AD, followed by a major high stand and incursion of the sea around 300-400AD.

Sea level was again rather lower in the seventh and eight centuries and possibly later, but seems to have been high again in the late thirteenth to fifteenth centuries.

Then of course we had the Little Ice Age, when there is abundant evidence that sea levels actually fell again:

For instance, this study by Hofstede found that sea levels in the Inner German Bight may have fallen by around 300mm between about 1400 and 1700AD. Prior to that, sea levels in the Middle Ages were similar to today:

 

 

image_thumb55

http://www.kwaad.net/Hofstede_1991.pdf

Lamb believes the drop was even greater, of the order of 500mm. [Over three centuries, this equates to 1.7mm/year, similar to the rate of rise in the 20thC]

What is absolutely certain is that there was a massive expansion of glaciers worldwide during the LIA. It would be surprising if sea levels did not fall sharply as a result.

 

To summarise, it is misleading to claim that sea level rise has been slow, gradual and smooth in the last few thousand years. Lamb presents clear evidence that sea levels dropped significantly between 2000 and 500BC, then rose again till 400AD, when they were comparable to today.

They then fell again during what we term the Dark Ages, rose in the Middle Ages, and then fell again in the Little Ice Age.

Which raises the question – how much of the sea level rise since the 19thC is simply a recovery from the Little Ice Age?

What we do know is that there is nothing remotely unprecedented about the current rate of rise.

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15 Comments
  1. August 22, 2018 12:18 pm

    Thanks, Paul.

    Cheers.

    Bob

  2. Jack Broughton permalink
    August 22, 2018 12:32 pm

    HH Lamb appreciated the complexity of climate history: the modern “climate experts” seem to believe that very approximate models of the climate (that few of them understand anyway)are more significant than historical experience. If all the so-called “climate scientists” who have not read Lamb’s work were fired I wonder how many would be left???

    Another great article, thanks.

  3. August 22, 2018 12:33 pm

    It would seem that sea level rises coincided with the rise of the Roman Empire and underwent lowering at the demise of the Roman Empire in 400 A.D. Hmmmmm.

    What conclusions can we draw from this? Did the Romans cause the rise in sea level? And once the western Roman Empire collapsed, the sea could relax and retire?

    Makes as much sense as the climate pronouncements from today’s elite learned community.

    • Malcolm Bell permalink
      August 22, 2018 1:58 pm

      Joan,

      You are right, that makes as much sense as most climate claptrap we hear.

      What you are emphasising is the classical “correlation error” in logic. Because one thing happens at the same time as another it is not logical to say one must cause the other.

      The Stork population in Belgium increased rapidly after WW2 and so did the human birth rate! Therefore Storks bring babies!!!

      That is the reasoning of most weatger people. You make the point perfectly.

  4. Graeme No.3 permalink
    August 22, 2018 12:45 pm

    The local aborigines in South Australia remember the rising sea level ‘cutting off’ Kangaroo Island (and those on it) about 6000 years ago. Backstairs Passage average depth 40 metres (max, 73 metres).
    The separation by flooding of Bass Strait must have been earlier as its average depth is 50 metres (wikipedia) or 60 metres (wikipedia). The rising sea level “forming a marine embayment from 11,800 BP to 8700 BP and the basin rim was completely flooded by about 8000 BP, at which point Bass Strait was formed and Tasmania became a separate island”.

    • Geoff Sherrington permalink
      August 23, 2018 2:55 am

      Graeme #3
      I doubt very much that the locals remember an event 6,000 years ago. They did not seem to have a time frame that distinguished last century from last millennium.
      What I have observed, through direct participation in the process, was the re-writing of aboriginal history by academics, usually titled as anthropologists. It was my sad lot for 20 years to be deeply involved in ‘aboriginal land rights’ whereby the anthropologists promised rewards to the aborigines in the form of legal ownership of land (and thus control over resource development) in return for going along with the fiction. We resources managers did not even have beads and trinkets to compete. We lost, but we learned. Geoff

      • Graeme No.3 permalink
        August 24, 2018 6:56 am

        Geoff:
        OK, but I was told by a local Aboriginal woman who knew that those on the Island were from her tribe, and described how they were able to move back and forth until the water got too deep.
        Incidentally she described the Hindmarsh Island claims as farcical.

  5. saparonia permalink
    August 22, 2018 1:09 pm

    The ‘slow and gradual’ aspect is a relic of the 1800’s, we have to shake it off.

  6. Broadlands permalink
    August 22, 2018 2:02 pm

    Tectonics and isostatic adjustment.

  7. August 22, 2018 5:36 pm

    Here’s another great graphic – Holocene – Rate of sea level rise

  8. Up2snuff permalink
    August 22, 2018 9:40 pm

    If I recall correctly, the earthquake that caused the Boxing Day Tsunami in 2004 left the largest ever trench – seen by modern humankind, in natural world events recording mode – in the Indian Ocean.

    Something has to fill it.

  9. August 23, 2018 1:58 pm

    Permafrost melting would have probably followed a similar but delayed trajectory – with no evidence of Methane Spikes? Most of the permafrost is long gone, worrying about what remains seems to assume there has been no prior melting?

  10. August 24, 2018 6:06 am

    Reblogged this on Climate Collections.

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