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  • 1
    Call number: Q 3403
    Type of Medium: Monograph available for loan
    Pages: 155 S.
    Location: Upper compact magazine
    Branch Library: GFZ Library
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  • 2
    ISSN: 0550-3213
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 3
    Publication Date: 2018-08-10
    Description: This chapter assesses the current state of knowledge of the rate of change of global-averaged and regional sea-level in relation to climate change. We focus on the 20th and 21st centuries.However, because of the slow response to past conditions of the oceans and ice sheets and the consequent land movements, we consider changes in sea level prior to the historical record, andwe also look over a thousand years into the future.Past changes in sea levelFrom recent analyses, our conclusions are as follows:since the Last Glacial Maximum about 20 000 years ago, sea level has risen by over 120 m at locations far from present and former ice sheets, as a result of loss of mass from these ice sheets. There was a rapid rise between 15 000 and 6000 years ago at an average rate of 10 mm/yr.based on geological data, global average sea level may have risen at an average rate of 0.5 mm/yr over the last 6000 years and at an average rate of 0.1 to 0.2 mm/yr over the last 3000 years.vertical land movements are still occurring today as a result of these large transfers of mass from the ice sheets to the ocean.during the last 6000 years, global average sea-level variations on the time scales of a few hundred years and longer are likely to have been less than 0.3 to 0.5 m.based on tide gauge data, the rate of global average sea-level rise during the 20th century is in the range 1.0 to 2.0 mm/yr, with a central value of 1.5 mm/yr (as with other ranges of uncertainty, it is not implied that the central value is the best estimate).based on the few very long tide-gauge records, the average rate of sea-level rise has been larger during the 20th century than the 19th century.no significant acceleration in the rate of sea-level rise during the 20th century has been detected.there is decadal variability in extreme sea levels but no evidence of widespread increases in extremes other than that associated with a change in the mean.Factors affecting present day sea level changeGlobal average sea level is affected by many factors. Our assessment of the most important is as follows.Ocean thermal expansion leads to an increase in ocean volume at constant mass. Observational estimates of about 1 mm/yr over recent decades are similar to values of 0.7 to 1.1 mm/yr obtained from Atmosphere-Ocean General Circulation Models (AOGCMs) over a comparable period. Averaged over the 20th century, AOGCM simulations result in rates of thermal expansion of 0.3 to 0.7 mm/yr.The mass of the ocean, and thus sea level, changes as water is exchanged with glaciers and ice caps. Observational and modelling studies of glaciers and ice-caps indicate a contribution to sea-level rise of 0.2 to 0.4 mm/yr averaged over the 20th century.Climate changes during the 20th century are estimated from modelling studies to have led to contributions of between Ð0.2 and 0.0 mm/yr from Antarctica (the results of increasing precipitation) and 0.0 to 0.1 mm/yr from Greenland (from changes in both precipitation and runoff).Greenland and Antarctica have contributed 0.0 to 0.5 mm/yr over the 20th century as a result of long term adjustment to past climate changes.Changes in terrestrial storage of water over the period 1910 to 1990 are estimated to have contributed from Ð1.1 to +0.4 mm/yr of sea-level rise.The sum of these components indicates a rate of eustatic sea-level rise (corresponding to a change in ocean volume) from 1910 to 1990 ranging from Ð0.8 mm/yr to 2.2 mm/yr, with a central value of 0.7 mm/yr. The upper bound is close to the observational upper bound (2.0 mm/yr), but the central value bound is less than the observational lower bound (1.0 mm/yr), i.e. the sum of components is biased low compared to the observational estimates. The sum of components indicates an acceleration of only 0.2 mm/yr/century, with a range from Ð1.1 to +0.7 mm/yr/century, consistent with observational finding of no acceleration in sea-level rise during the 20th century. The estimated rate of sea-level rise from anthropogenic climate change from 1910 to 1990 (from modelling studies of thermal expansion, glaciers and ice-sheets) ranges from 0.3 to 0.8 mm/yr. It is very likely that 20th century warming has contributed significantly to the observed sea level rise, through thermal expansion of sea water and widespread loss of land ice.Projected sea-level changes from 1990 to 2100Projections of components contributing to sea-level change from 1990 to 2100 (this period is chosen for consistency with the IPCC Second Assessment Report), using a range of AOGCMs following the IS92a scenario (including the direct effect of sulphate aerosol emissions) give:thermal expansion of 0.11 to 0.43 m, accelerating through the 21st century.a glacier contribution of 0.01 to 0.23 m.a Greenland contribution of -0.02 to 0.09 m.an Antarctic contribution of -0.17 to 0.02 m.Including thawing of permafrost, deposition of sediment, and the ongoing contributions from ice sheets as a result of climate change since the Last Glacial Maximum, we obtain a range of global-average sea-level rise from 0.11 to 0.77 m. This range reflects systematic uncertainties in modelling.For the 35 SRES scenarios, we project a sea-level rise of 0.09 to 0.88 m for 1990 to 2100, with a central value of 0.48 m. The central value gives an average rate of 2.2 to 4.4 times the rate over the 20th century. If terrestrial storage continued at its present rates, the projections could be changed by -0.21 to 0.11 m. For an average AOGCM, the SRES scenarios give results which differ by 0.02 m or less for the first half of the 21st century. By 2100, they vary over a range amounting to about 50% of the central value. Beyond the 21st century, sea level rise will depend strongly on the emission scenario.The West Antarctic Ice Sheet (WAIS) has attracted special attention because it contains enough ice to raise sea level by 6 m and because of suggestions that instabilities associated with its being grounded below sea level may result in rapid ice discharge when the surrounding ice shelves are weakened. The range of projections given above makes no allowance for ice-dynamic instability of the WAIS. It is now widely agreed that major loss of grounded ice and accelerated sea-level rise are very unlikely during the 21st century.Our confidence in the regional distribution of sea level change from AOGCMs is low because there is little similarity between models. However, models agree on the qualitative conclusion that the range of regional variation is substantial compared with the global average sea-level rise. Nearly all models project greater than average rise in the Arctic Ocean and less than average rise in the Southern Ocean.Land movements, both isostatic and tectonic, will continue through the 21st century at rates which are unaffected by climate change. It can be expected that by 2100 many regions currently experiencing relative sea-level fall will instead have a rising relative sea level.Extreme high water levels will occur with increasing frequency (i.e. with reducing return period) as a result of mean sea-level rise. Their frequency may be further increased if storms become more frequent or severe as a result of climate change.Longer term changesIf greenhouse gas concentrations were stabilised, sea level would nonetheless continue to rise for hundreds of years. After 500 years, sea-level rise from thermal expansion may have reached only half of its eventual level, which models suggest may lie within ranges of 0.5 to 2.0 m and 1 to 4 m for CO2 levels twice and four times pre-industrial, respectively.Glacier retreat will continue and the loss of a substantial fraction of the total glacier mass is likely. Areas that are currently marginally glaciated are most likely to become ice-free.Ice sheets will continue to react to climate change during the next several thousand years even if the climate is stabilised. Models project that a local annual-average warming of larger than 3°C sustained for millennia would lead to virtually a complete melting of the Greenland ice sheet. For a warming over Greenland of 5.5°C, consistent with mid-range stabilisation scenarios, theGreenland ice sheet contributes about 3 m in 1000 years. For a warming of 8°C, the contribution is about 6 m, the ice sheet being largely eliminated. For smaller warmings, the decay of the ice sheet would be substantially slower.Current ice dynamic models project that the WAIS will contribute no more than 3 mm/yr to sea-level rise over the next thousand years, even if significant changes were to occur in the ice shelves. However, we note that its dynamics are still inadequately understood to make firm projections, especially on the longer time scales.Apart from the possibility of an internal ice dynamic instability, surface melting will affect the long-term viability of the Antarctic ice sheet. For warmings of more than 10°C, simple runoff models predict that an ablation zone would develop on the ice sheet surface. Irreversible disintegration of the WAIS would result because the WAIS cannot retreat to higher ground once its margins are subjected to surface melting and begin to recede. Such a disintegration would take at least a few millennia. Thresholds for total disintegration of the East Antarctic ice sheet by surface melting involve warmings above 20*C, a situation that has not occurred for at least 15 million years and which is far more than predicted by any scenario of climate change currently under consideration.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Inbook , NonPeerReviewed
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  • 4
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Time series of annual Mean Tidal Range (MTR) have been assembled from 13 ports around the British Isles and secular trends in MTR computed at each site. Trends vary between – 1.8 and 1.3 mm yr-1 depending on location. At many sites the values are significantly non-zero implying different trends in Mean High Waters (MHWs) and Mean Low Waters (MLWs). Such tidal behaviour has also been observed previously at stations along the adjacent European coastline, but is not well understood. At several places, the trends are sufficiently large that they should be taken into account in investigations of impacts of sea level change and in extreme level engineering studies. They also suggest that, in general, time series of MWH should not be used as proxies for series of Mean Sea Level (MSL). For most of the British Isles data, MTR secular trend is larger (more positive) for larger trend in local MSL, or water depth. Lerwick and Newlyn hourly heights have been used to show that the observed MTR trends at most locations must be due primarly to changes in the dominant M2 tidal constituent. A comparison is given of the British Isles findings to those from neighbouring countries; British, Irish, French, Belgian and perhaps southern Dutch MTR trends are found to be considerably less than those reported from the northern Netherlands and the German Bight.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: A comparison has been made of secular trends in sea-level from the twentieth century and late Holocene period, determined from tide gauge and geological data respectively, for 18 sites from the UK and North Sea region. In the main the two data sets of trends are well correlated with a small number of possible exceptions, although even these are consistent with the general correlation within the errors. The tide gauge trends are systematically larger than the long-term sea-level trends inferred from geological data by approximately 1.0 ± 0.15 mm yr-1 (statistical error only) which can be interpreted as an estimate of the regional eustatic rate of sea-level change for the twentieth century. There is no evidence in the region for an acceleration of sea-level trends in recent decades, and this rate can consequently be inferred to be the current eustatic trend.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1432-1394
    Keywords: Key words. Ocean tide ; Harmonic analysis ; Response analysis ; TOPEX/POSEIDON altimetry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying
    Notes: Abstract. Three years of TOPEX/POSEIDON altimeter data have been processed at Delft Institute for Earth-Oriented Space Research (DEOS) to solve the major diurnal and semi-diurnal constituents of the global ocean tide using the two classical methods of tidal analysis, i.e. the harmonic and response analyses. Some experiments with the parameters in the response formalism show that the tidal admittance in both the diurnal and semi-diurnal band can be adequately described with a lag interval of 2 days and a number of lags of three. Results of both methods are evaluated from the differences with the most recent Grenoble hydrodynamic model (FES95.2) and from the fit with the harmonic constants of a globally distributed set of tide gauges. It was found that the solutions of the two methods differ at the millimeter level and are thus fully equivalent, which is confirmed by the tide gauges and the differences with FES95.2. From the comparisons with the Grenoble model it was found that the M 2 and S 2 solutions of that model likely contain bathymetric errors which are of the order of 1–2 cm for M 2 and 0.5 cm for S 2.
    Type of Medium: Electronic Resource
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  • 7
    Publication Date: 2017-07-04
    Description: The tools of geodesy have the potential to transform the Ocean Observing System. Geodetic observations are unique in the way that these methods produce accurate, quantitative, and integrated observations of gravity, ocean circulation, sea surface height, ocean bottom pressure, and mass exchanges among the ocean, cryosphere, and land. These observations have made fundamental contributions to the monitoring and understanding of physical ocean processes. In particular, geodesy is the fundamental science to enable determination of an accurate geoid model, allowing estimate of absolute surface geostrophic currents, which are necessary to quantify ocean’s heat transport. The present geodetic satellites can measure sea level, its mass component and their changes, both of which are vital for understanding global climate change. Continuation of current satellite missions and the development of new geodetic technologies can be expected to further support accurate monitoring of the ocean. The Global Geodetic Observing System (GGOS) of the International Association of Geodesy (IAG) provides the means for integrating the geodetic techniques that monitor the Earth's time-variable surface geometry (including ocean, hydrologic, land, and ice surfaces), gravity field, and Earth rotation/orientation into a consistent system for measuring ocean surface topography, ocean currents, ocean mass and volume changes. This system depends on both globally coordinated ground-based networks of tracking stations as well as an uninterrupted series of satellite missions. GGOS works with the Group on Earth Observations (GEO), the Committee on Earth Observation Satellites (CEOS) and space agencies to ensure the availability of the necessary expertise and infrastructure. In this white paper, we summarize the community consensus of critical oceanographic observables currently enabled by geodetic systems, and the requirements to continue such measurements. Achieving this potential will depend on merging the remote sensing techniques with in situ measurements of key variables as an integral part of the Ocean Observing System.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Book , NonPeerReviewed
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  • 8
    Publication Date: 2014-04-15
    Repository Name: EPIC Alfred Wegener Institut
    Type: Inbook , NonPeerReviewed
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  • 9
    Publication Date: 2018-08-10
    Description: Observations of sea level from coastal tide gauges indicates that global sea level has been rising at a rate of between 1 and 2 mm/yr during the 20th century. This is substantially faster than estimates of global sea-level rise of 0.5 mm/yr over the last 6000 years and 0.1-0.2 mm/yr over the last 3000 years. There is no discernible acceleration in the rate of sea-level rise during the 20th century.For the 21st century, models indicate that ocean thermal expansion will be the largest contributor to sea-level rise. The melting of glaciers and ice -caps also contributes to sea-level rise. For Greenland, increased ablation is estimated to be somewhat larger than increased precipitation. For Antarctica, increased accumulation is estimated topartially offset a rise in sea level from other sources. There will be a continuingcontribution to sea-level rise as a result of the response of the ice sheets to changes in climate since the Last Glacial Maximum. Changes in terrestrial storage is estimated to have partially offset sea-level rise from other sources. Combining estimates of each of these components results in a calculated rate of sea-level rise during the 20 thcentury which ranges from about zero to about 2 mm/yr, and with little computed acceleration over the period.Sea-level rise projections for 2100 are several tens of centimetres above 1990 levels. For the early decades of the 21st century, the range of projections is dominated by modelling uncertainties. For longer lead times, uncertainties in greenhouse gas emissions also contribute significantly to the range in sea -level projections. Beyond 2100, sea level will continue to rise for centuries after greenhouse gas concentrations have stabilised. After 500 years, sea-level rise from thermal expansion may onlyhave reached half of its eventual level. Ice sheets will continue to react to climate change during the next thousand years even if the warming is stabilised.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
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  • 10
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
    Type: Inbook , NonPeerReviewed
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