Sea Level Changes Past Records and Future Expectations

Abstract

The history and development of our understanding of sea level changes is reviewed. Sea level research is multi-fascetted and calls for integrated studies of a large number of parameters. Well established records indicate a post-LIA (1850-1950) sea level rise of 11 cm. During the same period of time, the Earth's rate of rotation experienced a slowing down (deceleration) equivalent to a sea level rise of about 10 cm. Sea level changes during the last 40-50 years are subjected to major controversies. The methodology applied and the views claimed by the IPCC are challenged. For the last 40-50 years strong observational facts indicate virtually stable sea level conditions. The Earth's rate of rotation records a mean acceleration from 1972 to 2012, contradicting all claims of a rapid global sea level rise, and instead suggests stable, to slightly falling, sea levels. Best estimates for future sea level changes up to the year 2100 are in the range of +5 cm ±15 cm.

Full text

Estimating future sea level changes from past records
Nils-Axel Mo¨rner*
Paleogeophysics and Geodynamics, Stockholm University, S-10691 Stockholm, Sweden
Received 13 November 2001; accepted 7 May 2003
Abstract
In the last 5000 years, global mean sea level has been dominated by the redistribution of water masses over the globe. In the
last 300 years, sea level has been oscillation close to the present with peak rates in the period 1890 – 1930. Between 1930 and
1950, sea fell. The late 20th century lack any sign of acceleration. Satellite altimetry indicates virtually no changes in the last
decade. Therefore, observationally based predictions of future sea level in the year 2100 will give a value of + 10 F10 cm (or
+5F15 cm), by this discarding model outputs by IPCC as well as global loading models. This implies that there is no fear of any
massive future flooding as claimed in most global warming scenarios.
D2003 Elsevier B.V. All rights reserved.
Keywords: Sea level changes; Past records; Future predictions; Models versus observations
1. Introduction
The recording and understanding of past changes
in sea level, and its relation to other changes (climate,
glacial volume, gravity potential variations, rotational
changes, ocean current variability, evaporation/precip-
itation changes, etc.) is the key to a sound estimation
of future changes in sea level.
In previous papers, I have discussed the separation
of the eustatic and isostatic factors in paleo-shoreline
data (Mo¨rner, 1969, 1971a, 1979), the eustatic factor
(Mo¨rner 1971b, 1986), geoid changes (Mo¨rner, 1976),
the effects of changes in Earth’s rate of rotation
(Mo¨rner, 1988, 1995a, 1996a), the multiple interaction
of parameters (Mo¨rner, 1987, 1996b, 2000a,b) and the
rates and amplitudes of different variables (Mo¨rner,
1996b,c, 2000a). All this material (together with the
rich literature by other researchers; e.g. Jelgersma,
1961; Tooley, 1974; Shennan, 1987; Newman et al.,
1980; Pirazzoli, 1991; Grossman et al., 1998) form the
base for the present paper where I try to apply all this
observational material and theoretical consideration for
a sound estimation of the sea level changes to be
expected in the near future.
2. The Late Holocene
Prior to 5000–6000 BP, all sea level curves are
dominated by a general rise in sea level in true glacial
eustatic response to the melting of continental ice caps.
The general rise in sea level from f20,000 to f5000
BP implied a corresponding increase in the radius of the
Earth. This radial increase (by basic laws in physics)
must be compensated by a general deceleration. In the
last 30,000 years, Earth passed through three main
eustatic-rotational modes (Table 1).
After 5000 –6000 BP, the Earth came into another
mode (Mo¨rner, 1996b,Fig. 2). The glacial eustatic rise
0921-8181/$ - see front matter D2003 Elsevier B.V. All rights reserved.
doi:10.1016/S0921-8181(03)00097-3
* Tel.: +46-8-164671; fax: +46-8-164675.
E-mail address: morner@pog.su.se (N.-A. Mo¨ rner).
www.elsevier.com/locate/gloplacha
Global and Planetary Change 40 (2004) 49 – 54

had ended because there were no more ice to melt and,
consequently, the rotational deceleration ended, too.
The sea level records are now dominated by the
irregular redistribution of water masses over the globe.
This redistribution of water masses is primarily driven
by variations in ocean current intensity (ocean circula-
tion) and in the atmospheric circulation system (mon-
soonal regime, evaporation/precipitation, etc.) and
maybe even in some deformation of the gravitational
potential surface.
The irregular changes in sea level set the character
of sea level changes in the Late Holocene. On a global
scale, they seem rather to be of a compensational
nature, lacking signs of any general trend.
These sea level changes have set the character of the
changes in sea level in the last century as well as in the
last decades and years. Therefore, they are also assumed
to come to set the dominant character in the near-future.
3. The near-past and present
When we go from Late Holocene sea level records
to last centuries’ records, we also change predominant
Table 1
Relations among sea level changes and Earth’s rate of rotation
implying that the Earth has passed through three main modes in the
last 30,000 years, the last 5000 years being characterised by an
irregular redistribution of the water masses over the globe and the
interchange of angular momentum between the solid Earth and the
hydrosphere (and the atmosphere and core, too) as further discussed
elsewhere (Mo¨rner, 1995a, 1996a,b)
Main modes I II III
Sea level Fall Rise Redistribution of
water masses
Rotation Acceleration Deceleration Interchange of
angular momentum
Time in BP 30,000– 20,000 20,000 – 5000 From 5000 – 6000
BP onwards
Fig. 1. Means and techniques of recording or estimating sea level changes and make predictions for the next century (AD 2100). Multiple field
observations (i.e. classical sea level research), tide gauges and satellite altimetry are all based on true observational data. They give a uniform
prospect for the future. The model-based outputs form the loading models and the scenario-based outputs of IPCC give higher to much higher
predictions values (cf. Fig. 4). The observational-based value of + 10 F10 cm ( + 5 F15 cm) for year 2100 is strongly advocated as more realistic
than the model outputs.
N.-A. Mo
¨rner / Global and Planetary Change 40 (2004) 49–5450

technique and date base. We change from stratigraphic
proxy data (based on geology, stratigraphy, morphol-
ogy, archaeology, biology, ecology and radiocarbon
dating) to instrumental records from water-marks, tide
gauges and mareographs and, in the last decade, to
satellite altimetry (Fig. 1).
From the geophysical loading models, Peltier and
Tushinghan (1989) arrived at a present mean global
rise in sea level of 2.4 mm/year (this value was
adopted by IGBP, 1992; later revised at 1.8 mm/year,
IPCC, 2001). This rate—if realistic—would imply a
total reversal of old observational records. So, for
example, would the North Sea region and the Dutch
coasts, known for their long-term subsidence, be
going up at a rate of about 1.2 mm/year. This was
unrealistic. To test the case, Mo¨rner (1992) used the
recorded rate in rotation and showed that any global
rise component, if real, can, at the most, amount to 1.1
mm/year. This value fits very well with a number of
observational records as illustrated in Table 2.
We therefore conclude that the mean eustatic rise in
sea level for the period 1850 – 1930 was in the order of
1.0–1.1 mm/year.
After 1930–1940, this rise seems to have stopped
(Pirazzoli et al., 1989; Mo¨ rner, 1973, 2000b). This
lasted, at least, up to the mid-60s.
During the 1970s and 1980s, our data are not really
clear enough for a proper evaluation of any general
trend in sea level. The first satellite altimetry record-
ing (Geosat) ranges over 1986–1988. There is hardly
any trend to be recognised. At the same time, the
technical precision was not good enough.
With the TOPEX/POSEIDON mission, the situa-
tion changed. We now have a very good cover of the
global mean sea level changes over the areas cov-
ered by the satellite. The record (Fig. 2) can be
Table 2
Recent, present and possible future changes in sea level as recorded
or calculated from different observational records
Time period Rates
(mm/yr)
Source of information Reference
1682 – 1940 1.1 mean of tide gauges 1
1860 – 1960 1.2 mean of tide gauges 2
1830 – 1930 1.1 NW Europe tide
gauge data
3
1830 – 1930 1.1 past uplift vs. present
uplift and eustasy
3
1830 – 1930 max. 1.1 Earth’s rotation vs.
tide gauge
4
Last 100 years 1.0 UK – North Sea
tide gauges
5
Last 100 years 1.1 Fennoscandian
tide gauges
6
1910 – 1990 0.9 estimates of all
water sources
7
1992 – 1996 0.0 Satellite altimetry 8
1997 – 1998 ENSO Satellite altimetry 8
1999 – 2000 < 0.5 Satellite altimetry 8
References: (1) Gutenberg (1941), (2) Fairbridge and Krebs (1962),
(3) Mo¨rner (1973), (4) Mo¨ rner (1992), (5) Shennan and Woodworth
(1992), (6) Lambeck et al. (1998), (7) IPCC (2001) (TAR-3), (8)
Fig. 2.
Fig. 2. Sea level changes in mm as recorded by TOPEX/POSEIDON between October 1992 and April 2000: raw data before any filtering or
sliding mean average. The variability is high, in the order of F5 –10 mm. From 1993 to 1996, no trend is recorded, just a noisy record around
zero. In 1997, something happens. High-amplitude oscillations are recorded; a rapid rise in early 1997 at a rate in the order of 2.5 mm/year,
followed by a rapid fall in late 1997 and early 1998 at a rate in the order of 1.5 mm/year, and finally, in late 1998 and 1999, a noisy record with
unclear trends. The new factor introduced in 1997 and responsible for the high-amplitude oscillations, no doubt, is the global ENSO event,
implying rapid redistribution of oceanic water masses (characteristic for mode III in Table 1). This means that this data set does not record any
general trend (rising or falling) in sea level, just variability around zero plus the temporary ENSO perturbations.
N.-A. Mo
¨rner / Global and Planetary Change 40 (2004) 49–54 51

divided into three parts: (1) 1993 –1996 with a clear
trend of total stability (and a noise of F0.5 cm), (2)
1997–1998 with a high-amplitude rise and fall
recording the ENSO event of these years and (3)
1998–2000 with an irregular record of no clear
tendency (but possibly with a small rise of < 0.5
cm/year in years 1999–2000). But most important,
there is a total absence of any recent ‘‘acceleration in
sea level rise’’ as often claimed by IPCC and related
groups.
IPCC (2001) made an estimate of all variables and
their possible contribution to sea level rise. They
arrived at a mean value of 0.9 mm/year. This value
is in harmony with the records of the present and near-
past given in Table 2.
Still—and this is remarkable —IPCC compared
their own value with a model value of 1.8 mm/year
(cf. above), which they termed ‘‘observed’’, and dis-
carded their own estimate as unrealistic. The mean
value 0.9 mm/year is close to the truly observed value
of 1.0 –1.1 mm/year for 1850 –1930 and, consequently,
quite reasonable.
Fig. 3 gives a summary of available data for the
last 300 years, the 0.9 mm/year volume-estimate by
IPCC (though discarded as unrealistic), the long-term
trends as given by the geophysical models of Peltier
and Lambeck (2.4 and 1.8 mm/year), and, to the
right, the future estimated by the INQUA Commis-
sion on Sea Level Changes and Coastal Evolution
(INQUA, 2000) and the scenario output values of
IPCC (2001).
4. Models versus observation
Fig. 4 illustrates the three different ways of han-
dling sea level data and predictions of the future. The
way of INQUA (Commission on Sea Level changes
and Coastal Evolution) and IGCP (their sea level
projects) is to consider all available data, make
quality estimates, and regional and global syntheses.
The output of this analysis is a possible future sea
level rise in the order of 10 cm, or maximum 20 cm,
in the next century (Mo¨rner, 1995b, 1996b; INQUA,
2001).
The global loading models (by Peltier, Lambeck
and others) make a highly personal selection of input
data (rather from model-fit, than from data quality).
The output is a present-to-future rise of 24 – 18 cm in a
century.
Fig. 3. Rates of sea level changes from 1700 to 2100 AD as given by (1) observed records (solid line), (2) volume estimates by IPCC (dashed
line) and (3) predictions (vertical bars) by INQUA and IPCC, respectively. Arrows to the right refer to loading model outputs.
N.-A. Mo
¨rner / Global and Planetary Change 40 (2004) 49–5452

IPCC uses loading-model values, some present-day
records and recycled model-output data as input-data
and arrives at a number of scenarios with a mean sea
level rise in the order of 47 F39 cm (i.e. 8 – 86 cm) in
a century (with higher values in previous estimates by
IPCC). From this value, IPCC launched their hypoth-
esis of a disastrous flooding of coastal low-lands and
low islands (like the Maldives) in the next century
(e.g. Hoffman et al., 1983).
When we (the INQUA Commision on Sea Level
Changes and Coastal Evolution) consider past
records, recorded variability, causational processes
involved and the last centuries’ data (Figs. 1, 2 and
4), our best estimate of possible future sea level
changes is + 10 F10 cm in a century or, maybe, even
+5F15 cm.
Therefore, we have to discard the model output of
IPCC (2001) as untenable, not to say impossible
(Mo¨rner, 1995b; INQUA, 2000), and we cite the
Gilgamesh Epos from about 5000 BP saying: Lay
upon the sinner his sin. Lay upon the transgressioner
his transgression.
Fig. 4. The three different ways of handling sea level data: (1) that of INQUA and IGCP leading to observational-based predictions, (2) that of
the glacial loading models leading to model-based predictions and (3) that of IPCC leading to scenario-based predictions. The predictions values
for year 2100 are given in Fig. 1.
N.-A. Mo
¨rner / Global and Planetary Change 40 (2004) 49–54 53

Acknowledgements
The main content of this paper was presented at
the conference on ‘‘Global Climate Changes during
the Late Quaternary’’ in Rome in May, 2001. It is a
contribution of the INQUA Commission on Sea
level Changes and Coastal Evolution, and can be
regarded as the commission’s official evaluation of
the sea level changes that are to be expected in the
near-future.
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