IGBP/GAIM Report SeriesReport #8

EGS Vening Meinesz Conference #1

GLOBAL AND REGIONAL SEA-LEVELCHANGES AND THE HYDROLOGICAL CYCLE

Loiri-Porto San PaoloSardinia, Italy

4-6 October, 1999

byDork Sahagian and Susanna Zerbini

with contributions by the conference participants:P. Axe, A. Belperio, N. Bernier, R. Bingley, M. Bolgov, W. Bosch, A. Braun, C. Cabanes, A. Cazaneve, J.Chen, S. Cloetingh, G. Di Donato, J. Gregory, R. Hohmann, V. Klemes, P. Knudsen, M. Kuhn, R. Lane, G.Liebsch, J. Lowe, O. Mason, F. Mercier, M. Negusini, C. Paniconi, W. Peltier, H. Plag, F. Remy, B. Richter,A. Selivanov, C. Shum, F. Singer, N. Slotsvik, E. Stanev, N. Teferle, D. Thomson, J. Titus, K. Van Onselen,I. Vilibic, G. Woppelmann, J. Zwally

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"Global and Regional Sea-Level Changes and the Hydrological Cycle"October 4-6, 1999 - Loiri-Porto San Paolo, Sardinia, Italy

The Conference on "global and regional sea-level changes and the hydrological cycle" addressedthe measurement, causes and consequences of recent and projected near-future sea level changes.This bears on the scientific issues facing IGBP/GAIM, BAHC, and LOICZ as well as WCRP andIHDP*. The Conference was sponsored by the EGS* as the first in the new Vening-Meinesztopical conference series.

Climate models currently predict that the global mean surface temperature will increase in thecoming decades in response to increasing greenhouse gases in the atmosphere. As one of theserious consequences of this climate change, a substantial rise of the global mean sea level isexpected. Knowledge of the rate of sea-level rise to be expected on regional to global scale is mostsignificant because of the potentially devastating impact on human society and coastal ecosystems.In fact, a large proportion of the world's population (currently about 2.5 billion), live within 60 kmof the coast, and these areas often have a well developed infrastructure that could be severelydisrupted by further sea level rise. Therefore, observations and scientific research are neededwhich can give guidance in the proper development of coastal zones in order to mitigate the socialand ecological impact of future climate change in an effective and economically affordable way.The specific future research priorities for addressing these issues were formulated at the conferenceand are included below.

Conference Objective

The objective of the conference was to provide a forum for critical discussion of the present state ofknowledge of sea-level variability in relation to the hydrological cycle both at global and regionalscales. The main focus was on the identification of problem areas which need to be investigatedand key parameters which need to be monitored in order to improve our understanding of thephysical phenomena and their interactions governing the spatial and temporal variations of sealevel. The key areas were identified as measurement & monitoring, quantification of globalhydrologic balance, and evaluation of impacts as they pertain to policy issues and the IPCCprocess.

Key Issues

The issues confronting investigations of modern sea level rise can be grouped into three categories:• Measurement• Mechanisms• Impacts.

Measurement of sea level change in the 20th century has traditionally been based on tide gaugerecords, corrected for coastal epeirogeny in response to glacial re-equilibration. The relatively longtide gauge records make it possible to extract a secular signal from highly variable short-termobservations. For almost two centuries, sea-level observations have been provided from a networkof tide gauges with sites along the coasts all around the world (but mostly in the northern * International Geosphere Biosphere Programme (IGBP)Global Analysis, Interpretation and Modelling (GAIM)Biospheric Aspects of the Hydrological Cycle (BAHC)Land-Ocean Interactions in the Coast Zone (LOICZ)World Climate Research Programme (WCRP)International Human Dimensions Programme on Global Environmental Change (IHDP)European Geophysical Society (EGS)Intergovernmental Panel on Climate Change (IPCC)

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hemisphere). Tide gauges measure sea-level relative to the land surface at the local coast.Therefore, vertical crustal movements originating, for example, from local subsidence, tectonicsand post-glacial rebound influence such measurements. In order to decouple global sea-levelchanges from local effects, epeirogenic motion needs to be monitored and better understood on thebasis of models of the Earth's mantle and lithosphere. In this way, the relative sea level recordedby tide gauges can be converted to the more globally relevant eustatic sea level which depends onthe relative volumes of the global ocean water and the global ocean basin.

More recently, satellite radar altimeter observations of sea level have made it possible to recordvariations in the open ocean as well as along the coastline, but these records exist only for the lastdecade or so mkaing it difficult to extract secular sea level trends. They will, however, becomeincreasingly important in the 21st century. Because these measurements are based on the satelliteheight relative to the center of mass of the Earth in a well-defined terrestrial reference system,rather than to the local land surface, global and regional absolute sea-level changes can now bedetermined. However, radar altimeter instruments experience drifts on the order of 1-2 mm/yr andmust be calibrated or modeled, causing the use of these instruments to measure sea level changevery challenging.

Available space and in situ techniques must be used routinely and combined for the monitoring ofabsolute and relative sea level changes at various spatio-temporal scales, i.e., from local or regionalto global scales and from seasonal to inter-decadal time scales. Such observations are offundamental importance for the understanding of how the volume and mass of the oceans changein response to global change as well as of the physical interactions between the cryosphere,hydrosphere and atmosphere involved in sea level changes.

In addition to measurements of global sea level change, satellite altimetry makes it possible tomeasure the spatial variability of sea level. This will enable the assessment of ocean circulationmodel and coupled model performance. For projections of the magnitude of future sea level rise, itis necessary to understand the mechanisms by which water is transferred between the ocean andother storage reservoirs. As such, measurement is closely coupled to mechanisms.

The mechanisms of sea level change can be grouped into two types–those that change the volumeof the Earth's ocean basin, and those that change the volume of the Earth's ocean water. On thetime scales of concern in modern global change (decade to century), only water volume changesare important globally, as the tectonic influences on basin geometry act slowly relative to the timescale of interest. (However, locally, "tectonic" processes such as glacial rebound and subsidencedue to ground water withdrawal can significantly affect local relative sea level.) Global ocean watervolume is increased by adding water to the ocean by melting grounded ice, by adding water by avariety of human activities, or by decreasing the density of the existing water mass throughwarming of the marine mixed layer.

A climate signal in sea-level can be expected for two reasons: firstly, the ocean volume changeswhenever a change in the heat content of ocean water takes place, and secondly, ocean masschanges due to a change in the mass flow between the ocean and other reservoirs of thehydrological cycle. Monitoring ocean temperature and ice volume is not a simple matter, however.While sea surface temperatures are relatively well measured, deep ocean thermal structure remainsunconstrained. Even the thermal structure of the mixed layer is not well monitored, although someefforts are being made toward that end. Ice volume can be measured by direct observation, butaccuracy has been a problem to date. Satellite radar altimeters are now capable of measuring large-scale (300 km or longer) ice sheet elevation changes over relatively smooth and level ice surfaces.Problems with radar penetration, and scattering in marginal and sloped ice surfaces have limited theaccuracy of such measurement to date. However, during the beginning of the next decade, aspaceborne laser altimeter (Icesat) will be launched that is capable of measuring ice thickness(elevation) change with much higher accuracy and smaller spatial scale than radar altimeters. The

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time series data from the existing radar altimeters together with those of Icesat, should providecritical insights regarding the measurement and causes of changes in contemporary (decadal) icesheet mass.

The ocean is the largest reservoir in the global hydrological cycle, and, moreover, the flowsbetween the ocean and the other reservoirs are generally larger than the flows between any pair ofthe other reservoirs. Water vapor, fluid water and/or ice are involved in most of the importantnatural processes on the Earth's surface. The energy available for the hydrological cycle thuscrucially determines the state and the processes in the system. Sea level and its spatial and temporalvariability, therefore, may not only be important for understanding the potential impacts of climatechange but also prove to be a key parameter of the Earth system.

Predicting future sea level changes in both important and difficult. Model projections for futureglobal and regional sea level changes are still highly uncertain due to uncertainties in the heat andmass balance of the ocean as well as in the near-term effect of climate change on Antarctic icebudgets. Although there is no doubt that a global warming will cause ocean thermal expansion,present results based on Atmosphere-Ocean General Circulation models are not yet reliable enoughbecause of the difficulty in modelling the complex thermodynamic interactions between ocean andatmosphere (in addition to difficulties modelling the ocean and atmosphere individually). Onclimatological time scale, the cryosphere has the largest potential to contribute to ocean mass andsea-level changes. Unfortunately, the present mass balance of polar ice sheets is not preciselyknown. Model predictions do not agree on the amount of warming expected at high latitudesrendering it difficult to understand how the equilibrium of polar ice masses will be altered by thechanging relationships between increases in precipitation and increases in ablation. While there issome consensus that mountain glaciers and Greenland ice sheet will lose mass in the future andcontribute to sea level rise, the role of Antarctica, the largest potential contributor is very poorlyconstrained. While there is general consensus that in the short-term, atmospheric warming will leadto southern ocean surface warming and will increase precipitation on the Antarctic ice sheet, thecounteracting effects (and time scale) of warming on ice rheology, ice streams, and the WestAntarctic grounding line in the long-term are less clearly defined, and remain unquantified.Moreover, contributions from other reservoirs such as ground water or terrestrial surface watersare difficult to estimate and more difficult to predict. Considering this present situation, a detailedmonitoring of the sea-level variability is essential.

The impacts of sea level rise are of greatest concern to the general population, particularly in andnear coastal communities. Direct hydrologic consequences include flooding of coastal wetlands,salinization of coastal aquifers, alterations of estuarine steam flow, and exacerbation of stormdamage to both ecosystems and human-built structures (e.g. houses, roads, bridges, etc.). Thepresent natural coastal defenses are, in most cases, insufficient because they rely on a dynamicinteraction between sea level, wave energy, and sediment transport that is corrupted by thepresence of artificial structures. Existing man-made coastal defenses will be unable toaccommodate an increase in storm activity super-imposed on a significant rise in mean sea-level. Abetter documentation of the rate of sea level rise (measurement) and understanding of the causes(mechanisms) will lead to better prediction of the consequences of future sea level rise. It is hopedthat this will place policy-makers and others in coastal communities in a better position for rationaldecision-making regarding local responses.

The most serious impacts of sea level rise were identified at the meeting as: Shoreline erosion - Shoreline systems, most notably beaches, are subject to increased

erosion as sea level rises. The loss of material is not necessarily limited to the shoreline, however.There is an equilibrium profile to be maintained in the coastal zone that will respond to sea levelrise by eroding as much as a kilometer inland from the present shoreface, thus extending the regionof impact. Nearshore topography and land use need to be documented at the local level in order tobe able to predict the impacts of sea level rise on local shorelines.

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Exacerbation of storm wave damage - Given the historical frequency and severity of coastalstorms such as hurricanes and typhoons, any rise in sea level will greatly increase the extent ofdamage within the coastal zone, particularly during high tide. If there is an increase in stormfrequency or severity as a part of other aspects of global change, then sea level rise will furtherexacerbate the risk of severe storm damage due to high waves.

Storm surges - In addition to damage caused by waves and erosion, flooding due to stormsurges will increase under conditions of higher sea level. As is true at present, damage due toflooding will be most severe when the surges strike during high tide.

Coastal ecosystem loss - As sea level rises, coastal ecosystems are subject to flooding, andin many cases cannot keep pace with rapidly rising sea level so are drowned. Because the existingequilibrium profile is often artificially maintained with levees, seawalls, and other means of“protection”, the low-level ecosystems cannot migrate landward and can be lost completely in thesecases. The resulting loss of hatcheries for coastal fisheries also had serious consequencesregarding marine ecosystems.

Aquifer salinization - A significant fraction of world population relies on groundwaterdrawn from coastal aquifers for their fresh water supply. As sea level rises, the depth of thefreshwater lens in the coastal zone is greatly reduced, leading to salinization of water supplies. Inextreme cases exacerbated by overpumping, the aquifer may rapidly become unsuitable fordrinking and even for irrigation.

Research Recommendations

It became clear at the conference that IPCC projections are limited by the lack of both observationaldata and quantitative understanding of the global hydrologic balance. It would appear that theuncertainties in sea level projections for the next 100 years have not greatly improved since thesecond IPCC assessment because the necessary observational and conceptual gaps have not beenfilled in the intervening years. Consequently, attention was paid at the conference to theidentification of the few most critical areas in which focused research will provide the necessaryinsights to enhance the reliability of sea level projections.

After a number of presentations of research results pertaining to measurement, analysis andmodelling of ice and other hydrologic budgets, and impacts & policy, the conference concludedwith a session aimed at identifying the research priorities appropriate for addressing the keyoutstanding issues. Although we separate measurement, causes and impacts in the discussionbelow, the three are intimately related, and conference participants recognized the need for theresearch community to forge stronger links between these research areas.

• Measurement Tide Gauges - The tide gauge record is invaluable because of its longevity, despite the

difference between records caused by local tectonics and postglacial rebound. With tide gaugestations tied to the Terrestrial Reference Frame using space geodetic techniques such as GPS, theserecords will provide an increasingly reliable means to monitor future sea level variations globally.Toward that end, it was determined that additional state-of-the-art tide gauges in the record-poor,but globally important southern ocean, will be critical to the coming years. While century-longrecords will not be available from new tide gauges for another century, geocentrically-referencedgauges will be of value immediately, as they will record not only relative sea level, but coastlineepeirogeny as well.

Satellites - Global ocean surface height records from TOPEX-POSEIDON and other radaraltimeters with greater high-latitude coverage (Geosat, ERS-1, and ERS-2) have provided aquantum leap in our ability to measure the topography of the global ocean, and even in the shorttime satellite altimetry has been operational and despite of the uncertainty of its accuracy at the levelof less than 1 mm/yr (due primarily to instrument drift), a clear signal of sea level change has beenrecorded. This change is not globally uniform, but varies spatially depending on climate, ocean

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circulation patterns, and non-homogeneities in the changes in mixed layer thermal structure.Additional satellite altimeters with greater high-latitude coverage are operational or planned for thenear future by NASA, the US Navy, CNES and ESA (e.g. GFO-1, JASON-1, ENVISAT),making the future bright for a global satellite observational network, provided the satellites areindeed launched, and the data become available. Radar altimeters can also measure large-scaleelevation change for interiors of ice sheets. Spaceborne laser altimeter, IceSat, to be launched in2001, is anticipated to enable the definitive determination of mass balance of the ice sheets, andthus their impact on sea level change. Advanced satellite gravity mapping missions, CHAMP,GRACE, and GOCE, to be launched by the middle of the next decade, will enable five-foldimprovement of the mean gravity field (geoid) of the Earth, and will allow accurate measurementsof mass redistribution of the Earth system components with a spatial scale of 300 km. GRACE isanticipated to be able to measure large-scale mass balance of the ice sheet, mass change of thehydrosphere and the ocean, to provide insights to the cause of the sea level change. The mostcritical need identified at the conference pertaining to satellite records was the need to continuousoperation and thus records. Gaps in records can lead to uncertainties and errors in the time series ofthese critical observations. The high-latitude coverage is obtained by merging the ERS and GFOaltimetry with the TOPEX/POSEIDON altimetry. It is recommended that these altimeter systemsbe calibrated and monitored for their respective instrument and geophysical and media correctiondrifts as well as their links to each other, using permanent calibration sites and island tide gauges,toward a consistent and long-term observation system for the long-term monitoring of global sealevel change.

•Causes Continental hydrologic budget - In what seemed at first as a surprising conclusion from a

primarily oceanographic research community, the most critical need (highest priority) wasidentified as better quantification of the hydrologic budget of the continents. This need arises fromthe large and variable water flux between oceans and continental interiors, as well as theknowledge that these fluxes are being altered by land use and water resource utilization. Acomprehensive data set is necessary for global information regarding river hydrographs, groundwater levels, lake and reservoir levels, soil moisture, and land cover for at least the present time,and if possible for the last century as well. A few of these issues are beginning to be addressedthrough international research programs such as WCRP, IGBP and IHDP, but it is not clear thatthey have the necessary resources available for this major international task. Much of the necessarydata already exist in a multitude of local, regional, and national archives, but the task of organizingand assembling these data into an integrated global data set is a major undertaking in itself, evenbefore it is used to identify data gaps for future observational programs. As such, it is imperativethat activities be initiated as soon as possible toward the end of a global hydrologic data base.

Ice budgets - The balance between increased melting as a result of atmospheric warming,and increased precipitation (as snow) in Antarctica plays a critical role in the global hydrologicbudget. As such, research is needed in observation of ice accumulation rates on the basis of surfaceelevations, monitoring of meteorology in and around the southern ocean and coastal Antarctica,and modeling of the relationship of sea surface temperatures to Antarctic atmospheric circulationand precipitation patterns.

Ocean temperature - Because a major factor in modern sea level rise is the thermal expansionof the mixed layer, better monitoring of ocean temperature will increase our ability to assess thepresent and future contribution to sea level rise. While sea surface temperatures are monitoredadequately, the thermal structure of the mixed layer over which we must integrate to determine itscontribution to sea level rise, is very poorly known. As a result, IPCC projects must include broadscenarios with great uncertainty regarding this term. However, detailed gravity data may providethe necessary constraints to determine the density profile of the mixed layer. It was concluded atthe conference that these should be collected and applied to the problem of shallow ocean density.On longer time scales, thermal structure of the deep ocean plays an increasingly imoprtant role.

Anthropogenic influences - With numerous mechanisms by which human activity directlytransfers water between continental interiors and the ocean, it will not be possible to accurately

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account for past (20th century) sea level changes, nor to project future changes without somesimple analysis of human intervention in the hydrologic cycle. Activities such as ground watermining, deforestation, and draining of wetlands contribute to sea level rise, while construction ofnew dams ameliorates sea level rise caused by other factors. In particular, the volume of waterstored behind dams both as surface and ground water is poorly constrained, but may besignificant. The latter half of the 20th century is the time period of the greatest rate of dam-buildingand water impoundment. It is also the time over which most tide gauge data is derived.Consequently, by impounding water at a significant rate globally, we be masking the sea level risebeing caused by other factors. If the rate of new dam construction slows or stops, then we shouldexpect the observed rate of sea level rise to increase accordingly in the 21st century, even if otherfactors remain unchanged from the 20th century. The magnitudes of the various anthropogeniceffects is not reliably known, but can be readily assessed through simple observational and datacompilation programs.

• ImpactsThe assessment of the impacts of sea level rise over the next century is hindered by a lack ofknowledge of the detailed topography of the near shore. New global elevation maps based ondetailed surveys at cm resolution will make it possible to accurately determine the areas which willbe inundated by storm surges under conditions of rising sea level. This will require a concertedeffort by the satellite altimetry community as well as local ground-based geodetic surveyors in allcoastal areas world-wide.

The policy sector is most concerned with the impacts of sea level rise because they could havesignificant economic, social, and therefore political consequences. While environmentally logicaland scientifically expedient solutions to sea level rise may include policies directed at "rollingeasements", and other land use regulations, these might be considered Draconian measures bythose landowners involved, and would thus be exceedingly difficult to enact locally. It was agreedat the conference, however, that the scientific commuity can contribute to teh porcess mosteffectively by placing assessments of flooding and storm damage risk into the context of theframework convention on climate change and should be an integral part of the IPCC process.

The issue of how involved the scientific community should become in the political process ofnational and international decision-making is complex and can lead to awkward situations forindividual scientists as well as research organizations. Nevertheless, the application of scientificresults to pressing current problems is a critical aspect of global change research that should not beskirted for fear of misinterpretation by the lay public and popular press. It was agreed at theconference that the sea level research community should make every reasonable effort to makeresearch results available to the public and to the decision-makers within the policy sector. Thismust involve both publication in the popular press as well as involvement in IPCC and additionalregional and local processes.

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Summary of Research Recommendations

Measurement Causes Impacts Assessment Policy

Satellites- continuity,high latitude coverage,GPS buoys, LinkedGPS-Tide Gaugesystem

ContinentalHydrologic Budget

Coastal ZoneElevation (cm-scaleresolution)

Scientific input intoIPCC process

Tide Gauges- additionof new gauges insouthern ocean (whilemantaining existinggauges)

Ice Budgets Community PositionStatement on SeaLevel

Ocean TemperatureAnthopogenicinfluences

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Agenda

3 October, 1999Sunday

18:00 - 19:00 Registration

4 October, 1999Monday a.m.

09:00 - 09:30 Opening

The hydrological cycle: What can we learn from sea level?Chairperson: S. Zerbini

09:30 - 10:00 J.L. Chen, C.R. Wilson and B.D. TapleyHydrological contribution to global mean sea level change.

10:00 - 10:30 V. KlemesCan the dynamics of global water balance cause sea-level anomalies?

10:30 - 11:00 Break

11:00 - 11:30 Mercier, F.Interannual lake level changes and regional hydrology.

11:30 – 12:00 M. V. BolgovClimate change and water level fluctuations in inland water bodies

12:00- 14:00 Lunch

Mass balance of the ocean: Where are the largest uncertainties and how canthey be reduced?Chairperson: A. Cazenave

14:00 - 14:30 F. Remy, B. LegresyIce sheet mass balance from space techniques.

14:30-15:00 J. H. ZwallyDetermination of interannual to decadal changes in ice sheet mass balance from satellite altimetry.

15:00-15:30 H.-P. PlagWhat can we learn from sea level about changes in ice sheets?

15:30 – 16:00 M. KuhnThe contribution of glaciers and small ice caps to sea level change

16:00 – 16:30 Break

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Chairperson: H.P. Plag

16:30 – 17:00 R. Hohmann, P. Schlosser, A. Ludin, R. WeppernigExcess Helium-4 in the Southern Ocean: a tracer for glacial melt water

17:00 – 17:30 W. R. PeltierGlobal models of post-glacial sea level history: the role of ”implicit ice”.

17.30 – 18:00 D. SahagianAnthropogenic alterations of global hydrology and sea level.

18:00- 18:30 S. Cloetingh Vertical motions of the lithospheric models and constraints.

20:30 Dinner

5 October, 1999Tuesday a.m.

Sea-level observations: What are our present and future capabilities to observechanges and variability?Chairperson: J. Zwally

09:00 – 09:30 A. CazenaveSea level change from satellite altimetry.

09:30 – 10:00 C. K. Shum, C. Y. Zhao, P. WoodworthDetermination and characterization of global mean sea level change.

10:00 - 10:30 A. Braun, A. Helm, M. Rentsch, T. SchoeneCalibration of ERS altimetric data in the Western Spitsbergen shelf throughtide gauge data.

10:30 – 11:00 Break

Sea-level observations: What are our present and future capabilities to observechanges and variability?Chairperson: W.R. Peltier

11:00 – 11:30 Richter B., S. Zerbini, M. Negusini, W. Schwahn, C. RomagnoliMean sea level and vertical crustal motions: an experiment in the Adriaticarea.

11:30 – 12:00 R. Bingley, N. T. Penna, A. H. Dodson, V. Ashkenazi, T.F. Baker, S. J. Waugh, F. N. Teferle

GPS Monitoring vertical land movements at tide Gauges in the UK.

12:00 – 12.30 E. V. Stanev, E.L. Peneva. P.-Y. Le TraonThe recent changes of Black Sea level. Estimates from mariograph,altimeter and hydrological data.

12:30 – 14:30 Lunch

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5 October, 1999Tuesday p.m.

Sea-level observations: What are our present and future capabilities to observechanges and variability? (cont.)Chairperson: C.K. Shum

14:30 – 15:00 W. BoschThe 1997 North Atlantic sea level anomaly.

15:00 – 15:30 P. Knudsen, O. B. AndersenChanges in sea level, sea surface temperature and atmospheric pressurefrom satellites.

15:30-16:00 K. van OnselenDetectability of sea level height variation patterns.

16:00 - 16:30 Break

Past Sea LevelsChairperson: S. Cloetingh

16:30 – 17:00 O.K. Mason, W. DupréEarly Medieval (AD 700-1100) avulsion of the Yukon river delta:climatological control due to increased precipitation?

17:30 – 18:00 G. Di Donato, R. Sabadini, L.L.A. Vermeersen, A.M. Negredo, E.CarminatiMulti-disciplinary approach to sea-level change in the Adriatic Sea and in thePo delta: insights from modeling and stratigraphic analysis.

18:00 – 18:30 N. Harvey, T. Belperio, B. BourmanRegional Variations in the Paleo sea-level record from Australia

18:30 – 19:00 A.O. SelivanovSpatial-temporal variability of sea-level changes on the coasts of Russiaduring the Late Pleistocene and Holocene: eustasy, tectonics or geoidalchanges?

20:30 Dinner

October 6, 1999Wednesday a. m.

Impacts of Sea Level RiseChairperson: D. Sahagian

9:30- 10:00 J. A. Lowe, J. M. GregoryPredicted changes in storm surge activity around the United Kingdomcoastline in a future climate with increased greenhouse forcing.

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10:00 - 10:30 D. ThomsonRelative sea-level change and modelling the altered hydrology of a rapidlysubsiding wetland.

10:30-11:00 Break

11:00 – 11:30 N.B. Bernier, K.R. Thompson, J. Bobanovic, H. RitchieModeling storm surges on the East coast of Canada: case studies andprojected changes in flooding risk.

11:30 - 12:00 J. TitusThe impacts, responses, and legal implications of rising sea level along theU.S. Atlantic and Gulf Coast: new maps and policies

12:00 – 14:00 Lunch

October 6, 1999Wednesday p. m.

Predicting future relative sea-level variations: How do we proceed from global toregional scales?Chairperson: J. Titus

14:00 – 14:30 S. F. Singer Will global warming raise sea levels?

14:30 – 15:00 J. A. Lowe, J. M. GregoryNatural inter-annual variability of sea surface height evaluated using a multi-century AOGCM simulation.

15:00– 15:30 J.M. Gregory, J.A. LoweGlobal and regional sea-level rise predictions from the HADCM3AOGCM.

15:30 – 16:00 J. M. Gregory, J.A. ChurchIPCC third assessment report on sea-level change 1900-2100.

16:00 - 16:30 Break

16:30 - 17:30 Chairs & The scientific organizing CommitteePANEL Discussion- Where do we go from here? Future research prioritiesfor the Sea Level community

17:30- 17:45 D. SahagianSummary

17:45 - 18:00 Discussion and concluding remarks

20:30 Cocktail and Gala Dinner

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Abstracts

MODELLING STORM SURGES ONTHE EAST COAST OF CANADA:CASE STUDIES AND PROJECTEDCHANGES IN FLOODING RISK

N.B. Bernier (1), K.R. Thompson(1), J.Bobanovic (1) and H. Ritchie (2)(1) Dalhousie University, Department ofOceanography, Halifax Canada B3H 4J1,(2) AEPRI, Recherche en prèvisionnumèrique, Dorval Canada H9P 1J3.natacha@phys.ocean.dal.ca /Fax: 902-494-2885

Concern over the serious economicconsequences of increased coastal erosionand flooding under future climate scenarioshas motivated our study of sea-levelvariations along the east coast of Canada. Aparticular focus is the damage associated withsevere winter storms. Here we report onresults from a 2-D barotropic ocean modeldriven by wind and pressure fields providedby the Atmospheric Environment Services ofCanada. First, we verify that sea-levelobservations in the region agree with ourmodel predictions. The numerical model iscomputationally expensive and so we alsoexplore the use of a much simpler statisticalmodel, for use in predictions. In thisstatistical model, we assumed that the sea-level variability is a linear combination of pastand present meteorological fields, so that thesea-level variation could be expressed as acombination of those fields. This allows us tocalculate site specific transfer functionsbetween the meteorological forcing and sea-level response. The transfer functions can beused to predict efficiently variations in futuresea-level variability based on predictions offuture climate.

GPS MONITORING OF VERTICALLAND MOVEMENTS AT TIDEGAUGES IN THE UK

R M Bingley (1), N T Penna (1), A HDodson (1), V Ashkenazi (1), T F Baker (2),S J Waugh (1) and F N Teferle (1)(1) Institute of Engineering Surveying andSpace Geodesy, University of Nottingham,UK, (2) Proudman OceanographicLaboratory, UKrichard.bingley@nottingham.ac.uk

Changes in mean sea level recorded by tidegauges are corrupted by land movements atthe tide gauge sites, which can be of a similarorder of magnitude. Since 1990, the IESSGand POL have carried out a series of projectsrelated to the development of techniques forthe application of GPS to monitoring verticalland movements at selected sites of the UKNational Tide Gauge Network.The initial projects were based on the use ofepisodic GPS campaigns. During the periodfrom 1991 to 1996, sub-sets of a network ofsixteen tide gauges were observed in a seriesof nine episodic GPS campaigns. In thelatest project, a combination of continuousand episodic GPS measurements are beingused. During 1997 and 1998, continuouslyoperating GPS receivers were established atfive of the tide gauges, and in 1999, a furtherset of episodic GPS measurements weremade at the other tide gauges in the network.This paper will present the results andexperiences from all of the episodic andcontinuous GPS observations that have beenmade at tide gauges in the UK.

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CLIMATE CHANGE AND WATERLEVEL FLUCTUATIONS ININLAND WATER BODIES.

Dr. Mikhail V.BolgovWater Problems Institute Russian Academyof Sciences, 3,Gubkin St., GSP-1,117735,Moscow, Russiabolgov@iwapr.msk.su, Fax: 7-095-135-54-15

The regime of the water level of inland seasand lakes is a basic problem of hydrology.The anomalies of these processes have beeninsufficiently investigated. Predictingvariations in the level of inland water bodiesis importance for ecological forecasts and forvalidating measures associated withdevelopment of water resources. Thehydrological regime of these water bodiesdepends both on natural processes (riverrunoff) and on the human impact. Abnormallevel variations in inland water bodies haveadverse effects on both the environment andon the economy of coastal and shore zones.For example, in the 1970s the significantdrop in the level of the Caspian Sea greatlyendangered biological productivity; at thepresent time, an increase in the water level isresulting in huge economic losses due to thesubmersion of settlements and industrialareas. The causes of abnormal variation in thehydrological regime of inland seas and lakes(Caspian etc.) during the last decades areinvestigated.

THE 1997 SEA SURFACE HEIGHTANOMALY OF THE NORTHATLANTIC SUBPOLAR GYRE

W. BoschDeutsches Geodätisches Forschungsinstitut,Marstallplatz 8, D-80539 München, GermanyEmail bosch@dgfi.badw.de

For the period 1992-1998 Topex/Poseidonaltimeter data is used to study the evolution ofNorth Atlantic sea level anomalies relative toa long term mean sea level. Comparing themean sea level with annual and seasonalmean fields an anomalous sea surface heightfeature can be significantly identified for theyear 1997. The anomalous evolution

becomes in particular clear when meanperiodic oscillations of the sea surface areidentified and removed. Variations in seasurface temperature (taken from AVHRR)and sea level pressure (from NCAR/NCEP)were analysed in parallel in order toinvestigate correlations between these datasets and to study the impact of the invertedbarometer correction to the altimeter data. Theobserved anomaly was preceded by a drasticdecrease of the NAO index in late 1996 andcoincides with a salinity anomaly in thenorthern North Atlantic. The evolution of seasurface temperature anomalies is similar tothat of the sea level anomalies. Thetemperature anomalies, however, appear as aprecursor with a phase, about one months inadvance.

CALIBRATION OF ERSALTIMETRIC DATA IN THEWESTERN SPITSBERGEN SHELFTHROUGH TIDE GAUGE DATA

A. Braun, A. Helm, M. Rentsch and T. SchöneGFZ Potsdam, division 1.2, c/o DLROberpfaffenhofen, D-82234 Weßling.braun@gfz-potsdam,de/Fax:++49-8153-281207

A sea level analysis using satellite altimetryrequires very accurate data and up-to-datemodels of ionospheric, tropospheric and tidaleffects. Beside this, other error sources likeinaccurate orbit recovery and insufficientretracking algorithms for extreme conditions,e.g. strong winds or high waves, lead to thefact, that large errors still remain in thecomputed sea level. A comparison with in-situ data, e.g. from sea level analysis of tidegauges, is one possibility to improve ourunderstanding of sea level change as seen bysatellite altimetry. A comparison of tidegauge data in Ny- Alesund, Svalbard, withthe ERS altimeter mission data over the lastseven years was performed to calibrate thealtimetry data. Although globally a sea levelrise of about 2 mm/year is expected, arelative sea level fall of about 10 mm/yearoccurs in Svalbard, which is mainly aconsequence of post-glacial rebound inFennoscandia. The vertical motions in thisregion are obtained from GPS and VLBImeasurements. The tide gauge data is

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available in hourly values, a wavelet analysiswas performed to identify the main tidalperiods. Trends of daily, weekly monthlyand yearly means were evaluated toinvestigate the temporal evolution of the tidegauge values. The remaining differencesbetween the altimetric data and the tide gaugedata will be presented and futurerequirements for processing altimetric datafor sea level studies will be discussed.

SEA LEVEL CHANGE FROMSATELLITE ALTIMETRY

Anny Cazenave, LEGOS-GRGS/CNES,Toulouse, France

Satellite altimetry, operational since thebegining of the 90s, appears as a new tool formonitoring the ëtrueí volume and masschange of the oceans in response to climatechanges. Satellite altimetry provides indeedprecise sea level measurements in a terrestrialreference frame tied to the Earthís center ofmass, with a high spatio-temporal coverage.Analysis of altimetry data from the Topex-Poseidon mission indicates a global mean sealevel rise of 2 mm/yr since early 1993.Geographical distributions, and globalaverages as well, of sea level and sea surfacetemperature trends over 1993-1998 are highlycorrelated, which suggests that at least part ofthe observed interannual sea level change hasa steric (thermal) origin. At the level of 1mm/yr however, several factors due toinstrumental drifts or non-modeled effects inthe altimetric system may still affect sea leveltrend estimates. Comparisons performedbetween Topex-Poseidon-based and tidegauge-based sea level change, have allowedthe detection of instrumental drifts onboardthe Topex-Poseidon satellite, demonstratingthe interest of tide gauge measurements forthe calibration of current altimetry missions.However tide gauge-based sea levelmeasurements are made relative to the land,hence are contaminated by vertical crustalmovements. It is thus of primary importanceto monitor vertical crustal motions at tidegauge sites with space geodesy positioningsystems.At the annual frequency, Topex-Poseidon hasdetected a mean sea level variation of 4 mmamplitude, maximum in autumn. This

oscillation results from the combined effectsof the thermal expansion of the sea watersand exchange of water with the atmosphereand continents. The steric contribution has anamplitude of 5 mm and is maximum inspring, i.e., in out of phase with theobserved mean sea level. Removing the stericcontribution thus produces an annual sealevel fluctuation of 9 mm amplitude,maximum in autumn, which may result fromchanges in the mass content of the oceans.Estimate of the annual changes of theatmospheric water vapor content, snow depthand coverage, and continental soil moistureleads to an equivalent sea level change of 8mm amplitude, almost in phase with theTopex-Poseidon minus steric sea level. Thisresult shows that it is possible to nearly closethe total seasonal water budget and confirmsthat at this time scale, the Greenland andAntarctica mass balances are nearly inequilibrium .

HYDROLOGICAL CONTRIBUTIONTO GLOBAL MEAN SEA LEVELCHANGE

J. L. Chen (1), C. R. Wilson (1,2), and B.D. Tapley (1)(1) Center for Space Research, University ofTexas at Austin, ; (2) Department ofGeological Sciences, University of Texas atAustinchen@csr.utexas.edu

Analysis of TOPEX/Poseidon satellitealtimeter data indicates that the global meansea level variation has a clear seasonal signalwith an amplitude of about 2 to 3 mm, alongwith a long term drift. This seasonal variationis associated with mass redistribution withinthe global hydrological cycle plus stericthermal contributions. We investigateseasonal variations of water vapor in theatmosphere and water storage on land usingboth assimilated atmospheric models andclimatological data, and to estimate thecorresponding global mean sea level changes.The predicted seasonal global mean sea levelchanges are then compared with the seasonalvariabilities observed by TOPEX/Poseidonaltimetry data, after the latter are corrected forthe steric effect using a simplified thermal

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model derived from the NOAA World OceanAtlas 1994 and space-measured sea surfacetemperature data. The good agreement in bothamplitude and phase betweenTOPEX/Poseidon observation andhydrological model prediction indicates thatthe TOPEX/Poseidon altimeter may providekey information for the global water massbudget by placing observational constraintson the mass budget variations predicted byglobal atmospheric and hydrological models.

MULTI-DISCIPLINARY APPROACHTO SEA-LEVEL CHANGE IN THEADRIATIC SEA AND IN THE PODELTA: INSIGHTS FROMMODELLING ANDSTRATIGRAPHIC ANALYSIS

G. Di Donato, (1) R. Sabadini, (2) L.L.A.Vermeersen, (1) A.M. Negredo, (1) E.Carminati(1) Sezione di Geofisica, Universit‡ diMilano, I-20129 Milano, Italy; (2) Faculty ofAerospace Engineering, Astrodynamics andSatellite Systems, Delft University ofTechnology, NL-2629 Delft,Netherlands

Present day sea-level changes in the Adriaticsea are the result of the superposition ofnatural and anthropogenic verticalmovements. Geophysical modelling of thetectonic mechanisms active in the centralMediterranean and of post-glacial reboundallows us to establish the contributions ofsuch processes to sea-level changes. Alongthe eastern part of the Italian peninsula, thecomparable effects of tectonic subsidence andpost-glacial rebound sum up to a total sea-level increase as high as 1 mm/yr. Inferenceson the effects of sediment load and sedimentcompaction on the vertical motions areobtained from stratigraphic data (commercialwells and seismic lines). The sum of all ofthese terms constitutes the natural componentof sea-level change. The obtained values arequite consistent with the sea-level changesinferred from archeological data which, beingaveraged over the last 2000 years, can beconsidered negligibly influenced byanthropogenic factors. The anthropogeniccomponent of sea-level change can be

inferred by comparison between the totalnatural vertical velocities we calculate andvertical velocities obtained from other datasets. An application is proposed using tidegauge records from Venice and Ravenna.

IPCC THIRD ASSESSMENTREPORT ON SEA-LEVEL CHANGE1900--2100

J. M. Gregory (1) and J. A. Church (2)(1) Hadley Centre for Climate Prediction andResearch, UK Meteorological Office;(2) CSIRO Marine Research, Australia.jmgregory@meto.gov.uk

Coupled atmosphere--ocean generalcirculation models (AOGCMs) are the maintools used for prediction of time-dependentclimate change during the 21st century.Results for sea-level change derived fromseveral AOGCMs have been made availablefor the IPCC Third Assessment Report,enabling comparisons to be made betweenmodels and with observations. The currentrate of global average sea-level rise can beaccounted for, when allowance is made forthe large uncertainties. Thermal expansion isprobably a larger contributor to eustaticchange than loss of mass from mountainglaciers. Over the next hundred years, thepredictions indicate that thermal expansionwill be the dominant term; estimates of theglobal average change have a central value ofabout 0.5 m, as in the Second AssessmentReport. All AOGCMs indicate substantialgeographical variation in sea-level change,principally because of the non-uniformity ofheat uptake and thermal expansitivity;changes in salinity, wind-stress, oceancirculation and atmospheric pressure alsohave an influence. Local eustatic change canbe at least 50% greater than the globalaverage. The models do not agree well on thedetail of geographical patterns, but do showsome similarities on large scales.

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GLOBAL AND REGIONAL SEALEVEL RISE PREDICTIONS FROMTHE HADCM3 AOGCM

J. M. Gregory and J. A. LoweHadley Centre for Climate Prediction andResearch, UK Meteorological Officejmgregory@meto.gov.uk

The recent availability of high-quality seasurface altimeter data offers an opportunityfor a new kind of evaluation of coupledatmosphere--ocean general circulation models(AOGCMs). Comparison withTOPEX/POSEIDON data shows that thegeographical distribution of mean sea surfaceheight relative to the geoid, which reflects thedensity and current structures of the ocean, iswell simulated by the HadCM2 and HadCM3AOGCMs. HadCM2 has a spatial resolutionof 2.5º X 3.75º, and has been widely used asa basis for global and regional climate changeprediction. HadCM3 is a newly developedmodel having a higher spatial resolution of1.25º X 1.25º, which permits an improvedsimulation of ocean currents and heattransports. The annual cycle of sea surfaceheight shows maxima in northern andsouthern mid-latitudes in autumn; thegeographical distribution of the phase of thecycle is in excellent agreement withobservations, and the amplitude isreasonable. This gives confidence in thesimulation of surface flux variations inseasonal time scales. The annual cycle ofboth the steric and the hydrologicalcomponents of global average sea level isalso consistent with observationally basedestimates.

REGIONAL VARIATIONS IN THEPALEO SEA-LEVEL RECORD FROMAUSTRALIA

Nick Harvey (1), Tony Belperio (2), andBob Bourman (1)(1) Mawson Graduate Centre forEnvironmental Studies, The University ofAdelaide, South Australia; (2) Minotaur GoldPty Ltd, 1a Gladstone Street, Fullarton,South Australia

Geological data from Australia provideevidence of Late Quaternary climatic andassociated sea-level fluctuations from anumber of different regions. Studies inSouth Australia provide evidence of LateQuaternary high sea-level stands associatedwith Oxygen Isotope stages 1 to 19, with themost comprehensive data for the lastinterglacial high sea-level stand. Welldefined geological data also exist forinterstadial events during the last glacial(Oxygen Isotope stages 3, 5a and 5c) and forthe Holocene postglacial sea-level rise,primarily from the marine and inter-tidalsediments of the South Australian gulfs.Against this backdrop, investigations havebeen conducted to determine regionalvariations in the Holocene sea-level curve.This paper describes paleo sea-level studiesfrom prograding coastal sediments adjacent tohistoric tide-gauge sites in South Australia.These sites are of interest given significantdifferences in mean sea-level trends betweenthe sites which suggest geological influenceson the tide-gauge data. Geologicalinvestigations using vibrocoring and backhoeexcavation techniques identified paleo-sea-level indicators within the sediments. Allsites were accurately levelled to determine theposition of the paleo sea-level indicatorsrelative to their modern counterparts. Thedominant indicators were the boundariesbetween the sub-tidal seagrass (Posidonia)facies and the inter-tidal sand flat facies;between the sand flat facies and the mangrove(Avicennia marina ) facies; and between themangrove facies and the samphire(Halosarcia-Sarcocornia andSclerostegia-Halosarcia ) marsh facies. Sediments fromthese boundaries were sampled andradiocarbon dated to produce sea-levelcurves. Results indicate a variation in the

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dominance of paleo-sea level indicators atdifferent sites. The data also reveal theinfluence of both postglacial hydroisostaticwarping of the shelf and anthropogenicinfluences. The paper draws conclusions onthe implications of this regional study withinthe broader context of both Australian meansea-level trends, as derived from historic tide-gauge data, and the emerging pattern ofcoastal response to the Holocene sea-leveltransgression in Australia.

EXCESS HELIUM-4 IN THESOUTHERN OCEAN: A TRACERFOR GLACIAL MELT WATER

R. Hohmann (1), P. Schlosser (1, 2), A.Ludin (1), R. Weppernig (1)(1) Lamont-Doherty Earth Observatory ofColumbia University, Palisades, NY;(2) Department of Earth and EnvironmentalSciences, Columbia University, NYhohmann@ldeo.columbia.edu

The ice shelves surrounding Antarcticacontain about 10% air by volume. During themelting of the glacial ice a significant fractionof this trapped air is dissolved in the seawater. Helium has the lowest solubilityamong the gases contained in air and,therefore, the meltwater is highlysupersaturated in helium. The He signalimprinted by addition of glacial meltwater canbe detected in large portions of the shelfregion of the Southern Ocean and can becorrelated to the volume of melted glacial ice.Excess 4He data were collected fromtransects in the shelf region extending fromthe eastern Ross Sea to the southwest coastof the Antarctic peninsula. Due to theprevailing wind direction, this region iscovered with sea ice most of the year and,therefore, gas exchange between the oceanand the atmosphere is to a large extentsuppressed. Particularly large 4Heconcentrations are observed in the upper 500m on the shelf. The inventory of 4He withlocal meltwater origin south of 70∞S isapproximately 1012 ccSTP. With an assumedair content of ice of 0.12 ccSTP/g, thisinventory represents a total amount of glacialmeltwater of 1500 Gt. With an averageresidence time of the shelfwater of 2.5 years,

the 4He data suggest an annual melting rateof approximately 600 Gt/yr (0.02 Sv).

CAN THE DYNAMICS OF GLOBALWATER BALANCE CAUSE SEA-LEVEL ANOMALIES?

V. KlemesConsultant, 3460 Fulton Rd., Victoria BC,V9C 3N2, Canada

The time change in the ocean mass, z(t), isthe result of the integration over a time period(t-t0) of the difference between the waterinputs, x(t), and outputs, y(t), so that

z (t) = z t0 + [x (τ) - y (τ)] d τt0

t

and the sea level, h(t)=f[z(t)], is a cumulativeprocess in t.One of the peculiar properties of cumulativeprocesses (studied by Slutzky, Yule, Fellerand others) is that their traces may displayquasi-periodic and cyclic properties evenwhen their forcing functions x(t) or y(t) arerandom. It has been shown (Klemes andKlemes, Water Resources Research, 24, 1,93-104, 1988) that the periodic patternbecomes more regular as the order of thecumulative process increases and, in certaincircumstances, it fast (in orders 3 to 4)converges to a pure sine wave over thesample size. The above reference showsexamples of this effect on the mass ofglaciers, lake levels and streamflow. Thepurpose of this presentation is to explore thequestion whether it might play a role in somequasi-regular patterns in sea-levelfluctuations, either directly through the waterbalance of the ocean reservoir or indirectlythrough higher order effects of the dynamicsof the polar ice mass balance or of the oceanheat balance.

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CHANGES IN SEA LEVEL, SEASURFACE TEMPERATURE ANDATMOSPHERIC PRESSURE FROMSATELLITES

Per Knudsen and Ole Baltazar Andersen(both at National Survey and Cadastre,Copenhagen NV, Denmark,email: pk@kms.dk ; oa@kms.dk

In studies of Global Change, sea surfacetemperature data may provide valuableinformation. Global sea surface temperaturedata may indicate changes in the heat budgetof the oceans. Five years of sea surfacetemperature data and sea level height for thesame period is analysed. Altimetry from theTOPEX/POSEIDON satellite will be usedalong pressure observations provided in theT/P records and low resolution averaged seasurface temperature data from the ATSR 1and 2 sensor onboard the ERS satellites andAVHRR data from the NOAA satellites.The global and regional characteristics of thesea level trends and the trends in the seasurface temperature as well as trends in theatmospheric pressure during 1992-1997 areinvestigated. The changes in the sea level arecompared with changes in sea surfacetemperature to decide whether the changes insea level are related to changes in the heatcontent of the ocean. Spatial and temporalcorrelation between the signals areinvestigated, and a bivariate coherencyanalysis of the sea level together with the seasurface temperature is carried out at differentspatial scales.

THE CONTRIBUTION OFGLACIERS AND SMALL ICE CAPSTO SEA LEVEL CHANGE

Michael Kuhn, Institute of Meteorology andGeophysicsInnrain 52, A-6020 Innsbruck, Austria

Although glaciers and small ice caps have atotal area of less than 5 percent of theAntarctic and Greenland ice sheets they arebelieved to have contributed about one thirdof the sea level rise of the past 100 years.This paper summarizes the advances thathave been made in calculating the meltwater

of glaciers and small ice caps since theSecond Assessment Report of the IPCC.Latest estimates of global glacier massbalance are based on individual treatment ofup to 100 regions and use local precipitationor GCM-produced energy and accumulationvalues. They indicate a present contributionof glaciers of 0.2 to 0.4 mm per year toglobal sea level rise.

NATURAL INTER-ANNUALVARIABILITY OF SEA SURFACEHEIGHT EVALUATED USING AMULTI-CENTURY AOGCMSIMULATION

J A Lowe and J M GregoryHadley Centre for Climate Prediction andResearch, UK Meteorological Office.jalowe@meto.gov.uk/Fax:+44 1344 854898

Sea surface height varies on a wide range oftemporal and spatial scales. A quantitativeunderstanding of the patterns of natural(internally generated) sea surface heightvariability is necessary in order to assess thesignificance of potential anthropogenicchanges in sea-level.In this study, sea surface height variability ontime scales longer than 1 year has beencalculated from multi-century simulations ofthe pre-industrial climate system made usingthe Hadley Centre Atmosphere-Ocean generalcirculation models (AOGCM). Results fromtwo versions of this model are presented. Theversions differ in the resolution of their oceancomponents, their use of flux corrections,and their parameterisation of the transport ofheat within the ocean. Spectral decompositionhas been used to discern the frequencies ofthe dominant modes of oscillation.The variance of the modelled sea surfaceheight is found to be spatiallyinhomogeneous; the magnitude of thevariance at some locations is an order ofmagnitude greater than the global mean value.The patterns of sea surface height variancewill be compared with results from theTOPEX/Poseidon altimeter and theimplications of the results for the detection ofa sea-level change signal on global and regionscales will be discussed.

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PREDICTED CHANGES IN STORMSURGE ACTIVITY AROUND THEUNITED KINGDOM COASTLINE INA FUTURE CLIMATE WITHINCREASED GREENHOUSEFORCING

J A Lowe and J M GregoryHadley Centre for Climate Prediction andResearch, UK Meteorological Office.jalowe@meto.gov.uk/Fax:+44 1344 854898

A potential consequence of climate change isan alteration of the frequency of extremecoastal storm surge events. It is these extremeevents which, from an impacts point of view,may be of more concern than the slowinundation of coastal areas by century scalechanges in mean sea level.In this study, a 35 km resolution storm surgemodel of the North Sea shelf region has beendriven by winds and pressures predicted bythe Hadley Centre nested regional climatemodel. Simulations of both present day andfuture climate (the end of the 21st century)have been performed; the effects of predictedchanges in weather and mean sea-level havebeen investigated.Results suggest that the return periods ofextreme storm surge events around theUnited Kingdom coastline decrease withincreases in mean sea-level. At mostlocations, changes in local meteorology leadto further changes in the return periods. Thestatistical significance of the predictedchanges in storm surge occurrence will bediscussed.

EARLY MEDIEVAL (AD 700-1100)AVULSION OF THE YUKON RIVERDELTA: CLIMATOLOGICALCONTROL DUE TO INCREASEDPRECIPITATION?

O.K. Mason (1) and William Dupré (2)(1) Alaska Quaternary Center, University ofAlaska; (2) Department of Geology,University of Houstonffokm@uaf.edu /Fax 907-455-9054

Hydrological input into the Yukon River ispredominantly nival, consisting of bothseasonal snow melt and melting glacial ice.

Although meteorological floods cansimultaneously affect extensive areas of theriver, localized ice-jam floods during break-up introduce anomalies that may preclude thereconstruction of basin-wide flood history.Yukon Delta cutbanks record flood historyand the river’s interaction with sea and stormlevel changes; its chenier plain witnessedstorm ridge addition before 1500 BCassociated with eustatic sea level in theadjacent Bering Sea at –1.5 m below present.The Yukon-Kuskokwim (YK) delta consistsof several sub-lobes, formed as depositionshifted northeastward, from the Black Riverlobe active 2500 BC-500 BC, to the presentlobe formed since 2000 BP. Limiting agesindicate that a major avulsion in the Yukon

Delta occurred in the late 1st millennium ADand led to the formation of a new lobe. Thisavulsion was contemporaneous witherosional truncation within beach ridgecomplexes throughout west and northwestAlaska. Limited sea level data indicate a 50cm drop in eustatic sea level as well.Correlations with regional (alluvial, tree ring,glacial advances), as well as global recordsfrom Greenland ice cores, and the Nile andEast Asian rivers favor a climatic cause.

INTERANNUAL LAKE LEVELCHANGES AND REGIONALHYDROLOGY

F. Mercier, A. CazenaveGroupe de Recherche de Geodesie Spatiale,CNES/GRGS-LEGOS, ToulouseFranck.Mercier@cnes.fr/ Fax: 33 561.25.32.05

Topex/Poseidon and ERS-1 altimeters wereprimarily designed to measure height of thesea surface. Nevertheless, we can also usesatellite altimetry to investigate level changesof continental lakes. We use 6 years ofTopex/Poseidon altimetry data to study levelchanges of African Lakes. We also analysethe ERS-1 Waveform Altimeter Product rawdata set to produce lake level time series. Dueto its shorter intertrack spacing, ERS-1provides a much denser coverage of lakesthan Topex/Poseidon. When avalaible, in situlake level measurements are compared withaltimetric time series.

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In this analysis, we focus on the seasonal andinterannual fluctuations of lake levels. Usingavailable regional hydrometeorological data,we further study the water balance over eachlake catchment basin. On the annual time-scale, we show a clear correlation betweenlake level and precipitation fluctuations whileon the interannual time-scale, regional as wellas global climatic changes are invoked.

GLOBAL MODELS OFPOSTGLACIAL SEA LEVELHISTORY: THE ROLE OF"IMPLICIT ICE"

W.R. PeltierDepartment of Physics, University ofToronto, Toronto, Ontario, Canada, M5S-1A7. peltier@atmsop.physics.utoronto.ca/Fax: 1-416-978-8905.

The gravitationally self-consistent globaltheory of postglacial relative sea level history,which includes the impact upon rsl of boththe viscoelastic deformation of the solid earthand the variations of both the surface ice andwater loads that induce this deformation,involves the solution of an integral equationthat I have previously referred to as the SeaLevel Equation. The inputs required to enablersl predictions to be made with this theoryinclude a space-time model of ice thicknessvariations ( i.e. a model of the glaciation-deglaciation process) and a model of theinternal viscoelasticity of the earth. Recentlypublished analyses (Peltier, 1998, GRL, 25,3057-3960) based upon the topographicallyself consistent form of this theory (Peltier,1994, Science, 265,195-201) demonstratethat the requirement of surface mass balanceserves to define an "implicit" component ofthe ice load that arises due to anonperturbative effect in the linear theorybased integral sea level equation. Thisconcept fully resolves a previously revealedmass balance discrepancy and has importantimplications concerning the action of thecryosphere in the hydrological cycle. A verypreliminary discussion of these ideas wasprovided in a recent review (Peltier, 1998,Rev. Geophys., 6, 603-689) but will bemuch more fully developed in thispresentation.

WHAT CAN WE LEARN FROM SEALEVEL ABOUT CHANGES IN ICESHEETS?

H.-P. PlagNorwegian Mapping Authority,Kartverksveien, N-3511 Honefoss,Norway,phone: +47-32118100, fax: +47-32118101,e-mail: plag@gdiv.statkart.no

Global ocean volume (GOV) and mass(GOM) characterize the ocean as a reservoirin the global hydrological cycle. These twoquantities are absolute numbers, which havea rather complex relationship with localrelative sea level (RSL) measured by tidegauges. On climatological time scales, thecryosphere has the greatest potential tocontribute to changes in GOM, with therelation between these GOM changes andRSL being described by the sea-levelequation. Thermal expansion is generallyconsidered as a major contributor to GOVchanges, with the resulting RSL changesdepending on where heat is being absorbed inocean water or released. Despite the complexrelationship between RSL and GOM/GOV,observations of coastal RSL have been usedrepeatedly to obtain estimates of a global sea-level rise (GSLR) in a simple arithmetic way,correcting the local RSL trends only foreffects of post-glacial rebound. The GSLRestimates have then been taken as constraintsfor GOV and/or GOM changes. In adifferent approach, here the physicalrelationship between mass changes in thecryosphere and resulting sea-level changes isused to invert the RSL trends for changes inthe Antarctic and Greenland ice sheets. In afirst step, the finger-prints of these two largeice sheets in sea level are fitted to the trendsfor all available tide gauges to determineaverage rates of the present-day masschanges in the Greenland and Antarctic icesheets. A basic uncertainty in this inversion isfound to be due to deficiencies in the post-glacial rebound models used to correct for thecontribution of past mass changes. However,the results indicate a significant difference inthe mass changes of the Antarctic andGreenland ice sheets.

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ICE SHEET MASS BALANCE FROMSPACE TECHNICS

F. Remy, B. LegresyCNRS-CNES-UPS, 18 Avenue E. Belin,Toulouse Cedex 31055 FRANCEfrederique.remy@cnes.fr

Each year, the equivalent of 6 mm of sealevel falls in Antarctica or Greenland. Aboutthe same quantity is rejected either viaicebergs or via melting. The exact massbalance is unknown: we do not know even ifit is positive or negative. Any space sensorsis able to look for long term evolution of theice sheet surface, but only the radar altimetreris able to estimate volume change and thusthe contribution of ice sheet to sea levelchange. We will show results from thecomparison between Seasat and ERSaltimeters above Antarctica and from 6 yearsof Topex above Greenland. The comparisonbetween Seasat and ERS suggests that theAntarctica ice sheet is not in balance: thesignature of topographic changes seems to bedue to a dynamic answer associated with sea-level rise at the end of the last glaciation. The6 years ofdual-frequency altimeter Topex aboveGreenland also suggest an imbalance mostlydue to atmospheric changes.

MEAN SEA LEVEL AND VERTICALCRUSTAL MOTIONS: ANEXPERIMENT IN THE ADRIATICAREA

B. Richter (1), S. Zerbini (2), M. Negusini(2), W. Schwahn (1), C. Romagnoli (3),(1) Bundesamt fuer Kartographie undGeodaesie, Frankfurt am Main, Germany;(2) Dipartimento di Fisica, Universit‡ diBologna, Viale Berti Pichat 8, 40127Bologna,Italy, zerbini@astbo1.bo.cnr.it;(3) Dip. di Scienze della Terra e GeologicoAmbientali, Universit‡ di Bologna, Italy.

To properly determine and understand sea-level fluctuations, it is necessary to measurevertical crustal motions at tide gauge stations.Within the many research activities of the EUSELF II project, an experiment was designedand initiated in order to optimize the GPS and

gravity observation strategies for a cost-effective determination of height changes andto assess the time variability of gravity relatedto environmental effects.In this experiment two GPS receivers havebeen installed at the Medicina and PortCorsini stations. Medicina is a fiducialreference site near Bologna, while at PortCorsini, located on the Adriatic coast near thecity of Ravenna, a tide gauge of the Italiannational network is operational. At bothstations continuous GPS observations arebeing performed since three years andrelevant meteorological parameters such as airpressure, temperature, relative humidity andprecipitation data are also collected on acontinuous basis. In addition, at Medicinacontinuous observations of water table arebeing recorded. At Medicina, asuperconducting gravimeter has beeninstalled since two and half years to monitorvariations of the gravity field continuously.This ensemble of different observationalcapacities establishes a powerful example ofan integrated multipurpose network for globalchange research.The analysis and interpretation of both theGPS and gravity data collected so far atMedicina made it possible to identify clearcommon signals. In the period June-November 1997 the gravity data show aremarkable increase of about 6 (Gal incorrespondence to a significantly increasedscatter in the GPS height time series (6 mmrms compared to 4 mm rms prior and afterthe mentioned period). Starting September1997, both time series exhibit a markedannual signal with a phase difference of about45 days, where gravity anticipates the surfaceeffects recorded by GPS. A non-tidalsemiannual signal is present as well in bothtime series with a similar phase difference.Episodic gravity and GPS height fluctuationsseem to correlate as well. Both gravity andGPS data series indicate the presence ofsubsidence in the order of 2-to-3 mm/yrwhich is confirmed by the latest VLBIsolutions referring to 10 years of data. Thesefindings will be interpreted on the basis of thepresent knowledge of the geology,geophysics, atmosphere and hydrology of thearea, not withstanding the possible responseof the site to climate change forcing andvariability. In particular, thermoelastic effects

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should be investigated in conjunction withthe observed periodic signals, and potentialtectonic influences connected with activecrustal deformations and seismic sequencesof both distant (Umbria region, September-October 1997) and more local (Reggio-Emiliaarea, second half of 1997) earthquakes asregards the observed anomalous behaviorduring the second half of 1997.The analysis of the Port Corsini GPS dataidentifies a subsidence rate of 7.7 mm/yrwhich is in excellent agreement with theresults provided by high-precision levelingmeasurements performed in the period 1992-1999. If this subsidence rate is accounted forwhen estimating the sea-level variation fromthe Port Corsini tide gauge data for the 1993-1997 time interval, a good agreement isfound with the sea-level rate estimated byCazenave et al. (1999) from the Topex datafor the northern Adriatic.

ANTHROPOGENIC ALTERATIONSOF GLOBAL HYDROLOGY ANDSEA LEVEL

D. L. SahagianClimate Change Research Center & Dept. ofEarth Sci., University of New Hampshire,Durham, NH 03824 USA, gaim@unh.edu;fax: 1 603 862 3874.

The influence of human activity on thehydrologic cycle has reached the point whereit affects the hydrologic balance betweenocean and continental storage reservoirs.Land use changes associated with expandingagriculture to support an increasing humanpopulation have already had a profoundinfluence on basin-scale hydrology, and inextreme cases, on regional climate. Majorhuman activities which lead to hydrologicalterations include irrigation (from groundwater mining and surface water diversion),deforestation, wetland filling or drainage, andnew dam construction. With the exception ofthe latter, these all contribute to the transfer ofwater from the continents to the ocean and areduction of continental water resources.However, water impoundment behind damsmay partially or completely counteract thecumulative effect of the others. Presentcompilations of reservoirs impounded by

dams include only the results of majorengineering projects. Smaller impoundmentshave largely been ignored. The cumulativevolume of the literally millions of smallreservoirs such as farm ponds and ricepaddies may approach that of the largerdocumented reservoirs. Unfortunately it isnot practical to make a global inventory ofmillions of small and unregistered reservoirs,so their volume may never be knownprecisely. The quantity of water stored inartifically raised water tables behind dams hasalso not yet been addressed. The issue ofwater impoundment or release fromcontinental drainage basins affects global sealevel. Recent estimates based solely on majordammed reservoirs suggest that if new damconstruction is not maintained at the rates ofthe 1960s through 1980s, the rate of sea levelrise could increase by about half a millimeterper year. If the water stored in smallimpoundments and ground water is taken intoaccount, this figure could be much greater.

SPATIAL-TEMPORAL VARIBILITYOF SEA-LEVEL CHANGES ON THECOASTS OF RUSSIA DURING THELATE PLEISTOCENE ANDHOLOCENE: EUSTASY,TECTONICS OR GEOIDALCHANGES?

A. O. SelivanovGeography Department, LomonosovMoscow State University, Moscow 119899,Russia, fax+7 095-9328836selivano@postman.ru

During the Late Pleistocene and Holocene(the last 120-130 Kyrs) drastic sea-levelchanges of over 100 m in an amplitudechanges occurred. The primary factor ofthese large-scale sea-level changes wasglacioeustatic one. However, sea-levelchanges indicated by ancient coastlines invarious coastal areas differed much from eachother. In many cases these differences areapparent and resulted from the subsequenttectonic deformations. However, our analysisdemonstrated obviously a close correlationbetween ancient coastlines elevations/depthsand recent geoidal anomalies. It appeared thatthe gravitational field of the Earth expressed

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in anomalies of geoidal surface relatively tothe hydrostatic spheroid was similar to thepresent one during the early Late Pleistoceneinterglacial (130-80 Kyrs B.P.), whereas inthe middle of the Late Pleistocene, 40-30Kyrs B.P., positive and negative anomaliesof the geoidal surface were 30-40% lessexpressed than now and the general shape ofthe Earth's surface was approximately halfcloser to the hydrostatically equilibrium one.The range of geoidal changes in the relativesea level during the last 100 Kyrs could be ashigh as 50-100 m thus comparable to thedirect glacioeustatic changes. Geoidal-induced sea-level changes were clearlypronounced on the coasts of Russia in theLateglacial and Postglacial time.

DETERMINATION ANDCHARACTERIZATION OF GLOBALMEAN SEA LEVEL CHANGE

C.K. Shum (1), C.Y. Zhao (1), and PhilipWoodworth (2)(1) Department of Civil and EnvironmentalEngineering and Geodetic Science, The OhioState University, 470 Hitchcock Hall, 2070Neil Avenue, Columbus, OH 43210-1275,USA, ckshum@osu.edu; 614-292-7118,614-292-2957 (fax); (2) ProudmanOceanographic Laboratory, Bidston, UK,plw@pol.ac.uk, 44-151-653-8633

Recent studies of global sea level changehave concluded that the global eustatic rate ofsea level rise during the last century has been1-2 mm/yr [Warrick et al., 1993]. Althoughthere is no firm evidence of an acceleration inthe rate of sea level rise over this time period[Woodworth, 1990], the projected future sealevel rise is 13 +/- 4 cm during the next 40years (1987-2027), and 61 cm over the next100 years (1987-2087) [Woodworth, 1995].Sea level change represents consequences ofcomplicated interactions of the solid Earth-atmosphere-hydrosphere-ocean-cryospheresystem and in part forced by human-originated greenhouse effect. Current long-term (40-100 years) sea level changeestimates (e.g., IPCC studies) are primarilyprovided by long-term tide gauges locatednear coastal regions and continental margins.The estimate has deficiencies from vertical

land movements (e.g., due to postglacialrebound and local land motion) and theassociated vertical datum knowledge, and thefact that the data only covers less than 5% ofthe global ocean. Satellite radar altimetrymissions, both historic and current (Geos-3,Seasat, Geosat, ERS-1,TOPEX/POSEIDON, ERS-2, GFO-1, andfuture (Envisat, Jason-1, NPOESS), wouldprovide global coverage but has much shorterdata span (less than 10 years of continuousdata), and lack of adequate knowledge of therespective instrument biases. In this study,we will provide an analysis of the present-day global mean sea level change usingmultiple mission altimeter measurements andtide gauge data. Second part of the study isintended to provide a characterization of thesea level change by using modernobservations, including global sea surfacetemperature (spaceborne and in situ), iceextents, postglacial rebound models, glacierand ice sheet mass balance data, and thepotential use of future gravity changemapping mission, such as GRACE.

WILL GLOBAL WARMING RAISESEA LEVELS?

S. Fred SingerThe Science & Environmental Policy Project4084 University Drive Fairfax, VA 22030Tel: 703-934-9640/ email: singer@sepp.orghttp://www.sepp.org/ http://www.sepp.org

Global sea level (SL) has undergone a risingtrend, averaging about 1.8 mm per year for atleast a century (Figure 1) [1], and probablymuch longer. Its cause appears to beunrelated to decadalscale climate fluctuations;it may be a consequence of the millennial-scale warming that began about 15,000 yearsago. This argument is strengthened when wenote that all climate-related factors togethercan account only for about 20 percent of theobserved rise since 1990 (Figure 2). Weobserve, furthermore, that departures(anomalies) from a linear SL rise during1905-1975 show a pronounced inversecorrelation with global average temperature(GAT) -- and even more so with tropicalaverage sea surface temperature (TASST)(Figure 3). These findings suggest that --

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under current conditions -- evaporation fromthe sea surface with subsequent deposition onthe polar ice caps, principally in the Antarctic,produces negative changes in SL thatoutweigh increases from the melting ofmountain glaciers and the thermal expansionof ocean water. It is likely, therefore, that anyfuture moderate warming -- from whatevercause -- will also slow down the ongoing SLrise of 18 cm per century, rather than speed itup. Theoretical studies of precipitationincreases in the Polar Regions [2] and resultsfrom General Circulation Models (GCMs) [3,4, 5] support this conclusion. Furthersupport comes from the (albeit limited) recordof annual ice accumulation in polar ice caps[6, 7].

THE RECENT CHANGES OF THEBLACK SEA LEVEL. ESTIMATESFROM MARIOGRAPH, ALTIMETERAND HYDROLOGICAL DATA

E. V. Stanev (1), E. L. Peneva (1), P.-Y. LeTraon (2)(1) Department of Meteorology andGeophysics, University of Sofia, 5 JamesBourchier St., 1126, Sofia, Bulgaria,stanev@phys.uni-sofia.bg, (2) CLS-SpaceOceanography Division, Toulouse, France

The sensitivity of Black Sea level variationsto hydrological cycle is extremely strongsince the ratio between fresh water flux andthe volume of the sea is relatively large valuein comparison to other semi-enclosed seas.The well-constrained water balance of thissea makes possible to produce accurateestimates of the fluxes. In the present paperwe analyze TOPEX/POSEIDON altimeterdata in the Black Sea in parallel with availablehydrological and meteorological data with theaim to study the water balance and thedependency of sea level oscillations onmeteorological and hydrological forcing. Theconsistency between satellite and pegel data isalso analyzed. It is proved that using altimeterdata can contribute to improving waterbalance estimates at seasonal and inter-annualtime scales. The main focus is on theobserved variability in the last 70 years. Therelationship between the amplitude ofseasonal oscillations of mean sea level (about10 cm) and fresh water fluxes is quantified.

This is very important to understanding themechanisms of circulation and water massformation in the interconnected system BlackSea-Mediterranean Sea.

RELATIVE SEA-LEVEL CHANGEAND MODELING THE ALTEREDHYDROLOGY OF A RAPIDLYSUBSIDING WETLAND

D. ThomsonTurtle Cove Environmental Research Station,Southeastern Louisiana Universitydthomson@selu.edu

Alluvial floodplains are some of the mostproductive regions in the world. Riversfeeding these systems collect and concentratenutrients from their watersheds which drivesincreased production in associated systems.Their productivity is attractive, however thedynamics of these systems are not conduciveto human settlement and were subsequentlyaltered to make them more habitable.Alteration has removed the source of theirlong-term productivity and in some casesjeopardized their existence. Both the natureand importance of these systems makes thema focal point for studying the land-seainterface. By nature, alluvial floodplains aretransient structures that interact strongly withsea-level changes. For millennia, theMississippi River and the Gulf of Mexicorestructured this region (Mississippi RiverDeltaic Plain). Now control structures alterthe riverís load and force most of what is leftoff the continental shelf. Restoration seemsunlikely, sea-level changes and naturalsubsidence are no longer offset by riverinesediment deposition, and it is believed thatthere will be 50% less land in Louisianaíscoastal zone by the year 2050. Implicationsfor the Pontchartrain Estuary (SoutheasternLouisiana) are similar in the long term butcurrently the estuary seems more influencedby runoff than by the Gulf of Mexico.Drought years have led to increased salinitythroughout the estuary and alterations tocommunity structure in primary producersthat are the major contributors to verticalaccretion in areas isolated from sedimentdeposition.

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THE IMPACTS, RESPONSES, ANDLEGAL IMPLICATIONS OF RISINGSEA LEVEL ALONG THE U.S.ATLANTIC AND GULF COAST:NEW MAPS AND NEW POLICIES

Jim Titus, U.S. Environmental ProtectionAgency, 401 M Street, SW, Washington, DC20460, USA, +1-202-260-7821,titus.jim@epa.gov

Along most of the U.S. coast, sea level isrising and shores are retreating. Increasingconcentrations of carbon dioxide and othergreenhouse gases are expected to acceleratethe rate at which the sea rises, with a two-foot rise likely in the next century and a muchlarger rise possible. Given current land useand shore protection policies, a large-scaleloss of sandy estuarine beaches, wetlandshores, and very shallow water habitats islikely. Fortunately, environmental policiescould be developed to enable theseecosystems to survive rising sea level.Unfortunately, those policies are notcurrently being implemented outside of a fewstates, and society is missing an opportunityto inexpensively safeguard the coastalenvironment.Ocean beaches are more likely to survive sealevel rise than the bay shores. There is astrong constituency to protect public uses ofocean beaches. The common technology forholding back the sea along ocean shores(beach nourishment) does not destroy thebeach. Private seawalls along the ocean aremuch more expensive than the bulkheadsnecessary to hold back a bay. Finally,existing policies to protect natural shoressuch as setbacks and bulkhead prohibitionsgenerally only apply to ocean shores.This paper focuses on land use measures forensuring the survival of bay shores in theface of coastal erosion and rising sea level.Unlike coastal engineering projects whichoften can only be implemented at a scale oftens of millions of dollars, these measurescan be implemented by counties, borough,towns, and private property ownersinterested in protecting natural shores inperpetuity. We also present maps based onthe use of USGS digital elevation model data.Causes of Sea Level Rise. Tidal gaugemeasurements show that sea level is rising

about 2.5-3 mm/yr along most of the Atlanticand Gulf Coast. About 50% of this rise canbe explained by land subsidence in theseareas, 10% from a retreat of alpine glaciers,and 5-15% from the warming and resultingexpansion of the ocean; th remaining 25-35%is unexplained. EPA projects that globalwarming could raise sea level 50-60 cm alongmost of the U.S. coast in the next century,with a 5% chance that the rise could begreater than 100 cm.For purposed of this conference, one issueworth flagging is the distinction betweenglobal and relative sea level rise projections.Many impact studies of global warming eitherassume that relative sea level rise will equalIPCC-projected global sea level rise, orcalculate relative sea level rise as equal toIPCC-projections plus a local subsidencecomponent estimated as historic relative sealevel rise minus an estimate of global sealevel rise. The problem with that approach isthat it fails to deal with the fact that IPCC(and other) model runs estimate that climatechange only added 5-10 cm to sea level in thelast century, whereas the data suggests thatthe rise was closer to 20 cm. The IPCC lowscenario projects that greenhouse gases willcontribute1.8 mm/yr to sea level, anacceleration compared with the 0.5 mm/yrhistoric contribution–but a decelerationcompared with the measured contribution.Therefore, we are left with the absurdsituation in which people analyzing theimpacts of the low scenario would assumethat sea level will decelerate in the nextcentury, even though the model on whichthey are relying assumes acceleration! (Ofcourse, if one genuinely believes that thehistoric discrepancy between models and dataresulted from unusual random fluctuationsthat had nothing to do with global warmingand that will not be repeated in the nextcentury, then this approach is reasonable.)The EPA reports on the Probability of SeaLevel Rise employ an alternative procedure:use the models to estimate the projectedacceleration of sea level due to climatechange, and then add that to the current trendin relative sea level. This approach avoidsthe forgoing inconsistency problem.Inundation of Low Lands . Rising seas tendto inundate low land, erode wetlands andbeaches, increase coastal flooding, and

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increase the salinity of aquifers and estuaries.Previous assessments have estimated that a50-100 cm rise would inundate 9000-18000square miles of land, and that it would cost$100-500 billion to hold back the sea andprotect developed areas. Only recently,however, has EPA developed mapsillustrating the vulnerable land. Using digitalelevation model output and NOAA shorelinedata, we have prepared a map of the USAtlantic and Gulf Coasts illustrating the 1.5-meter contour, which is about 1.3 metersabove sea level. That map is being publishedat scales in which a single U.S. state appearson a sheet of paper, as well as a mapshowing the entire eastern half of the nation.The map does not purport to project thefuture shoreline, but rather that area mostvulnerable to inundation.EPA is also proceeding, slowly, on a secondmapping effort that will project changes inshorelines. That efforts requires one to makean assumption regarding which areas will beprotected and which areas will be inundated;EPA is developing those scenarios through acollaboration with local government plannersin New Jersey and North Carolina, and effortthat will be expanded to include other states.We are also developing maps that can bepresented at thbe 1:100.000 scale, andthereby illustrate impacts of sea level rise onthe county scale.Loss of Estuarine Shores . If our coastalzones were not developed, natural systemscould migrate inland and rising sea levelwould not cause a major reduction inestuarine beaches or shallow habitats. Therewould be a net loss of coastal wetlands,because the area of wetland is far greater thanthe area of land just above the wetlands. Butthe overall integrity of coastal ecosystemswould remain intact.Most of the coast is or will becomedeveloped, however, and homeowners rarelychoose to give up their land to the sea.Along ocean shores, beach nourishment isthe preferred strategy, which enablesproperty to be protected without the loss ofthe beach. The estuarine shore, however, isbeing replaced with walls or concrete, rock,steel, and wood. In Maryland alone, 300miles of shoreline have been armored in thelast 15-20 years. These structures eliminate

beaches, narrow strip of tidal wetlands, andeventually, shallow waters as well.Federal Programs Fail to Protect EstuarineShores Even Today. Federal programs havetwo fundamental limitations. First, wetlandprograms generally focus on marshes,swamps, and other vegetated wetlands, butignore the estuarine beaches. Second, theytend to focus on the total area of habitat beingprotected, to the exclusion of other measuressuch as the length of shoreline or land/waterinterface being threatened. As a result, thevalue of estuarine beaches, adjacent shallowwaters, and narrow riparian strips ofwetlands are automatically devalued; a mile ofbeach, for example, may represent only oneacre of land. Nevertheless where the loss ofnatural shores has an important cumulativeenvironmental impact, the law may requirefederal agencies to address the directdestruction of estuarine shores.The law does not, however, require thefederal government to address the indirectdestruction resulting from the beaches andwetlands being squeezed between the risingsea and development. Our institutions assumethat sea level and shorelines are stable.Federal jurisdiction to regulate wetlands isbased on where the high water mark is today.Federal programs can prevent filling andarmoring of wetlands and beaches; but theygenerally lack the authority to prevent thefilling, development, and armoring of landthat is dry today but would become a beachor wetland in the future as the sea rises. Stateand local governments may have to take thelead.Current and Possible Future Efforts toProtect Natural Wetlands and Beaches asShores Erode. State efforts to recognizeshoreline migration have been mixed.Several states have policies to allow oceanbeaches to survive rising sea level; but thosepolicies do not apply to protect estuarineshores. Nevertheless, they probably serve asa good model for bay beaches and wetlandshores. Several states have enacted setbacksbased on current erosion rates, as a means ofpreventing ocean shores from being armored.Even this approach is only a temporarysolution, because the shore will eventuallyerode up to the setback.Texas, Maine, Rhode Island, Oregon, and (toa limited extent) South Carolina have adopted

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an alternative approach: the “rollingeasement.” The term “rolling easement”refers to a broad collection of institutionalmechanisms which guarantee that naturallymigrating shorelines have the right of wayover the desires of private property owners tohold back the sea. To the private propertyowner, this approach is less draconian than asetback, because one is allowed to developone’s land--but only on the condition that heor she will not eliminate the intertidal beacheswhich are, for the most part, owned by thepublic. If the sea does not rise, then theenvironmental policy does not impose amajor cost on the property owner; if the seadoes rise, however, the environment is notsacrificed In addition to setbacks and rollingeasements, density restrictions, clusterdevelopment, land purchases andnondevelopment easements may be theeffectiveThe Takings Question. Allowing wetlandsand beaches to migrate inland requires peopleto abandon their land to the sea which, at firstglance, would appear to run afoul of the U.S.Constitution’s admonition that “nor shallprivate property be taken for public usewithout just compensation.” Setbacks thatprevent any beneficial use of a given propertyare likely to be takings ( See Lucas v. SouthCarolina Coastal Coun cil). Rollingeasements, by contrast, will not be a taking,because (a) they allow property owners touse their property until the sea threatens it;and (b) under the public trust doctrine, thepublic owns (or has an easement along) allintertidal wetlands. Even though thesepolicies need not be takings, simple fairnessmay suggest that stringent policies should notbe implemented without some compensation.In the case of a rolling easement, the faircompensation would be small, because therequired abandonment of the property wouldbe many decades hence.Why Local Entities May Be Best Suited forProtecting Natural Shores . The first stepshould probably not be statewideimplementation of controversial land usemeasures. Such an approach may have beenwarranted along ocean coasts, where manystates had a strong consensus on the need tokeep recreational beaches. There is no suchconsensus along estuaries, however. Amore realistic step is for states to decide

whether they want to keep any significantfraction of their natural shores, and if so,which ones.Is the state the appropriate level ofgovernment to undertake such anassessment? As the owner of the intertidallands in most cases, the state ultimately mustdecide how to deal with these issues. But atthe first instance, local government is themore appropriate level of government inmany states. Local governments havegenerally enacted land-use plans and zoningregulations that determine which private landsare likely to remain open space and whichwill become urbanized. The same type ofthinking could be applied to determine whichshores should be armored and which shouldremain in their natural conditions. Especiallyin the case of land that has not yet beendeveloped, the local government is in theposition to ensure that future subdivisions aredesigned in a fashion consistent with theplan. For example, if the shore is going toretreat, a local government can make sure thatall homes are accessible by shore-perpendicular roads.Private parties can also play an importantrole. Conservation groups that findthemselves selling coastal lands to raise fundsfor other purposes, can reserve a rollingeasement on any property they sell, therebyensuring that the shore is not armored.Developers can propose to reserve rollingeasements and donate it to a public or privateconservation entity, as part of environmentalmitigation or enhancement programs neededto secure permits. Finally, individual ownersof coastal property can donate rollingeasements on their property to conservanciesor public conservation entities–and claim atax deduction.

DETECTABILITY OF SEA LEVELHEIGHT VARIATION PATTERNS

K. van OnselenDelft Institute for Earth-Oriented Research(DEOS), onselen@geo.tudelft.nl

In order to distinguish anthropogenicinfluences (e.g., those due to greenhouse-gasinduced warming) from ìnaturalî variations insea level height, long data series are required.Sea level height time series containing in the

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order of 100 years of data are available froma number of tide gauges. From theseindividual time series, local patterns inrelative sea level can be determined.If data sets for tide gauges in a region arecombined, a better estimate of sea levelvariation patterns common to this regioncould be obtained. However, in order tocombine the various time series, heights ofthe tide gauge bench marks have to be relatedto a common reference system. This heightconnection introduces measuring andsystematic errors into the data sets.The purpose of this work is to examine howthe detectability of a common pattern in sealevel data is influenced by the limitedaccuracy of the geodetic measuringtechniques used to connect the tide gauges inheight. Time series used are a combination ofsimulated patterns with periodic variationsobtained from tide gauges (with more than100 years of observations) situated along theDutch coast. Sea level variation patternsunder consideration are linear patternspossibly in combination with a sea level riseacceleration at the beginning or towards theend of the time series.

DETERMINATION OFINTERANNUAL TO DECADALCHANGES IN ICE SHEET MASSBALANCE FROM SATELLITEALTIMETRY

H. Jay ZwallyNASA Goddard Space Flight CenterGreenbelt, MD 20771, USAjay.zwally@gsfc.nasa.gov

A major uncertainty in predicting sea levelrise is the sensitivity of ice sheet massbalance to climate change, as well as theuncertainty in present mass balance. Sincethe annual water exchange is about 8 mm ofglobal sea level equivalent, the ± 25%uncertainty in current mass balancecorresponds to ± 2 mm/yr in sea levelchange. Furthermore, estimates of thesensitivity of the mass balance to temperaturechange range from perhaps as much as - 10%to + 10% per K. Although the overall icemass balance and seasonal and inter-annualvariations can be derived from time-series of

ice surface elevations from satellite altimetry,satellite radar altimeters have been limited inspatial coverage and elevation accuracy.Nevertheless, new data analysis showsmixed patterns of ice elevation increases anddecreases that are significant in terms ofregional-scale mass balances. In addition,observed seasonal and interannual variationsin elevation demonstrate the potential forrelating the variability in mass balance tochanges in precipitation, temperature, andmelting. From 2001, NASA’s ICESat laseraltimeter mission will provide significantlybetter elevation accuracy and spatial coverageto 86˚ latitude and to the margins of the icesheets. During 3 to 5 years of ICESat-1operation, an estimate of the overall ice sheetmass balance and sea level contribution willbe obtained. The importance of continued icemonitoring after the first ICESat is illustratedby the variability in the area of Greenlandsurface melt observed over 17-years and itscorrelation with temperature. In addition,measurement of ice sheet changes, alongwith measurements of sea level change by aseries of ocean altimeters, should enabledirect detection of ice level and global sealevel correlations.

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Participants

Axe, Philip G.UK Natural Environment Research CouncilProudman Oceanographic LaboratoryBidston ObservatoryBirkenheadMerseyside L43 7RAUnited KingdomTel: +44-151-653-8633Fax: +44-151-653-6269E-mail: paxe@ccms.ac.uk

Belperio, AntonioMinotaur1A Gladstone st. Fullarton5063 AdelaideAustraliaTel: +61-8-833-83-333Fax: +61-8-833-83-233E-mail: tbelperi@camtech.net.au

Bernier, Natacha B.Dept. of OceanographyDalhousie UniversityHalifax, Nova Scotia B3H 4J1CanadaTel: +1-902-494-7007Fax: +1-902-494-2885E-mail: natacha@phys.ocean.dal.ca

Bingley, Richard M.Institute of Engineering Surveying and Space GeodesyUniversity of NottinghamUniversity ParkNottingham, NG7 2RDUnited KingdomTel: +44-115-951-3932Fax: +44-115-951-3881E-mail: richard.bingley@nottingham.ac.uk

Bolgov, Michail V.Water Problems Institute of RussianAcademy of SciencesGubkina 3Moscow 117971RussiaFax: +7-095-1355415E-mail: bolgov@iwapr.msk.su

Bosch, WolfgangDeutsches Geodätisches ForschungsinstitutMarstallplatz 880539 MünchenGermanyTel: +49-89-23031-115Fax: +49-89-23031-240E-mail: bosch@dgfi.badw-muenchen.de

Braun, AlexanderDivision 1.2GeoForschungsZentrumDLRMünchenerstr. 20Postfach 111682230 OberpfaffenhofenGermanyTel: +49-8153-28-1208Fax: +49-8153-28-1207E-mail: alexander.braun@dlr.de

Cabanes, CecileLEGOSCNES18, Avenue E. Belin31401 Toulouse Cedex 4FranceTel: +33-561-332922Fax: +33-561-253205E-mail: anny.cazenave@cnes.fr

Cazenave, AnnyLEGOS-GRGSCNES18, Avenue E. Belin31401 Toulouse Cedex 4FranceTel: +33-561-332922Fax: +33-561-253205E-mail: anny.cazenave@cnes.fr

Chen, JianliCenter for Space ResearchUniversity of Texas at Austin3925 West Braker Lane, Suite 200Austin, TX 78759-5321USATel: +1-512-471-5573Fax: +1-512-471-3570E-mail: chen@csr.utexas.edu

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Cloetingh, Sierd A.P.L.Faculty of Earth Sciences, Room E160Vrije UniversiteitDe Boelelaan 10851081 HV AmsterdamThe NetherlandsTel: +31-20-444-7341Fax: +31-20-646-2457E-mail: cloeting@geo.vu.nl

Di Donato, GinevraDip. di Scienze della TerraUniversita di Milanovia L. Cicognara 720129 MilanoItalyTel: +39-02-2369-8403Fax: +39-02-7490588E-mail: ginevra@alpha1.geofisica.unimi.it

Gregory, Jonathan M.Hadley CentreMeteorological OfficeLondon RoadBracknell, Berkshire RG12 2SZUnited KingdomTel: +44-1344-854 542Fax: +44-1344-854 898E-mail: jmgregory@meto.govt.uk

Hohmann, RolandLamont-Doherty Earth ObservatoryColumbia UniversityRoute 9WPalisades, NY 10964USATel: +1-914-365-8514Fax: +1-914-365-8155E-mail: hohmann@ldeo.columbia.edu

Klemes, VitNational Hydrology Research Institute3460 Fulton Rd.Victoria BC, V9C 3N2CanadaTel: +1-250-478-1908E-mail: wj072@victoria.tc.ca

Knudsen, PerGeodetic DepartmentNational Survey and Cadastre DenmarkRentemestervej 82400 Copenhagen NVDenmarkTel: +45-3587-5318Fax: +45-3587-5052E-mail: pk@kms.dk

Kuhn, MichaelInstitut f. Meteorologie und GeophysikUniversität InnsbruckInnrain 526020 InnsbruckAustriaTel: +43-512-507-5451Fax: +43-512-507-2924E-mail: michael.kuhn@uibk.ac.at

Lane, H. RichardEarth Sciences Division, Geology andPalaeontology ProgramNational Science Foundation4201 Wilson Blvd., #785Arlington, VA 22230USATel: +1-703-306-1551Fax: +1-703-306-0382E-mail: hlane@nsf.gov

Liebsch, GunterInstitut f. Planetare GeodäsieTechnische Universität DresdenMommsenstr. 1301062 DresdenGermanyTel: +49-351-463-3045Fax: +49-351-463-7063E-mail: liebsch@ipg.geo.tu-dresden.de

Lowe, Jason A.Meteorological OfficeHadley Centre for Climate Research and PredictionLondon RoadBracknell, Berkshire RG12 2SYUnited KingdomTel: +44-1344-856-883Fax: +44-1344-854-898E-mail: jalowe@meto.gov.uk

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Mason, Owen K.Alaska Quarternary CenterUniversity of Alaska MuseumP.O. Box 755960Fairbanks, AK 99775-6960USATel: +1-907-474-6293Fax: +1-907-455-9054E-mail: ffokm@aurora.alaska.edu

Mercier, FranckLEGOS/GRGSCNES18, Avenue E. Belin31401 Toulouse Cedex 4FranceTel: +33-561-332925Fax: +33-561-253205E-mail: franck.mercier@cnes.fr

Negusini, MoniaDipartimento di FisicaUniversita di BolognaViale Berti Pichat 840127 BolognaItalyTel: +39-051-209-5010Fax: +39-051-209-5058E-mail: negusini@astbo1.bo.cnr.it

Paniconi, ClaudioEnvironment GroupCRS4C.P. 9409010 CagliariItalyTel: +39-070-2796291Fax: +39-070-2796216E-mail: cxpanico@crs4.it

Peltier, William RichardDept. of PhysicsUniversity of Toronto60 St. George StreetToronto, Ont. M5S 1A7CanadaTel: +1-416-923-0829Fax: +1-416-978-8905E-mail: peltier@atmosp.physics.utoronto.ca

Plag, Hans-PeterGeodetic InstituteNorwegian Mapping AuthorityKartverksveien3511 HonefossNorwayTel: +47-3211-8100Fax: +47-3211-8101E-mail: plag@gdiv.statkart.no

Remy, FrederiqueCNRS/UMR5566CNES18, Avenue E. Belin31401 Toulouse Cedex 4FranceTel: +33-561332958Fax: +33-561253205E-mail: frederique.remy@cnes.fr

Richter, Bernd D.Bundesamt für Kartographie und GeodäsieRichard-Strauss Allee 1160598 Frankfurt/MainGermanyTel: +49-69-6333-273Fax: +49-69-6333-425E-mail: richter@ifag.de

Sahagian, DorkIGBP/GAIMInstitute for the Study of Earth, Oceans andSpaceMorse Hall, University of New HampshireDurham, NH 03824USATel: +1-603-862-3875Fax: +1-603-862-3874E-mail: gaim@unh.edu

Selivanov, Andrei O.Geography Dept.Moscow State UniversityVorobjevy GoryMoscow 119899RussiaFax: +7-095-932-8836E-mail: selivano@postman.ru

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Shum, C.K.Dept. of Civil and EnvironmentalEngineering and Geodetic ScienceOhio State University1735 Neil Ave.Columbus, OH 43210USATel: +1-614-292-7118Fax: +1-614-292-2957E-mail: ckshum+@osu.edu

Singer, Fred S.Dept. of Science and Environmental PolicyProjectGeorge Mason University4084 University DriveFairfax, VA 22030USATel: +1-703-934-9640Fax: +1-703-352-7535E-mail: ssinger1@gmu.edu

Slotsvik, NoralfDepartment of GeophysicsNorwegian Hydrographic ServiceP.O. Box 60N-4001 StavangerNorwayTel: +47-5185-8813Fax: +47-5185-7901E-mail: noralf.slotsvik@statkart.no

Stanev, Emil VassilevDept. of Meteorology and GeophysicsUniversity of Sofia5, J. Bourchier Street1126 SofiaBulgariaTel: +359-2-6256-289Fax: +359-2-9625-276E-mail: stanev@phys.uni-sofia.bg

Teferle, NormanIESSGUniversity of NottinghamUniversity ParkNottingham, NG7 2RDUnited KingdomTel: +44-115-951-3880Fax: +44-115-951-3881E-mail: isxnt@isn1.nottingham.ac.uk

Thomson, DavidSoutheastern Louisiana UniversityBox 10585Hammond, LouisianaUSAFax: +1-504-5495008E-mail: dthomson@selu.edu

Titus, Jim2174USEPA Headquarters401 M Street, SWWashington, DC 20460USATel: +1-202-260-7821E-mail: titus.jim@epa.gov

Van Onselen, KyraFaculty of Geodetic EngineeringDelft University of TechnologyP.O. Box 50302600 AA DelftThe NetherlandsTel: +31-15-278-2587Fax: +31-15-278-3711E-mail: onselen@geo.tudelft.nl

Vilibic, IvicaOceanographic Dept.State Hydrographic InstituteZrinsko Frankopanska 16121000 SplitCroatiaTel: +385-21-361-840Fax: +385-21-347-242E-mail: dhi-oco@dhi.tel.hr

Woppelmann, GuyService Hydrographique et Oceanographiquede la MarineEPSHOMBP 426, 13 rue du Chatellier29275 Brest CedexFranceTel: +33-298-221742Fax: +33-298-220899E-mail: guy@ensg.ign.fr

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Zerbini, SusannaDip. di Fisica, Settore di GeofisicaUniversita di BolognaViale Berti Pichat 840127 BolognaItalyTel: +39-051-209-5019Fax: +39-051-209-5058E-mail: zerbini@astbo1.bo.cnr.it

Zwally, H. JayOceans and Ice Branch, Code 971NASA - Goddard Space Flight CenterGreenbelt, MD 20771USATel: +1-301-6145643Fax: +1-301-614-5644E-mail: jay.zwally@gsfc.nasa.gov

Acknowledgements

The conveners thank the US National Science Foundation (EAR, SBE) and the EU (DG12) fortravel support for many of the participants. We are also grateful to European Geophysical Societyfor organizational support, and to Sabine Lubba for logistical and other detailed arrangements.