scholarly journals Brief communication: A roadmap towards credible projections of ice sheet contribution to sea-level

2021 ◽  
Author(s):  
Andy Aschwanden ◽  
Timothy C. Bartholomaus ◽  
Douglas J. Brinkerhoff ◽  
Martin Truffer
Keyword(s):  
Mass Loss ◽  
Sea Level ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Mass Change ◽  
Recent Effort ◽  
Government Investment ◽  
Formal Process ◽  
The Future ◽  
Volunteer Effort

Abstract. Accurately projecting mass loss from ice sheets is of critical societal importance. However, despite recent improvements in ice sheet models, our analysis of a recent effort to project Greenland's contribution to future sea-level suggests that few models reproduce historical mass loss accurately, and that they appear much too confident in the spread of predicted outcomes. The inability of models to reproduce historical observations raises concerns about the models' skill at projecting mass loss. Here we suggest that the future sea level contribution from Greenland may well be significantly higher than reported in that study. We propose a roadmap to enable a more realistic accounting of uncertainties associated with such forecasts, and a formal process by which observations of mass change be used to refine projections of mass change. Finally, we note that tremendous government investment and planning affecting 10s to 100s of millions of people is founded on the work of several tens of scientists involved in a significantly volunteer effort. To achieve the goal of credible projections of ice sheet contribution to sea-level, we strongly believe that investment in research must be commensurate with the scale of the challenge.

scholarly journals Brief communication: A roadmap towards credible projections of ice sheet contribution to sea level

2021 ◽  
Vol 15 (12) ◽  
pp. 5705-5715
Author(s):  
Andy Aschwanden ◽  
Timothy C. Bartholomaus ◽  
Douglas J. Brinkerhoff ◽  
Martin Truffer
Keyword(s):  
Mass Loss ◽  
Sea Level ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Mass Change ◽  
Recent Effort ◽  
Government Investment ◽  
Formal Process ◽  
The Future

Abstract. Accurately projecting mass loss from ice sheets is of critical societal importance. However, despite recent improvements in ice sheet models, our analysis of a recent effort to project ice sheet contribution to future sea level suggests that few models reproduce historical mass loss accurately and that they appear much too confident in the spread of predicted outcomes. The inability of models to reproduce historical observations raises concerns about the models' skill at projecting mass loss. Here we suggest that uncertainties in the future sea level contribution from Greenland and Antarctica may well be significantly higher than reported in that study. We propose a roadmap to enable a more realistic accounting of uncertainties associated with such forecasts and a formal process by which observations of mass change should be used to refine projections of mass change. Finally, we note that tremendous government investment and planning affecting tens to hundreds of millions of people is founded on the work of just a few tens of scientists. To achieve the goal of credible projections of ice sheet contribution to sea level, we strongly believe that investment in research must be commensurate with the scale of the challenge.

scholarly journals Pervasive ice sheet mass loss reflects competing ocean and atmosphere processes

Science ◽  
2020 ◽  
Vol 368 (6496) ◽  
pp. 1239-1242 ◽  
Author(s):  
Ben Smith ◽  
Helen A. Fricker ◽  
Alex S. Gardner ◽  
Brooke Medley ◽  
Johan Nilsson ◽  
...  
Keyword(s):  
Dynamic Response ◽  
Mass Loss ◽  
Sea Level ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Snow Accumulation ◽  
Mass Change ◽  
Laser Altimetry ◽  
Ice Shelves ◽  
Ice Cloud

Quantifying changes in Earth’s ice sheets and identifying the climate drivers are central to improving sea level projections. We provide unified estimates of grounded and floating ice mass change from 2003 to 2019 using NASA’s Ice, Cloud and land Elevation Satellite (ICESat) and ICESat-2 satellite laser altimetry. Our data reveal patterns likely linked to competing climate processes: Ice loss from coastal Greenland (increased surface melt), Antarctic ice shelves (increased ocean melting), and Greenland and Antarctic outlet glaciers (dynamic response to ocean melting) was partially compensated by mass gains over ice sheet interiors (increased snow accumulation). Losses outpaced gains, with grounded-ice loss from Greenland (200 billion tonnes per year) and Antarctica (118 billion tonnes per year) contributing 14 millimeters to sea level. Mass lost from West Antarctica’s ice shelves accounted for more than 30% of that region’s total.

scholarly journals 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

2021 ◽  
Vol 15 (2) ◽  
pp. 1015-1030 ◽  
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.

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

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

<p>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.</p>

scholarly journals The GRISLI-LSCE contribution to ISMIP6, Part 1: projections of the Greenland ice sheet evolution by the end of the 21<sup>st</sup> century

2020 ◽  
Author(s):  
Aurélien Quiquet ◽  
Christophe Dumas
Keyword(s):  
Mass Loss ◽  
Sea Level Rise ◽  
Sea Level ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Companion Paper ◽  
The Arctic ◽  
The Future ◽  
Common Framework ◽  
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 increase 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 behind 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 CMIP6. While in a companion paper we present the GRISLI-LSCE 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 be thus as low as 20 mmSLE to as high as 160 mmSLE. The CMIP6 models produce much larger ice sheet retreat than their CMIP5 counterparts. Low emission scenarios in the future drastically reduce the ice mass loss. The mass loss is mostly driven by atmospheric warming and associated ablation at the ice sheet margin while oceanic forcing contributes to about 10 mmSLE in 2100 in our simulations.

Improving the representation of ice-sheet mass changes in the global inversion for sea-level contributions

2020 ◽  
Author(s):  
Matthias O. Willen ◽  
Bernd Uebbing ◽  
Martin Horwath ◽  
Jürgen Kusche ◽  
Roelof Rietbroek ◽  
...  
Keyword(s):  
Sea Level ◽  
A Priori ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Mass Change ◽  
Altimetry Data ◽  
Isostatic Adjustment ◽  
Ocean Mass ◽  
First Results ◽  
Ocean Altimetry

&lt;p&gt;&lt;span&gt;G&lt;/span&gt;&lt;span&gt;lobal-mean sea level rises (GMSLR) by 3.1-3.5 mm a&lt;sup&gt;-1 &lt;/sup&gt;&lt;/span&gt;&lt;span&gt;(1993-2017)&lt;/span&gt;&lt;span&gt; and &lt;/span&gt;&lt;span&gt;of which&lt;/span&gt;&lt;span&gt; about 50 % can be attributed to changes in global-mean ocean mass due to hydrological variations, m&lt;/span&gt;&lt;span&gt;ass changes&lt;/span&gt;&lt;span&gt; of land glaciers, &lt;/span&gt;&lt;span&gt;and&lt;/span&gt; &lt;span&gt;mass &lt;/span&gt;&lt;span&gt;c&lt;/span&gt;&lt;span&gt;hanges&lt;/span&gt;&lt;span&gt; of the major ice sheets in Greenland and Antarctica. The i&lt;/span&gt;&lt;span&gt;ce-sheet contributions&lt;/span&gt;&lt;span&gt; account for more than &lt;/span&gt;&lt;span&gt;the&lt;/span&gt;&lt;span&gt; half of the contemporary ocean mass change &lt;/span&gt;&lt;span&gt;and can be&lt;/span&gt;&lt;span&gt; observed w&lt;/span&gt;&lt;span&gt;ith&lt;/span&gt;&lt;span&gt; time-variable gravi&lt;/span&gt;&lt;span&gt;metry&lt;/span&gt;&lt;span&gt; by the Gravity Recovery and Climate Experiment (GRACE) and its follow-on mission (GRACE-FO). In addition, geometric surface changes due to &lt;/span&gt;&lt;span&gt;the volume change of&lt;/span&gt;&lt;span&gt; ice sheets is also observed b&lt;/span&gt;&lt;span&gt;y polar &lt;/span&gt;&lt;span&gt;altimetry &lt;/span&gt;&lt;span&gt;missions&lt;/span&gt;&lt;span&gt;. &lt;/span&gt;&lt;span&gt;Of particular importance here is the signal of glacial isostatic adjustment (GIA) which is superimposed with i&lt;/span&gt;&lt;span&gt;ce mass change&lt;/span&gt;&lt;span&gt;.&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;Conventionally, the g&lt;/span&gt;&lt;span&gt;ravimetry&lt;/span&gt;&lt;span&gt; and ice-altimetry observations are processed independently. For ocean applications, a global fingerprint inversion (Rietbroek et al., 2016) allows to estimate individual mass and steric contributors to the sea-level budget by combi&lt;/span&gt;&lt;span&gt;ni&lt;/span&gt;&lt;span&gt;ng GRACE and ocean-altimetry data in a joint approach. To improve the estimates of the ice-sheet contributions to GMSLR, we present first results from additionally incorporating independent ice-altimetry data over Greenland and Antarctica into the fingerprint inversion. We examine the sensitivity of the sea-level contributions to the additional ice-altimetry data &lt;/span&gt;&lt;span&gt;(from &lt;/span&gt;&lt;span&gt;ERS-2, Envisat, ICESat, CryoSat-2 &lt;/span&gt;&lt;span&gt;missions)&lt;/span&gt;&lt;span&gt; and provide validation against independent estimates. &lt;/span&gt;&lt;span&gt;I&lt;/span&gt;&lt;span&gt;n our standard runs&lt;/span&gt;&lt;span&gt;, &lt;/span&gt;&lt;span&gt;GIA is &lt;/span&gt;&lt;span&gt;accounted for &lt;/span&gt;&lt;span&gt;a&lt;/span&gt;&lt;span&gt;s an a-priori correction during the inversion.&lt;/span&gt;&lt;span&gt; H&lt;/span&gt;&lt;span&gt;owever,&lt;/span&gt;&lt;span&gt; we demonstrate the potential and limitations of a regional inverse approach i&lt;/span&gt;&lt;span&gt;n which&lt;/span&gt;&lt;span&gt; GIA is separated from ice mass change &lt;/span&gt;&lt;span&gt;over Antarctica&lt;/span&gt;&lt;span&gt; using GRACE and ice altimetry. In our future work, we a&lt;/span&gt;&lt;span&gt;im to &lt;/span&gt;&lt;span&gt;parametrise&lt;/span&gt;&lt;span&gt; and&lt;/span&gt;&lt;span&gt; co-&lt;/span&gt;&lt;span&gt;estimate GIA &lt;/span&gt;&lt;span&gt;with&lt;/span&gt;&lt;span&gt;in the global inversion framework.&lt;/span&gt;&lt;/p&gt;

scholarly journals Ice-sheet mass balance: assessment, attribution and prognosis

2007 ◽  
Vol 46 ◽  
pp. 1-7 ◽  
Author(s):  
Richard B. Alley ◽  
Matthew K. Spencer ◽  
Sridhar Anandakrishnan
Keyword(s):  
Mass Loss ◽  
Mass Balance ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Balance Assessment ◽  
Additional Mass ◽  
Recent Warming ◽  
The Future ◽  
Ice Sheet Mass Balance ◽  
Antarctic Ice Sheets

AbstractContrary to prior expectations that warming would cause mass addition averaged over the Greenland and Antarctic ice sheets and over the next century, the ice sheets appear to be losing mass, at least partly in response to recent warming. With warming projected for the future, additional mass loss appears more likely than not.

scholarly journals Sensitivity experiments for the Antarctic ice sheet with varied sub-ice-shelf melting rates

2012 ◽  
Vol 53 (60) ◽  
pp. 221-228 ◽  
Author(s):  
Tatsuru Sato ◽  
Ralf Greve
Keyword(s):  
Sea Level ◽  
Initial Conditions ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Ice Shelf ◽  
Simulation Code ◽  
Antarctic Ice Sheet ◽  
Temperature And Precipitation ◽  
The Future ◽  
The Antarctic

AbstractIce-sheet modelling is an important tool for predicting the possible response of ice sheets to climate change in the past and future. An established ice-sheet model is SICOPOLIS (SImulation COde for POLythermal Ice Sheets), and for this study the previously grounded-ice-only model was complemented by an ice-shelf module. The new version of SICOPOLIS is applied to the Antarctic ice sheet, driven by standard forcings defined by the SeaRISE (Sea-level Response to Ice Sheet Evolution) community effort. A crucial point for simulations into the future is to obtain reasonable initial conditions by a palaeoclimatic spin-up, which we carry out over 125 000 years from the Eemian until today. We then carry out a set of experiments for 500 years into the future, in which the surface temperature and precipitation are kept at their present-day distributions, while sub-ice-shelf melting rates between 0 and 200 ma–1 are applied. These simulations show a significant, but not catastrophic, sensitivity of the ice sheet. Grounded-ice volumes decrease with increasing melting rates, and the spread of the results from the zero to the maximum melting case is ~0.65ms.l.e. (metres sea-level equivalent) after 100 years and ~2.25ms.l.e. after 500 years.

scholarly journals Monitoring southwest Greenland’s ice sheet melt with ambient seismic noise

2016 ◽  
Vol 2 (5) ◽  
pp. e1501538 ◽  
Author(s):  
Aurélien Mordret ◽  
T. Dylan Mikesell ◽  
Christopher Harig ◽  
Bradley P. Lipovsky ◽  
Germán A. Prieto
Keyword(s):  
Mass Loss ◽  
Mass Balance ◽  
Sea Level ◽  
Seismic Noise ◽  
Seismic Velocity ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Sea Level Changes ◽  
Ice Sheet Mass Balance ◽  
Velocity Changes

The Greenland ice sheet presently accounts for ~70% of global ice sheet mass loss. Because this mass loss is associated with sea-level rise at a rate of 0.7 mm/year, the development of improved monitoring techniques to observe ongoing changes in ice sheet mass balance is of paramount concern. Spaceborne mass balance techniques are commonly used; however, they are inadequate for many purposes because of their low spatial and/or temporal resolution. We demonstrate that small variations in seismic wave speed in Earth’s crust, as measured with the correlation of seismic noise, may be used to infer seasonal ice sheet mass balance. Seasonal loading and unloading of glacial mass induces strain in the crust, and these strains then result in seismic velocity changes due to poroelastic processes. Our method provides a new and independent way of monitoring (in near real time) ice sheet mass balance, yielding new constraints on ice sheet evolution and its contribution to global sea-level changes. An increased number of seismic stations in the vicinity of ice sheets will enhance our ability to create detailed space-time records of ice mass variations.

Relative control of bedrock roughness versus topography on global glacier bed friction

2021 ◽  
Author(s):  
Olivier Gagliardini ◽  
Fabien Gillet-Chaulet ◽  
Florent Gimbert
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Inverse Method ◽  
Ad Hoc ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Grid Resolution ◽  
Classical Approach ◽  
Bed Topography ◽  
Bed Friction

&lt;p&gt;Friction at the base of ice-sheets has been shown to be one of the largest uncertainty of model projections for the contribution of ice-sheet to future sea level rise. On hard beds, most of the apparent friction is the result of ice flowing over the bumps that have a size smaller than described by the grid resolution of ice-sheet models. To account for this friction, the classical approach is to replace this under resolved roughness by an ad-hoc friction law. In an imaginary world of unlimited computing resource and highly resolved bedrock DEM, one should solve for all bed roughnesses assuming pure sliding at the bedrock-ice interface. If such solutions are not affordable at the scale of an ice-sheet or even at the scale of a glacier, the effect of small bumps can be inferred using synthetical periodic geometry. In this presentation,&lt;span&gt;&amp;#160; &lt;/span&gt;beds are constructed using the superposition of up to five bed geometries made of sinusoidal bumps of decreasing wavelength and amplitudes. The contribution to the total friction of all five beds is evaluated by inverse methods using the most resolved solution as observation. It is shown that small features of few meters can contribute up to almost half of the total friction, depending on the wavelengths and amplitudes distribution. This work also confirms that the basal friction inferred using inverse method&lt;span&gt;&amp;#160; &lt;/span&gt;is very sensitive to how the bed topography is described by the model grid, and therefore depends on the size of the model grid itself.&lt;span&gt;&amp;#160;&lt;/span&gt;&lt;/p&gt;

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