scholarly journals Large and irreversible future decline of the Greenland ice-sheet

2020 ◽  
Author(s):  
Jonathan M. Gregory ◽  
Steven E. George ◽  
Robin S. Smith
Keyword(s):  
Climate Change ◽  
Steady State ◽  
Sea Level ◽  
General Circulation ◽  
Initial Perturbation ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Circulation Model ◽  
Intergovernmental Panel ◽  
Recent Climate

Abstract. We have studied the evolution of the Greenland ice-sheet under a range of constant climates typical of those projected for the end of the present century, using a dynamical ice-sheet model (Glimmer) coupled to an atmospheric general circulation model (FAMOUS-ice AGCM). The ice-sheet surface mass balance (SMB) is simulated by the AGCM, including its dependence on altitude within AGCM gridboxes. Over millennia under a warmer climate, the ice-sheet reaches a new steady state, whose mass is correlated with the initial perturbation in SMB, and hence with the magnitude of global climate change imposed. For the largest global warming considered (about +5 K), the contribution to global-mean sea-level rise (GMSLR) is initially 2.7 mm yr−1, and the ice-sheet is eventually practically eliminated (giving over 7 m of GMSLR). For all RCP8.5 climates, final GMSLR exceeds 4 m. If recent climate were maintained, GMSLR would reach 1.5–2.5 m. Contrary to expectation from earlier work, we find no evidence for a threshold warming that divides scenarios in which the ice-sheet suffers little reduction from those which it is mostly lost. This is because the dominant effect is reduction of area, not reduction of surface altitude, and the geographical variation of SMB must be taken into account. The final steady state is achieved by withdrawal from the coast in some places, and a tendency for increasing SMB due to enhancement of cloudiness and snowfall over the remaining ice-sheet, through the effects of topographic change on atmospheric circulation. If late twentieth-century climate is restored, the ice-sheet will not regrow to its present extent, owing to such effects, once its mass has fallen below a threshold of about 4 m of sea-level equivalent. In that case, about 2 m of GMSLR would become irreversible. In order to avoid this outcome, anthropogenic climate change must be reversed before the ice-sheet has declined to the threshold mass, which would be reached in about 600 years at the highest rate of mass-loss within the likely range of the Fifth Assessment Report of the Intergovernmental Panel on Climate Change.

scholarly journals Large and irreversible future decline of the Greenland ice sheet

2020 ◽  
Vol 14 (12) ◽  
pp. 4299-4322
Author(s):  
Jonathan M. Gregory ◽  
Steven E. George ◽  
Robin S. Smith
Keyword(s):  
Climate Change ◽  
Global Warming ◽  
Steady State ◽  
Sea Level ◽  
General Circulation ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Circulation Model ◽  
Intergovernmental Panel ◽  
Late 20Th Century

Abstract. We have studied the evolution of the Greenland ice sheet under a range of constant climates typical of those projected for the end of the present century using a dynamical ice sheet model (Glimmer) coupled to an atmosphere general circulation model (FAMOUS–ice AGCM). The ice sheet surface mass balance (SMB) is simulated within the AGCM by a multilayer snow scheme from snowfall and surface energy fluxes, including refreezing and dependence on altitude within AGCM grid boxes. Over millennia under any warmer climate, the ice sheet reaches a new steady state, whose mass is correlated with the magnitude of global climate change imposed. If a climate that gives the recently observed SMB were maintained, global-mean sea level rise (GMSLR) would reach 0.5–2.5 m. For any global warming exceeding 3 K, the contribution to GMSLR exceeds 5 m. For the largest global warming considered (about +5 K), the rate of GMSLR is initially 2.7 mm yr−1, and eventually only a small ice cap endures, resulting in over 7 m of GMSLR. Our analysis gives a qualitatively different impression from previous work in that we do not find a sharp threshold warming that divides scenarios in which the ice sheet suffers little reduction from those in which it is mostly lost. The final steady state is achieved by withdrawal from the coast in some places and a tendency for increasing SMB due to enhancement of cloudiness and snowfall over the remaining ice sheet by the effects of topographic change on atmospheric circulation, outweighing the tendency for decreasing SMB from the reduction in surface altitude. If late 20th-century climate is restored after the ice sheet mass has fallen below a threshold of about 4 m of sea level equivalent, it will not regrow to its present extent because the snowfall in the northern part of the island is reduced once the ice sheet retreats from there. In that case, about 2 m of GMSLR would become irreversible. In order to avoid this outcome, anthropogenic climate change must be reversed before the ice sheet has declined to the threshold mass, which would be reached in about 600 years at the highest rate of mass loss within the likely range of the Fifth Assessment Report of the Intergovernmental Panel on Climate Change.

scholarly journals The response of the Greenland ice sheet to climate changes in the 21st century by interactive coupling of an AOGCM with a thermomechanical ice-sheet model

2002 ◽  
Vol 35 ◽  
pp. 409-415 ◽  
Author(s):  
Philippe Huybrechts ◽  
Ives Janssens ◽  
Chantal Poncin ◽  
Thierry Fichefet
Keyword(s):  
Climate Change ◽  
Sea Ice ◽  
Sea Level Rise ◽  
Sea Level ◽  
Fresh Water ◽  
General Circulation Model ◽  
General Circulation ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Circulation Model

AbstractWe present results from a greenhouse warming experiment obtained from an atmosphere–ocean–sea-ice general circulation model that is interactively coupled with a three-dimensional model of the Greenland ice sheet. the experiment covers the period 1970–2099 and is driven by the mid-range Intergovernmental Panel on Climate Change SRESB2 scenario. the Greenland model is a thermomechanical high-resolution (20 km) model coupled with a viscoelastic bedrock model. the melt-and-runoff model is based on the positive degree-day method and includes meltwater retention in the snowpack and the formation of superimposed ice. the atmospheric–oceanic general circulation model (AOGCM) is a coarse-resolution model without flux correction based on the Laboratoire de Météorologie Dynamique (Paris) LMD 5.3 atmospheric model coupled with a primitive-equation, free-surface oceanic component incorporating sea ice (coupled large-scale ice–ocean (CLIO)). By 2100, average Greenland annual temperature is found to rise by about 4.5˚C and mean precipitation by about 35%. the total fresh-water flux approximately doubles over this period due to increased runoff from the ice sheet and the ice-free land, but the calving rate is found to decrease by 25%. the ice sheet shrinks equivalent to 4 cm of sea-level rise. the contribution from the background evolution is not more than 5% of the total predicted sea-level rise. We did not find significant changes in the patterns of climate change over the North Atlantic region compared with a climate-change run without Greenland fresh-water feedback.

scholarly journals 21st century ocean forcing of the Greenland Ice Sheet for modeling of sea level contribution

2019 ◽  
Author(s):  
Donald A. Slater ◽  
Denis Felikson ◽  
Fiamma Straneo ◽  
Heiko Goelzer ◽  
Christopher M. Little ◽  
...  
Keyword(s):  
Sea Level ◽  
21St Century ◽  
General Circulation ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
General Circulation Models ◽  
Glacier Retreat ◽  
Small Scale ◽  
Intergovernmental Panel ◽  
Continental Scale

Abstract. Changes in the ocean are expected to be an important determinant of the Greenland Ice Sheet's future sea level contribution. Yet representing these changes in continental-scale ice sheet models remains challenging due to the small scale of the key physics, and limitations in processing understanding. Here we present the ocean forcing strategy for Greenland Ice Sheet models taking part in the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6), the primary community effort to provide 21st century sea level projections for the Intergovernmental Panel on Climate Change 6th Assessment Report. Beginning from global atmosphere-ocean general circulation models, we describe two complementary approaches to provide ocean boundary conditions for Greenland Ice Sheet models, termed the retreat and submarine melt implementations. The retreat implementation parameterizes glacier retreat as a function of projected submarine melting, is designed to be implementable by all ice sheet models, and results in retreat of around 1 and 15 km by 2100 in RCP2.6 and 8.5 scenarios respectively. The submarine melt implementation provides estimated submarine melting only, leaving the ice sheet model to solve for the resulting calving and glacier retreat, and suggests submarine melt rates will change little under RCP2.6 but will approximately triple by 2100 under RCP8.5. Both implementations have necessarily made use of simplifying assumptions and poorly-constrained parameterisations and as such, further research on submarine melting, calving and fjord-shelf exchange should remain a priority. Nevertheless, the presented framework will allow an ensemble of Greenland Ice Sheet models to be systematically and consistently forced by the ocean for the first time, and should therefore result in a significant improvement in projections of the Greenland ice sheet's contribution to future sea level change.

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.

The Arctic cryosphere in the Mid-Pliocene and the future

2008 ◽  
Vol 367 (1886) ◽  
pp. 49-67 ◽  
Author(s):  
Daniel J Lunt ◽  
Alan M Haywood ◽  
Gavin L Foster ◽  
Emma J Stone
Keyword(s):  
Climate Change ◽  
General Circulation ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Circulation Model ◽  
Future Climate ◽  
Arctic Climate ◽  
The Arctic ◽  
Future Climate Change ◽  
The Future

The Mid-Pliocene ( ca 3 Myr ago) was a relatively warm period, with increased atmospheric CO 2 relative to pre-industrial. It has therefore been highlighted as a possible palaeo-analogue for the future. However, changed vegetation patterns, orography and smaller ice sheets also influenced the Mid-Pliocene climate. Here, using a general circulation model and ice-sheet model, we determine the relative contribution of vegetation and soils, orography and ice, and CO 2 to the Mid-Pliocene Arctic climate and cryosphere. Compared with pre-industrial, we find that increased Mid-Pliocene CO 2 contributes 35 per cent, lower orography and ice-sheet feedbacks contribute 42 per cent, and vegetation changes contribute 23 per cent of Arctic temperature change. The simulated Mid-Pliocene Greenland ice sheet is substantially smaller than that of modern, mostly due to the higher CO 2 . However, our simulations of future climate change indicate that the same increase in CO 2 is not sufficient to melt the modern ice sheet substantially. We conclude that, although the Mid-Pliocene resembles the future in some respects, care must be taken when interpreting it as an exact analogue due to vegetation and ice-sheet feedbacks. These act to intensify Mid-Pliocene Arctic climate change, and act on a longer time scale than the century scale usually addressed in future climate prediction.

scholarly journals Twenty-first century ocean forcing of the Greenland ice sheet for modelling of sea level contribution

2020 ◽  
Vol 14 (3) ◽  
pp. 985-1008 ◽  
Author(s):  
Donald A. Slater ◽  
Denis Felikson ◽  
Fiamma Straneo ◽  
Heiko Goelzer ◽  
Christopher M. Little ◽  
...  
Keyword(s):  
Sea Level ◽  
General Circulation ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
General Circulation Models ◽  
Glacier Retreat ◽  
Small Scale ◽  
Intergovernmental Panel ◽  
Continental Scale ◽  
The Impact

Abstract. Changes in ocean temperature and salinity are expected to be an important determinant of the Greenland ice sheet's future sea level contribution. Yet, simulating the impact of these changes in continental-scale ice sheet models remains challenging due to the small scale of key physics, such as fjord circulation and plume dynamics, and poor understanding of critical processes, such as calving and submarine melting. Here we present the ocean forcing strategy for Greenland ice sheet models taking part in the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6), the primary community effort to provide 21st century sea level projections for the Intergovernmental Panel on Climate Change Sixth Assessment Report. Beginning from global atmosphere–ocean general circulation models, we describe two complementary approaches to provide ocean boundary conditions for Greenland ice sheet models, termed the “retreat” and “submarine melt” implementations. The retreat implementation parameterises glacier retreat as a function of projected subglacial discharge and ocean thermal forcing, is designed to be implementable by all ice sheet models and results in retreat of around 1 and 15 km by 2100 in RCP2.6 and 8.5 scenarios, respectively. The submarine melt implementation provides estimated submarine melting only, leaving the ice sheet model to solve for the resulting calving and glacier retreat and suggests submarine melt rates will change little under RCP2.6 but will approximately triple by 2100 under RCP8.5. Both implementations have necessarily made use of simplifying assumptions and poorly constrained parameterisations and, as such, further research on submarine melting, calving and fjord–shelf exchange should remain a priority. Nevertheless, the presented framework will allow an ensemble of Greenland ice sheet models to be systematically and consistently forced by the ocean for the first time and should result in a significant improvement in projections of the Greenland ice sheet's contribution to future sea level change.

scholarly journals Greenland ice sheet contribution to sea level rise during the last interglacial period: a modelling study driven and constrained by ice core data

2013 ◽  
Vol 9 (1) ◽  
pp. 353-366 ◽  
Author(s):  
A. Quiquet ◽  
C. Ritz ◽  
H. J. Punge ◽  
D. Salas y Mélia
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Ice Core ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Interglacial Period ◽  
Last Interglacial ◽  
Intergovernmental Panel ◽  
Orbital Configuration ◽  
Global Sea Level

Abstract. As pointed out by the forth assessment report of the Intergovernmental Panel on Climate Change, IPCC-AR4 (Meehl et al., 2007), the contribution of the two major ice sheets, Antarctica and Greenland, to global sea level rise, is a subject of key importance for the scientific community. By the end of the next century, a 3–5 °C warming is expected in Greenland. Similar temperatures in this region were reached during the last interglacial (LIG) period, 130–115 ka BP, due to a change in orbital configuration rather than to an anthropogenic forcing. Ice core evidence suggests that the Greenland ice sheet (GIS) survived this warm period, but great uncertainties remain about the total Greenland ice reduction during the LIG. Here we perform long-term simulations of the GIS using an improved ice sheet model. Both the methodologies chosen to reconstruct palaeoclimate and to calibrate the model are strongly based on proxy data. We suggest a relatively low contribution to LIG sea level rise from Greenland melting, ranging from 0.7 to 1.5 m of sea level equivalent, contrasting with previous studies. Our results suggest an important contribution of the Antarctic ice sheet to the LIG highstand.

scholarly journals The Steady-State Atmospheric Circulation Response to Climate Change–like Thermal Forcings in a Simple General Circulation Model

2010 ◽  
Vol 23 (13) ◽  
pp. 3474-3496 ◽  
Author(s):  
Amy H. Butler ◽  
David W. J. Thompson ◽  
Ross Heikes
Keyword(s):  
Climate Change ◽  
Steady State ◽  
General Circulation Model ◽  
General Circulation ◽  
Storm Track ◽  
Circulation Model ◽  
Storm Tracks ◽  
Polar Surface ◽  
Tropical Troposphere ◽  
Polar Stratosphere

Abstract The steady-state extratropical atmospheric response to thermal forcing is investigated in a simple atmospheric general circulation model. The thermal forcings qualitatively mimic three key aspects of anthropogenic climate change: warming in the tropical troposphere, cooling in the polar stratosphere, and warming at the polar surface. The principal novel findings are the following: 1) Warming in the tropical troposphere drives two robust responses in the model extratropical circulation: poleward shifts in the extratropical tropospheric storm tracks and a weakened stratospheric Brewer–Dobson circulation. The former result suggests heating in the tropical troposphere plays a fundamental role in the poleward contraction of the storm tracks found in Intergovernmental Panel on Climate Change (IPCC)-class climate change simulations; the latter result is in the opposite sense of the trends in the Brewer–Dobson circulation found in most previous climate change experiments. 2) Cooling in the polar stratosphere also drives a poleward shift in the extratropical storm tracks. The tropospheric response is largely consistent with that found in previous studies, but it is shown to be very sensitive to the level and depth of the forcing. In the stratosphere, the Brewer–Dobson circulation weakens at midlatitudes, but it strengthens at high latitudes because of anomalously poleward heat fluxes on the flank of the polar vortex. 3) Warming at the polar surface drives an equatorward shift of the storm tracks. The storm-track response to polar warming is in the opposite sense of the response to tropical tropospheric heating; hence large warming over the Arctic may act to attenuate the response of the Northern Hemisphere storm track to tropical heating. 4) The signs of the tropospheric and stratospheric responses to all thermal forcings considered here are robust to seasonal changes in the basic state, but the amplitude and details of the responses exhibit noticeable differences between equinoctial and wintertime conditions. Additionally, the responses exhibit marked nonlinearity in the sense that the response to multiple thermal forcings applied simultaneously is quantitatively different from the sum of the responses to the same forcings applied independently. Thus the response of the model to a given thermal forcing is demonstrably dependent on the other thermal forcings applied to the model.

scholarly journals Future Changes in Drought Characteristics under Extreme Climate Change over South Korea

2016 ◽  
Vol 2016 ◽  
pp. 1-19 ◽  
Author(s):  
Joo-Heon Lee ◽  
Hyun-Han Kwon ◽  
Ho-Won Jang ◽  
Tae-Woong Kim
Keyword(s):  
Climate Change ◽  
South Korea ◽  
General Circulation ◽  
Standardized Precipitation Index ◽  
Low Frequency ◽  
Circulation Model ◽  
Significance Test ◽  
Precipitation Index ◽  
Intergovernmental Panel ◽  
The Future

This study attempts to analyze several drought features in South Korea from various perspectives using a three-month standard precipitation index. In particular, this study aims to evaluate changes in spatial distribution in terms of frequency and severity of droughts in the future due to climate change, using IPCC (intergovernmental panel on climate change) GCM (general circulation model) simulations. First, the Mann-Kendall method was adopted to identify drought trends at the five major watersheds. The simulated temporal evolution of SPI (standardized precipitation index) during the winter showed significant drying trends in most parts of the watersheds, while the simulated SPI during the spring showed a somewhat different feature in the GCMs. Second, this study explored the low-frequency patterns associated with drought by comparing global wavelet power, with significance test. Future spectra decreased in the fractional variance attributed to a reduction in the interannual band from 2 to 8 years. Finally, the changes in the frequency and the severity under climate change were evaluated through the drought spell analyses. Overall features of drought conditions in the future showed a tendency to increase (about 6%) in frequency and severity of droughts during the dry season (i.e., from October to May) under climate change.

scholarly journals A hybrid GCM paleo ice-sheet model, ANICE2.1 – [email protected]: set up and benchmark experiments

2018 ◽  
Author(s):  
Constantijn J. Berends ◽  
Bas de Boer ◽  
Roderik S. W. van de Wal
Keyword(s):  
Sea Level ◽  
General Circulation ◽  
Climate Model ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Circulation Model ◽  
Climate Modelling ◽  
Last Glacial ◽  
Model Set ◽  
Set Up

Abstract. Fully coupled ice-sheet-climate modelling over 10,000–100,000-year time scales on high spatial and temporal resolution remains beyond the capability of current computational systems. Hybrid GCM-ice-sheet modelling offers a middle ground, balancing the need to accurately capture both long-term processes, in particular circulation driven changes in precipitation, and processes requiring a high spatial resolution like ablation. Here, we present and evaluate a model set-up that forces the ANICE 3D thermodynamic ice-sheet-shelf model calculating all ice on Earth, with pre-calculated output from several steady-state simulations with the HadCM3 general circulation model (GCM), using a so-called matrix method of coupling both components, where simulations with various levels of pCO2 and ice-sheet configuration are combined to form a time-continuous transient climate forcing consistent with the modelled ice-sheets. We address the difficulties in downscaling low-resolution GCM output to the higher-resolution grid of an ice-sheet model, and account for differences between GCM and ice-sheet model surface topography ranging from interglacial to glacial conditions. As a benchmark experiment to assess the validity of this model set-up, we perform a simulation of the entire last glacial cycle, from 120 kyr ago to present-day. The simulated eustatic sea-level drop at the Last Glacial maximum (LGM) for the combined Antarctic, Greenland, Eurasian and North-American ice-sheets amounts to 100 m, in line with many other studies. The simulated ice-sheets at LGM agree well with the ICE-5G reconstruction and the more recent DATED-1 reconstruction in terms of total volume and geographical location of the ice sheets. Moreover, modelled benthic oxygen isotope abundance and the relative contributions from global ice volume and deep-water temperature agree well with available data, as do surface temperature histories for the Greenland and Antarctic ice-sheets. This model strategy can be used to create time-continuous ice-sheet distribution and sea-level reconstructions for geological periods up to several millions of years in duration, capturing climate model driven variations in the mass balance of the ice sheet.

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