By Paul Homewood
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:
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.
via NOT A LOT OF PEOPLE KNOW THAT
August 22, 2018 at 05:54AM
Iowa Climate Science Education 
