The Experts below are selected from a list of 30555 Experts worldwide ranked by ideXlab platform
J X Mitrovica - One of the best experts on this subject based on the ideXlab platform.
-
spatial variation in late ordovician glacioeustatic Sea Level Change
Earth and Planetary Science Letters, 2018Co-Authors: Jessica R Creveling, J X Mitrovica, Seth Finnegan, Kristin D BergmannAbstract:Abstract Mass extinction of Late Ordovician marine fauna closely coincided with southern hemisphere glaciation. The sequence stratigraphic architecture of shallow marine deposits informs estimates of glacioeustatic Sea-Level Change at sites both proximal and distal to the reconstructed Ordovician ice sheet(s) and contemporaneous Changes in ice volume. A recent correlation framework for the stratigraphic architectures of one near and one far field Late Ordovician margin concluded that the Late Ordovician glaciation encompassed multiple long-term cycles of ice volume growth and retreat with superimposed higher frequency cycles. Here we posit that—similar to Cenozoic glacial cycles—glacial isostatic adjustment can preclude synchronous and similar magnitude (or directional) Changes in Late Ordovician Sea Level between ice proximal and ice distal locations and, hence, distort a globally correlative sequence stratigraphy. We explored whether long-duration (i.e., million year) Late Ordovician glacial cycles should produce a globally coherent, eustatic record of Sea-Level Change between ice proximal and ice distal margins using a gravitationally self-consistent theory that accounts for the deformational, gravitational and rotational perturbations to Sea Level on a viscoelastic Earth model. We adopted a Late Ordovician paleogeography and a synthetic continental ice-sheet distribution and volume informed by the areal extent of glaciogenic deposits and geochemical records, respectively. We demonstrate that modeled million year Late Ordovician glacial cycles produce Sea-Level histories on near and far field margins that differ from eustasy, and from one another, due primarily to elastic flexure and associated gravitational effects. While predicted far-field Sea-Level histories faithfully preserve the temporal structure of modeled glacioeustasy, their amplitude may differ from eustasy by as much as 30–40%. The impact of glacial isostatic adjustment is largest at the margins of glaciated continents, and these effects can be of the same order of magnitude as the eustatic, and even induce a local Sea-Level rise during an episode of ice growth and eustatic Sea-Level fall, and vice versa. In this regard, stratal surfaces of maximum regression and flooding expressed at near-field margins need not reflect global (‘eustatic’) trends in ice sheet growth and decay, respectively, and thus may not provide chronostratigraphic horizons for correlation with far-field sequence stratigraphic architectures.
-
bias in estimates of global mean Sea Level Change inferred from satellite altimetry
Journal of Climate, 2018Co-Authors: Megan Lickley, Mark E Tamisiea, J X MitrovicaAbstract:abstractEstimates of regional and global average Sea Level Change remain a focus of climate Change reSearch. One complication in obtaining coherent estimates is that geodetic datasets measure different aspects of the Sea Level field. Satellite altimetry constrains Changes in the Sea surface height (SSH; or absolute Sea Level), whereas tide gauge data provide a measure of Changes in SSH relative to the crust (i.e., relative Sea Level). The latter is a direct measure of Changes in ocean volume (and the combined impacts of ice sheet melt and steric effects), but the former is not since it does not account for crustal deformation. Nevertheless, the literature commonly conflates the two estimates by directly comparing them. We demonstrate that using satellite altimetry records to estimate global ocean volume Changes can lead to biases that can exceed 15%. The Level of bias will depend on the relative contributions to Sea Level Changes from the Antarctic and Greenland Ice Sheets. The bias is also more sensitive...
-
geographic variability of Sea Level Change
Current Climate Change Reports, 2015Co-Authors: Robert E Kopp, Christopher M Little, J X MitrovicaAbstract:Local Sea-Level Changes differ significantly from global-mean Sea-Level Change as a result of (1) non-climatic, geological background processes; (2) atmosphere/ocean dynamics; and (3) the gravitational, elastic, and rotational “fingerprint” effects of ice and ocean mass redistribution. Though the reSearch communities working on these different effects each have a long history, the integration of all these different processes into interpretations of past Changes and projections of future Change is an active area of reSearch. Fully characterizing the past contributions of these processes requires information from sources covering a range of timescales, including geological proxies, tide-gauge observations from the last ~3 centuries, and satellite-altimetry data from the last ~2 decades. Local Sea-Level rise projections must account for the different spatial patterns of different processes, as well as potential correlations between different drivers.
-
the moving boundaries of Sea Level Change understanding the origins of geographic variability
Oceanography, 2011Co-Authors: Mark E Tamisiea, J X MitrovicaAbstract:As ice sheets gain or lose mass, and as water moves between the continents and the ocean, the solid Earth deforms and the gravitational field of the planet is perturbed. Both of these effects lead to regional patterns in Sea Level Change that depart dramatically from the global average. Understanding these patterns will lead to better constraints on the various contributors to the observed Sea Level Change and, ultimately, to more robust projections of future Changes. In both of these applications, a key step is to apply a correction to Sea Level observations, based on data from tide gauges, satellite altimetry, or gravity, to remove the contaminating signal that is due to the ongoing Earth response to the last ice age. Failure to accurately account for this so-called glacial isostatic adjustment has the potential to significantly bias our understanding of the magnitude and sources of present-day global Sea Level rise. This paper summarizes the physics of several important sources of regional Sea Level Change. Moreover, we discuss several promising strategies that take advantage of this regional variation to more fully use Sea Level data sets to monitor the impact of climate Change on the Earth system
-
understanding and projecting Sea Level Change
Oceanography, 2011Co-Authors: John A Church, Jonathan M Gregory, Neil J White, Skye Platten, J X MitrovicaAbstract:There is intense scientific and public interest in the Intergovernmental Panel on Climate Change (IPCC) projections of Sea Level for the twenty-first century and beyond. The Fourth Assessment Report (AR4) projections, obtained by applying standard methods to the results of the World Climate ReSearch Programme Coupled Model Experiment, includes estimates of ocean thermal expansion, the melting of glaciers and ice caps (G&ICs), increased melting of the Greenland Ice Sheet, and increased precipitation over Greenland and Antarctica, partially offsetting other contributions. The AR4 recognized the potential for a rapid dynamic ice sheet response but robust methods for quantifying it were not available. Illustrative scenarios suggested additional Sea Level rise on the order of 10 to 20 cm or more, giving a wide range in the global averaged projections of about 20 to 80 cm by 2100. Currently, Sea Level is rising at a rate near the upper end of these projections. Since publication of the AR4 in 2007, biases in historical ocean temperature observations have been identified and significantly reduced, resulting in improved estimates of ocean thermal expansion. Models that include all climate forcings are in good agreement with these improved observations and indicate the importance of stratospheric aerosol loadings from volcanic eruptions. Estimates of the volumes of G&ICs and their contributions to Sea Level rise have improved. Results from recent (but possibly incomplete) efforts to develop improved ice sheet models should be available for the 2013 IPCC projections. Improved understanding of Sea Level rise is paving the way for using observations to constrain projections. Understanding of the regional variations in Sea Level Change as a result of Changes in ocean properties, wind-stress patterns, and heat and freshwater inputs into the ocean is improving. Recently, estimates of Sea Level Changes resulting from Changes in Earth's gravitational field and the solid Earth response to Changes in surface loading have been included in regional projections. While potentially valuable, semi-empirical models have important limitations, and their projections should be treated with caution
Jonathan M Gregory - One of the best experts on this subject based on the ideXlab platform.
-
analysis of the regional pattern of Sea Level Change due to ocean dynamics and density Change for 1993 2099 in observations and cmip5 aogcms
Climate Dynamics, 2015Co-Authors: Roberto A F Bilbao, Jonathan M Gregory, N BouttesAbstract:Predictions of twenty-first century Sea Level Change show strong regional variation. Regional Sea Level Change observed by satellite altimetry since 1993 is also not spatially homogenous. By comparison with historical and pre-industrial control simulations using the atmosphere–ocean general circulation models (AOGCMs) of the CMIP5 project, we conclude that the observed pattern is generally dominated by unforced (internal generated) variability, although some regions, especially in the Southern Ocean, may already show an externally forced response. Simulated unforced variability cannot explain the observed trends in the tropical Pacific, but we suggest that this is due to inadequate simulation of variability by CMIP5 AOGCMs, rather than evidence of anthropogenic Change. We apply the method of pattern scaling to projections of Sea Level Change and show that it gives accurate estimates of future local Sea Level Change in response to anthropogenic forcing as simulated by the AOGCMs under RCP scenarios, implying that the pattern will remain stable in future decades. We note, however, that use of a single integration to evaluate the performance of the pattern-scaling method tends to exaggerate its accuracy. We find that ocean volume mean temperature is generally a better predictor than global mean surface temperature of the magnitude of Sea Level Change, and that the pattern is very similar under the different RCPs for a given model. We determine that the forced signal will be detectable above the noise of unforced internal variability within the next decade globally and may already be detectable in the tropical Atlantic.
-
evaluating the ability of process based models to project Sea Level Change
Environmental Research Letters, 2013Co-Authors: John A Church, Jonathan M Gregory, Didier Monselesan, Ben MarzeionAbstract:We evaluate the ability of process based models to reproduce observed global mean Sea-Level Change. When the models are forced by Changes in natural and anthropogenic radiative forcing of the climate system and anthropogenic Changes in land-water storage, the average of the modelled Sea-Level Change for the periods 1900‐2010, 1961‐2010 and 1990‐2010 is about 80%, 85% and 90% of the observed rise. The modelled rate of rise is over 1 mm yr 1 prior to 1950, decreases to less than 0.5 mm yr 1 in the 1960s, and increases to 3 mm yr 1 by 2000. When observed regional climate Changes are used to drive a glacier model and an allowance is included for an ongoing adjustment of the ice sheets, the modelled Sea-Level rise is about 2 mm yr 1 prior to 1950, similar to the observations. The model results encompass the observed rise and the model average is within 20% of the observations, about 10% when the observed ice sheet contributions since 1993 are added, increasing confidence in future projections for the 21st century. The increased rate of rise since 1990 is not part of a natural cycle but a direct response to increased radiative forcing (both anthropogenic and natural), which will continue to grow with ongoing greenhouse gas emissions.
-
The effect of windstress Change on future Sea Level Change in the Southern Ocean
Geophysical Research Letters, 2012Co-Authors: N Bouttes, Jonathan M Gregory, Till Kuhlbrodt, Tatsuo SuzukiAbstract:[1] AOGCMs of the two latest phases (CMIP3 and CMIP5) of the Coupled Model Intercomparison Project, like earlier AOGCMs, predict large regional variations in future Sea Level Change. The model-mean pattern of Change in CMIP3 and CMIP5 is very similar, and its most prominent feature is a zonal dipole in the Southern Ocean: Sea Level rise is larger than the global mean north of 50°S and smaller than the global mean south of 50°S in most models. The individual models show widely varying patterns, although the inter-model spread in local Sea Level Change is smaller in CMIP5 than in CMIP3. Here we investigate whether Changes in windstress can explain the different patterns of projected Sea Level Change, especially the Southern Ocean feature, using two AOGCMs forced by the Changes in windstress from the CMIP3 and CMIP5 AOGCMs. We show that the strengthening and poleward shift of westerly windstress accounts for the most of the large spread among models in magnitude of this feature. In the Indian, North Pacific and Arctic Oceans, the windstress Change is influential, but does not completely account for the projected Sea Level Change.
-
Understanding processes contributing to regional Sea Level Change
Eos Transactions American Geophysical Union, 2011Co-Authors: Detlef Stammer, Jonathan M GregoryAbstract:[1] WCRP/IOC Workshop on Regional Sea-Level Change; Paris, France, 7–9 February 2011. A joint World Climate ReSearch Programme (WCRP)/Intergovernmental Oceanographic Commission (IOC) workshop was held to discuss regional Changes of Sea Level. The workshop was attended by 41 experts from the world over who compared observed regional Sea Level Changes with those inferred from numerical simulations and compared future predictions and their analyses in terms of processes. Satellite altimetry observations continue to be essential in revealing that Sea Level is changing prominently on a regional scale. However, existing climate models are largely in disagreement about patterns and magnitudes of observed Sea Level variability, and it is unclear how accurate they may be in predicting regional Sea Level.
-
understanding and projecting Sea Level Change
Oceanography, 2011Co-Authors: John A Church, Jonathan M Gregory, Neil J White, Skye Platten, J X MitrovicaAbstract:There is intense scientific and public interest in the Intergovernmental Panel on Climate Change (IPCC) projections of Sea Level for the twenty-first century and beyond. The Fourth Assessment Report (AR4) projections, obtained by applying standard methods to the results of the World Climate ReSearch Programme Coupled Model Experiment, includes estimates of ocean thermal expansion, the melting of glaciers and ice caps (G&ICs), increased melting of the Greenland Ice Sheet, and increased precipitation over Greenland and Antarctica, partially offsetting other contributions. The AR4 recognized the potential for a rapid dynamic ice sheet response but robust methods for quantifying it were not available. Illustrative scenarios suggested additional Sea Level rise on the order of 10 to 20 cm or more, giving a wide range in the global averaged projections of about 20 to 80 cm by 2100. Currently, Sea Level is rising at a rate near the upper end of these projections. Since publication of the AR4 in 2007, biases in historical ocean temperature observations have been identified and significantly reduced, resulting in improved estimates of ocean thermal expansion. Models that include all climate forcings are in good agreement with these improved observations and indicate the importance of stratospheric aerosol loadings from volcanic eruptions. Estimates of the volumes of G&ICs and their contributions to Sea Level rise have improved. Results from recent (but possibly incomplete) efforts to develop improved ice sheet models should be available for the 2013 IPCC projections. Improved understanding of Sea Level rise is paving the way for using observations to constrain projections. Understanding of the regional variations in Sea Level Change as a result of Changes in ocean properties, wind-stress patterns, and heat and freshwater inputs into the ocean is improving. Recently, estimates of Sea Level Changes resulting from Changes in Earth's gravitational field and the solid Earth response to Changes in surface loading have been included in regional projections. While potentially valuable, semi-empirical models have important limitations, and their projections should be treated with caution
Kurt Lambeck - One of the best experts on this subject based on the ideXlab platform.
-
Sea Level Change through the last glacial cycle : Paleoclimate
Science, 2020Co-Authors: Kurt Lambeck, John ChappellAbstract:Sea Level Change during the Quaternary is primarily a consequence of the cyclic growth and decay of ice sheets, resulting in a complex spatial and temporal pattern. Observations of this variability provide constraints on the timing, rates, and magnitudes of the Changes in ice mass during a glacial cycle, as well as more limited information on the distribution of ice between the major ice sheets at any time. Observations of glacially induced Sea Level Changes also provide information on the response of the mantle to surface loading on time scales of 10 3 to 10 5 years. Regional analyses indicate that the earth-response function is depth dependent as well as spatially variable. Comprehensive models of Sea Level Change enable the migration of coastlines to be predicted during glacial cycles, including the anthropologically important period from about 60,000 to 20,000 years ago.
-
Sea Level Change along the italian coast during the holocene and projections for the future
Quaternary International, 2011Co-Authors: Kurt Lambeck, Fabrizio Antonioli, Marco Anzidei, L Ferranti, G Leoni, Giovanni Scicchitano, S SilenziAbstract:Published and new Sea Level data are used to provide projections of Sea Level Change in Italy for the year 2100 by adding new isostatic and tectonic component to the IPCC and Rahmstorf projections. Comparison of the observations from more than 130 sites (with different geomorphological and archaeological Sea Level markers) with the predicted Sea Level curves provides estimates of the vertical tectonic contribution to the relative Sea Level Change. The results are based on the most recent ANU model for the ice sheets of both hemispheres, including an alpine deglaciation model. On the basis of the eustatic, tectonic and isostatic components to the Sea Level Change, projections are provided for marine inundation scenarios for the Italian coastal plains for the year 2100, that today are at elevations close to current Sea Level.
-
new insights on the relative Sea Level Change during holocene along the coasts of tunisia and western libya from archaeological and geomorphological markers
Quaternary International, 2011Co-Authors: Marco Anzidei, Kurt Lambeck, Fabrizio Antonioli, Alessandra Benini, M Soussi, R LakhdarAbstract:Abstract New data of Sea Level Changes for the Mediterranean region along the coasts of northern Africa are presented. Data are inferred from archaeological sites of Punic-Roman age located along the coast of Tunisia, between Tunis and Jerba island and along the western coast of Libya, between Sabratha and Leptis Magna. Data are based on precise measures of presently submerged archaeological markers that are good indicators of past Sea-Level elevation. Nineteen selected archaeological sites were studied in Tunisia and four in Libya, all aged between ∼2.0 and ∼1.5 ka BP. The functional elevations of significant archaeological markers were measured with respect to the Sea Level at the time of measurements, applying corrections for tide and atmospheric pressure values. The functional elevations of specific architectural parts of the sites were interpreted, related to Sea Level at the time of their construction providing data on the relative Changes between land and Sea. Observations were compared against Sea Level Change predictions derived from the glacio-hydro-isostatic model associated with the Last Glacial cycle. The results indicate that local relative Sea Level Change along the coast of Tunisia and Libya, has increased 0.2 ÷ 0.5 m since the last ∼2 ka. Besides minor vertical tectonic movements of the land, the observed Changes are produced by eustatic and glacio-hydro-isostatic variations acting in the Mediterranean basin since the end of the last glacial maximum.
-
Sea Level Change during the holocene in sardinia and in the northeastern adriatic central mediterranean Sea from archaeological and geomorphological data
Quaternary Science Reviews, 2007Co-Authors: Fabrizio Antonioli, Kurt Lambeck, Marco Anzidei, Rita Auriemma, Dario Gaddi, Stefano Furlani, Paolo E Orru, Emanuela Solinas, A Gaspari, S KarinjaAbstract:Abstract We provide new data on relative Sea-Level Change from the late Holocene for two locations in the central Mediterranean: Sardinia and NE Adriatico. They are based on precise measures of submerged archaeological and tide notch markers that are good indicators of past Sea-Level elevation. Twelve submerged archaeological sites were studied: six, aged between 2.5 and 1.6 ka BP, located along the Sardinia coast, and a further six, dated ∼2.0 ka BP, located along the NE Adriatic coast (Italy, Slovenia and Croatia). For Sardinia, we also use beach rock and core data that can be related to Holocene Sea Level. The elevations of selected significant archaeological markers were measured with respect to the present Sea Level, applying corrections for tide and atmospheric pressure values at the time of surveys. The interpretation of the functional heights related to Sea Level at the time of their construction provides data on the relative Changes between land and Sea; these data are compared with predictions derived from a new glacio–hydro-isostatic model associated with the Last Glacial cycle. Sardinia is tectonically relatively stable and we use the Sea-Level data from this island to calibrate our models for eustatic and glacio–hydro-isostatic Change. The results are consistent with those from another tectonically stable site, the Versilia Plain of Italy. The northeast Adriatic (Italy, Slovenia and Croatia) is an area of subsidence and we use the calibrated model results to separate out the isostatic from the tectonic contributions. This indicates that the Adriatic coast from the Gulf of Trieste to the southern end of Istria has tectonically subsided by ∼1.5 m since Roman times.
-
Sea Level Change in the mediterranean Sea since the lgm model predictions for tectonically stable areas
Quaternary Science Reviews, 2005Co-Authors: Kurt Lambeck, Anthony W PurcellAbstract:Abstract Sea-Level Change in the Mediterranean Sea during glacial cycles is determined by the temporally variable eustatic Change and by the spatially variable glacio-hydro-isostatic response of the earth and ocean to the growth and decay of ice sheets. Superimposed upon this are the relative Changes from any vertical tectonic movement of the land. For sites that are either tectonically stable or where the magnitude of tectonic uplift is known, comparisons of observed Change with predictions of the glacio-hydro-eustatic signals provide constraints on the earth–ice parameters used. The resulting predictive models can then be used to interpolate Sea-Level Change and shoreline migration between the spatially and temporally limited observational data set. Whether such parameters reflect the true properties of the mantle and ice sheets depends on whether an effective separation has been achieved from the inversion of the observational data set. This paper explores this issue and demonstrates that observations from certain regions in the Mediterranean are particularly important in effecting the separation. This is supported by a trial analysis of a small observation data set from sites that exhibit some of the desirable features of an ideal data set. Basin-wide predictions of Sea-Level Change, palaeo-water depth and shoreline locations based on these analyses are presented for selected epochs.
Mark E Tamisiea - One of the best experts on this subject based on the ideXlab platform.
-
bias in estimates of global mean Sea Level Change inferred from satellite altimetry
Journal of Climate, 2018Co-Authors: Megan Lickley, Mark E Tamisiea, J X MitrovicaAbstract:abstractEstimates of regional and global average Sea Level Change remain a focus of climate Change reSearch. One complication in obtaining coherent estimates is that geodetic datasets measure different aspects of the Sea Level field. Satellite altimetry constrains Changes in the Sea surface height (SSH; or absolute Sea Level), whereas tide gauge data provide a measure of Changes in SSH relative to the crust (i.e., relative Sea Level). The latter is a direct measure of Changes in ocean volume (and the combined impacts of ice sheet melt and steric effects), but the former is not since it does not account for crustal deformation. Nevertheless, the literature commonly conflates the two estimates by directly comparing them. We demonstrate that using satellite altimetry records to estimate global ocean volume Changes can lead to biases that can exceed 15%. The Level of bias will depend on the relative contributions to Sea Level Changes from the Antarctic and Greenland Ice Sheets. The bias is also more sensitive...
-
Contribution from the last glacial period to satellite estimates of Sea-Level Change
2013Co-Authors: Mark E TamisieaAbstract:The ongoing response of the Earth and the ocean to the collapse of the ice sheets since the last glacial maximum, called Glacial Isostatic Adjustment (GIA), makes a significant contribution to satellite observations of Sea-Level Change. We demonstrated the possible range of the GIA contributions to Sea-Level Change observed by satellite altimetry and gravity missions given the uncertainty of the parameters that go into the GIA modelling. The GIA contributions to these observations are very different, and additionally we demonstrated a subtlety that was frequently overlooked in the analysis. The ranges of the GIA contributions were cited in the IPCC AR5 WG1: Tamisiea, M. E., 2011: Ongoing glacial isostatic contributions to observations of Sea Level Change. Geophysical Journal International, 186, 1036-1044.
-
ongoing glacial isostatic contributions to observations of Sea Level Change
Geophysical Journal International, 2011Co-Authors: Mark E TamisieaAbstract:Studies determining the contribution of water fluxes to Sea Level rise typically remove the ongoing effects of glacial isostatic adjustment (GIA). Unfortunately, use of inconsistent terminology between various disciplines has caused confusion as to how contributions from GIA should be removed from altimetry and GRACE measurements. In this paper, we review the physics of the GIA corrections applicable to these measurements and discuss the differing nomenclature between the GIA literature and other studies of Sea Level Change. We then examine a range of estimates for the GIA contribution derived by varying the Earth and ice models employed in the prediction. We find, similar to early studies, that GIA produces a small (compared to the observed value) but systematic contribution to the altimetry estimates, with a maximum range of -0.15 to -0.5 mm yr-1. Moreover, we also find that the GIA contribution to the mass Change measured by GRACE over the ocean is significant. In this regard, we demonstrate that confusion in nomenclature between the terms 'absolute Sea Level' and 'geoid' has led to an overestimation of this contribution in some previous studies. A component of this overestimation is the incorrect inclusion of the direct effect of the contemporaneous perturbations of the rotation vector, which leads to a factor of ˜two larger value of the degree two, order one spherical harmonic component of the model results. Aside from this confusion, uncertainties in Earth model structure and ice sheet history yield a spread of up to 1.4 mm yr-1 in the estimates of this contribution. However, even if the ice and Earth models were perfectly known, the processing techniques used in GRACE data analysis can introduce variations of up to 0.4 mm yr-1. Thus, we conclude that a single-valued 'GIA correction' is not appropriate for Sea Level studies based on gravity data; each study must estimate a bound on the GIA correction consistent with the adopted data-analysis scheme
-
the moving boundaries of Sea Level Change understanding the origins of geographic variability
Oceanography, 2011Co-Authors: Mark E Tamisiea, J X MitrovicaAbstract:As ice sheets gain or lose mass, and as water moves between the continents and the ocean, the solid Earth deforms and the gravitational field of the planet is perturbed. Both of these effects lead to regional patterns in Sea Level Change that depart dramatically from the global average. Understanding these patterns will lead to better constraints on the various contributors to the observed Sea Level Change and, ultimately, to more robust projections of future Changes. In both of these applications, a key step is to apply a correction to Sea Level observations, based on data from tide gauges, satellite altimetry, or gravity, to remove the contaminating signal that is due to the ongoing Earth response to the last ice age. Failure to accurately account for this so-called glacial isostatic adjustment has the potential to significantly bias our understanding of the magnitude and sources of present-day global Sea Level rise. This paper summarizes the physics of several important sources of regional Sea Level Change. Moreover, we discuss several promising strategies that take advantage of this regional variation to more fully use Sea Level data sets to monitor the impact of climate Change on the Earth system
-
a new projection of Sea Level Change in response to collapse of marine sectors of the antarctic ice sheet
Geophysical Journal International, 2010Co-Authors: Natalya Gomez, Mark E Tamisiea, J X Mitrovica, Peter U ClarkAbstract:We present gravitationally self-consistent predictions of Sea Level Change that would follow the disappearance of either the West Antarctic Ice Sheet (WAIS) or marine sectors of the East Antarctic Ice Sheet (EAIS). Our predictions are based on a state-of-the-art pseudo-spectral Sea Level algorithm that incorporates deformational, gravitational and rotational effects on Sea Level, as well as the migration of shorelines due to both local Sea-Level variations and Changes in the extent of marine-based ice cover. If we define the effective eustatic value (EEV) as the geographically uniform rise in Sea Level once all marine-based sectors have been filled with water, then we find that some locations can experience a Sea Level rise that is ∼40 per cent higher than the EEV. This enhancement is due to the migration of water away from the zone of melting in response to the loss of gravitational attraction towards the ice sheet (load self-attraction), the expulsion of water from marine areas as these regions rebound due to the unloading, and the feedback into Sea Level of a contemporaneous perturbation in Earth rotation. In the WAIS case, this peak enhancement is twice the value predicted in a previous projection that did not include expulsion of water from exposed marine-sectors of the West Antarctic or rotational feedback. The peak enhancements occur over the coasts of the United States and in the Indian Ocean in the WAIS melt scenario, and over the south Atlantic and northwest Pacific in the EAIS scenario. We conclude that accurate projections of the Sea Level hazard associated with ongoing global warming should be based on a theory that includes the complete suite of physical processes described above.
Glenn A Milne - One of the best experts on this subject based on the ideXlab platform.
-
the contribution of glacial isostatic adjustment to projections of Sea Level Change along the atlantic and gulf coasts of north america
Earth’s Future, 2016Co-Authors: Glenn A Milne, Benjamin P Horton, Ryan Love, Lev Tarasov, Simon E Engelhart, M P Hijma, K Latychev, Torbjorn E TornqvistAbstract:We determine the contribution of glacial isostatic adjustment (GIA) to future relative Sea-Level Change for the North American coastline between Newfoundland and Texas. We infer GIA model parameters using recently compiled and quality-assessed databases of past Sea-Level Changes, including new databases for the United States Gulf Coast and Atlantic Canada. At 13 cities along this coastline, we estimate the GIA contribution to range from a few centimeters (e.g., 3 [−1 to 9] cm Miami) to a few decimeters (e.g., 18 [12–22] cm, Halifax) for the period 2085–2100 relative to 2006–2015 (1−σ ranges given). We provide estimates of uncertainty in the GIA component using two different methods; the more conservative approach produces total ranges (1−σ confidence) that vary from 3 to 16 cm for the cities considered. Contributions from ocean steric and dynamic Changes as well as those from Changes in land ice are also estimated to provide context for the GIA projections. When summing the contributions from all three processes at the 13 cities considered along this coastline, using median or best-estimate values, the GIA signal comprises 5–38% of the total depending on the adopted climate forcing and location. The contributions from ocean dynamic/steric Changes and ice mass loss are similar in amplitude but with spatial variation that approximately cancels, resulting in GIA dominating the net spatial variability north of 35°N.
-
consequences of twenty first century policy for multi millennial climate and Sea Level Change
Nature Climate Change, 2016Co-Authors: Peter U Clark, Glenn A Milne, Jeremy D Shakun, Shaun A Marcott, Scott Kulp, Anders Levermann, Patrik L Pfister, Benjamin D SanterAbstract:Consequences of twenty-first-century policy for multi-millennial climate and Sea-Level Change
-
identifying the causes of Sea Level Change
Nature Geoscience, 2009Co-Authors: Glenn A Milne, Roland W Gehrels, Chris W Hughes, Mark E TamisieaAbstract:Global mean Sea-Level Change has increased from a few centimetres per century over recent millennia to a few tens of centimetres per century in recent decades. A review of the latest work shows that global mean Sea-Level rise is unlikely to exceed one metre over the twenty-first century, but regional departures from this global mean could reach several decimetres.
-
recent mass balance of polar ice sheets inferred from patterns of global Sea Level Change
Nature, 2001Co-Authors: J X Mitrovica, Mark E Tamisiea, J L Davis, Glenn A MilneAbstract:Global Sea Level is an indicator of climate Change1,2,3, as it is sensitive to both thermal expansion of the oceans and a reduction of land-based glaciers. Global Sea-Level rise has been estimated by correcting observations from tide gauges for glacial isostatic adjustment—the continuing Sea-Level response due to melting of Late Pleistocene ice—and by computing the global mean of these residual trends4,5,6,7,8,9. In such analyses, spatial patterns of Sea-Level rise are assumed to be signals that will average out over geographically distributed tide-gauge data. But a long history of modelling studies10,11,12 has demonstrated that non-uniform—that is, non-eustatic—Sea-Level redistributions can be produced by variations in the volume of the polar ice sheets. Here we present numerical predictions of gravitationally consistent patterns of Sea-Level Change following variations in either the Antarctic or Greenland ice sheets or the melting of a suite of small mountain glaciers. These predictions are characterized by geometrically distinct patterns that reconcile spatial variations in previously published Sea-Level records. Under the—albeit coarse—assumption of a globally uniform thermal expansion of the oceans, our approach suggests melting of the Greenland ice complex over the last century equivalent to ∼0.6 mm yr-1 of Sea-Level rise.
-
postglacial Sea Level Change on a rotating earth
Geophysical Journal International, 1998Co-Authors: Glenn A Milne, J X MitrovicaAbstract:SUMMARY We present a complete derivation of the equation governing long-term Sea-Level variations on a spherically symmetric, self-gravitating, Maxwell viscoelastic planet. This new ‘Sea-Level equation’ extends earlier work by incorporating, in a gravitationally self-consistent manner, both a time-dependent ocean^continent geometry and the in£uence of contemporaneous perturbations to the rotation vector of the planet. We also outline an e⁄cient, pseudo-spectral, numerical methodology for the solution of this equation, and present a variety of predictions, based on a suite of earth models, of relative Sea Level (RSL) variations due to glacial isostatic adjustment (GIA). These results show that the contribution to the predicted RSL signal from GIA-induced perturbations to the rotation vector can reach 7^8 m over the postglacial period in geographic regions where the rotationally induced signal is a maximum. This result is sensitive to variations in the adopted lower-mantle viscosity and is relatively insensitive to variations in the adopted lithospheric thickness. We also show that the rotationally induced component of RSL Change is su⁄cient to in£uence previous estimates of Late Holocene melting events and ongoing Sea-Level Change due to GIAwhich were based on a RSL theory for a non-rotating Earth. In particular, estimates of Antarctic melting over the last 5 kyr, based on the amplitude of Sea-Level highstands from the Australian region, may require an adjustment downwards of the order of 0.5 m of equivalent Sea-Level rise. Furthermore, present-day rates of Sea-Level Change are perturbed by as much as *0.2 mm yr {1 by the rotational component of Sea-Level Change, and this has implications for GIA corrections of the global tide gauge record. Over the period from the last glacial maximum to the present, we predict a distinctly non-monotonic variation in the rotation-induced component of RSL. This is in agreement with our previous preliminary study (Milne & Mitrovica 1996), but contrasts signi¢cantly with predictions presented by Han & Wahr (1989) and Bills & James (1996).We demonstrate that the disagreement arises as a consequence of approximations adopted in the latter studies. We furthermore refute an assertion by Bills & James (1996) that previously published constraints on mantle viscosity and ice-sheet histories which did not incorporate a rotation-induced RSL component are ‘largely invalidated’ by this omission.
