Sea tells price of progress

October 13, 2000

The first hints that the industrial revolution may have triggered a surge in the rate of sea level rise are beginning to emerge.

Preliminary results of a pioneering study of salt marshes are providing tentative, circumstantial evidence that atmospheric pollution has added to natural global warming trends.

However, Roland Gehrels, a quaternary scientist at Plymouth University, warned that more data was needed to confirm the initial findings.

The research, which has been presented to the American Geophysical Union and is being prepared for publication, has found that the sea level at two locations in Maine, in the United States, is rising more rapidly than at any time in the last millennium.

Dr Gehrels and his international collaborators uncovered the evidence from the remains of plants and microscopic animals trapped in coastal salt marshes.

The tops of these plant-capped formations of clay, sand and silt remain close to the high tide mark - as sea levels rise so do the salt marshes.

The scientists extracted peat cores from the structures, drilling back to layers laid down many centuries ago.

Plant material recovered from these was carbon-dated to determine the age of a particular section while tiny fossil marine organisms called foraminifera were recovered.

Different species of these single-celled creatures possess different tolerances to air and live at different heights on the salt marshes.

Dr Gehrels was able to use the relative distribution of foraminifera species, in combination with the carbon and lead dating, to calculate changes in sea level over time. Since 1800, levels have risen by up to 50cm.

He said: "It is an unprecedented rate of rise. I also think I can see from the data an acceleration taking place some time in the past 150 years that would be at least circumstantial evidence of manmade global warming." But he added that the error bars on his data remained too high to be conclusive in this analysis.

In a bid to reduce the uncertainty, Dr Gehrels is analysing further data from three more North American sites while planning expeditions along the Atlantic coast of Europe.

Steve Farrar

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