Skip to comments.Tasmania: Long-lost records confirm rising sea level
Posted on 01/23/2003 2:11:40 PM PST by cogitator
Long-Lost Records Confirm Rising Sea Level
Hobart - Jan 22, 2003
The discovery of 160 year old records in the archives of the Royal Society, London, has given scientists further evidence that Australian sea levels are rising with an estimate of 16 centimeters since 1890.
Observations taken at Tasmania's Port Arthur convict settlement 160 years ago by an amateur meteorologist have been compared with data from a modern tide gauge.
"There is a rate of sea level rise of about 1mm a year, consistent with other Australian observations," says Dr David Pugh, from the UK's Southampton Oceanography Centre.
"This is an important result for the Southern Hemisphere, and especially for Australia, providing a benchmark against which Australian regional sea level can be measured in 10, 50 or 100 years time," says Dr Pugh.
Working with Dr Pugh on the three year project were the University of Tasmania's Dr John Hunter, Dr Richard Coleman and Mr Chris Watson.
In 1837, a rudimentary tide gauge was made by the amateur meteorologist, Thomas Lempriere and probably installed in the nearby Port Arthur settlement.
In 1841 Lempriere cut a benchmark, in the form of a broad arrow, on a vertical rock face on the Isle of the Dead, which was used as a cemetery for the Port Arthur complex.
The discovery of two full years of carefully recorded measurements (1841 and 1842) of average sea level was the start of a scientific quest through early European history in Tasmania.
CSIRO oceanographer Dr Bruce Hamon, researching Lempriere's work in 1985, concluded that the surviving benchmark would not be of scientific value today.
"The position of course would be different if Lempriere's original observations ever came to light," Dr Hamon wrote.
In addition to discovering the 'lost' files, the project involved analysis of 19th century sea level data, and a suite of modern measurement and analysis techniques.
Dr Hunter said that scientific and popular interest in possible rises of global sea level, with attendant increased risks of coastal flooding have emphasised the need for a long time series of sea level measurements.
"Unfortunately, few records exist from the nineteenth century, and even fewer have well documented benchmark information against which changes can be monitored.
"At Port Arthur we have a unique series of sea level measurements.
"Our research during this project has shown that the work of John Franklin, James Clark Ross and Thomas Lempriere generated a significant benchmark long before any effect of global warming was apparent.
"The scientific interest at the time was the question of vertical motion or uplifting of the continents rather than changes in volume of the oceans.
"Our observations are consistent with the lower end of estimates by the Intergovernmental Panel on Climate Change and with records from Fremantle and Fort Denison," Dr Hunter said.
Measurements have been taken at Fremantle in Western Australia for 91 years and at Fort Denison, Sydney for 82 years.
At the rate of one millimeter a year (roughly a foot every 330~340 years) New York will be underwater just in time for the next Ice Age...
Hell... Volcanoes and other vents in the crust and ocean floor probably outgas that much 'new water' over time.
They proved the water moved up or the rock moved down. The answer as to which may be effectd by the agenda of the observer.
Gilligan have been moving the Professor's tide marking stick over time so as to tie up his crab traps in deeper water. Professor announced that the Island was sinking. Ginger had such a fit that I thought (I was ten then) she was going to come out that dress she wears.
You may be joking, but that's not such a ridiculous possibility.
The measured change is about 1 mm per year -- in constrast, continental drift causes the continents on each side of the Atlantic to slide apart by about 25 mm per year.
If entire continents can move laterally by 25 mm per year, it's not unreasonable to think that an isolated one (Australia) might rise or sink by 1/25th of that amount in the same time.
Basically, the sea level is always either rising or falling. Welcome to Planet Earth.
After reading the responses here, and re-reading Daly's report on the Royal Society Lecture, a couple of things are not clear. I would hope that Daly or the researchers might strive to resolve these questions. I may hope in vain, but nevertheless:
Daly says this in his report:
"Now that we have additional information to hand than existed in September last year when I first presented the story of the `Isle of the Dead', particularly the Lempriere tidal data for 1841 and 1842 (but not his earlier data) and the recent measurements by the CSIRO as reported at the lecture at the Royal Society, we can postulate more accurately what happened."
So the Lempriere tidal data for 1841-42 is "new" for his report.
Daly also says this (text in bold is my emphasis):
"They [Ross and Lempriere] then decide to calculate mean sea level from Lemprieres long term tidal records. How they do this is not known, nor what corrections they might have applied to the data, such as allowance for barometric pressure etc. Ross himself is already an expert in assessing the effect of atmospheric pressure on tide heights, having even worked out a correction factor ."
Here's one of the main problems. To establish mean sea level from tidal records, a record 19 years long is required! Look at the terms "National Tidal Datum Epoch" on this page: http://co-ops.nos.noaa.gov/glossary/gloss_n.html and "Mean Sea Level" on this page: http://co-ops.nos.noaa.gov/glossary/gloss_m.html. The last message in Daly's "Open Review" also refers to this period of time.
At most, Lempriere had five years of data before the benchmark was cut. That's not enough. For example, in the years 1990-93, the Pacific went into a strange El Nino phase in which El Nino conditions developed every summer and faded every winter. If something like that had happened while Lempriere was collecting data, his calculations could have been way off.
According to the CSIRO press release, the only data that they found was for 1841-42. So the predominant question is, could they use this data in combination with other techniques (see below) to establish the true mean sea level that is applicable to the position of the benchmark?
Here are the other techniques that the press release indicates were applied:
- Analysis of 19th Century sea level data
- Installing a modern tide gauge similar to those now used all over the world to measure sea level rise
- 20th Century measurements and analysis
- Site surveying using GPS (global positioning system) and modern surveying techniques
- Assessing the vertical motion of the land surface at Port Arthur using geological evidence from a shell bed at Mary Anne Bay, 42 km from Port Arthur and dated to 125,000 years ago.
- Modelling of the response of the earth since the end of the last glaciation about 6,000 years ago.
OK. Now I agree with Daly that it's not a good idea to discard the Ross account of the placing of the benchmark. At the same time, what Daly doesn't discuss is the fact that Lempriere did not have enough data to truly establish mean sea level. As he notes, how they did it using the data at hand (which was insufficient anyway) is completely unknown.
Daly overlooks or misses this point. He states in the part 2 of his "Isle of the Dead" article that Lempriere had "all the data necessary to calculate that point" (mean sea level). That's incorrect; Lempriere needed about 14 more years of data to do it.
The final possible key to the question is what Dr. Pugh says in the BBC article that Daly links to his site:
"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."
So my feeling is, without having read the report (and it's unlikely I ever will, given that International Hydrological Review is not an online journal), that CSIRO has done the necessary work to establish what the 1841 mean sea level was at Port Arthur. Even if Ross and Lempriere did the best job of establishing mean sea level from Lempriere's data that they could, they didn't have enough data to actually do it.
The uncertainty about CSIRO's method of establishing the 1841 mean sea level is what I'd like to see cleared up. The paper probably tells how they did it -- so if anyone can get that paper and report what it says, I would be grateful.
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