HH Lamb & Sea Level Changes

By Paul Homewood

We are often fed the impression that sea levels have remained pretty much constant since they stopped rising after the ice age ended, until the last century.

It is worth, therefore, seeing what HH Lamb had to say on the subject, in his book “Climate, History And The Modern World”.

First, he finds that there is considerable agreement that

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. [The book was published in 1982].

He then goes on to state that

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.

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.

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. There is other evidence to suggest this between the seventh and tenth centuries.

But many later saltpans are known in the area, also on the sea-banks, standing up to 3 metre above the present mean sea level

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 that sea level was rising from some centuries before up to a maximum attained in the last century BC. There was then some recession of the water until about 200 AD, followed by a major high stand and incursion of the sea around 300 – 400 AD. Sea level was again rather lower in the 7th and 8th centuries, but seems to have been again high in the late 13th to 15th centuries.

The present writer’s opinion [Lamb] is that the impression of a high level of the sea as late as the 15thC may in reality owe a good deal to storm surges – i.e.to recurrent sea floods as storminess increased.

 

MWP

Lamb goes on to offer some more detail about the Middle Ages.

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 – and particularly in the area around the southern North Sea where the land-sinking due to the folding of the Earth’s crust in that basin was presumably going on then as now.

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. The English fenland south of the Wash provided provided an extensive watery landscape of shallow brackish channels and low islands, fringed by reeds and brushwood, in which the island of Ely was so cut off that the Anglo-Danish inhabitants were able to hold out for seven to ten years after the Norman conquest.

And the coastal plain of the Netherlands and Belgium had a fluctuating population in the 11th and 12th centuries, as the state of flooding varied, leading finally to a more general emigration to Germany.

[It is worth pointing out that the East Anglian coastline is believed to be sinking at a rate of about 0.5mm/year, so over the last millennium this would have amounted to 500mm, or about 20 inches. If it is true that sea levels in the region during the Middle Ages were as high as present, then absolute sea level, excluding isostatic effects, would actually be lower now]

Conclusions

It is clear that sea levels have risen and fallen at different times during the last 4000 years, probably by as much as a metre or two over periods of a few centuries. These changes have been the result of successive switches from warm to cold and back to warm climates again.

Lamb makes no specific reference to sea levels during the Little Ice Age, but it is apparent that sea levels fell between the Middle Ages and the 19thC, inevitably so as glaciers expanded around the world.

Given this background, there is nothing unnatural about current sea levels, or the rate of rise we have seen since the 19thC.

Source

HH Lamb’s “Climate, History & The Modern World”

Pages 115/6, 154=3, 162/3, 165 & 185