scholarly journals Influence of temperature fluctuations on equilibrium ice sheet volume

2017 ◽  
Author(s):  
Troels Bøgeholm Mikkelsen ◽  
Aslak Grinsted ◽  
Peter Ditlevsen
Keyword(s):  
Mass Balance ◽  
Climate Change Scenario ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Effect Of Temperature ◽  
Change Scenario ◽  
Surface Mass ◽  
The Earth ◽  
The Future

Abstract. Forecasting the future sea level relies on accurate modeling of the response of the Greenland and Antarctic ice sheets to changing temperatures. We show why the steady state of an ice sheet is biased toward larger size if the interannual weather generated fluctuations in temperature are not taken into account in numerical modeling of the ice sheet. We illustrate this in a simple ice sheet model. This bias could, if not taken into account, imply that the risk of collapse in a given climate change scenario is underestimated. We estimate that the effect of temperature variability on the surface mass balance of the Greenland Ice Sheet in recent ensemble forecasting should be adjusted downward by approximately 13 percent of the present day observed value, if assuming a 2 degree warming. Many predicted scenarios of the future climate show an increased variability in temperature over much of the Earth. In light of our findings it is important to gauge the extent to which this increased variability will further influence the mass balance of the ice sheets.

Trends and projections in ice sheet mass balance

2020 ◽  
Author(s):  
Andrew Shepherd ◽  
Keyword(s):  
Mass Balance ◽  
Sea Level Rise ◽  
Sea Level ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Ice Dynamics ◽  
Surface Mass ◽  
Sea Levels ◽  
Global Sea Level

<p>In recent decades, the Antarctic and Greenland Ice Sheets have been major contributors to global sea-level rise and are expected to be so in the future. Although increases in glacier flow and surface melting have been driven by oceanic and atmospheric warming, the degree and trajectory of today’s imbalance remain uncertain. Here we compare and combine 26 individual satellite records of changes in polar ice sheet volume, flow and gravitational potential to produce a reconciled estimate of their mass balance. <strong>Since the early 1990’s, ice losses from Antarctica and Greenland have caused global sea-levels to rise by 18.4 millimetres, on average, and there has been a sixfold increase in the volume of ice loss over time. Of this total, 41 % (7.6 millimetres) originates from Antarctica and 59 % (10.8 millimetres) is from Greenland. In this presentation, we compare our reconciled estimates of Antarctic and Greenland ice sheet mass change to IPCC projection of sea level rise to assess the model skill in predicting changes in ice dynamics and surface mass balance.  </strong>Cumulative ice losses from both ice sheets have been close to the IPCC’s predicted rates for their high-end climate warming scenario, which forecast an additional 170 millimetres of global sea-level rise by 2100 when compared to their central estimate.</p>

scholarly journals Greenland Ice Sheet Surface Mass-Balance Modeling in a 131-Yr Perspective, 1950–2080

2010 ◽  
Vol 11 (1) ◽  
pp. 3-25 ◽  
Author(s):  
Sebastian H. Mernild ◽  
Glen E. Liston ◽  
Christopher A. Hiemstra ◽  
Jens H. Christensen
Keyword(s):  
Mass Balance ◽  
Sea Level ◽  
General Circulation ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Circulation Model ◽  
Change Scenario ◽  
Surface Mass Balance ◽  
Surface Mass ◽  
Freshwater Runoff

Abstract Fluctuations in the Greenland ice sheet (GrIS) surface mass balance (SMB) and freshwater influx to the surrounding oceans closely follow climate fluctuations and are of considerable importance to the global eustatic sea level rise. A state-of-the-art snow-evolution modeling system (SnowModel) was used to simulate variations in the GrIS melt extent, surface water balance components, changes in SMB, and freshwater influx to the ocean. The simulations are based on the Intergovernmental Panel on Climate Change scenario A1B modeled by the HIRHAM4 regional climate model (RCM) using boundary conditions from the ECHAM5 atmosphere–ocean general circulation model (AOGCM) from 1950 through 2080. In situ meteorological station [Greenland Climate Network (GC-Net) and World Meteorological Organization (WMO) Danish Meteorological Institute (DMI)] observations from inside and outside the GrIS were used to validate and correct RCM output data before they were used as input for SnowModel. Satellite observations and independent SMB studies were used to validate the SnowModel output and confirm the model’s robustness. The authors simulated an ∼90% increase in end-of-summer surface melt extent (0.483 × 106 km2) from 1950 to 2080 and a melt index (above 2000-m elevation) increase of 138% (1.96 × 106 km2 × days). The greatest difference in melt extent occurred in the southern part of the GrIS, and the greatest changes in the number of melt days were seen in the eastern part of the GrIS (∼50%–70%) and were lowest in the west (∼20%–30%). The rate of SMB loss, largely tied to changes in ablation processes, leads to an enhanced average loss of 331 km3 from 1950 to 2080 and an average SMB level of −99 km3 for the period 2070–80. GrIS surface freshwater runoff yielded a eustatic rise in sea level from 0.8 ± 0.1 (1950–59) to 1.9 ± 0.1 mm (2070–80) sea level equivalent (SLE) yr−1. The accumulated GrIS freshwater runoff contribution from surface melting equaled 160-mm SLE from 1950 through 2080.

scholarly journals Influence of albedo parameterization on surface mass balance in the perspective of Greenland ice sheet modelling in EC-Earth

2016 ◽  
Author(s):  
Michiel Helsen ◽  
Roderik Van de Wal ◽  
Thomas Reerink ◽  
Richard Bintanja ◽  
Marianne Sloth Madsen ◽  
...  
Keyword(s):  
Mass Balance ◽  
Climate Model ◽  
Global Climate ◽  
Global Climate Model ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Surface Mass Balance ◽  
Surface Mass

Abstract. The albedo of the surface of ice sheets changes as a function of time, due to the effects of deposition of new snow, ageing of dry snow, melting and runoff. Currently, the calculation of the albedo of ice sheets is highly parameterized within the Earth System Model EC-Earth, by taking a constant value for areas with thick perennial snow cover. This is one of the reasons that the surface mass balance (SMB) of the Greenland ice sheet (GrIS) is poorly resolved in the model. To improve this, eight snow albedo schemes are evaluated here. The resulting SMB is downscaled from the lower resolution global climate model topography to the higher resolution ice sheet topography of the GrIS, such that the influence of these different SMB climatologies on the long-term evolution of the GrIS is tested by ice sheet model simulations. This results in an optimised albedo parameterization that can be used in future EC-Earth simulations with an interactive ice sheet component.

scholarly journals Influence of temperature fluctuations on equilibrium ice sheet volume

2018 ◽  
Vol 12 (1) ◽  
pp. 39-47 ◽  
Author(s):  
Troels Bøgeholm Mikkelsen ◽  
Aslak Grinsted ◽  
Peter Ditlevsen
Keyword(s):  
Mass Balance ◽  
Sea Level ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Temperature Fluctuations ◽  
Surface Mass ◽  
Ice Volume ◽  
Recent Estimate ◽  
Interannual Fluctuations

Abstract. Forecasting the future sea level relies on accurate modeling of the response of the Greenland and Antarctic ice sheets to changing temperatures. The surface mass balance (SMB) of the Greenland Ice Sheet (GrIS) has a nonlinear response to warming. Cold and warm anomalies of equal size do not cancel out and it is therefore important to consider the effect of interannual fluctuations in temperature. We find that the steady-state volume of an ice sheet is biased toward larger size if interannual temperature fluctuations are not taken into account in numerical modeling of the ice sheet. We illustrate this in a simple ice sheet model and find that the equilibrium ice volume is approximately 1 m SLE (meters sea level equivalent) smaller when the simple model is forced with fluctuating temperatures as opposed to a stable climate. It is therefore important to consider the effect of interannual temperature fluctuations when designing long experiments such as paleo-spin-ups. We show how the magnitude of the potential bias can be quantified statistically. For recent simulations of the Greenland Ice Sheet, we estimate the bias to be 30 Gt yr−1 (24–59 Gt yr−1, 95 % credibility) for a warming of 3 °C above preindustrial values, or 13 % (10–25, 95 % credibility) of the present-day rate of ice loss. Models of the Greenland Ice Sheet show a collapse threshold beyond which the ice sheet becomes unsustainable. The proximity of the threshold will be underestimated if temperature fluctuations are not taken into account. We estimate the bias to be 0.12 °C (0.10–0.18 °C, 95 % credibility) for a recent estimate of the threshold. In light of our findings it is important to gauge the extent to which this increased variability will influence the mass balance of the ice sheets.

scholarly journals Forty-year Simulations of Firn Processes over the Greenland and Antarctic Ice Sheets

2020 ◽  
Author(s):  
Brooke Medley ◽  
Thomas A. Neumann ◽  
H. Jay Zwally ◽  
Benjamin E. Smith
Keyword(s):  
Mass Balance ◽  
Accumulation Rate ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Surface Mass Balance ◽  
Surface Mass ◽  
Air Content ◽  
Semi Empirical ◽  
Antarctic Ice Sheets

Abstract. Conversion of altimetry-derived ice-sheet volume change to mass requires an understanding of the evolution of the combined ice and air content within the firn column. In the absence of suitable techniques to observe the changes to the firn column across the entirety of an ice sheet, the firn column processes are typically modelled. Here, we present new 40-year simulations of firn processes over the Greenland and Antarctic Ice Sheets using the Community Firn Model and atmospheric reanalysis variables. A dataset of more than 250 measured depth-density profiles from both ice sheets provides the basis of the calibration of the dry-snow densification scheme. The resulting scheme results in a reduction in the rate of densification, relative to a commonly used semi-empirical model, through a decreased dependence on the accumulation rate, a proxy for overburden stress. The modelled firn column runoff, when combined with atmospheric variables from MERRA-2, generates realistic mean integrated surface mass balance values for the Greenland (+361 Gt yr−1) and Antarctic (+2623 Gt yr−1) ice sheets when compared to published model-ensemble means. We find that seasonal volume changes associated with firn air content are approximately 3 times larger than those associated with surface mass balance; however, when averaged over multiple years, ice and air-volume fluctuations within the firn column are of comparable magnitudes. Between 1996 and 2019, the Greenland Ice Sheet lost more than 5 % of its firn air content indicating a reduction in the total meltwater retention capability. Nearly all (>98 %) of the meltwater produced over the Antarctic Ice Sheet is retained within the firn column through infiltration and refreezing.

scholarly journals Reconstruction of the 1979–2006 Greenland ice sheet surface mass balance using the regional climate model MAR

2007 ◽  
Vol 1 (1) ◽  
pp. 21-40 ◽  
Author(s):  
X. Fettweis
Keyword(s):  
Heat Flux ◽  
Mass Balance ◽  
Thermohaline Circulation ◽  
Climate Model ◽  
Sensible Heat Flux ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Surface Mass Balance ◽  
Surface Mass ◽  
The Future

Abstract. Results from a 28-year simulation (1979–2006) over the Greenland ice sheet (GrIS) reveal an increase of solid precipitation (+0.4±2.5 km3 yr−2) and run-off (+7.9±3.3 km3 yr−2) of surface meltwater. The net effect of these competing factors is a significant Surface Mass Balance (SMB) loss of −7.2±5.1 km3 yr−2. The contribution of changes in the net water vapour flux (+0.02±0.09 km3 yr−2) and rainfall (+0.2±0.2 km3 yr−2) to the SMB variability is negligible. The meltwater supply has increased because the GrIS surface has been warming up +2.4°C since 1979. Sensible heat flux, latent heat flux and net solar radiation have not varied significantly over the last three decades. However, the simulated downward infrared flux has increased by 9.3 W m−2 since 1979. The natural climate variability (e.g. the North Atlantic Oscillation) does not explain these changes. The recent global warming, due to the greenhouse gas concentration increase induced by human activities, could be a cause of these changes. The doubling of surface meltwater flux into the ocean over the period 1979–2006 suggests that the overall ice sheet mass balance has been increasingly negative, given the likely meltwater-induced acceleration of outlet glaciers. This study suggests that increased melting overshadows over an increased accumulation in a warming scenario and that the GrIS is likely to keep losing mass in the future. An enduring GrIS melting will probably affect in the future an certain effect on the stability of the thermohaline circulation and the global sea level rise.

scholarly journals Design and results of the ice sheet model initialisation experiments initMIP-Greenland: an ISMIP6 intercomparison

2018 ◽  
Vol 12 (4) ◽  
pp. 1433-1460 ◽  
Author(s):  
Heiko Goelzer ◽  
Sophie Nowicki ◽  
Tamsin Edwards ◽  
Matthew Beckley ◽  
Ayako Abe-Ouchi ◽  
...  
Keyword(s):  
Mass Balance ◽  
Sea Level ◽  
Large Scale ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Surface Mass Balance ◽  
Model Intercomparison ◽  
Surface Mass ◽  
Intercomparison Project

Abstract. Earlier large-scale Greenland ice sheet sea-level projections (e.g. those run during the ice2sea and SeaRISE initiatives) have shown that ice sheet initial conditions have a large effect on the projections and give rise to important uncertainties. The goal of this initMIP-Greenland intercomparison exercise is to compare, evaluate, and improve the initialisation techniques used in the ice sheet modelling community and to estimate the associated uncertainties in modelled mass changes. initMIP-Greenland is the first in a series of ice sheet model intercomparison activities within ISMIP6 (the Ice Sheet Model Intercomparison Project for CMIP6), which is the primary activity within the Coupled Model Intercomparison Project Phase 6 (CMIP6) focusing on the ice sheets. Two experiments for the large-scale Greenland ice sheet have been designed to allow intercomparison between participating models of (1) the initial present-day state of the ice sheet and (2) the response in two idealised forward experiments. The forward experiments serve to evaluate the initialisation in terms of model drift (forward run without additional forcing) and in response to a large perturbation (prescribed surface mass balance anomaly); they should not be interpreted as sea-level projections. We present and discuss results that highlight the diversity of data sets, boundary conditions, and initialisation techniques used in the community to generate initial states of the Greenland ice sheet. We find good agreement across the ensemble for the dynamic response to surface mass balance changes in areas where the simulated ice sheets overlap but differences arising from the initial size of the ice sheet. The model drift in the control experiment is reduced for models that participated in earlier intercomparison exercises.

Subglacial Discharge of the Greenland Ice Sheet from Basal Melt

2021 ◽  
Author(s):  
Nanna Bjørnholt Karlsson ◽  
Anne M Solgaard ◽  
Kenneth D Mankoff ◽  
Fabien Gillet-Chaulet ◽  
Joseph A. MacGregor ◽  
...  
Keyword(s):  
Mass Balance ◽  
Total Mass ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Frictional Heat ◽  
Geothermal Heat ◽  
Surface Mass ◽  
Ice Volume ◽  
Friction Term

<p>The total mass balance of ice sheets is determined using estimates of ice volume change from satellite altimetry, measurements of gravity changes, or by differencing solid ice discharge and surface mass balance. The basal melt is only implicitly included in the first two and entirely neglected by the last method. Here, we show that the basal mass loss of the Greenland Ice Sheet is a non-negligible component of the total mass budget. We estimate that the basal melt is 21.4 +4.4/-4.0 Gt per year corresponding to 8% of the ice sheet’s total mass balance. The basal melt is composed of three separate terms; melt caused by frictional heat, geothermal heat and heat from surface meltwater, respectively, and the basal friction term is responsible for half of the basal melt.</p><p>Importantly, the geothermal and friction heat are active year round. This implies that a quantifiable volume of freshwater is discharged into the Greenlandic fjords during the winter where the ice-fjord interactions often are assumed dormant. Here, we present basal melt volumes from different outlet glaciers that discharge into Greenlandic fjords. We compare the basal melt to the freshwater volumes generated by surface meltwater, and identify locations where basal melt volumes are comparable to surface meltwater during the winter.</p>

Relative importance of surface mass balance and outlet glacier forcing in ISMIP6 Greenland ice sheet sea-level projections

2021 ◽  
Author(s):  
Heiko Goelzer ◽  
Keyword(s):  
Mass Balance ◽  
Sea Level ◽  
General Circulation ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Surface Mass Balance ◽  
Relative Importance ◽  
Outlet Glacier ◽  
Surface Mass ◽  
The Future

<p>The Greenland ice sheet (GrIS) is one of the largest contributors to global mean sea-level rise today and is expected to continue losing mass in the future under increasing Arctic warming. Mass loss in the future is caused by the thinning and retreat of marine-terminating outlet glaciers and to a larger extent by decreasing surface mass balance (SMB) due to increased surface meltwater runoff. In this paper we study the relative importance of changes in SMB and outlet glacier retreat by means of model simulations that have been performed as part of the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6). The effect of the two forcing mechanisms can be separated based on a comparison between full projections and single forcing experiments up to year 2100 for a number of ice sheet models, driving General Circulation Models and two forcing scenarios (RCP2.6 and RCP8.5). We can confirm earlier findings for the high forcing scenario that a compensation between the two processes renders the sea-level contribution from the full experiment lower than the sum of the single forcing experiments.</p>

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