Global Mean Sea-level Changes in the Last Two Millennia

Instrumental records show that global mean sea level (GMSL) rose by approximately 15 cm in the 20th Century, with estimates of contributing factors suggesting the major components are ocean thermal expansion and melting of continental ice sheets and glaciers. However, little is known about the individual contributions to GMSL changes over the preindustrial common era (PCE) and the potential differences in the mechanisms controlling those changes between different time periods. Here, we describe the GMSL changes in the PCE by comparing proxy-based reconstructions with estimates derived from model experiments. The ocean thermal expansion is estimated on the basis of Coupled (Paleoclimate) Model Intercomparison Project (CMIP/PMIP) experiments. The contributions of ice sheets and glaciers are based on simulations with an ice-sheet model (IMAU-ICE) and a global glacier model (The Open Global Glacier Model), respectively. We also describe the thermal expansion response in the different ocean basins over the last millennium. The findings provide new insights on the current anthropogenic warming and sea-level rise in a wider context.

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Correcting Late Cenozoic Sea-Level Records for Dynamic Topography: Examples from Australia

10.5194/egusphere-egu21-12420 ◽

2021 ◽

Author(s):

Fred Richards ◽

Sophie Coulson ◽

Jacqueline Austermann ◽

Mark Hoggard ◽

Jerry Mitrovica

Keyword(s):

Sea Level ◽

Upper Mantle ◽

Ice Sheets ◽

Dynamic Topography ◽

Sea Level Changes ◽

Relative Sea Level ◽

Mean Sea Level ◽

Ice Volume ◽

Global Mean Sea Level ◽

Global Mean

Much of our understanding of ice sheet sensitivity to climatic forcing is derived from palaeoshoreline records of past sea-level. However, the present-day elevations of these sea-level markers reflect the integrated effect of both ice volume change and solid Earth processes. Accurately quantifying the latter contribution is therefore essential for making reliable inferences of past ice volume. While uncertainties associated with glacial isostatic adjustment (GIA) can be mitigated by focusing on sites far from ice sheets, the same is not true for mantle flow-driven dynamic topography, which is ubiquitous and can generate vertical motions of ~&#177;100 m on million-year timescales. As a result, improved knowledge of the spatio-temporal evolution of this transient topography is required to refine constraints on ice sheet stability and to guide modelling of future trajectories.Since the shortest wavelength and fastest evolving contributions to dynamic topography originate in the shallow mantle, reconstructing dynamic topography over 1&#8211;10 Myr timescales requires accurate models of Earth&#8217;s lithosphere and asthenosphere. Here, we construct these models by mapping upper mantle shear wave velocities from high-resolution surface wave tomographic models into thermomechanical structure using calibrated parameterisations of anelasticity at seismic frequency. Resulting numerical predictions of present-day dynamic topography are in good agreement with residual depth measurements, with particularly good fits obtained around Australia. In this region, predicted temperatures are also compatible with palaeogeotherms extracted from xenolith suites, indicating that present-day upper mantle structure is well characterised and that numerical &#8220;retrodictions&#8221; of vertical motions are more likely to be reliable. In addition, Australia is sufficiently distant from major ice sheets that uncertainty in GIA contributions to sea-level change are relatively small. These considerations, combined with new compilations of continent-wide sea-level indicators, make Australia a particularly promising location for separating out ice volume-driven global mean sea-level changes from local sea-level variations related to vertical land motions and gravitational effects.By back-advecting density perturbations from an ensemble of Earth models, we demonstrate that ~&#177;200 m relative sea-level changes across Australia since the Mid-Pliocene Warm Period (MPWP; &#8764;3 Ma) can be tied directly to changes in dynamic topography. Significantly, after removing this signal from observed relative sea-level changes,&#160; a consistent global mean sea-level during the MPWP of 12&#177;8 m above present is obtained, towards the lower end of previous estimates.

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Data products from the ESA CCI Sea Level Budget Closure project

10.5194/egusphere-egu2020-12811 ◽

2020 ◽

Author(s):

Martin Horwath ◽

Keyword(s):

Sea Level ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Sea Level Changes ◽

Ocean Mass ◽

Data Products ◽

Global Mean Sea Level ◽

The Individual ◽

Land Water ◽

Global Mean

Studies of the sea-level budget are a means of assessing our ability to quantify and understand sea-level changes and their causes. ESA's Climate Change Initiative (CCI) projects include Sea Level CCI, Greenland Ice Sheet CCI, Antarctic Ice Sheet CCI, Glaciers CCI and the Sea Surface Temperature CCI, all addressing Essential Climate Variables (ECVs) related to sea level. The cross-ECV project CCI Sea Level Budget Closure used different products for the sea level and its components, based on the above CCI projects in conjunction with in situ data for ocean thermal expansion (e.g., Argo), GRACE-based assessments of ocean mass change, land water and land ice mass change, and model-based data for glaciers and land hydrology. The involvement of the authors of the individual data products facilitated consistency and enabled a unified treatment of uncertainties and their propagation to the overall budget closure.&#160;After conclusion of the project, the developed data products are now available for science users and the public. This poster summarizes the project results with a focus on presenting these data products. They include time series (for the periods 1993-2016 and 2003-2016) of global mean sea level changes and global mean sea level contributions from the steric component, from the ocean mass component and from the individual mass contributions by glaciers, the Greenland Ice Sheet, the Antarctic Ice Sheet and changes in land water storage. They are designed and documented in the consistent framework of ESA SLBC_cci and include uncertainty measures per datum. Additional more comprehensive information, such as geographic grids underlying the global means, are available for some components.For the long-term trend, the budget is closed within uncertainties on the order of 0.3 mm/yr (1 sigma). Moreover, the budget is also closed within uncertainties for interannual variations.

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The rate and acceleration of the global mean sea level revisited

10.5194/egusphere-egu2020-4643 ◽

2020 ◽

Author(s):

Lorena Moreira ◽

Anny Cazenave ◽

Denise Cáceres ◽

Hindumathi Palanisamy ◽

Habib Dieng

Keyword(s):

Thermal Expansion ◽

Global Warming ◽

Sea Level Rise ◽

Interannual Variability ◽

Sea Level ◽

Water Storage ◽

Mean Sea Level ◽

Global Mean Sea Level ◽

Land Water ◽

Global Mean

Since nearly 3 decades, high-precision satellite altimetry allows us to precisely measure the mean sea level evolution at global and regional scales. In terms of global mean, sea level is rising at a mean rate of 3.2 mm/yr. The altimetry record is also suggesting that the global mean sea level rise is accelerating. However, the exact value of the acceleration and even its mere existence are still debated. Determination of the global warming-related sea level rate and acceleration are somewhat hindered by the interannual signal caused by natural climate variability. During the recent years, several studies have shown that at interannual time scale, the global mean sea level is mostly due to ENSO-driven land water storage variations. But thermal expansion fluctuations may also contribute. Thus, to isolate the global warming signal in the global mean sea level, we need to remove the ENSO-related interannual variability. For that purpose we use the Water Gap Global Hydrological model developed by the University of Frankfurt for land water storage as well as GRACE space gravimetry data on land and empirical models based on ENSO indices. We also extract the ENSO-related signal in thermal expansion. After removing the total interannual variability signal due to both mass and steric components, we compute the evolution with time of the &#8216;residual&#8217; rate of sea level rise over successive 5-year moving windows, as well as the associated acceleration. Using time series of thermal expansion and ice sheet mass balances, we also estimate the respective contributions of each component to the global mean sea level acceleration.

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Modelling ice sheet evolution and atmospheric CO2 during the Late Pliocene

10.5194/cp-2019-34 ◽

2019 ◽

Author(s):

Constantijn J. Berends ◽

Bas de Boer ◽

Aisling M. Dolan ◽

Daniel J. Hill ◽

Roderik S. W. van de Wal

Keyword(s):

Sea Level ◽

Ice Sheets ◽

Ice Sheet ◽

Co2 Concentration ◽

Atmospheric Co2 ◽

Mean Sea Level ◽

Late Pliocene ◽

Proxy Records ◽

Global Mean Sea Level ◽

Global Mean

Abstract. In order to investigate the relation between ice sheets and climate in a warmer-than-present world, recent research has focussed on the Late Pliocene, 3.6 to 2.58 million years ago. It is the most recent period in Earth history when such a climate state existed for a significant duration of time. Marine Isotope Stage (MIS) M2 (~ 3.3 Myr ago) is a strong positive excursion in benthic oxygen records in the middle of the otherwise warm and relatively stable Late Pliocene. However, the relative contributions to the benthic δ18O signal from deep-ocean cooling and growing ice sheets are still uncertain. Here, we present results from simulations of the late Pliocene with a hybrid ice-sheet–climate model, showing a reconstruction of ice sheet geometry, sea-level and atmospheric CO2. Initial experiments simulating the last four glacial cycles indicate that this model yields results which are in good agreement with proxy records in terms of global mean sea level, benthic oxygen isotope abundance, ice core-derived surface temperature and atmospheric CO2 concentration. For the Late Pliocene, our results show an atmospheric CO2 concentration during MIS M2 of 233–249 ppmv, and a drop in global mean sea level of 10 to 25 m. Uncertainties are larger during the warmer periods leading up to and following MIS M2. CO2 concentrations during the warm intervals in the Pliocene, with sea-level high stands of 8–14 m above present-day, varied between 320 and 400 ppmv, lower than indicated by some proxy records but in line with earlier model reconstructions.

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Thermosteric Effects on Interannual and Long-term Global Mean Sea Level Changes

Journal of Geodesy ◽

10.1007/s00190-006-0055-7 ◽

2006 ◽

Vol 80 (5) ◽

pp. 240-247 ◽

Cited By ~ 2

Author(s):

J. L. Chen ◽

C. R. Wilson ◽

B. D. Tapley ◽

X. G. Hu

Keyword(s):

Sea Level ◽

Sea Level Changes ◽

Mean Sea Level ◽

Global Mean Sea Level ◽

Global Mean

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Challenges and research priorities to understand interactions between climate, ice sheets and global mean sea level during past interglacials

Quaternary Science Reviews ◽

10.1016/j.quascirev.2019.06.030 ◽

2019 ◽

Vol 219 ◽

pp. 308-311 ◽

Cited By ~ 1

Author(s):

Emilie Capron ◽

Alessio Rovere ◽

Jacqueline Austermann ◽

Yarrow Axford ◽

Natasha L.M. Barlow ◽

...

Keyword(s):

Sea Level ◽

Ice Sheets ◽

Research Priorities ◽

Mean Sea Level ◽

Global Mean Sea Level ◽

Global Mean

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Evaluating Model Simulations of Twentieth-Century Sea Level Rise. Part I: Global Mean Sea Level Change

Journal of Climate ◽

10.1175/jcli-d-17-0110.1 ◽

2017 ◽

Vol 30 (21) ◽

pp. 8539-8563 ◽

Cited By ~ 23

Author(s):

Aimée B. A. Slangen ◽

Benoit Meyssignac ◽

Cecile Agosta ◽

Nicolas Champollion ◽

John A. Church ◽

...

Keyword(s):

Twentieth Century ◽

Thermal Expansion ◽

Sea Level Rise ◽

Sea Level ◽

Sea Level Change ◽

Mean Sea Level ◽

Level Change ◽

The World ◽

Global Mean Sea Level ◽

Global Mean

Sea level change is one of the major consequences of climate change and is projected to affect coastal communities around the world. Here, global mean sea level (GMSL) change estimated by 12 climate models from phase 5 of the World Climate Research Programme’s Climate Model Intercomparison Project (CMIP5) is compared to observational estimates for the period 1900–2015. Observed and simulated individual contributions to GMSL change (thermal expansion, glacier mass change, ice sheet mass change, landwater storage change) are analyzed and compared to observed GMSL change over the period 1900–2007 using tide gauge reconstructions, and over the period 1993–2015 using satellite altimetry estimates. The model-simulated contributions explain 50% ± 30% (uncertainties 1.65 σ unless indicated otherwise) of the mean observed change from 1901–20 to 1988–2007. Based on attributable biases between observations and models, a number of corrections are proposed, which result in an improved explanation of 75% ± 38% of the observed change. For the satellite era (from 1993–97 to 2011–15) an improved budget closure of 102% ± 33% is found (105% ± 35% when including the proposed bias corrections). Simulated decadal trends increase over the twentieth century, both in the thermal expansion and the combined mass contributions (glaciers, ice sheets, and landwater storage). The mass components explain the majority of sea level rise over the twentieth century, but the thermal expansion has increasingly contributed to sea level rise, starting from 1910 onward and in 2015 accounting for 46% of the total simulated sea level change.

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Kinematics of global mean thermosteric sea level during 1993–2019

Journal of Geodetic Science ◽

10.1515/jogs-2020-0121 ◽

2021 ◽

Vol 11 (1) ◽

pp. 75-82

Author(s):

H. Bâki İz

Keyword(s):

Time Series ◽

Sea Level ◽

Temperature Gradients ◽

Sea Surface ◽

Sea Level Changes ◽

Mean Sea Level ◽

Mean Sea Surface ◽

Global Mean Sea Level ◽

Global Sea Level ◽

Global Mean

Abstract Because oceans cover 71% of Earth’s surface, ocean warming, consequential for thermal expansion of sea water, has been the largest contributor to the global mean sea level rise averaged over the 20 th and the early 21 st century. This study first generates quasi-observed monthly globally averaged thermosteric sea level time series by removing the contributions of global mean sea level budget components, namely, Glaciers, Greenland, Antarctica, and Terrestrial Water Storage from satellite altimetry measured global sea level changes during 1993–2019. A baseline kinematic model with global mean thermosteric sea level trend and a uniform acceleration is solved to evaluate the performance of a rigorous mixed kinematic model. The model also includes coefficients of monthly lagged 60 yearlong cumulative global mean sea surface temperature gradients and control variables of lunisolar origins and representations for first order autoregressive disturbances. The mixed kinematic model explains 94% (Adjusted R 2)1 of the total variability in quasi-observed monthly and globally averaged thermosteric time series compared to the 46% of the baseline kinematic model’s Adjusted R 2. The estimated trend, 1.19±0.03 mm/yr., is attributed to the long-term ocean warming. Whereas eleven statistically significant (α = 0.05) monthly lagged cumulative global mean sea surface temperature gradients each having a memory of 60 years explain the remainder transient global mean thermosteric sea level changes due to the episodic ocean surface warming and cooling during this period. The series also exhibit signatures of a statistically significant contingent uniform global sea level acceleration and periodic lunisolar forcings.

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