Sea Levels In The Holocene
By Paul Homewood
Perhaps the alarmist scare which gains most traction is that of catastrophic sea level rise. The idea that at some undefined point in the future our coastal cities will be under several meters of water.
It is, however, one that is easy to dismiss. Quite simply, we know that global climate has been much warmer than now for most of the years since the ice age ended. There was obviously a very rapid and large rise in sea levels when the ice age ended, but it is generally accepted that things stabilised around 6000 years ago. During that time, despite higher temperatures, there has been no catastrophic melt of the Greenland or Antarctic ice sheets, and no corresponding large jump in sea levels of the type currently touted.
Before we move on, let’s get one thing clear. It is often claimed that there has been very little change in sea levels during the last few thousand years, prior to the industrial revolution. The notoriously unreliable Wikipedia for instance quote a rise of only 0.07 mm/yr for the last 2000 years. However what they don’t mention is that there have been ups and downs during this time.
HH Lamb in his book, Climate, History and the Modern World, offers many examples of this, eg:
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.]
But back to the issue of temperatures. We know from Greenland ice cores just how much warmer it has been there during most of the Holocene, yet there was no spectacular meltdown then.
And it was not just Greenland. Glaciologists are clear that in Iceland the Little Ice Age was the coldest period for 8000years, and glaciers reached their post ice age maximum.
There is also abundant evidence from tree line and glacier studies in South America that temperatures were much higher until about 3000 years ago.
I could go on with similar evidence from New Zealand, the Rockies, California and the Alps. According to Lamb, for example, “Most – and perhaps all – of the glaciers present today in the United States Rockies south of the Canadian border are believed to have formed since 1500 BC.”
If global temperatures were so much higher, and for so long, back then, why do we not see the sort of sea level rise now being forecast?
What we do know is that there was a massive expansion of glaciers worldwide during the Little Ice Age. And, unsurprisingly, sea levels dropped.
Many studies, such as the Hofstede one below, suggest that sea levels were at a similar level to today in the Middle Ages, before falling by 300mm up to AD 1700. Lamb reckons the drop may have been even greater, up to 500mm.
It was also found that sea levels rose by about 0.2cm a year between AD 600 and AD 1200, a similar rate to today.
Given the massive advance of glaciers in the LIA, it is little wonder that we have seen a recovery in sea levels since.
There is no evidence that the current rate of increase is in any way abnormal, and the history of the last few thousand years tells us that we are not going to get the inundations promised.