This might belong in GD, but as it is a question with a scientific/historical/factual answer, I’m starting it in GQ. Moderators, please feel free to move it if you think it’s appropriate.
Environmentalists, discussing the dangers of “global warming,” sometimes assert that it would cause enough of the polar icecaps to melt to significantly raise the sea level worldwide, which would not only flood coastal cities, but cause some islands to entirely disappear beneath the waves. Especially some of the very small islands of the Pacific. (I have never heard anyone seriously argue that this process would inundate the whole world, as in Kevin Costner’s Waterworld.)
But “global warming” has happened before, hasn’t it? I mean, within the global cycle of major ice ages and warm periods, there is a less extreme cycle of warming and cooling, and it works fast enough to be perceptible within recorded human history. In the Middle Ages, Greenland was warm enough that the south part, at least, was suitable for farming. Then the earth became cooler, and the Norse colony of Greenland died out. In Shakespeare’s time, the world was in a cool period, a “little ice age,” and the Thames usually froze over in winter.
What I’m wondering is, have any of these warming cycles caused the sea level to rise enough to inundate whole islands? Is there any record of this happening?
It raised it enough to inundate vallleys, which became the Mediterranean and Black Seas, for instance.
Most of the islands that are so close to sea level that this could have happened say between 1000 and 500 years ago, are coral islands in the Pacific so there wouldn’t be any written record.
According to
it is already happening: “Sections of the islands are inundated during high tide, erosion has caused houses to collapse and some regions have been evacuated”.
I haven’t a cite for islands being inundated, but I’d comment that it’s not polar ice caps melting that cause the initial rise, but expansion of the existing water as it warms up.
As for land areas being covered or exposed as water levels change, over a longer time period, look at atlases that show land masses as they were during pre-historic times, i.e. 250,000 years ago or several million years ago.
What about the Bering land bridge that allowed the first settlers to cross into the Americas? It’s now submerged. Weren’t there also connections between the various islands of South Asia that allowed humans to walk there?
“Banaba (Ocean Island) in Kiribati is one of the three great phosphate rock islands in the Pacific Ocean,” it says. And a coral atoll is by definition the subsidence of a volcanic island. So, has anyone made a (relatively) fixed point measurement and determined whether the sea is rising towards Banaba, or whether Banaba is doing the only thing it can do, geologically, which is to sink?
I’m not sure what the question of a ‘record’ of this kind of thing refers to – evidence that it has happened in the past or a smoking gun in recent times to use as damning evidence – but in terms of geological time there are sea fossils to be found at the top of the Rocky Mountains, since once upon a geological epoch or three ago they were thrust up out of what was then nothing but sea to slimy sea. All manner of theories abound, but the planet seems not to be all that malleable, even though we think we can make any difference one way or the other, and takes its own sweet time deciding what to do next.
Islands have disappeared, islands have been formed, and much as I’d like to be that arrogant I’m pretty sure that men had nothing at all to say about it.
I think BrainGlutton is asking whether any islands have been inundated since the last great rise in sea level caused by the end of the last glacial period. I’m not 100% sure, but I think any changes in sea level brought about by the little ice age, or other ‘minor warmings’, would have been tiny, on the order of centimetres at most, and so would have been insignificant in comparison to the tides.
On the other hand, the vertical movement of the tectonic plates may have caused land to either become submerged, or emerge from the ocean, within the last 8000 years or so. I vaguely remember reading about how parts of England that were by the sea in the middle ages are currently considerably inland, due to that whole section of plate rising slowly. This process is independant of global warming, of course, but it could have had the same effect.
Perhaps it’s because the city was built on a swamp and its buildings are supported by thousands of stone pilings which are, after many centuries, finally starting to sink into the mud?
Of course, I originally proposed this topic to cast light on the question of whether any islands really are in danger of being submerged by global warming in the future. My thinking was, how could that happen, if it’s never happened before? But has it happened before?
Posted by Kiwi Fruit:
That’s news to me! Got a cite for that? I always hear the problem discussed in terms of the icecaps; and I never hear anybody mention how much water there is in the icecaps, or whether that amount, melted, really would be enough to raise the sea level.
According to an item of p20 of the August 2 2003 issue of New Scientist, the level of the Adriatic Sea is rising four millimetres per year owing to global warming. At the same time, the tectonic plate on which Venice rides is sinking at about 1 millimetre per year as it is subducted under another plate. There is no mention of how rapidly the pilings on which Venetian buildings stand are sinking into the sediment on which the city is built, but I guess that that figure would vary from building to building.
Harvard astrophysicist Willie Soon believes the global warming now being observed is part of a natural climatic cycle. There was the “Medieval Warm Period” (MWP)from roughly 800 to 1300 A.D., and then there was the Little Ice Age (LIA) from 1300 to 1900, and now we’re again entering a warm period:
University of Virginia climate statistician Michael Mann and his colleagues not only deny the present global warming is a natural phenomenon, they deny the MWP or the LIA ever took place: