scholarly journals Ice sheet contributions to future sea-level rise from structured expert judgment

2019 ◽  
Vol 116 (23) ◽  
pp. 11195-11200 ◽  
Author(s):  
Jonathan L. Bamber ◽  
Michael Oppenheimer ◽  
Robert E. Kopp ◽  
Willy P. Aspinall ◽  
Roger M. Cooke
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Ice Sheet ◽  
Predictive Capability ◽  
Intergovernmental Panel ◽  
Process Understanding ◽  
Temperature Scenario ◽  
Global Mean Sea Level ◽  
Observational Record ◽  
Global Mean

Despite considerable advances in process understanding, numerical modeling, and the observational record of ice sheet contributions to global mean sea-level rise (SLR) since the Fifth Assessment Report (AR5) of the Intergovernmental Panel on Climate Change, severe limitations remain in the predictive capability of ice sheet models. As a consequence, the potential contributions of ice sheets remain the largest source of uncertainty in projecting future SLR. Here, we report the findings of a structured expert judgement study, using unique techniques for modeling correlations between inter- and intra-ice sheet processes and their tail dependences. We find that since the AR5, expert uncertainty has grown, in particular because of uncertain ice dynamic effects. For a +2 °C temperature scenario consistent with the Paris Agreement, we obtain a median estimate of a 26 cm SLR contribution by 2100, with a 95th percentile value of 81 cm. For a +5 °C temperature scenario more consistent with unchecked emissions growth, the corresponding values are 51 and 178 cm, respectively. Inclusion of thermal expansion and glacier contributions results in a global total SLR estimate that exceeds 2 m at the 95th percentile. Our findings support the use of scenarios of 21st century global total SLR exceeding 2 m for planning purposes. Beyond 2100, uncertainty and projected SLR increase rapidly. The 95th percentile ice sheet contribution by 2200, for the +5 °C scenario, is 7.5 m as a result of instabilities coming into play in both West and East Antarctica. Introducing process correlations and tail dependences increases estimates by roughly 15%.

The contribution of the East Antarctic Ice Sheet to future sea level rise

2020 ◽  
Author(s):  
Jim Jordan ◽  
Hilmar Gudmundsson ◽  
Adrian Jenkins ◽  
Chris Stokes ◽  
Stewart Jamieson ◽  
...  
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Ice Sheet ◽  
Ice Shelf ◽  
Antarctic Ice Sheet ◽  
Mean Sea Level ◽  
Potential Contributor ◽  
Global Mean Sea Level ◽  
Global Mean ◽  
East Antarctic Ice Sheet

<p>The East Antarctic Ice Sheet (EAIS) is the single largest potential contributor to future global mean sea level rise, containing a water mass equivalent of 53 m. Recent work has found the overall mass balance of the EAIS to be approximately in equilibrium, albeit with large uncertainties. However, changes in oceanic conditions have the potential to upset this balance. This could happen by both a general warming of the ocean and also by shifts in oceanic conditions allowing warmer water masses to intrude into ice shelf cavities.</p><p>We use the Úa numerical ice-flow model, combined with ocean-melt rates parameterized by the PICO box mode, to predict the future contribution to global-mean sea level of the EAIS. Results are shown for the next 100 years under a range of emission scenarios and oceanic conditions on a region by region basis, as well as for the whole of the EAIS. </p>

scholarly journals Quantifying the potential future contribution to global mean sea level from the Filchner-Ronne basin, Antarctica

2021 ◽  
Author(s):  
Emily A. Hill ◽  
Sebastian H. R. Rosier ◽  
G. Hilmar Gudmundsson ◽  
Matthew Collins
Keyword(s):  
Uncertainty Quantification ◽  
Sea Level Rise ◽  
Sea Level ◽  
Parameter Space ◽  
Ice Sheet ◽  
Ice Shelf ◽  
Mean Sea Level ◽  
Future Studies ◽  
Global Mean Sea Level ◽  
Global Mean

Abstract. The future of the Antarctic Ice Sheet in response to climate warming is one of the largest sources of uncertainty in estimates of future changes in global mean sea level (∆GMSL). Mass loss is currently concentrated in regions of warm circumpolar deep water, but it is unclear how ice shelves currently surrounded by relatively cold ocean waters will respond to climatic changes in the future. Studies suggest that warm water could flush the Filchner-Ronne (FR) ice shelf cavity during the 21st century, but the inland ice sheet response to a drastic increase in ice shelf melt rates, is poorly known. Here, we use an ice flow model and uncertainty quantification approach to project the GMSL contribution of the FR basin under RCP emissions scenarios, and assess the forward propagation and proportional contribution of uncertainties in model parameters (related to ice dynamics, and atmospheric/oceanic forcing) on these projections. Our probabilistic projections, derived from an extensive sample of the parameter space using a surrogate model, reveal that the FR basin is unlikely to contribute positively to sea level rise by the 23rd century. This is primarily due to the mitigating effect of increased accumulation with warming, which is capable of suppressing ice loss associated with ocean–driven increases in sub-shelf melt. Mass gain (negative ∆GMSL) from the FR basin increases with warming, but uncertainties in these projections also become larger. In the highest emission scenario RCP 8.5, ∆GMSL is likely to range from −103 to 26 mm, and this large spread can be apportioned predominantly to uncertainties in parameters driving increases in precipitation (30 %) and sub-shelf melting (44 %). There is potential, within the bounds of our input parameter space, for major collapse and retreat of ice streams feeding the FR ice shelf, and a substantial positive contribution to GMSL (up to approx. 300 mm), but we consider such a scenario to be very unlikely. Adopting uncertainty quantification techniques in future studies will help to provide robust estimates of potential sea level rise and further identify target areas for constraining projections.

scholarly journals Climate-change–driven accelerated sea-level rise detected in the altimeter era

2018 ◽  
Vol 115 (9) ◽  
pp. 2022-2025 ◽  
Author(s):  
R. S. Nerem ◽  
B. D. Beckley ◽  
J. T. Fasullo ◽  
B. D. Hamlington ◽  
D. Masters ◽  
...  
Keyword(s):  
Climate Change ◽  
Sea Level Rise ◽  
Sea Level ◽  
Altimeter Data ◽  
Intergovernmental Panel ◽  
Mean Sea Level ◽  
Simple Extrapolation ◽  
Global Mean Sea Level ◽  
Satellite Altimeter Data ◽  
Global Mean

Using a 25-y time series of precision satellite altimeter data from TOPEX/Poseidon, Jason-1, Jason-2, and Jason-3, we estimate the climate-change–driven acceleration of global mean sea level over the last 25 y to be 0.084 ± 0.025 mm/y2. Coupled with the average climate-change–driven rate of sea level rise over these same 25 y of 2.9 mm/y, simple extrapolation of the quadratic implies global mean sea level could rise 65 ± 12 cm by 2100 compared with 2005, roughly in agreement with the Intergovernmental Panel on Climate Change (IPCC) 5th Assessment Report (AR5) model projections.

Coupled ice-climate simulation of future Greenland ice sheet evolution: mechanisms, thresholds and feedbacks for accelerated mass loss

2020 ◽  
Author(s):  
Miren Vizcaino ◽  
Laura Muntjewerf ◽  
Raymond Sellevold ◽  
Carolina Ernani da Silva ◽  
Michele Petrini ◽  
...  
Keyword(s):  
Global Warming ◽  
Mass Loss ◽  
Sea Level Rise ◽  
Sea Level ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Mean Sea Level ◽  
Model Version ◽  
Global Mean Sea Level ◽  
Global Mean

<p>The Greenland ice sheet (GrIS) has been losing mass in the last several decades, with a current contributing of around 0.7 mm per year to global mean sea level rise (SLR). Projections of future melt rates are often derived from standalone ice sheet models, forced by data from global or regional climate models. In many cases, the surface mass balance parameterization relies on simplified schemes that relate melt with surface temperature.</p><p>In this study, we present a mass and energy conserving, 350-year simulation with the Community Earth System Model version 2.1 (CESM2.1) bidirectionally coupled to the Community Ice Sheet Model version 2.1 (CISM2.1). In this simulation, the carbon dioxide concentration is initially increasing by 1% per year  from pre-industrial levels (287 ppmv), to a quadrupling (1140 ppmv) and stabilization after year 140. The model simulates a global warming of 5.3 K and 8.5 K with respect to preindustrial by years 131-150 and 331-150, respectively, and a strong decline in the North Atlantic Meridional Overturning Circulation that is initiated before GrIS runoff substantially increases. 91% of the total GrIS contribution to global mean sea level rise (SLR, 1140 mm) is simulated in the two centuries following CO2 stabilization, as the mass loss increases from 2.2 mm SLR per year in 131-150 to 6.6 mm SLR per year in 331-351. This increase is caused by melt acceleration as the ablation areas expand, and Greenland summer surface temperatures predominantly approach melt conditions when the global warming exceeds a certain threshold (around 4.2 K).  This enhances the albedo and turbulent heat fluxes contribution to total melt energy.  </p>

scholarly journals Quantifying the potential future contribution to global mean sea level from the Filchner–Ronne basin, Antarctica

2021 ◽  
Vol 15 (10) ◽  
pp. 4675-4702
Author(s):  
Emily A. Hill ◽  
Sebastian H. R. Rosier ◽  
G. Hilmar Gudmundsson ◽  
Matthew Collins
Keyword(s):  
Uncertainty Quantification ◽  
Sea Level Rise ◽  
Sea Level ◽  
Parameter Space ◽  
Ice Sheet ◽  
Ice Shelf ◽  
Mean Sea Level ◽  
Future Studies ◽  
Global Mean Sea Level ◽  
Global Mean

Abstract. The future of the Antarctic Ice Sheet in response to climate warming is one of the largest sources of uncertainty in estimates of future changes in global mean sea level (ΔGMSL). Mass loss is currently concentrated in regions of warm circumpolar deep water, but it is unclear how ice shelves currently surrounded by relatively cold ocean waters will respond to climatic changes in the future. Studies suggest that warm water could flush the Filchner–Ronne (FR) ice shelf cavity during the 21st century, but the inland ice sheet response to a drastic increase in ice shelf melt rates is poorly known. Here, we use an ice flow model and uncertainty quantification approach to project the GMSL contribution of the FR basin under RCP emissions scenarios, and we assess the forward propagation and proportional contribution of uncertainties in model parameters (related to ice dynamics and atmospheric/oceanic forcing) on these projections. Our probabilistic projections, derived from an extensive sample of the parameter space using a surrogate model, reveal that the FR basin is unlikely to contribute positively to sea level rise by the 23rd century. This is primarily due to the mitigating effect of increased accumulation with warming, which is capable of suppressing ice loss associated with ocean-driven increases in sub-shelf melt. Mass gain (negative ΔGMSL) from the FR basin increases with warming, but uncertainties in these projections also become larger. In the highest emission scenario RCP8.5, ΔGMSL is likely to range from −103 to 26 mm, and this large spread can be apportioned predominantly to uncertainties in parameters driving increases in precipitation (30 %) and sub-shelf melting (44 %). There is potential, within the bounds of our input parameter space, for major collapse and retreat of ice streams feeding the FR ice shelf, and a substantial positive contribution to GMSL (up to approx. 300 mm), but we consider such a scenario to be very unlikely. Adopting uncertainty quantification techniques in future studies will help to provide robust estimates of potential sea level rise and further identify target areas for constraining projections.

scholarly journals The Antarctic contribution to 21st century sea-level rise predicted by the UK Earth System Model with an interactive ice sheet

2021 ◽  
Author(s):  
Antony Siahaan ◽  
Robin Smith ◽  
Paul Holland ◽  
Adrian Jenkins ◽  
Jonathan M. Gregory ◽  
...  
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Ice Sheet ◽  
System Model ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Global Mean Sea Level ◽  
Basal Melting ◽  
The Antarctic ◽  
Global Mean

Abstract. The Antarctic Ice Sheet will play a crucial role in the evolution of global mean sea-level as the climate warms. An interactively coupled climate and ice sheet model is needed to understand the impacts of ice—climate feedbacks during this evolution. Here we use a two-way coupling between the U.K. Earth System Model and the BISICLES dynamic ice sheet model to investigate Antarctic ice—climate interactions under two climate change scenarios. We perform ensembles of SSP1-1.9 and SSP5-8.5 scenario simulations to 2100, which we believe are the first such simulations with a climate model with two-way coupling between both atmosphere and ocean models to dynamic models of the Greenland and Antarctic ice sheets. In SSP1-1.9 simulations, ice shelf basal melting and grounded ice mass loss are generally lower than present rates during the entire simulation period. In contrast, the responses to SSP5-8.5 forcing are strong. By the end of 21st century, these simulations feature order-of-magnitude increases in basal melting of the Ross and Filchner-Ronne ice shelves, caused by intrusions of warm ocean water masses. Due to the slow response of ice sheet drawdown, this strong melting does not cause a substantial increase in ice discharge during the simulations. The surface mass balance in SSP5-8.5 simulations shows a pattern of strong decrease on ice shelves, caused by increased melting, and strong increase on grounded ice, caused by increased snowfall. Despite strong surface and basal melting of the ice shelves, increased snowfall dominates the mass budget of the grounded ice, leading to an ensemble-mean Antarctic contribution to global mean sea level of a fall of 22 mm by 2100 in the SSP5-8.5 scenario. We hypothesise that this signal would revert to sea-level rise on longer timescales, caused by the ice sheet dynamic response to ice shelf thinning. These results demonstrate the need for fully coupled ice—climate models in reducing the substantial uncertainty in sea-level rise from the Antarctic Ice Sheet.

scholarly journals Twentieth-Century Global-Mean Sea Level Rise: Is the Whole Greater than the Sum of the Parts?

2013 ◽  
Vol 26 (13) ◽  
pp. 4476-4499 ◽  
Author(s):  
J. M. Gregory ◽  
N. J. White ◽  
J. A. Church ◽  
M. F. P. Bierkens ◽  
J. E. Box ◽  
...  
Keyword(s):  
Twentieth Century ◽  
Thermal Expansion ◽  
Mass Loss ◽  
Sea Level Rise ◽  
Sea Level ◽  
Ice Sheet ◽  
Mean Sea Level ◽  
Reservoir Impoundment ◽  
Global Mean Sea Level ◽  
Global Mean

Abstract Confidence in projections of global-mean sea level rise (GMSLR) depends on an ability to account for GMSLR during the twentieth century. There are contributions from ocean thermal expansion, mass loss from glaciers and ice sheets, groundwater extraction, and reservoir impoundment. Progress has been made toward solving the “enigma” of twentieth-century GMSLR, which is that the observed GMSLR has previously been found to exceed the sum of estimated contributions, especially for the earlier decades. The authors propose the following: thermal expansion simulated by climate models may previously have been underestimated because of their not including volcanic forcing in their control state; the rate of glacier mass loss was larger than previously estimated and was not smaller in the first half than in the second half of the century; the Greenland ice sheet could have made a positive contribution throughout the century; and groundwater depletion and reservoir impoundment, which are of opposite sign, may have been approximately equal in magnitude. It is possible to reconstruct the time series of GMSLR from the quantified contributions, apart from a constant residual term, which is small enough to be explained as a long-term contribution from the Antarctic ice sheet. The reconstructions account for the observation that the rate of GMSLR was not much larger during the last 50 years than during the twentieth century as a whole, despite the increasing anthropogenic forcing. Semiempirical methods for projecting GMSLR depend on the existence of a relationship between global climate change and the rate of GMSLR, but the implication of the authors' closure of the budget is that such a relationship is weak or absent during the twentieth century.

Gaussian Process emulation of multi-model ice sheet and glacier projections

2021 ◽  
Author(s):  
Tamsin Edwards ◽  
Keyword(s):  
Gaussian Process ◽  
Sea Level Rise ◽  
Sea Level ◽  
Climate Models ◽  
Ice Sheet ◽  
Surface Air Temperature ◽  
Model Parameters ◽  
Gaussian Process Emulation ◽  
Model Ensembles ◽  
Global Mean

<p><strong>The land ice contribution to global mean sea level rise has not yet been predicted with ice sheet and glacier models for the latest set of socio-economic scenarios (SSPs), nor with coordinated exploration of uncertainties arising from the various computer models involved. Two recent international projects (ISMIP6 and GlacierMIP) generated a large suite of projections using multiple models, but mostly used previous generation scenarios and climate models, and could not fully explore known uncertainties. </strong></p><p><strong>Here we estimate probability distributions for these projections for the SSPs using Gaussian Process emulation of the ice sheet and glacier model ensembles. We model the sea level contribution as a function of global mean surface air temperature forcing and (for the ice sheets) model parameters, with the 'nugget' allowing for multi-model structural uncertainty. Approximate independence of ice sheet and glacier models is assumed, because a given model responds very differently under different setups (such as initialisation). </strong></p><p><strong>We find that limiting global warming to 1.5</strong>°<strong>C </strong><strong>would halve the land ice contribution to 21<sup>st</sup> century </strong><strong>sea level rise</strong><strong>, relative to current emissions pledges: t</strong><strong>he median decreases from 25 to 13 cm sea level equivalent (SLE) by 2100. However, the Antarctic contribution does not show a clear response to emissions scenario, due to competing processes of increasing ice loss and snowfall accumulation in a warming climate. </strong></p><p><strong>However, under risk-averse (pessimistic) assumptions for climate and Antarctic ice sheet model selection and ice sheet model parameter values, Antarctic ice loss could be five times higher, increasing the median land ice contribution to 42 cm SLE under current policies and pledges, with the 95<sup>th</sup> percentile exceeding half a metre even under 1.5</strong>°<strong>C warming. </strong></p><p><strong>Gaussian Process emulation can therefore be a powerful tool for estimating probability density functions from multi-model ensembles and testing the sensitivity of the results to assumptions.</strong></p>

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