Greater Greenland Ice Sheet contribution to global sea level rise in CMIP6

AbstractFuture climate projections show a marked increase in Greenland Ice Sheet (GrIS) runoff during the 21st century, a direct consequence of the Polar Amplification signal. Regional climate models (RCMs) are a widely used tool to downscale ensembles of projections from global climate models (GCMs) to assess the impact of global warming on GrIS melt and sea level rise contribution. Initial results of the CMIP6 GCM model intercomparison project have revealed a greater 21st century temperature rise than in CMIP5 models. However, so far very little is known about the subsequent impacts on the future GrIS surface melt and therefore sea level rise contribution. Here, we show that the total GrIS sea level rise contribution from surface mass loss in our high-resolution (15 km) regional climate projections is 17.8 ± 7.8 cm in SSP585, 7.9 cm more than in our RCP8.5 simulations using CMIP5 input. We identify a +1.3 °C greater Arctic Amplification and associated cloud and sea ice feedbacks in the CMIP6 SSP585 scenario as the main drivers. Additionally, an assessment of the GrIS sea level contribution across all emission scenarios highlights, that the GrIS mass loss in CMIP6 is equivalent to a CMIP5 scenario with twice the global radiative forcing.

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Doubling of future Greenland Ice Sheet surface melt revealed by the new CMIP6 high-emission scenario

10.5194/egusphere-egu2020-19502 ◽

2020 ◽

Author(s):

Stefan Hofer ◽

Charlotte Lang ◽

Charles Amory ◽

Christoph Kittel ◽

Alison Delhasse ◽

...

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

21St Century ◽

Radiative Forcing ◽

Climate Models ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Cmip5 Models ◽

Surface Melt ◽

The Impact

Future climate projections show a marked increase in Greenland Ice Sheet (GrIS) runoff during the 21st century, a direct consequence of the Polar Amplification signal. Regional climate models (RCMs) are a widely used tool to downscale ensembles of projections from global climate models (GCMs) to assess the impact of global warming on GrIS melt and sea level rise contribution. Initial results of the CMIP6 GCM model intercomparison project have revealed a greater 21st century temperature rise than in CMIP5 models. However, so far very little is known about the subsequent impacts on the future GrIS surface melt and therefore sea level rise contribution. Here, we show that the total GrIS melt during the 21st century almost doubles when using CMIP6 forcing compared to the previous CMIP5 model ensemble, despite an equal global radiative forcing of +8.5 W/m2 in 2100 in both RCP8.5 and SSP58.5 scenarios. The total GrIS sea level rise contribution from surface melt in our high-resolution (15 km) projections is 17.8 cm in SSP58.5, 7.9 cm more than in our RCP8.5 simulations, despite the same radiative forcing. We identify a +1.7&#176;C greater Arctic amplification in the CMIP6 ensemble as the main driver behind the presented doubling of future GrIS sea level rise contribution

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Improved modelling of the present-day Greenland firn layer

10.5194/egusphere-egu21-7634 ◽

2021 ◽

Author(s):

Max Brils ◽

Peter Kuipers Munneke ◽

Willem Jan van de Berg ◽

Achim Heilig ◽

Baptiste Vandercrux ◽

...

Keyword(s):

Mass Loss ◽

Sea Level Rise ◽

Sea Level ◽

Climate Model ◽

Pore Space ◽

Regional Climate ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Surface Mass ◽

Meltwater Runoff

Recent studies indicate that a declining surface mass balance will dominate the Greenland Ice Sheet&#8217;s (GrIS) contribution to 21st century sea level rise. It is therefore crucial to understand the liquid water balance of the ice sheet and its response to increasing temperatures and surface melt if we want to accurately predict future sea level rise. The ice sheet firn layer covers ~90% of the GrIS and provides pore space for storage and refreezing of meltwater. Because of this, the firn layer can retain up to ~45% of the surface meltwater and thus act as an efficient buffer to ice sheet mass loss. However, in a warming climate this buffer capacity of the firn layer is expected to decrease, amplifying meltwater runoff and sea-level rise. Dedicated firn models are used to understand how firn layers evolve and affect runoff. Additionally, firn models are used to estimate the changing thickness of the firn layer, which is necessary in altimetry to convert surface height change into ice sheet mass loss.Here, we present the latest version of our firn model IMAU-FDM. With respect to the previous version, changes have been made to the handling of the freshly fallen snow, the densification rate of the firn and the conduction of heat. These changes lead to an improved representation of firn density and temperature. The results have been thoroughly validated using an extensive dataset of density and temperature measurements that we have compiled covering 126 different locations on the GrIS. Meltwater behaviour in the model is validated with upward-looking GPR measurements at Dye-2. Lastly, we present an in-depth look at the evolution firn characteristics at some typical locations in Greenland.Dedicated, stand-alone firn models offer various benefits to using a regional climate model with an embedded firn model. Firstly, the vertical resolution for buried snow and ice layers can be larger, improving accuracy. Secondly, a stand-alone firn model allows for spinning up the model to a more accurate equilibrium state. And thirdly, a stand-alone model is more cost- and time-effective to use. Firn models are increasingly capable of simulating the firn layer, but areas with large amounts of melt still pose the greatest challenge.

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A regional atmospheric warming threshold for irreversible Greenland ice sheet mass loss

10.5194/egusphere-egu2020-19032 ◽

2020 ◽

Author(s):

Michiel van den Broeke ◽

Brice Noël ◽

Leo van Kampenhout ◽

Willem-Jan van de Berg

Keyword(s):

Mass Loss ◽

Mass Balance ◽

Sea Level Rise ◽

Sea Level ◽

Climate Models ◽

Climate Model ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Global Climate Models ◽

The Future

The mass balance of the Greenland ice sheet (GrIS, units Gt per year) equals the surface mass balance (SMB) minus solid ice discharge across the grounding line. As the latter is definite positive, an important threshold for irreversible GrIS mass loss occurs when long-term average SMB becomes negative. For this to happen, runoff (mainly meltwater, some rain) must exceed mass accumulation (mainly snowfall minus sublimation). Even for a single year, this threshold has not been passed since at least 1958, the first year with reliable estimates of SMB components, although recent years with warm summers (e.g. 2012 and 2019) came close. Simply extrapolating the recent (1991-present) negative SMB trend into the future suggests that the SMB = 0 threshold could be reached before ~2040, but such predictions are extremely uncertain given the very large interannual SMB variability, the relative brevity of the time series and the uncertainty in future warming. In this study we use a cascade of models, extensively evaluated with in-situ and remotely sensed (GRACE) SMB observations, to better constrain the future regional warming threshold for the 5-year average GrIS SMB to become negative. To this end, a 1950-2100 climate change run with the global model CESM2 (app. 100 km resolution) was dynamically downscaled using the regional climate model RACMO2 (app. 11 km), which in turn was statistically downscaled to 1 km resolution. The result is a threshold regional Greenland warming of close to 4 degrees. We then use a range of CMIP5 and CMIP6 global climate models to translate the regional value into a global warming threshold for various warming scenarios, including its timing this century. We find substantial differences, ranging from stabilization before the threshold is reached in the RCP/SSP2.6 scenarios with a limited but still significant sea-level rise contribution (< 5 cm by 2100) to an imminent crossing of the warming threshold for the RCP/SSP8.5 scenarios with substantial and ever-growing contributions to sea level rise (> 10 cm by 2100). These results stress the need for strong mitigation to avoid irreversible GrIS mass loss. We finish by discussing the caveats and uncertainties of our approach.

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Role of model initialization for projections of 21st-century Greenland ice sheet mass loss

Journal of Glaciology ◽

10.3189/2014jog13j202 ◽

2014 ◽

Vol 60 (222) ◽

pp. 782-794 ◽

Cited By ~ 17

Author(s):

G. Ađalgeirsdóttir ◽

A. Aschwanden ◽

C. Khroulev ◽

F. Boberg ◽

R. Mottram ◽

...

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

21St Century ◽

Climate Models ◽

Regional Climate ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Regional Climate Models ◽

Climate Forcing ◽

Model Simulations

AbstractModel simulations of the Greenland ice sheet contribution to 21st-century sea-level rise are performed with a state-of-the-art ice-sheet model (Parallel Ice Sheet Model (PISM)). The climate-forcing fields are obtained from the European Union’s Seventh Framework Programme project ice2sea, in which three regional climate models are used to dynamically downscale two scenarios (A1B and E1) from two general circulation models (ECHAM5 and HadCM3). To assess the sensitivity of the projections to the model initial state, four initialization methods are applied. In these experiments, the simulated contribution to sea-level rise by 2100 ranges from an equivalent of 0.2 to 6.8 cm. The largest uncertainties arise from different formulations of the regional climate models (0.8–3.9 cm) and applied scenarios (0.65–1.9 cm), but an important source of uncertainty is the initialization method (0.1–0.8 cm). These model simulations do not account for the recently observed acceleration of ice streams and consequent thinning rates, the changing ice discharge that may result from the spatial and temporal variability of ocean forcing, or the feedback occurring between ice-sheet elevation changes and climate forcing. Thus the results should be considered the lower limit of Greenland ice sheet contributions to sea-level rise, until such processes have been integrated into large-scale ice-sheet models.

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ISMIP6 Future Projections for Antarctica performed using the AWI PISM ice sheet model

10.5194/egusphere-egu2020-16948 ◽

2020 ◽

Author(s):

Thomas Kleiner ◽

Jeremie Schmiedel ◽

Angelika Humbert

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Climate Models ◽

Ice Sheets ◽

Ice Sheet ◽

Ice Shelf ◽

Initial State ◽

Intercomparison Project ◽

Non Local ◽

The Impact

Ice sheets constitute the largest and most uncertain potential source of future sea-level rise. The Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6) brings together a consortium of international ice sheet and climate models to explore the contribution from the Greenland and Antarctic ice sheets to future sea-level rise. We use the Parallel Ice Sheet Model (PISM, pism-docs.org) to carry out spinup and projection simulations for the Antarctic Ice Sheet. Our treatment of the ice-ocean boundary condition previously based on 3D ocean temperatures (initMIP-Antarctica) has been adopted to use the ISMIP6 parameterisation and 3D ocean forcing fields (temperature and salinity) according to the ISMIP6 protocol. In this study, we analyse the impact of the choices made during the model initialisation procedure on the initial state. We present the AWI PISM results of the ISMIP6 projection simulations and investigate the ice sheet response for individual basins. In the analysis, we distinguish between the local and non-local ice shelf basal melt parameterisation.

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Probabilistic calibration of a Greenland Ice Sheet model using spatially resolved synthetic observations: toward projections of ice mass loss with uncertainties

Geoscientific Model Development ◽

10.5194/gmd-7-1933-2014 ◽

2014 ◽

Vol 7 (5) ◽

pp. 1933-1943 ◽

Cited By ~ 9

Author(s):

W. Chang ◽

P. J. Applegate ◽

M. Haran ◽

K. Keller

Keyword(s):

Mass Loss ◽

Sea Level Rise ◽

Sea Level ◽

Data Model ◽

Spatial Information ◽

Full Range ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Parametric Uncertainty ◽

Model Parameters

Abstract. Computer models of ice sheet behavior are important tools for projecting future sea level rise. The simulated modern ice sheets generated by these models differ markedly as input parameters are varied. To ensure accurate ice sheet mass loss projections, these parameters must be constrained using observational data. Which model parameter combinations make sense, given observations? Our method assigns probabilities to parameter combinations based on how well the model reproduces the Greenland Ice Sheet profile. We improve on the previous state of the art by accounting for spatial information and by carefully sampling the full range of realistic parameter combinations, using statistically rigorous methods. Specifically, we estimate the joint posterior probability density function of model parameters using Gaussian process-based emulation and calibration. This method is an important step toward calibrated probabilistic projections of ice sheet contributions to sea level rise, in that it uses data–model fusion to learn about parameter values. This information can, in turn, be used to make projections while taking into account various sources of uncertainty, including parametric uncertainty, data–model discrepancy, and spatial correlation in the error structure. We demonstrate the utility of our method using a perfect model experiment, which shows that many different parameter combinations can generate similar modern ice sheet profiles. This result suggests that the large divergence of projections from different ice sheet models is partly due to parametric uncertainty. Moreover, our method enables insight into ice sheet processes represented by parameter interactions in the model.

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Greenland ice sheet surface mass balance: evaluating simulations and making projections with regional climate models

The Cryosphere ◽

10.5194/tc-6-1275-2012 ◽

2012 ◽

Vol 6 (6) ◽

pp. 1275-1294 ◽

Cited By ~ 88

Author(s):

J. G. L. Rae ◽

G. Aðalgeirsdóttir ◽

T. L. Edwards ◽

X. Fettweis ◽

J. M. Gregory ◽

...

Keyword(s):

Mass Balance ◽

Sea Level ◽

Climate Models ◽

Regional Climate ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Regional Climate Models ◽

Surface Mass Balance ◽

Surface Mass ◽

Sheet Surface

Abstract. Four high-resolution regional climate models (RCMs) have been set up for the area of Greenland, with the aim of providing future projections of Greenland ice sheet surface mass balance (SMB), and its contribution to sea level rise, with greater accuracy than is possible from coarser-resolution general circulation models (GCMs). This is the first time an intercomparison has been carried out of RCM results for Greenland climate and SMB. Output from RCM simulations for the recent past with the four RCMs is evaluated against available observations. The evaluation highlights the importance of using a detailed snow physics scheme, especially regarding the representations of albedo and meltwater refreezing. Simulations with three of the RCMs for the 21st century using SRES scenario A1B from two GCMs produce trends of between −5.5 and −1.1 Gt yr−2 in SMB (equivalent to +0.015 and +0.003 mm sea level equivalent yr−2), with trends of smaller magnitude for scenario E1, in which emissions are mitigated. Results from one of the RCMs whose present-day simulation is most realistic indicate that an annual mean near-surface air temperature increase over Greenland of ~ 2°C would be required for the mass loss to increase such that it exceeds accumulation, thereby causing the SMB to become negative, which has been suggested as a threshold beyond which the ice sheet would eventually be eliminated.

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The GRISLI-LSCE contribution to the Ice Sheet Model Intercomparison Project for phase 6 of the Coupled Model Intercomparison Project (ISMIP6) – Part 1: Projections of the Greenland ice sheet evolution by the end of the 21st century

The Cryosphere ◽

10.5194/tc-15-1015-2021 ◽

2021 ◽

Vol 15 (2) ◽

pp. 1015-1030 ◽

Cited By ~ 1

Author(s):

Aurélien Quiquet ◽

Christophe Dumas

Keyword(s):

Mass Loss ◽

Sea Level Rise ◽

Sea Level ◽

Ice Sheet ◽

Coupled Model ◽

Greenland Ice Sheet ◽

Model Intercomparison ◽

The Future ◽

Intercomparison Project ◽

Global Sea Level

Abstract. Polar amplification will result in amplified temperature changes in the Arctic with respect to the rest of the globe, making the Greenland ice sheet particularly vulnerable to global warming. While the ice sheet has been showing an increased mass loss in the past decades, its contribution to global sea level rise in the future is of primary importance since it is at present the largest single-source contribution after the thermosteric contribution. The question of the fate of the Greenland and Antarctic ice sheets for the next century has recently gathered various ice sheet models in a common framework within the Ice Sheet Model Intercomparison Project for the Coupled Model Intercomparison Project – phase 6 (ISMIP6). While in a companion paper we present the GRISLI-LSCE (Grenoble Ice Sheet and Land Ice model of the Laboratoire des Sciences du Climat et de l'Environnement) contribution to ISMIP6-Antarctica, we present here the GRISLI-LSCE contribution to ISMIP6-Greenland. We show an important spread in the simulated Greenland ice loss in the future depending on the climate forcing used. The contribution of the ice sheet to global sea level rise in 2100 can thus be from as low as 20 mm sea level equivalent (SLE) to as high as 160 mm SLE. Amongst the models tested in ISMIP6, the Coupled Model Intercomparison Project – phase 6 (CMIP6) models produce larger ice sheet retreat than their CMIP5 counterparts. Low-emission scenarios in the future drastically reduce the ice mass loss. The oceanic forcing contributes to about 10 mm SLE in 2100 in our simulations. In addition, the dynamical contribution to ice thickness change is small compared to the impact of surface mass balance. This suggests that mass loss is mostly driven by atmospheric warming and associated ablation at the ice sheet margin. With additional sensitivity experiments we also show that the spread in mass loss is only weakly affected by the choice of the ice sheet model mechanical parameters.

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Mass loss from an ice-sheet drainage basin in West Greenland

Geological Survey of Denmark and Greenland Bulletin ◽

10.34194/geusb.v31.4670 ◽

1969 ◽

Vol 31 ◽

pp. 87-90

Author(s):

Morten L. Andersen ◽

Signe B. Andersen ◽

Lars Stenseng ◽

Henriette Skourup ◽

William Colgan ◽

...

Keyword(s):

Mass Loss ◽

Sea Level Rise ◽

Sea Level ◽

21St Century ◽

Drainage Basin ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Present Rate ◽

Negative Balance ◽

Observation Period

The Greenland ice sheet is losing mass to the ocean at an increasing rate (Thomas et al. 2006). During the 1980s the ice sheet was believed to be in near-equilibrium (van den Broeke et al. 2009). Within the first decade of the 21st century, however, a net negative balance was observed. Greenland’s present rate of ice loss is c. 250 Gt yr–1, equivalent to a sea-level rise contribution of c. 0.69 mm yr–1. The rate of ice loss has increased over the post 1992 observation period (Shepherd et al. 2012).

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Recent retreat of Greenland's marine terminating glaciers has a lasting impact on velocity and mass loss during the 21st Century

10.5194/egusphere-egu21-9908 ◽

2021 ◽

Author(s):

Isabel Nias ◽

Sophie Nowicki ◽

Denis Felikson

Keyword(s):

Mass Loss ◽

Sea Level Rise ◽

Sea Level ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Initial State ◽

Ice Dynamics ◽

Total Contribution ◽

Surface Mass ◽

Glacier Terminus

Mass loss from the Greenland Ice Sheet (GrIS) can be partitioned between surface mass balance (SMB) and discharge due to ice dynamics through its marine-terminating outlet glaciers. A perturbation to a glacier terminus (e.g. a calving event) results in an instantaneous response in velocity and mass loss, but also a diffusive response due to the evolution of ice thickness over time. This diffusive response means the total impact of a retreat event can take decades to be fully realised. Here we model the committed response of the GrIS to recent observed changes in terminus position, neglecting any future climate perturbations. Our simulations quantify the sea level contribution that is locked in due to the slow dynamic response of the ice. Using the Ice Sheet System Model (ISSM), we run forward simulations starting from an initial state representative of the 2007 ice sheet. We apply perturbations to the marine-terminating glacier termini that represent recent observed changes, and simulate the response over the 21st Century, holding the climate forcing constant. The sensitivity of the ice sheet response to model parameter uncertainty is explored with in an ensemble framework, and GRACE data is used to constrain the results. We find that terminus retreat observed between 2007 and 2015 results in approximately 6 mm of sea level rise by 2100, with retreat having a lasting impact on velocity and mass loss. Our results complement the ISMIP6 projections, which report the ice sheet response to future forcing, excluding the background committed response. In this way, we can obtain estimates of Greenland&#8217;s total contribution to sea level rise by 2100.

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