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Thursday, 7 October, 1999, 10:27 GMT 11:27 UK
Mark of hot dispute
Mark, Daly
The Lempriere-Ross mark is still visible (Photo by J Daly)
By Jonathan Amos

Is this the picture that takes the heat out of global warming? It shows an Ordnance Survey Bench Mark engraved into a rock face on a little island near Port Arthur, Tasmania.

It was put there in 1841 by the famous Antarctic explorer Captain Sir James Clark Ross and amateur meteorologist Thomas Lempriere to mark mean sea level.

What is so fascinating is that the mark appears to some to be 30 centimetres above the current mean sea level. Scientists who are sceptical about the existence of global warming say it clearly undermines oft-repeated claims that sea levels have risen over the past century because of rising temperatures on Earth.

"This is the oldest known such bench mark in the world," says greenhouse dissenter John Daly, who took the photograph. "Ross put it in an ideal location which is both geologically stable and open to the vast Southern ocean, with no local estuary effects to distort the tides."

The benchmark - a broad arrow containing a horizontal line about 20cm long - was cut into a sandstone cliff on the Isle of the Dead, so-called because it was used as a cemetery for dead convicts.

Scientific scrutiny

It has been the subject of intense scientific scrutiny in the last few years. Australia's Commonwealth Science and Industry Research Organisation (CSIRO) have resorted to navigational satellites, sophisticated tidal gauges, and precision surveying to measure sea levels in the local area today.

Island, Daly
The Island was a cemetery for dead convicts (Photo by J Daly)
Some of Lempriere's old tidal data have also been rediscovered and analysed.

But little of this research has been published so far, says John Daly, and he wants to know why.

"The tax-paying public is entitled to be informed about the 1841 benchmark and why there is so much scientific interest in it. Little or nothing is being offered in the public domain in spite of large expenditure of public money. After all, he who pays the piper should at least hear the tune."

John Daly suspects the results, when they do come out, will confirm the accuracy of the Lempriere-Ross work and raise a big question mark over the claims of the scientific establishment that sea levels are on the rise.

Patchy record

Those claims are also based on historical data from tidal stations like the Port Arthur one, but much younger. The record is somewhat patchy, with most of the data concentrated in the Northern Hemisphere.

Nevertheless, taken together, these more modern marks would appear to show sea levels have risen by about 20cm over the past 100 years.

The UN's Intergovernmental Panel on Climate Change (IPCC) has informed world governments that computer modelling suggests this rise will continue well into the next century if global temperatures increase.

"It is a claim which has been repeated numerous times as part of the Kyoto Protocol politics," says John Daly.

"But when we look at the Ross-Lempriere 1841 bench mark, one thing becomes crystal clear: There has been no sea level rise this century - none at all."

Hot dispute

John Daly's interpretation has been dismissed by Dr David Pugh, from the Southampton Oceanography Centre, UK. Dr Pugh has gone over Lempriere's original work which had been buried in the Royal Society's archives. The Southampton scientist is now assisting CSIRO in their current research programme.

"John Daly has taken the mark, which is a nice clear bench mark, and said 'that is the mean level of the sea at that time', and it wasn't," says Dr Pugh.

"From all the evidence we know it was the high water level at that time - it's like the difference between mid-tide and high-tide. He's wrong."

Dr Pugh says technical problems have prevented CSIRO from recording reliable data until just the last few months and, because mean sea level can change over the course of a year through seasonal water temperature changes, no results will be published until the year 2000.

"Thomas Lempriere was a very bright environmentalist for 1841 and I think he did very good work. And when we have the CSIRO data, we'll then be able to make a direct comparison of the sea levels in 1841 and 1999."

See also:

02 Oct 99 | Science/Nature
20 Sep 99 | Science/Nature
10 Sep 99 | Science/Nature
28 Jul 99 | Science/Nature
03 Jun 99 | Science/Nature
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