House of Representatives Committees

Joint Standing Committee on Treaties

JSCOT Submission- Section 3

Testing the Waters

A Report on Sea Levels

by
John L. Daly

The Ross-Lempriere sea level benchmark on the `Isle of the Dead'

"Is this the mark that takes the heat out of Global Warming?" - asks the BBC [2]

 

Introduction

A serious problem confronts any researcher who looks into the question of tides and sea levels, especially when searching for that elusive concept known as `mean sea level', (MSL) or "Zero Point of the Sea" (as Captain Sir James Clark Ross, the 19th century British Antarctic explorer, called it [36]). Not only is it difficult to determine true MSL at any one location, it is even more difficult to detect any changes occurring with that level. For example, imagine attempting to measure mean sea level on a Hawaiian surfing beach. Sea level and tides work over longer timescales, but the essence of the problem is much the same. Study of sea level has now taken on a more urgent importance due to the predictions of sea level rise which might result from any global warming resulting from increased emissions of carbon dioxide (CO2) [23].

Climate modelers and the Intergovernmental Panel on Climate Change (IPCC) have predicted that one of the consequences of global warming will be rising sea levels due to thermal expansion of the ocean water mass and melting of non-polar glaciers [21] [23]. They claim the oceans have already risen 18 cm during the 20th century, an annual rate of 1.8 mm/yr. They further predict that the oceans will rise a further 50 cm approximately during the 21st century [45], an accelerated annual rate of 5 mm/yr [25].

These predictions are now taking on hysterical proportions by policy institutions such as the EPA [44], who readily adopt a worse than `worst case' scenario. They claim that a 1 meter sea level rise will inundate 7,000 square miles of dry land, 50-80% of U.S. wetlands, and cost over $270 - 475 billion in the U.S. alone. As a final touch, they claim their estimates `are almost certainly too low'.

To support their assertions about past sea level rise, the IPCC cite records from tide gauges, one of the oldest being from Brest in France (Fig.1) [35] -

Annual MSL at Brest, France
Fig.1 - Annual MSL at Brest, France [34]

Here we have a sea level in 1805 at around 6,900 mm rising to around 7,100 mm by the late 1990s, a rise of 200 mm, or approximately +1 mm per year.

The future rise in sea level, according to the IPCC [23] [25], will be caused by two factors. Firstly, the waters of the oceans will expand in volume due to global warming, just as metals expand when heated. Secondly, warming will result in melting of many non-polar glaciers, adding further water to the ocean mass. Looking beyond the 21st century, there are hints of greater sea level rises of several meters if the great ice sheets of Antarctica and/or Greenland begin melting into the sea.

Another school of thought, first postulated by British meteorologist, Sir George Simpson in 1938 [40], and confirmed by several studies since [30] [41] [31] [26], suggests that a warming ocean will result in more evaporation and thus more cloudiness. The `Simpson Effect' as it has been called [13], would increase precipitation over the polar regions in the form of snowfall, building up the ice mass, and thus become frozen water permanently lost from the oceans. Yet more moisture will precipitate over internal land catchments such as the Caspian Sea and Lake Victoria in east Africa, again removing water from the ocean mass. These latter processes are believed to be sufficient not only to offset the rise in sea level predicted from ocean warming, but could result in a fall in sea level of up to 7 mm/yr [30].

Prof S. Fred Singer demonstrated that not only does warming not raise sea levels, but there is also an observed inverse relation between global temperature and sea levels due mainly to the increased removal of water from the oceans to the ice caps cancelling out the sea level effect of any thermal expansion of the oceans during periods of climatic warming. [41].

The IPCC predictions of sea level rise presupposes there will be a significant human-induced global warming to begin with, a questionable assumption, given the lack of warming to date as measured from satellites, and the lack of polar warming which would be a signature unique to a greenhouse induced warming. By `significant' is meant a warming of 1°C or more. Current trends would suggest an insignificant warming over the next 100 years of only a few tenths of a degree, not whole degrees.

 

Time and Tide

We are all familiar with `tides', the twice daily rise and fall of the level of the sea as the fluid mass of the oceans adjusts to the changing gravity interactions between Earth, Moon and Sun. There are the `spring tides' and `neap tides', the tendency for the tides to be greater during a full moon and a new moon, than they are during a half moon. Less obvious are the other variations in the tides, of the numerous subtle `harmonics' which can be superimposed on the basic tidal pattern, and on the observed changes in general sea level which ebb and flow over many years.

The moon is the primary influence on our tides. As the Earth rotates, the moon's gravity `pulls' at the ocean, causing it to rise in a wide wave riding in the wake of the moons relative passage across the sky. The sun also raises a similar, though smaller tide, being 46% of the moon's tide. When the sun and moon are in in line with the Earth. the combined sun-moon gravity raises a larger tide than usual - a `spring tide'. When the moon is at right angles to the Earth-Sun axis during a half-moon, the two gravity forces act against each other, resulting in a smaller tide than usual - a `neap tide'. Every 28 days, the orbital period of the moon, there are two periods of spring tides and two periods of neap tides.

The moon's orbit is not circular but elliptical and so the effect of the moon's gravity is not uniform throughout the 28 days. The Earth's orbit around the Sun is also elliptical which causes the effect of the Sun's gravity to vary throughout the year. Finally, the moon does not orbit the Earth on the same plane as the Earth's equator, but orbits at an angle to it. This results in the Moon sometimes passing directly overhead regions of the Northern Hemisphere, while at other times it is over the Southern Hemisphere. Since the tide follows the moon, the tides will be higher in those regions where the moon's orbital path periodically takes it high in the sky, and lower in those regions where the moon's orbit periodically takes it lower in the sky.

There are many more Sun-Earth-Moon orbital variables or `harmonics' to be considered, supplemented by strictly earthbound variables such as coastline and seabed topography, ocean currents, and meteorological effects of winds and pressure. Strong winds can push the tides higher against some coasts, commonly known as `king tides'. High atmospheric pressure can depress the level of the sea by about 1 cm per millibar, while low pressure `pulls' it up by a similar amount.

The above list of variables is not exhaustive but is enough to demonstrate the complexity of the problem. At any one time, some variables act to reinforce the tide, others to dampen it. It takes 18.6 years for every permutation and combination of the astronomical variables to play themselves out at any one location [18]. Only then could a researcher calculate a long-term MSL with some degree of confidence and exactness.

A global `Zero Point of the Sea' is indeed an elusive concept.

 

Mean Sea Level - `Zero Point of the Sea'

`Mean Sea Level' or MSL is defined as "the mean level of the water surface over a specific long series of measurements. No matter how long a period of data is averaged, the ideal true mean sea level is unattainable because changes are taking place over long and short time scales." [7]. Where sea level is measured at only one location, it is sometimes referred to as `Relative Sea Level' or RSL, since the measurement only specifies the height of the sea in relation to local landmarks. If the land itself is rising or sinking, this would manifest itself as apparent sea level falls or rises, even if the actual level of the ocean had not changed. Until the advent of satellites, it was not possible to establish a truly global MSL.

`Mean Sea Level' as a descriptive term is often used to mean either the MSL at one location (ie. RSL), or over an entire region. Global MSL is ultimately determined by the quantity of water in the oceans, the temperature of that water, the volume of ice stored on the Antarctic and Greenland ice sheets, the volume of ice stored in non-polar glaciers, and the quantity of water stored in natural and man-made inland catchments, lakes, and reservoirs.

The standard instrument to determine MSL and the tidal extremes is a `tide gauge', which measures the height of the sea at regular intervals to record the passage of high and low tides and the harmonics unique to the location where the tide gauge is situated. Most such gauges are installed in the populated areas of the northern hemisphere, particularly in Europe and North America, there being relatively few such gauges with long records in the southern hemisphere.

Annual mean sea level at Aberdeen, Scotland, UK
Fig.2 - Annual mean sea level at Aberdeen, Scotland, UK [35]

Fig.2 shows one of the oldest tide gauge records in the world, Aberdeen on the east coast of Scotland. There are a few European ones which are older, such as Brest in France (Fig.1) and Amsterdam in Holland, but their records are broken, with gaps of several years making height comparisons between data periods somewhat problematic. Aberdeen is interesting in that its record is continuous since 1862.

The peak level at Aberdeen was around 1950 at 7087 mm and the lowest point around 1889 at 6887 mm. The overall sea level rise since 1862 is around 70 mm (ie. less than 3 inches), or an averaged annual rate of around +0.5 mm/yr, half the rate recorded at Brest and less than one third the global rate claimed by the IPCC.

Can this Aberdeen record be taken at face value? Does it really reflect trends in global sea level? The short answer is we don't know. Tide gauges, like surface temperatures, are subject to several local errors which can distort the data. Just as temperature data is affected by urban heat islands, tide gauges located at major cities or ports are subject to urbanization also, mainly the tendency of large cities to subside due to the weight of the structures and the changes in the underground water table. The larger the city, the greater is the tendency toward subsidence, a creeping effect over time which will manifest itself at a tide gauge as a creeping rise in relative sea level. Cities located on alluvial low lying coasts are the most affected.

For example, Adelaide in South Australia is showing a strong sea level `rise' which is not evident at nearby smaller ports (Port Pirie, Port Lincoln, Victor Harbour). The Adelaide anomaly has since been found to be caused by long-term withdrawal of groundwater since European settlement, giving rise to local urban subsidence [3]. Another bad case of subsidence exists in Bangkok, where the sea has risen by a meter in the last 30 years. The sea has not really risen, the land is merely sinking [38].

A second subsidence error arises from the fact that most tide gauges are mounted on man-made structures such as piers and docks. Over many decades, these will undergo some subsidence unless they are built on bedrock.

In the Netherlands, the tide gauge record from Amsterdam, cited in the IPCC draft report [25], is the longest in the world, extending back to 1700. Another Dutch record from Hoek Van Holland dates from1865. Both show a distinctive long-term sea level rise since the mid 19th century. This may of course be due to urban subsidence also, but one factor makes all Dutch tide gauge data questionable for global sea level studies. "God made the world, but the Dutch made Holland" is a popular saying which acknowledges the extensive reclamation of land from the sea which has characterized Dutch history for centuries.

Two of the key variables determining tide height is seabed topography and coastal topography. The Dutch have changed both in extensive ways. Over several centuries, the Dutch have been reclaiming land from the sea, altering their own coastline and thus permanently changing tidal flow patterns [38].

During the 20th century, the Dutch reclaimed much of the large inland gulf known as the Zuider Zee (Fig.3 map) and dammed off the rest from the North Sea. Before these coastline changes were made it was a large tidal sink. Tidal water flowing up and down the English Channel and North Sea which previously could drain in and out of the Zuider Zee is now unable to do so, thus raising local sea level outside, particularly during high tides. The surrounding sea is shallow, being typically only 25 to 30 meters in depth, and this makes the whole region tidally sensitive to coastal terraforming.

Map of Holland, showing the former Zuider Zee, now landlocked by the Ijsselmeer Dam
Fig.3 Map of Holland, showing the former Zuider Zee, now landlocked by the Ijsselmeer Dam
(Based on map from Microsoft Encarta96 World Atlas)

Although the Dutch are among the more strident advocates of the Kyoto Protocol due to their sensitivity about the prospect of sea level rise, their own programs of land reclamation over several centuries may have contributed significantly to the very problem they now perceive as threatening to their national interest.

In Sweden, we have a very different record from Stockholm as shown in Fig.4 below

The raw sea level record from Stockholm
Fig.4 - The raw sea level record from Stockholm [35]

The sea level is clearly falling, by about 40 cm over 110 years. This is in spite of the possibility of city subsidence. But here is how the IPCC portrays Stockholm in the latest Third Assessment Report draft.

The IPCC corrected sea level record from Stockholm
Fig.5 - The IPCC corrected sea level record from Stockholm (scale in mm) [25]

Fig.5 is a `detrended' record to correct for a phenomenon which puts all European and North American tide gauge data in doubt. It is `Post Glacial Rebound' or `PGR'. During the last ice age, Stockholm was buried under several kilometers of ice. The ice age ended about 10,500 years ago with a rapid melting of ice sheets over Europe and North America with a resulting rise in sea level. With the ice gone, the plasticity of the mantle below the solid crust of the earth is forcing the crust upwards now that the dead weight of the ice is no longer there. This process has been ongoing since the last ice age and will continue well into the future.

The North Atlantic Basin, showing the areas most affected by PGR
Fig.6 The North Atlantic Basin, showing the areas most affected by PGR
(Based on map from Microsoft Encarta96 World Atlas)

PGR is underway all over Europe, North America, and east Asia (see Fig.6) [34], the continents most affected by these enormous ice sheets. It causes those regions which were weighed down by ice (bounded by a continuous red line) to uplift like Sweden, and causes peripheral regions around the margins of the former ice masses (bounded by a dashed red line) to subside as the continental crusts adjust and rebalance to the new weight redistribution.

The North Atlantic is actually a huge basin semi-enclosed by continental land masses, with a 1,400 nautical mile gap between west Africa and South America to connect it to the remainder of the world's oceans. This may partly explain why long-term tide gauge records from within that basin are not always consistent with records from outside the basin. It is also unfortunate that all the really old tide gauge records extending back into the 19th century come from Europe, right in the center of the PGR zone. The later American ones are similarly affected.

We can see a clear example of PGR from the steady rise in relative sea level at Trieste, Italy, located at the northern end of the Adriatic Sea which has hardly any tides at all to complicate sea level.

Monthly mean sea level atTrieste, Italy. 1905 -1999
         Fig.7 Monthly mean sea level atTrieste, Italy. 1905 -1999 (year marks not shown but can be inferred)

The Trieste record mirrors that of Venice just across the Gulf of Venice from Trieste. Since northern Italy is on the margins of the great ice sheets from the last ice age, the steady and largely linear rise in sea level from 1905, amounting to about 15 cm is clearly unrelated to transient climate events, but due to an underlying geological cause, namely PGR. This long-term rise even pre-dates 1905 as a comparison of paintings of the famous Rialto Bridge in Venice by 18th century artists Francesco Guardi and Canaletto with modern photographs of the same bridge (Fig.8), reveal a sea level much lower than the 15 cms represented in the 20th century tide gauge record from Trieste.

  Rialto Bridge, Venice around 1770 (Canaletto) compared with the same bridge today
Fig.8 - Rialto Bridge, Venice around 1770 (Canaletto) compared with the same bridge today

Local sea level rise in Venice has been occurring for hundreds of years, well before greenhouse gases became an issue, and is clearly of geological, not climatic, origin. Urban subsidence is also a major contributing factor in the case of Venice.

It is not just the removal of the weight of the ice which causes uplift and subsidence in the regions directly affected, but the melting of the ice itself has raised global sea levels by over 120 meters [25]. This changes geological stresses on regions far away from the ice due to the added weight of water on continental shelves, causing a slow readjustment and rebalancing of continental crusts everywhere to compensate for the added weight of water.

Most tide gauge records which extend back into the 19th century are of generally poor quality with extensive breaks in data, as shown in IPCC charts [25]. Unfortunately, these records also originate in places affected by PGR, showing sea level falls in places like Sweden and equally large rises (3.5 mm/yr) in areas like Chesapeake Bay on the US Atlantic coast [15]. In these cases, it is the vertical movement of the land itself which is causing the apparent, or `relative', sea level to change.

In other parts of the world, we have many tide gauges installed in tectonically active areas, such as the Pacific coast of North America [19], Japan and New Zealand [15]. Here too, we cannot attribute any apparent sea level changes solely to the sea itself due to the geological instability of the land upon which the tide gauge is mounted. Indeed, we have to regard tide gauge data from anywhere on the geologically active parts of the Pacific rim (the so-called `Ring of Fire') as being profoundly compromised by tectonic activity. Tide gauges on any other coastline affected by tectonic activity must be equally compromised.

We could of course, disregard all tide gauge data from geologically unsuitable locations, but if we do that, we end up with hardly any data at all [38]. So it should at least be recognised that much of the data being analysed is of very poor quality and badly distributed geographically.

To make some sense out of the mass of contradictory sea level data, a series of `de-glaciation' models were developed using calculations of earth mantle viscosity to determine how the mantle and overlying continental and seabed crusts would react to the melting of the great ice sheets at the end of the last ice age.

 

The `ICE-3G' Model

In the earlier case of Stockholm, with its sharply falling sea level, IPCC scientists made a massive correction to the data, turning a relative sea level fall into a mean sea level `rise'. This outcome resulted from adjusting the observed data with correction factors derived from the ICE-3G model developed by Peltier and Tushingham in 1991 [34]. This model purports to describe crustal movements of the continents and sea bed in the wake of the demise of the great ice sheets. The model depends on calculations about the plasticity of the earth's mantle upon which the crustal land masses `float'.

ICE-3G is the most used model for correcting tide gauge data against PGR [15].  It's creators, Peltier and Tushingham were among the first scientists to make the linkage between global sea level rise and the Greenhouse Effect, claiming in 1989 that sea levels were rising at a rate in excess of 1 mm/yr [33].

The impression has been conveyed to the world's public, media, and policymakers, that the sea level rise of 18 cm in the past century is an observed quantity and therefore not open to much dispute. What is not widely known is that this quantity is largely the product of modeling, not observation, and thus very much open to dispute, especially as sea level data in many parts of the world fails to live up to the IPCC claims.

The ICE-3G model is a global theoretical treatment describing how the ice masses melted and disentegrated at the end of the last ice age and the consequent readjustments made by the crust under pressure from the lithosphere below. However, the model does have some inherent weaknesses.

What is very clear is that the ICE-3G global de-glaciation model is really a North Atlantic-Arctic model, the accuracy of which must deteriorate as distance increases from the ancient ice sheets, particularly in regions outside the North Atlantic basin. For the rest of the world's oceans and crust, this model may have little relevance at all, especially given the paucity of RSL sites in the Pacific and southern hemisphere oceans against which to calibrate the model.

Even within the North Atlantic basin where the model would be expected to exhibit its greatest degree of accuracy, a 1996 study by Davis & Mitrovica [14] of the southeastern seaboard of the U.S. found that the ICE-3G model overestimated sea level rise in that region due to incorrect calculation of lower mantle viscosity. From Key West to Cape Hatteras, their recalculation of mantle viscosity resulted in a reduced estimate of sea level rise from 2.28 mm/yr to 1.45 mm/yr.

For the other four great oceans of the world, the model can only be judged, not according to its theoretical elegance, but in observing how its application to the sea level problem accords with observed reality. The IPCC estimate of +1.8 mm/yr sea level rise in the 20th century is critically dependent opon the processing of tide gauge data using this model.

Finally, it must be stressed that the ICE-3G model does not and cannot correct for tectonics such as exists on the `Ring of Fire' in the Pacific. It does not and cannot correct for local urban subsidence such as exists in Adelaide, Venice and Bangkok. It cannot correct for subsidence of man-structures upon which tide gauges are mounted. With or without the ICE-3G model, all these other local errors still exist and make global estimates of sea level change very difficult to validate.

Whatever degree of confidence is placed in this model, its use in determining past global sea level changes means that the IPCC estimate of +18 cm sea level rise over the last 100 years cannot be regarded as an observed value, but as a largely modelled value with a high error margin due to local distortions.

 

The IPCC Claims ...

Using historical tide gauge data, Atmosphere-Ocean General Circulation Models (AOGCMs) and the ICE-3G model, IPCC scientists have interpreted the past, present and future of sea levels to make these basic claims [25] -

Contributing factor Lowest estimate (cm) Highest estimate (cm)
Thermal expansion of the ocean
Non-polar glacier melt
[21]
Antarctica ice accumulation/melt
Greenland ice accumulation/melt
Melting of permafrost

+20
  +8
   - 8
  +2
 +10

+37
+11
- 2
 +5
+10

Most of the claims are qualified by caveats relating to changes in water storage on land which may reduce the sea level rise by 10 cm. If the figures appear to be inconsistent with the broader estimates, this reflects the confusion within the IPCC itself as it wrestles with multiple scenarios, contradictory model results and caveats about unknown quantities such as water storage on land.

There are other significant contributing factors to sea level change such as human land use [37] and the effect of natural internal catchments in removing water from the ocean, but the above are considered to be the major ones. Human activities such as irrigation, land reclamation, flood levees, building dams and reservoirs was estimated by Sahagian et al to have contributed at least a third of the `observed' sea level rise during the last 100 years and will continue to do so at a rate they estimate of 0.54 mm/yr [37]. The negative `lowest estimate' value shown for Antarctica indicates that the IPCC now acknowledge the possibility that the `Simpson Effect' involving increased precipitation over the polar regions may result in a negative contribution to sea level change in the 21st century.

The West Antarctic Ice Sheet has frequently been pointed to by environmental activists as a source of possible catastrophic sea level rise as its collapse would raise sea levels by about 5 meters. But according to the IPCC and numerous other research bodies including the Australian Antarctic Division, this possibility is off the climatic agenda for at least 1,000 years and probably as long as 7,000 years, even with global warming. As to the chances of it collapsing due to purely natural reasons, this is rated by the IPCC at only 100,000:1 [25].

The IPCC have made it very clear that in their view, the changes in sea level, past and future, are mostly driven by the state of the climate. We must now examine the credibility of these IPCC claims, beginning with their claim that sea levels have already risen 18 cm during the 20th century.

 

20th Century Sea Levels

Recent studies of tide gauge data suggest that there has been a sea level rise in the last 100 years of between 10 and 25 cm, with a preferred value of 18 cm, but it requires the application of the ICE-3G model correcting the data for the effects of PGR, to establish a rise of that magnitude. Expressed as an annual rate, the average rate of increase is 1 to 2.5 mm/yr, with a preferred value of 1.8 mm/yr.

Once we depart from the northern hemisphere tide gauges, particularly those from within the North Atlantic basin, and those compromised by local tectonic activity, a very different picture emerges about sea levels. The following graphs are either directly from the Permanent Service for Mean Sea Level (PSMSL) [35], or drafted from data originating from the same source.

Here is the monthly MSL from Montevideo in Uruguay, with a 12-month smoothing added -

Monthly and smoothed relative MSL from Montevideo, Uruguay
                 Fig.9 - Monthly and smoothed relative MSL from Montevideo, Uruguay

The record has several short breaks, and with the exception of an anomalous peak in sea levels during the early 1980s, there appears to be little change at all.

Crossing the South Atlantic east from Montevideo, we arrive at East London, South Africa.

Monthly MSL from East London, South Africa, 1967 to 1998
Fig.10 - Monthly MSL from East London, South Africa, 1967 to 1998

This record is also broken in parts, but other South African tide gauges are even worse, a common problem all over the world. There we see a peak variation in sea level of around 40 cm during the early 1970s although there is no significant long-term trend.

Crossing the Indian Ocean, we arrive at Vishakhapatnam on the east coast of India.

Monthly MSL from Vishakhapatnam, India
Fig.11 - Monthly MSL from Vishakhapatnam, India

This is a good quality record overall with only a few brief breaks. There is little overall change over a 57-year record, sufficient time to have resulted in a sea level rise of over 10 cm if the IPCC claim were correct.

Moving southeast, we reach Australia. Here is a short-run sea level series from Newcastle, New South Wales, Australia -

Monthly MSL from Newcastle, NSW, Australia, 1972 to 1986
Fig.12 - Monthly MSL from Newcastle, NSW, Australia, 1972 to 1986 [34]

The time duration is only 14 years, less than the 18.6 years required for a full cycle of astronomical variables to be played out, but we can see that there has been an overall fall in sea level during that time.

Moving south to Tasmania (an island state of Australia 200 miles south of the mainland, deep in southern latitudes) at latitude 42S, we reach Spring Bay (Fig.13).

Monthly MSL from Spring Bay, Tasmania, Australia, 1992 through 1998
Fig.13 - Monthly MSL from Spring Bay, Tasmania, Australia, 1992 through 1998 (scale in cm)

Spring Bay has a modern state-of-art tide acoustic gauge mounted in a rural location on coastal bedrock, thus avoiding urban subsidence problems. This site faces directly onto the Southern Ocean and has a very small tidal range of about 70 cm between high and low tides. Although the record is short, there is no long-term change evident as yet.

Moving north into the western Pacific Ocean, we finish the journey at Nauru (Fig.14).

Monthly MSL from Nauru, western Pacific Ocean
Fig.14 - Monthly MSL from Nauru, western Pacific Ocean.

Nauru clearly demonstrates the impact of the El Niño Southern Oscillation on sea levels in the western Pacific. During the two major El Niño events of recent years, 1982-83 and 1997-98, there is a sharp, but temporary, fall in sea level. Statistically, this would amount to a long-term fall in sea level over the period of record, but it is clear from the graph that sea levels either side of the El Niño events are largely unchanged. For this reason, it would be prudent to exclude the anomalous effect of El Niño events from statistical estimates of long-term sea level.

From these examples of sea level data from places known to be tectonically stable, there is little evidence of long-term sea level rise at all. We know that the partially enclosed North Atlantic basin is severely affected by PGR, but once out of that basin, the effect of PGR seems to diminish significantly, raising questions as to just how much confidence should be placed in the ICE-3G model as it affects regions well removed from the North Atlantic.

The Australian National Tidal Facility (NTF) at Flinders University in Adelaide published a `Mean Sea Level Survey' in 1998 to establish sea level trends around the Australian coast from tide gauges having more than 23 years of hourly data in their archive [29]. This survey was particularly relevant for global application since Australia is tectonically stable and much less affected by PGR than either Europe, Asia or North America. Since nearly two-thirds of the world's total oceanic area is in the southern hemisphere, Australia is best placed to monitor southern hemisphere trends and probably best represents the true MSL globally. Also, the Australian coast adjoins the Indian, Pacific, and Southern Oceans, making its data indicative of sea levels in three oceans, not just one.

The NTF identified the following tide gauges as meeting the criteria, and calculated the annual sea level change for each (in mm/yr). Sea level rises are shown in red, falls in blue. The stations run anti-clockwise around the Australian continent, starting with Darwin in the Northern Territory. Compare these results against the claimed IPCC rate of +1.8 mm/yr.

Location

Years of data  

Est. trend
(mm per year)

Darwin, NT
Wyndham, WA
Port Hedland, WA
Carnarvon, WA
Geraldton, WA
Fremantle, WA
Bunbury, WA
Albany, WA
Esperance, WA
Thevenard, SA
Port Lincoln, SA
Port Pirie, SA
Port Adelaide - Inner, SA
Port Adelaide - Outer, SA
Victor Harbour, SA
Hobart, TAS
George Town, TAS
Williamstown, VIC
Geelong, VIC
Point Lonsdale, VIC
Fort Denison, NSW
Newcastle, NSW
Brisbane, QLD
Bundaberg, QLD
Mackay, QLD
Townsville, QLD
Cairns, QLD

34.9
26.4
27.7
23.9
31.5
90.6
30.2
31.2
31.2
31.0
32.3
63.2
41.0
55.1
30.8
29.3
28.8
31.8
25.0
34.4
81.8
31.6
23.7
30.2
24.3
38.3
23.6

-0.02
-0.59
-1.32
+0.24
-0.95
+1.38
+0.04
-0.86
-0.45
+0.02
+0.63
-0.19
+2.06
+2.08
+0.47
+0.58
+0.3
+0.26
+0.97
-0.63
+0.86
+1.18
-0.22
-0.03
+1.24
+1.12
-0.02

Eleven of the 27 stations recorded a sea level fall, while the mean rate of sea level rise for all the stations combined is only +0.3 mm/yr, with an average record length of 36.4 years. This is only one sixth of the IPCC figure. There was also no obvious geographical pattern of falls versus rises as both were distributed along all parts of the coast.

But there's more. It was shown earlier that Adelaide was a prime example of local sea level rise due to urban subsidence [3]. It's two stations in the above list are the only ones to record a sea level rise greater than the IPCC estimate. The same NTF survey pointed out the Adelaide anomaly and directly attributed it to local subsidence, not sea level rise, on the grounds that the neighboring stations of Port Lincoln, Port Pirie and Victor Harbour only show a rise of +0.3 mm/yr between them. If we exclude Adelaide from the list, the average sea level rise for the other 25 stations is then only +0.16 mm/yr, or less than one tenth of the IPCC estimate.

If this world tour, ending with the Australian survey, were not convincing enough, there is one further piece of evidence from Australia which demonstrates that the IPCC, and the ICE-3G model which underpins their predictions, is wrong about the magnitude of 20th century sea level rise.

 

The `Isle of the Dead'

The `Isle of the Dead' with Point Puer in the immediate foreground (Photo John L. Daly, Aug 29th 1999, late afternoon)
Fig.15 - The `Isle of the Dead' with Point Puer in the immediate foreground
(Photo John L. Daly, Aug 29th 1999, late afternoon)

" `Dead Men's Isle' is a picturesquely sorrowful spot - so soothing in its melancholy,
so placid in its solitude." (David Burn - a visitor to the `Isle of the Dead' in 1842)

The `Isle of the Dead' is not mentioned at all by the IPCC in any of its reports. However, there is intensive research presently underway by several institutions [24] including Australia's `Commonwealth Science and Industry Research Organisation' (CSIRO Marine Research Division), assisted by the head of the Inter-Agency Committee on Marine Science & Technology, Dr David Pugh, who is based at the University of Southampton, UK, all focused on this sleepy little isle at the bottom of the world in Tasmania.

The `Isle of the Dead' is over two acres in size, situated within the harbor of Port Arthur in southeastern Tasmania . This large and undeveloped harbor opens out directly to the Southern Ocean. The isle itself is actually a graveyard (thus its eerie name), containing the graves of some 2,000 British convicts and free persons from the 19th century who lived and died at the nearby convict colony of Port Arthur between 1832 and 1870. Port Arthur is now a heritage historic site, visited by thousands of tourists every year to see the convict buildings and ruins, and to enjoy the popular night-time `ghost tours'.

To understand why there is so much scientific interest in the Isle, we must travel back in time ...

British Antarctic explorer, Captain Sir James Clark RossIn September 1840, the renowned British Antarctic explorer, Captain Sir James Clark Ross (photo), sailed from Hobart Town, the capital of Van Diemen's Land (the former name for Tasmania) for a 6-month voyage of discovery and exploration to the Antarctic with his two expedition ships, `Erebus' and `Terror'.

After a highly successful voyage, he returned in April 1841 for a refit and resupply of his ships and spend the southern winter in temperate latitudes. Upon arrival at Hobart Town, he was disappointed to learn that a golden scientific opportunity had been lost. A proposal by Baron Von Humboldt to the British Colonial Secretary, Lord Minto, that mean sea level marks should be struck on newly discovered coasts and islands, had arrived during Ross' absence in the Antarctic. Ross was unaware of Humboldt's proposal until he returned to Hobart Town in 1841. He later related this in his book (published in 1847) [36] -

In spite of the missed opportunity, Humboldt's idea still appealed to Ross and to the Governor of Van Diemen's Land, Sir John Franklin, himself a naval man. Consequently, both Ross and Franklin made a point of visiting Port Arthur, 40 miles from Hobart Town, to meet Thomas Lempriere, a senior official of the convict colony there, but who was also a methodical observer and recorder of meteorological, tidal, and astronomical data. Here is the account Ross gives of his visit to Lempriere at Port Arthur - .

Ross further explained why he chose Port Arthur for a mean sea level mark instead of in the Derwent estuary closer to Hobart Town, where his ships `Erebus' and `Terror' were moored.

The `permanent mark' at the `zero point, or general mean level of the sea' that Ross wrote about has proved to be more permanent than even he bargained for -

The mark is still there, and in perfect condition.

The Ross-Lempriere sea level benchmark on the `Isle of the Dead'    The Ross-Lempriere sea level benchmark on the `Isle of the Dead' (photo taken by John L. Daly at mean tide, Aug 29, 1999. Benchmark is 50 cm across)
Fig.16 - The Ross-Lempriere sea level benchmark on the `Isle of the Dead'
(photo taken by John L. Daly at mean tide, Aug 29, 1999. Benchmark is 50 cm across)

In the photo above, the line and arrow mark is a standard British Ordnance Survey Benchmark, 50 cm across, and is standing in the photo about 35 cm above the water level. Since the photo was deliberately taken at the time of mean or half-tide for that day, we see in this one photo the enigma that is the `Isle of the Dead'. Because, how can a benchmark struck at "zero point" or the "mean level of the sea", as described so explicitly by Ross, now be 35 cm above the mean level today? Has the sea level fallen?

(For a more detailed discussion about the fascinating origins of this benchmark, see the Appendix)

Of course, mean tide on the day of the photo may not be the long-term MSL. However, the CSIRO has been researching the benchmark since 1995, installing a new state-of-the-art acoustic tide gauge at the Port Arthur jetty a mile away, setting up a network of GPS buoys around the harbor, and involving other institutions in the effort. Their unpublished conclusion is that the benchmark is indeed 35 cm above current mean sea level [12].

And they cannot explain it in a manner consistent with the Ross account.

Southeastern Tasmania is believed to be uplifting very slightly due to PGR, although there is no tectonic activity in the region. The CSIRO installed GPS receivers and GPS marine buoys in the Port Arthur area to test for the effect of PGR. It takes several years to get an uplift rate accurate to within millimeters using GPS positioning. However, the CSIRO have made a preliminary, though unpublished, uplift estimate of 0.61 mm/yr ±0.22 mm/yr. Over the full period of 159 years since the benchmark was struck, this uplift rate would result in a relative sea level fall of between 6.2 cm and 13.2 cm, with a mid range value of 9.7 cm. This is only a fraction of the 35 cm to be accounted for. However, local geological shoreline evidence indicates an uplift much less than this at around 0.19 mm/yr, giving a total uplift since 1841 of only 3 cm [6]. The geological figure is probably the more accurate because it represents actual past uplift, whereas the albeit preliminary GPS result can only represent a current rate of uplift.

In 1888, a scientific assessment of the benchmark was made by Capt. Shortt, who surveyed it in an effort to determine its exact origins and meaning. He searched archives in Hobart and Port Arthur for information and reported his findings in a short paper published by the Royal Society in Hobart [39].

A small tablet was found above the benchmark (the tablet went missing around 1913 [28]) and this gave Shortt the date the benchmark was struck as July 1st 1841, at a point in the lunar month when the age of the moon was 12 days. In order to measure sea level under similar conditions which existed then, Shortt made his calculation of MSL and the benchmark height when the age of the moon was also 12 days, as cited on the tablet. His conclusion, in 1888, was that the benchmark was 34 cm above mean sea level, only a centimetre less than the CSIRO estimate of 35 cm 112 years later. As Shortt was familiar with the Ross account given above, he was perplexed as to why a `mean sea level' benchmark should now be 34 cm above MSL 47 years later.

Moving forward in time to 1985, Bruce Hamon, a scientist from Sydney, also studied the benchmark. He concluded that it was 36 cm above MSL [22]. He examined tide data from nearby Hobart to establish the current point in the 18.6 year cycle, so we can be confident of his 36 cm estimate.

Hamon's was only the second, and the last, paper to appear in the scientific literature about the Ross-Lempriere benchmark. Since then, nothing has been published, not even interim results from the recent CSIRO research. All that has appeared in the public domain are a few media releases, none of which impart the vital information to the public that a mean sea level benchmark struck in 1841 now spends most of its time out of the water.

Since the benchmark has been observed to be the same height above relative MSL on three sets of good observations 112 years apart (Capt Shortt [1888], Hamon [1985] and the CSIRO [2000]), sea levels have clearly not changed at Port Arthur in all that time. Being tectonically stable and subject to only minor PGR, land uplift will hardly provide an adequate explanation for the lack of sea level rise since 1888 and a possible sea level fall between 1841 and 1888.

The benchmark powerfully confirms what the Australian Mean Sea Level Survey [29] tells us, namely that the rate of sea level rise over much of the 20th century has only been +0.16 mm/yr, less than one tenth of the IPCC's estimate of 1.8 mm/yr. This survey would imply a sea level rise of only +1.6 cm for the whole century, consistent with observations and measurements of the Ross-Lempriere benchmark since Capt. Shortt first observed it in 1888.

The joint `Co-ordinating Lead Author' of Chapter 11 (sea levels) of the draft Third Assessment Report of the IPCC [25] is Dr John Church, who heads the CSIRO Marine Research Division in Hobart, Tasmania. The organization he heads is deeply involved in researching the benchmark as shown by their press release of 1998. In spite of this, there is no discussion about the benchmark, or its implications for historical sea levels, in the IPCC draft co-authored by Church. The draft cites old tide records from PGR-ridden Europe and even complains about the lack of data from the southern hemisphere, but nothing is mentioned about a 159-year-old sea level benchmark in the data-sparse southern hemisphere which predates most other records, and is located only 1 hour's drive from Hobart.

The most comprehensive information about the benchmark and the historical events and personalities surrounding it comes from this author's website, from which futher details can be obtained at the linked references given [10] [11] [12].

There is also a discussion about the origins of the benchmark in the Appendix

 

Sea Level `Secession' for the Southern Oceans

The Australian Mean Sea Level Survey of 1998 [29] may be one reason why the IPCC have made the somewhat strange suggestion in their Third Assessment Report draft that sea level rises in the Southern Ocean will be less than those in the northern hemisphere. This conclusion stems from the outputs of Ocean-Atmosphere General Circulation Models (AOGCMs) some of which predict sharp differential trends in sea levels between regions during the 21st century.

From the results of the survey, and the evidence of the Ross-Lempriere benchmark which supports it, we can see that the IPCC's 1.8 mm/yr claim for past global sea level rise is simply wrong. The source of the error is quite probably the ICE-3G model when used to adjust tide gauge data beyond the North Atlantic basin, and the fact that too many global inferences are being drawn from North Atlantic data.

Rather than confront this issue directly, the IPCC and the modelers have chosen instead to `quarantine' the Australian survey by suggesting that the Southern Oceans can somehow go their own way when it comes to sea level rise. Given that the southern hemisphere holds nearly two-thirds of the world's oceans, this is clearly not a tenable position in the long term.

Their suggestion also puts a whole new meaning on the term 'Down Under'.

 

The previous 5,000 years

Another claim by the IPCC was that sea levels have been largely stable since the end of the last ice age, changing less than 30 - 50 cm over time scales of several centuries during the previous 5,000 years [25]. This suggests to the world's public, media and policymakers that prior to industrialization, sea levels varied only slightly over thousands of years.

But were sea levels really that stable over the last 5 millenia?

Not according to scientists Prof Peter Flood, Dr Robert Baker and Dr Bob Haworth of the University of New England in New South Wales, Australia. Their research into semi-fossilized shellfish and calcareous coated worms in caves and walls surrounding Sydney beaches has shown that sea levels fell 1 to 2 metres in less than 100 years around 3,500 years ago [42] [43].

Their research challenges the assumption that sea levels have been stable since the end of the last de-glaciation 6,000 years ago. It also demonstrates that sea levels and climates can change significantly within the span of a single human lifetime, that they have been changing for centuries before industrialisation, and will continue to do so in the future.

These scientists further point out that if sea levels were today what they were 6,000 years ago, the present site of the Sydney 2000 Olympic Games would be underwater. Similar rapid oscillations in sea level took place elsewhere on the southeast Australian coast throughout the last 4000 years, again marked by horizontal strata of fossil shellfish remains (common barnacles and tubeworms), 1 - 2 meters above the limit of the same species at the present time. These relative sea-level changes are unlikely to be caused by local tectonic movement, because at least 10 sites were studied from Brisbane in Queensland to Fremantle in Western Australia, where much the same thing happened at much the same time, all verified by AMS radiocarbon dating.

From all these sites, Prof Flood et al found there has been a net decline of sea level over the last 4000 years of almost 2 meters around southern and eastern Australia. They further point out that other researchers using similar indicators have found the same general picture in other tectonically stable, mid-latitude, far-field sites in Brazil, Madagascar, and New Caledonia.

 

Back to the Future

The IPCC predictions for the 21st century of sea level rises between 21 and 92 cm, with a preferred average of around 50 cm are based on aggregating the `Atmosphere-Ocean General Circulation Models' (AOGCMs) used in various countries. The only thing these models agree on is sea level rise. Beyond that, their regional distributions contradict each other as can be seen in Fig.17 below [25].

Sea level change predicted between the pre-industrial period and the late 21st century
Fig.17 - Sea level change predicted between the pre-industrial period and the late 21st century [25]

When models disagree to this extent, is there any value in averaging them in an attempt to claim the averaged value is then more authoritative? The ECHAM model in the top right must be the most bizarre, showing a simultaneous difference in sea level trends in the southeastern Pacific of over 2 meters in closely adjacent parts of the same region. The Australian CSIRO model shows a more even global picture, while the two British HadCM models bear little resemblance to each other. The two American GFDL models are equally at odds at the regional level.

One interesting feature of the ECHAM model is its treatment of the North Atlantic basin, showing it to have a smaller sea level rise than the remainder of the world's oceans, and predicting greater sea level rises in the southern hemisphere.

One of the key baseline parameters of all these models is that they follow the IPCC's `IS92a' scenario [25]. This means they have built into them the assumption that greenhouse gases, expressed as `CO2 equivalent' will increase at a rate of 1% per year until 2100. This is an old assumption dating back to before 1992 and is still being recycled for the 2000 assessment.

This 1% assumption has already been overtaken by events.

One of the gases in that assumption is methane. It has stopped growing in the atmosphere as of 1992 and has now largely stabilized [20]. CFC is now controlled by the Montreal Protocol and is no longer a relevant factor in the long term. Other halocarbons are too insignificant to affect the climate either way, and Nitrous Oxides are also insignificant. We are really only left with carbon dioxide (CO2) to achieve this 1% per year growth.

Fig.18 - CO2 growth scenarios
CO2 growth scenarios
But CO2 is not rising like that at all. Firstly, its growth is linear, not exponential (as would be suggested by expressing it as a percentage). Secondly, it has been growing for the last few decades by an average of 1.5 ppm per year. The effect is that the IPCC's IS92a scenario would see an effective CO2 level of nearly 1,000 ppm by the year 2100, but at 1.5 ppm/yr it could only reach around 500 ppm.

This has major implications for the AOGCMs in their sea level predictions since they are using outdated, unrealistic, and exaggerated estimates of what CO2 will be 100 years from now. Even without the issues raised in this article about the state of sea level science generally, the IPCC predictions themselves should be about half of what they claim them to be, simply because of the obsolete 1% assumption.

 

The Poseidon Adventure

The use of satellites equipped with altimetry instruments, particularly the `TOPEX-Poseidon' satellites, have revealed a sea level profile of the earth which was hardly guessed at before the era of satellites [8]. Instead of finding a `mean sea level' applicable everywhere, modulated only by tides and weather, we find instead that the mean `Zero Point of the Sea' can actually be different from place to place, by several feet in some cases.

The variable height of the sea as seen by Topex/Poseidon on cycle 273
Fig 19 - The variable height of the sea as seen by Topex/Poseidon on cycle 273 [8]

As we can see in Fig.19 there is a difference in real time sea level by up to 1.5 metres, or around 5 feet, between the western Pacific and the Southern Ocean. Even on the same latitudes, the western Pacific is 1 metre higher than the eastern Pacific. During a major El Niño, this pattern is reversed.

This is the normal background state of sea level as a similar pattern was evident from the very earliest of the TOPEX-Poseidon missions in 1992. The difference in level between the tropics and high latitudes is due to the centrifugal forces arising from the earth's rotation having greatest effect at the equator. However, this would not prevent the southern oceans from rising in level if the tropical oceans were also rising.

Just as satellites have created a crisis within IPCC circles as to global temperature [20], so too are TOPEX-Poseidon satellites proving to be a problem for alarmist sea level predictions. The satellite altimeters measure sea level on a global basis to an accuracy of 5 cm on each pass and compare the actual surface of the earth with a `geoid' represented by an integration between the satellite's orbital height and the center of the earth.

Although the single-cycle accuracy of 5 cm does not seem adequate for sea level studies where fractions of a millimeter per year are involved, this level of accuracy can be achieved statistically once there are multiple cycles to work with. The latest data (Fig.20) is from cycle 276 where we now have an accumulated record of data over 8 years to establish mean sea level change to an improving degree of accuracy. One key advantage of TOPEX-Poseidon is that sea level heights can even be measured in the open ocean whereas tide gauges are restricted to coastlines and islands.

global MSL variation acc. to TOPEX/Poseidon satellites
Fig.20 - global MSL variation acc. to TOPEX/Poseidon satellites. [8]

The TOPEX-Poseidon project has also established a set of tide gauges on islands in the Pacific Ocean fitted with GPS equipment, the purpose of which is to calibrate the satellites to a greater level of accuracy. In time, they should make tide gauge data redundant.

The IPCC predicts that their sea level rise rate estimate of +1.8 mm/yr will be accelerated during the 21st century to around +5 mm/yr. As Fig.20 shows, the current sea level rate of rise after cycle 276 is +0.9 mm/yr, half the rate claimed for the last 100 years, and less than one fifth the rate claimed for the 21st century. Clearly, not only have recent sea level changes not matched the 20th century rate of rise claimed by the IPCC, but contradicts any idea that an acceleration might be underway as a result of climatic warming. According to the IPCC, the 1990s has been characterized by human-induced warming (a claim contradicted by satellite temperature data), but the accelerated sea level rise they expected from that `warming' has simply not happened.

As the graph in Fig.20 also shows, even that small amount of sea level rise is primarily due to the intense El Niño of 1997-98 which has been demonstrated to cause a temporary rise in global sea level (although it causes a local fall in level in the western Pacific). We can see that the sea level following the El Niño is much the same as sea level prior that event. The CNES based in Toulouse in France which co-sponsors the satellites, also attributes the sea level rise since 1992 squarely on the 1997-98 El Niño [9].

Once there is a longer period of satellite data, the effect of that El Niño will diminish in the statistically averaged sea level result. If we were to exclude the effect of the El Niño from the sea level result, there would scarcely be any sea level rise registered at all.

 

Conclusion

The world's public was given the clear impression that the claimed 18 cm sea level rise for the 20th century was an observed quantity. It is now clear that this is not the case. The 18 cm figure arrived at is the product of combining data from tide gauges with the output of the ICE-3G de-glaciation model.

The logical equation here is simple.

an observed quantity ± a modeled quantity = a modeled quantity

Thus, the claimed 18 cm sea level rise is a model construct, not an observed value at all.

Worse still, the model which has created it is primarily focused on the North Atlantic basin which shows relative sea level trends quite unlike those observed outside that region. Thus, global estimates cannot be inferred with any confidence from modeled trends which mainly affect only that basin.

In the remaining oceans of the world, there is a clear lack of evidence of sea level rise during the 20th century, particularly around the Australian coast which is representative of three oceans, with a good quality record of tide gauge data. The rise recorded there is an insignificant 1.6 cm for the whole century, or just over half an inch.

The lack of sea level rise around Australia is confirmed by a similar lack of sea level change as measured since at least 1888 against the Ross-Lempriere benchmark carved on a rocky natural cliff on the `Isle of the Dead' in Port Arthur, Tasmania. It is also possible that a significant sea level fall took place between 1841 (when the benchmark was struck) and 1888 when its height was accurately measured. The only other tide gauge records which go back that far are very few in number and all come from regions severely affected by PGR within the North Atlantic basin. Thus, they cannot be considered as conclusive evidence against a possible global sea level fall during that period.

Outside the North Atlantic basin, most of the other tide gauges with long-term records have been mounted in tectonically active areas, especially on the west coast of North America and New Zealand, and are thus unsuitable for measuring global trends. Many others are subject to local subsidence.

As to the future, the IPCC suggest an acceleration in sea level rise to nearly 5 cm/yr [25]. However, the TOPEX-Poseidon satellites are now showing a current sea level rise of only 0.9 mm/yr, [8], all of which has been attributed to the 1997-98 El Niño event [9]. Sea levels have been largely unchanged from both before and after that event and so the 0.9 mm/yr `rise' shown is merely a statistical artifact and not a true rise in the background sea level.

Finally, it should not be forgotten that whatever is said about sea levels is entirely dependent upon how global climate responds to greenhouse gases, whether the planet will warm significantly or not [45]. Sea level rise is contingent on atmospheric warming.

No warming, no sea level rise.

The record of atmospheric temperature as recorded by satellites since 1979 has shown no significant warming in spite of numerous model predictions to the contrary.

 

John L. Daly
19th August 2000


Appendix

The Origins of the `Isle of the Dead' Benchmark

by    John L. Daly

In the attached report, the main focus on the 1841 Ross-Lempriere sea level benchmark was to demonstrate how sea levels had scarcely moved since 1888 when it was first investigated and its exact height measured by Capt. Shortt [39]. But where the mark was struck originally and the circumstances surrounding it is still the subject of some dispute and makes a fascinating story in its own right.

The benchmark is engraved on a rocky natural cliff on a small isle (the `Isle of the Dead') within the harbor of Port Arthur in southeastern Tasmania, an undeveloped harbor which opens directly to the Southern Ocean. The idea for the benchmark came from Capt. Sir James Clark Ross, the renowned British Antarctic explorer and marine scientist, acting in collaboration with Thomas Lempriere, an official of the convict colony at Port Arthur.

Here again is what Ross said about the benchmark in his 1847 book.

Having missed that opportunity, he went with Governor Franklin to Port Arthur in 1841 to see Thomas Lempriere who had observed and recorded tidal, astronomical, and meteorological observations over several years. Ross goes on -

Explaining why he chose Port Arthur for a mean sea level mark instead of in the Derwent estuary closer to Hobart Town, where his ships `Erebus' and `Terror' were moored, he wrote -

The emphases have been added to highlight key points. Ross refers to the intended mark as being `mean sea level' or `zero point', no less than 5 times in these short extracts. His intention in respect of the benchmark is therefore clear and unmistakeable. The mark was intended as a mean sea level mark, not a mere tide mark which would only be of use in Port Arthur, nowhere else. The CSIRO did not mention any of Ross' words in a lecture they gave to the Hobart Royal Society in April 2000, and repeatedly used the expression `tide mark' instead of `sea level mark' throughout the lecture.

The exact date on which the Ross-Lempriere benchmark was struck is known - July 1st 1841, because a small stone tablet was placed above it on the clifftop. The tablet went missing around 1913 [28], but there are two witnesses who reported what was inscribed on it. The first, a Mr Mason [39] acting for Capt. Shortt, complained the tablet was badly eroded and difficult to read. He quoted its words in 1888 as follows -

Three years later in 1891, a second witness, a yachtsman cruising aboard the yacht `Wanderer' , wrote an account of his voyage in a Melbourne magazine under the pen name `Eight Bells' [16]. He visited the Isle of the Dead and was interested in the numerous gravestones, one of which he sketched and quoted (the gravestone he quoted from is still there today, bearing the exact words he reported) [28]. Then he noticed that -

Both quotes from the tablet are presented above exactly as published, word for word, comma for comma. The differences between the two versions are clearly evident. The grammar is different (Mason's `now struck' versus the yachtsman's `was struck'), the time formatting is different (Mason's `4h. 44m. p.m.' versus the yachtsman's `2.44 p.m.') and as is now obvious, the big 2-hour disagreement over the time. Lempriere's tide gauge data for 1841 and 1842, has only recently been discovered in the Royal Society archives in London, and here is a section from his tide log in his own handwriting for July 1841, including July 1st. [27].

Lempriere's tide entries for July 1841. Note the similarity of 5's and 6's
Fig.x Lempriere's tide entries for July 1841. Note the similarity of 5's and 6's

From the data shown here for July 1st 1841, low tide was at 11.28 a.m. with a height of 3 ft 10 in. High tide was at 5.58 pm with a height of 6 ft 4 in. It was sometime between these two tides that the benchmark was struck.

We can infer that mid tide for that day occurred at exactly 2.43 p.m. with a tide height of 5 ft 1 in. These are the exact mid-points between the two times and the two tide heights logged. The reported tide gauge height of 6 ft. 1 in. is only 3 inches short of high tide and could not possibly represent MSL. However, 5ft 1in certainly could be Ross' `zero point of the sea', as this height was not only the mid-tide height for that day, but is also the MSL average for the preceding month of June just prior to the striking of the mark on July 1st. If the yachtsman was right about the time, he merely mis-read the `6' in the `6 ft 1 in' entry on an eroded tablet when it should have been a `5' to give 5 ft 1 in.

Mistaking a `6' for a `5' and vice-versa is a common mistake we all make even today, especially when reading poorly reproduced photocopies and faxes. A 50-year old tablet exposed to the elements would be just as difficult to read as any bad fax copy. In the unlikely event of Mr Mason being right about the time being 4.44 p.m. that would have coincided with a tide of 6 ft 2 in, not 6 ft 1 in. - close, but not exact.

High and Low tides for Port Arthur in June/July 1841, with a two-tide smoothing
               Fig.x High and Low tides for Port Arthur in June/July 1841, with a two-tide smoothing (in red)

This chart of the tides in Port Arthur for the month preceding July 1st shows that 5ft 1in was clearly the closest height to MSL for that month, 6ft 1in being outside the range of possible estimates.

Four factors point to the yachtsman's time of 2.44 p.m. being correct, with a consequent height of 5 ft. 1 in, instead of the 6 ft. 1 in. he actually reported.

There was clearly no point in striking a benchmark at 6 ft. 1 in. when it does not mark mean sea level (as insisted upon by Ross several times), does not mark high water (which occurred over an hour later), does not mark low water, and indeed does not mark anything at all except an arbitrary height on a tide gauge which no longer exists. A `benchmark' which depends on the continued existence of a local tide gauge for its meaning, is not really benchmarking anything.

Since high or low tide is specific only to the location in which it occurs, only a mean sea level mark, having wider global implications, would have interested Ross, given what he said about Baron Von Humboldt's proposal. Ross and the colonial governor, Sir John Franklin, were both keenly interested in this benchmark precisely because of Humboldt's proposal, and it is inconceivable that the mark would be struck anywhere else other than `zero point' or `mean sea level' as stated very explicitly by Ross several times. Anything less would hardly have rated a mention in his book about his Antarctic voyages.

The conclusion to be drawn from the body of evidence is that the yachtsman got the time right, and that the only possible associated tide height for that time, Ross' `zero point', must therefore be 5ft 1in.

Even allowing for the CSIRO's provisional mid-range GPS estimate of 9.7 cm for land uplift over the 159-year period, there is still have an apparent fall in sea level of just over 25 cm to be accounted for (35 - 9.7 = 25.3 cm). Since most tide gauges record variations in sea level of that magnitude over months and years, as is clearly demonstrated in the tide gauge graphs in the main article, there may not really be any need to account for it at all. It is clear that a general fall in sea level did not happen in the 20th century as other tide gauges around the world (which became more numerous in the 20th century than in the 19th), would have recorded it, so we must look to the 19th century for an answer to the `Isle of the Dead' enigma.

Mr Mason who read the tablet with some difficulty in 1888 was acting for a marine researcher, Capt. Shortt, who was investigating the origins of the benchmark and searching archives in Hobart and Port Arthur for information about it, and without the benefit of Lempriere's tide data. Shortt reported his findings in a short (sic.) paper published by the Royal Society in Hobart [39].

In order to measure sea level under similar conditions which existed on July 1st 1841, Shortt compared MSL and the benchmark height when the age of the moon was 12 days, as cited on the tablet. His conclusion, in 1888, was that the benchmark was 34 cm above mean sea level, only a centimetre less than the CSIRO estimate of 35 cm 112 years later. Shortt also noted that -

(The Furneaux Islands are half way between Tasmania and the mainland at the eastern end of Bass Strait. Descendants of Tasmanian aborigines were resettled there during the 19th century by the colonial authorities. A general sea level fall at Port Arthur during the 19th century would certainly have been noticed there also as the aborigines frequently engaged in inshore fishing).

Further evidence for a sea level fall comes from period paintings of Port Arthur, all of which show a higher shoreline in the colony precincts than exists today. Indeed, large wooden vessels were unloading cargoes right inside the cove where Port Arthur sits, but today there is insufficient depth of water to do that.

In 1985, Hamon used `hindcasting' of the Hobart data to predict, retrospectively, the state of the tide back in 1841 [22]. Hamon's hindcasting matches Lempriere's data closely, so it can be safely assumed that Lempriere's tide gauge and his data log are also accurate.

Drs John Hunter (CSIRO), David Pugh (Univ. of Southampton, UK) and Richard Coleman (Univ. of Tasmania) jointly authored a confidential internal report for the CSIRO [24], but have not published anything in the scientific literature. Their recent conclusions, reported in this article, comes from a lecture they jointly delivered in April 2000 to a small audience at the Royal Society in Hobart [12], a lecture I also attended.

Surprisingly, the Ross written account about the benchmark was not raised once by either of the three speakers. They merely mentioned him as having an idea for a `tide' mark (as distinct from a `sea level' mark) without informing the audience exactly what he had written. When relating the details about the tablet, they informed the audience about Mr Mason's version, but not a word about the yachtsman's version, even though they are familiar with both.

When earlier questioned by the Melbourne `Herald-Sun' on the issue [4], Hunter claimed that Ross must have `mis-remembered', and in fact carved the mark above mean tide to show where he'd measured the tide in a tide gauge. This scenario would render the whole exercise pointless and contrary to Humboldt's proposal and contrary to the Governor's instructions. When questioned by the BBC, [2] Pugh said "From all the evidence we know, it was the high water level at that time". He obviously did not regard Ross' own words on the matter as constituting any part of "all the evidence".

Ross was an early pioneer of sea level research, being the first scientist to be credited with calculating a correction factor for sea levels due to variations in atmospheric pressure [32]. Thus he was no mere amateur at the science of sea levels as Hunter and Pugh seem to imply.

In keeping with the lack of publicaton in scientific journals about the benchmark, no written paper was offered at the lecture, the information given here being based on notes taken by myself. Without publication in the scientific literature, the IPCC can choose to ignore even of the existence of the benchmark, let alone integrate it into their assessments of past and present sea level change.

 

John L. Daly
19th August 2000

 

References

(This references list is common to both the main sea levels report and the appendix)

[1] Balling R. & Michaels P, "The Satanic Gases", Cato Institute, Washington D.C., 2000
[2] BBC Sci/Tech Online News, "Mark of a Hot Dispute", Oct 7 1999
[3] Belperio, A, "Land Subsidence and Sea-level Rise in the Port Adelaide Estuary: Implications for Monitoring
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