Testing the Waters
A Report on Sea Levels
for the Greening Earth Society
by
John L. Daly
"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]
-
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.
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.
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
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.
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.
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.
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.
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.
- It is assumed in the model that when the great ice sheets melted, there
was no change in the surface area of the oceans. This assumption
is of course wrong as vast areas of continental
margins were flooded as the seas rose. The authors of the model
acknowledge this,
but believe the sea level effect is small, something very much open
to dispute.
- It is assumed in ICE-3G that the mantle and crust were in equilibrium,
or in general balance,
before the big meltdown began. This is not a realistic assumption
as the ice age was itself a
very dynamic period geologically.
- ICE-3G was calibrated against 192 `Relative Sea Level' (RSL) sites
from around the world.
However, 169 of these were in the North Atlantic basin
(including the Arctic). Only 18 were listed for the Pacific Ocean,
most of them on the Pacific coast of North America, a region known to be
tectonically active. Only 5 sites were listed to cover the South Atlantic, Indian
and Southern Oceans, representing nearly two-thirds of the world's oceans
between them.
- ICE-3G used `fudge factors'. Where there was a mismatch between the
observed RSL site
and the model result, the modelled ice load in that region was either `increased
in thickness' or
its `melting delayed'. This is reminiscent of a similar procedure used
in some climate models
where the sun could be `turned up' or `turned down' to stabilize the model
at the desired
temperature.
- ICE-3G predicted a sea level rise of 115 meters during the de-glaciation.
But physical evidence
from most other studies puts the figure at 120 - 130 meters [34].
The discrepancy is attributed by Peltier & Tushingham to `missing ice'
in regions which are assumed to have been ice free, but which might in
fact have been glaciated.
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] -
- Sea levels have already risen between 10 and 25 cms during the 20th
century, with a
preferred value of 18 cm, a historical rise of 1.8 mm/yr
- A `less than average' rise will occur in the Southern Ocean, how much
less is not specified.
- Sea levels changed by only 30-50 cm over timescales of several
centuries during the previous 5,000 years.
- A sea level rise of 21 to 92 cm is projected over the next 100
years, with a preferred
value of around 50 cm (representing an acceleration in sea
level rise to 5 mm/yr)
- The predicted 21st century sea level rise, is partly made up as follows
-
|
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 -
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.
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.
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 -
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).
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).
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
|
|
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'
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 ...
In
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]
-
"The fixing of solid and well secured marks
for the purpose of showing the mean level of the ocean at a given epoch,
was suggested by Baron von Humboldt, in a letter to Lord Minto, subsequent
to the sailing of the expedition (Ross' own
expedition of the `Terror' and `Erebus'),
and of which I did not receive any account until our return (to
Tasmania) from the Antarctic seas, which is
the reason of my not having established a similar mark on the rocks of
Kerguelen Island, or some part of the shores of Victoria Land
(in Antarctica)."
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 - .
"My principal object in visiting Port Arthur
was to afford a comparison of our standard barometer with that which had
been employed for several years by Mr. Lempriere, the Deputy Assistant
Commissary General, in accordance with my instructions, and also to establish
a permanent mark at the zero point, or general mean level of the sea as
determined by the tidal observations which Mr. Lempriere had conducted
with perseverance and exactness for some time: by which means any secular
variation in the relative level of the land and sea, which is known to
occur on some coasts, might at any future period be detected, and its amount
determined.
The point chosen for this purpose was the perpendicular
cliff of the small islet off Point Puer, which, being near to the tide
register, rendered the operation more simple and exact. The Governor, whom
I had accompanied on an official visit to the settlement, gave directions
to afford Mr. Lempriere every assistance of labourers he required, to have
the mark cut deeply in the rock in the exact spot which his tidal observations
indicated as the mean level of the ocean."
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 tides in the Derwent were too irregular,
being influenced greatly by the prevalence of winds outside and the freshes
from the interior, so that we could not ascertain with the required degree
of exactness the point of mean level."
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.
|
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].
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
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.
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.
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.
Click
here for Appendix
Click
here for References
