JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 115, C08013, 15 PP., 2010

Reconstruction of regional mean sea level anomalies from tide gauges using neural networks
Authors: Manfred Wenzel, Jens Schröter

The 20th century regional and global sea level variations are estimated based on long-term tide gauge records. For this the neural network technique is utilized that connects the coastal sea level with the regional and global mean via a nonlinear empirical relationship. Two major difficulties are overcome this way: the vertical movement of tide gauges over time and the problem of what weighting function to choose for each individual tide gauge record. Neural networks are also used to fill data gaps in the tide gauge records, which is a prerequisite for our analysis technique. A suite of different gap-filling strategies is tested which provides information about stability and variance of the results. The global mean sea level for the period January 1900 to December 2006 is estimated to rise at a rate of 1.56 ± 0.25 mm/yr which is reasonably consistent with earlier estimates, but we do not find significant acceleration. The regional mean sea level of the single ocean basins show mixed long-term behavior. While most of the basins show a sea level rise of varying strength there is an indication for a mean sea level fall in the southern Indian Ocean. Also for the the tropical Indian and the South Atlantic no significant trend can be detected. Nevertheless, the South Atlantic as well as the tropical Atlantic are the only basins that show significant acceleration. On shorter timescales, but longer than the annual cycle, the basins sea level are dominated by oscillations with periods of about 50–75 years and of about 25 years. Consequently, we find high (lagged) correlations between the single basins.

Note: The 1.56 mm/yr non-accelerating rate of sea level rise would result in sea levels 6 inches higher than the present in 100 years. The oscillations noted in this study correspond to the typical full and half-cycle lengths of the natural Pacific Decadal Oscillation and the natural 60-year climate cycle. The Pacific Decadal Oscillation warm phase has been shown to produce a marked temporary rise in global mean sea levels.

The Hockey Schtick: Paper: Sea Level Rise Not Accelerating

It has been thought that as the sea level goes up, islands will sit there and drown. But they won’t. The sea level will go up and the island will start responding.  Paul Kench, Auckland University, 2 June 2010

Full story in New Scientist: Shape-shifting islands defy sea-level rise

Previous studies have largely overestimated mass loss from Alaskan glaciers over the past 40-plus years, according to Erik Schiefer, a Northern Arizona University geographer who coauthored a paper in the February issue of Nature Geoscience that recalculates glacier melt in Alaska.

The research team, led by Étienne Berthier of the Laboratory for Space Studies in Geophysics and Oceanography at the Université de Toulouse in France, says that glacier melt in Alaska between 1962 and 2006 contributed about one-third less to sea-level rise than previously estimated.

Science Daily: Mass Loss from Alaskan Glaciers Overestimated? Previous Melt Contributed a Third Less to Sea-Level Rise Than Estimated

Sea-Level Highstand 81,000 Years Ago in Mallorca

Jeffrey A. Dorale,1,* Bogdan P. Onac,2,* Joan J. Fornós,3 Joaquin Ginés,3 Angel Ginés,3 Paola Tuccimei,4 David W. Peate1

Abstract:

Global sea level and Earth’s climate are closely linked. Using speleothem encrustations from coastal caves on the island of Mallorca, we determined that western Mediterranean relative sea level was ~1 meter above modern sea level ~81,000 years ago during marine isotope stage (MIS) 5a. Although our findings seemingly conflict with the eustatic sea-level curve of far-field sites, they corroborate an alternative view that MIS 5a was at least as ice-free as the present, and they challenge the prevailing view of MIS 5 sea-level history and certain facets of ice-age theory.

1 Department of Geoscience, University of Iowa, 121 Trowbridge Hall, Iowa City, IA 52242, USA.
2 Department of Geology, University of South Florida, 4202 East Fowler Avenue, SCA 528, Tampa, FL 33620, USA; and Department of Geology, Babes-Bolyai University, Emil Racovita Institute of Speleology Cluj, Romania.
3 Departament de Ciències de la Terra, Universitat de les Illes Balears, Carretera Valldemossa km 7.5, Palma de Mallorca, 07122, Spain.
4 Dipartimento di Scienze Geologiche, Università di Roma III, Largo St. Leonardo Murialdo, 1, 00146 Roma, Italy.

Excerpts:

Sea-level rises and falls as Earth’s giant ice sheets shrink and grow. It has been thought that sea level around 81,000 years ago—well into the last glacial period—was 15 to 20 meters below that of today and, thus, that the ice sheets were more extensive. Dorale et al. (p. 860; see the Perspective by Edwards) now challenge this view. A speleothem that has been intermittently submerged in a cave on the island of Mallorca was dated to show that, historically, sea level was more than a meter above its present height. This data implies that temperatures were as high as or higher than now, even though the concentration of CO2 in the atmosphere was much lower.

Because of its relation to continental ice volume, an accurate Quaternary sea-level curve has been a long-term goal of scientists interested in ice-age cycles and their causes. Ice-age theory has long assumed gradual ice buildup and more rapid ice melting in the generally accepted model of the ~100-ky cycle of glaciation. Instead, the emerging body of evidence suggests that both melting and accumulation can be very rapid during discrete intervals of time when specific conditions prevail. Furthermore, the 100-ky model of glaciation has always faced the problem that although the deep-sea 18O record is dominated by a 100-ky cycle, northern high-latitude summer insolation has negligible power in this band. Our data from Mallorca and data from other sites around the world indicate the possibility that eustatic sea level was near modern levels at ~80 ka. If this is true, the 100-ky cycle so universally accepted as the main rhythm of the Middle and Late Quaternary glaciations, in fact, applies rather poorly to ice growth and decay, but much better to carbon dioxide, methane, and temperatures recorded by polar ice.

CRN comment: The science isn’t settled!

The sea level in Israel has been rising and falling over the past 2,500 years, with a one-meter difference between the highest and lowest levels, most of the time below the present-day level. This has been shown in a new study supervised by Dr. Dorit Sivan, Head of the Department of Maritime Civilizations at the University of Haifa. “Rises and falls in sea level over relatively short periods do not testify to a long-term trend. It is early yet to conclude from the short-term increases in sea level that this is a set course that will not take a change in direction,” explains Dr. Sivan.

EurekAlert: The sea level has been rising and falling over the last 2,500 years

The research, published by the Potsdam Institute for Climate Impact Research in Germany, created headline news during the United Nations summit on climate change in Denmark last month.

However, the studies, led by Stefan Rahmstorf, professor of ocean physics at Potsdam, have caused growing concern among other experts. They say his methods are flawed and that the real increase in sea levels by 2100 is likely to be far lower than he predicts.

Jason Lowe, a leading Met Office climate researcher, said: “These predictions of a rise in sea level potentially exceeding 6ft have got a huge amount of attention, but we think such a big rise by 2100 is actually incredibly unlikely. The mathematical approach used to calculate the rise is simplistic and unsatisfactory.”

Another critic is Simon Holgate, a sea-level expert at the Proudman Oceanographic Laboratory, Merseyside. He has written to Science magazine, attacking Rahmstorf’s work as “simplistic”.

“Rahmstorf is very good at publishing extreme papers just before big conferences like Copenhagen when they are guaranteed attention,” said Holgate. “The problem is that his methods are biased to generate large numbers for sea-level rise which cannot be justified but which attract headlines.”

Timesonline.co.uk: Climate change experts clash over sea-rise ‘apocalypse’

They said the well preserved stone pieces near the island of Damsay are the only such examples around the UK.

It is thought some of the structures may date back thousands of years.

Geomorphologist Sue Dawson said that people have survived and adapted in the past and it is that adaption to climate change that needs to be learned from.

Caroline Wickham-Jones said: “The really interesting thing about this bay is the stories relating to things under the sea and sea-level change. Our ancestors were dealing with similar problems to ourselves and we’d like to see how they coped with it.”

BBC News website: Rising seas ‘clue’ in sunken world off Orkney

Probabilistic assessment of sea level during the last interglacial stage
Robert E. Kopp, Frederik J. Simons, Jerry X. Mitrovica, Adam C. Maloof & Michael Oppenheimer, doi:10.1038/nature0868

Abstract:

With polar temperatures ~3–5 °C warmer than today, the last interglacial stage (~125 kyr ago) serves as a partial analogue for 1–2 °C global warming scenarios. Geological records from several sites indicate that local sea levels during the last interglacial were higher than today, but because local sea levels differ from global sea level, accurately reconstructing past global sea level requires an integrated analysis of globally distributed data sets. Here we present an extensive compilation of local sea level indicators and a statistical approach for estimating global sea level, local sea levels, ice sheet volumes and their associated uncertainties. We find a 95% probability that global sea level peaked at least 6.6 m higher than today during the last interglacial; it is likely (67% probability) to have exceeded 8.0 m but is unlikely (33% probability) to have exceeded 9.4 m. When global sea level was close to its current level (≥-10 m), the millennial average rate of global sea level rise is very likely to have exceeded 5.6 m kyr-1 but is unlikely to have exceeded 9.2 m kyr-1. Our analysis extends previous last interglacial sea level studies by integrating literature observations within a probabilistic framework that accounts for the physics of sea level change. The results highlight the long-term vulnerability of ice sheets to even relatively low levels of sustained global warming.

No, instead with have a climate scare-fest timed to support the Copenhagen summit. As for East and West Antarctica, they have had divergent climate histories for the past 14 million years – Data from the Dry Valleys reveals an East Antarctic Ice Sheet that is high, dry, cold, and stable, at least in its central area. And the ANDRILL cores suggest a more volatile West Antarctic Ice Sheet that is subject to the changing temperatures of the sea in which it wades (Science 30 May 2008). In fact, in the published literature, global mean sea level rise is constrained to lesss than 1 metre by 2100:

Identifying the causes of sea-level change by Glenn A. Milne, W.Roland Gehrels, Chris W. Hughes & Mark E. Tamisiea, Nature Geoscience Published online: 14 June 2009 | doi:10.1038/ngeo544

Kinematic Constraints on Glacier Contributions to 21st-Century Sea-Level Rise by W. T. Pfeffer, J. T. Harper, S. O’Neel, Science 5 September 2008: Vol. 321. no. 5894, pp. 1340 – 1343 DOI:10.1126/science.1159099

Also, The ice melt during the Antarctic summer (October-January) of 2008-2009 was the lowest ever recorded in the satellite history:

from Tedesco M., and A. J. Monaghan, 2009. An updated Antarctic melt record through 2009 and its linkages to high-latitude and tropical climate variability. Geophysical Research Letters, 36, L18502.

Currently, we are in a decade long period of global temperature stagnation, there has been no increase in Ocean Heat Content since about 2004, global average sea levels haven’t risen since 2006. No one knows what is going to happen next, but an interesting take from flip-flop scientist, new ice age/global warming, Stephen Schneider from the leaked CRU emails:

On Oct 12, 2009, at 2:32 AM, Stephen H Schneider wrote:
Hi all. Any of you want to explain decadal natural variability and
signal to noise and sampling errors to this new “IPCC Lead Author”
from the BBC?  As we enter an El Nino year and as soon, as the
sunspots get over their temporary–presumed–vacation worth a few tenths
of a Watt per meter squared reduced forcing, there will likely be
another dramatic upward spike like 1992-2000.

Kevin Trenberth said: The fact is that we can’t account for the lack
of warming at the moment and it is a travesty that we can’t. The CERES
data published in the August BAMS 09 supplement on 2008 shows there
should be even more warming: but the data are surely wrong. Our
observing system is inadequate.

On Oct 14, 2009, at 10:17 AM, Kevin Trenberth wrote:
Hi Tom
How come you do not agree with a statement that says we are no where
close to knowing where energy is going or whether clouds are changing
to make the planet brighter. We are not close to balancing the energy
budget. The fact that we can not account for what is happening in the
climate system makes any consideration of geoengineering quite
hopeless as we will never be able to tell if it is successful or not!
It is a travesty!
Kevin

So much for ‘settled science.’ The BBC have effectively censored the revelations of the CRU email/data leaks in favour of unfounded, unverifiable climate alarmism aimed at supporting UN global governance and taxation via a Copenhagen, or subsequent, Treaty in the false name of climate control.

Identifying the causes of sea-level change

Glenn A. Milne, W. Roland Gehrels, Chris W. Hughes & Mark E. Tamisiea

Abstract

Global mean sea-level change has increased from a few centimetres per century over recent millennia to a few tens of centimetres per century in recent decades. This tenfold increase in the rate of rise can be attributed to climate change through the melting of land ice and the thermal expansion of ocean water. As the present warming trend is expected to continue, global mean sea level will continue to rise. Here we review recent insights into past sea-level changes on decadal to millennial timescales and how they may help constrain future changes. We find that most studies constrain global mean sea-level rise to less than one metre over the twenty-first century, but departures from this global mean could reach several decimetres in many areas. We conclude that improving estimates of the spatial variability in future sea-level change is an important research target in coming years.

Nature Geoscience
Published online: 14 June 2009 | doi:10.1038/ngeo544

See also:

Kinematic Constraints on Glacier Contributions to 21st-Century Sea-Level Rise

W. T. Pfeffer, J. T. Harper, S. O’Neel

Abstract

On the basis of climate modelling and analogies with past conditions, the potential for multimeter increases in sea level by the end of the 21st century has been proposed. We consider glaciological conditions required for large sea-level rise to occur by 2100 and conclude that increases in excess of 2 meters are physically untenable. We find that a total sea-level rise of about 2 meters by 2100 could occur under physically possible glaciological conditions but only if all variables are quickly accelerated to extremely high limits. More plausible but still accelerated conditions lead to total sea-level rise by 2100 of about 0.8 meter. These roughly constrained scenarios provide a “most likely” starting point for refinements in sea-level forecasts that include ice flow dynamics.

Science 5 September 2008:
Vol. 321. no. 5894, pp. 1340 – 1343
DOI: 10.1126/science.1159099