Posted on 08/16/2004 5:06:16 AM PDT by ckilmer
Ancient Rome's fish pens confirm sea-level fears
09:30 16 August 04
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Coastal fish pens built by the Romans have unexpectedly provided the most accurate record so far of changes in sea level over the past 2000 years. It appears that nearly all the rise in sea level since Roman times has happened in the past 100 years, and is most likely the result of human activity.
Sea-level change is a measure of the relative movement between land and sea surfaces. Tide-gauge records show that the sea level has been rising 1 to 2 millimetres a year since widespread measurements began around 1900, but do not pinpoint when the trend started.
Earlier sea levels can be estimated from geological data, but the accuracy is limited to about half a metre, which is not enough to precisely chart the history of sea-level rise.
So Kurt Lambeck of the Australian National University in Canberra turned to fish pens on the Tyrrhenian coast of Italy for a more accurate record of ancient sea level.
Ice age rebound
The Romans dug these fish pens into bedrock, and the water line in these well-preserved structures shows that the sea level along the Italian coast 2000 years ago was 1.35 metres below today's levels. "They were used for only a very short time, so they make rather nice markers," says Lambeck.
He then analysed how land elevations changed along the Italian coast due to both plate tectonics and the after-effects of the last ice age. In a paper to appear in the journal Earth and Planetary Science Letters, he concludes that geological processes pushed the land up by 1.22 metres over last two millennia, which means that the global sea level rose by 13 centimetres.
That is only about 100 years' worth of rise at the present rate of around 1 to 2 millimetres per year, implying that nearly all of it has occurred since 1900. While there is no proof that human activity is to blame, "I can't think of a natural process that would have started in 1900," he says.
The result "is a significant one", says Jonathan Gregory, who studies global changes in sea level at the University of Reading, UK. The finding supports the idea, based on the few tide-gauge records that extend back two centuries, that the rise in sea level did indeed accelerate about a century ago.
While Gregory cautions that this does not prove that global warming is responsible, both he and Lambeck agree that the results fit the rise in ocean volume expected from global warming melting glaciers in the industrial age.
Jeff Hecht
How come you have such a dinky little profile?
BTTT for later reading.
He was so precise in his anaysis of the plate tectonics and ice age effects that he could be accurate to a millimeter? Suuuure.
I learned a very important scientific technique in high school physics and chemistry classes. If you know the results you need, you can adjust the data just enough to give you those results. In my school days, this technique served to get a me better grade. For this "scientist", it is to get the respect of his peers (i.e. publish or perish), and continued research grants (i.e. free research expeditions to Italy).
You nailed it.
Venice is built on deep alluvial sediments (i.e., not bedrock). It is sinking because the sediments are naturally compacting under their own weight. The same thing is happening to our Mississippi delta.
There's something wrong with this. The land would have had to have FALLEN by 1.22 meters, not risen, for his figures to be correct.
"...Has anyone noticed the Tidal Basin in DC rearing up to swallow the national monuments in the last century ?..."
I live downstream from DC along the Chesapeake. Broomes Island IS being swallowed by the Patuxent River (as are some other low islands and terraces), as sea level rises. Locally, we calculate that net rise (sea level rise plus terrestrial subsidence) to be about an inch per century.
All around this area one can see the remains of old waterfront homes, built 100 years ago or more, that are now lapped by high tides.
btt
The world experts on this are the Dutch and the people of Venice.
They have noticed a slight rise in sea level over the past 200 years. A few inches.
And the seas have been rising every since the end of the ice age 18,000 and 12,000 years ago. They will continue to rise slowly until the next ice age starts, (then beachfront property will be worth nothing.)
Good for another bump.
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