The waxing and waning of the Northern Hemisphere ice sheets

Past modelling studies have shown that the energy balance of the ice-sheet surface is of primary importance in representing the 100 000 year glacial cycle. In particular, modelling of the net mass-balance function is an important part of coupled ice-sheet/climate models. We conduct a series of palaeoclimatic simulations with a vertically integrated ice-flow model coupled to the two-dimensional statistical-dynamical LLN (Louvain-la-Neuve) climate model. The models are coupled through a land-surface model which computes seasonal cycles of surface temperature and precipitation at the real altitude of the surface and evaluates the annual snow and/or ice-mass budget. The present-day climate of the Northern Hemisphere, the Greenland mass balance and the snowfield characteristics are quite well represented despite the relative simplicity of the model. Total ice-volume and sea-level variations during the last glacial cycle are well simulated. This suggests that the physical mechanisms included in the models are sufficient to explain the most striking features of the ice-age cycle. Introducing an improved and more detailed topography improves the simulation of the total ice volume but fails to correct inadequacies in the simulated ice distribution on the surface of the Earth.

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The waxing and waning of the Northern Hemisphere ice sheets

Annals of Glaciology ◽

10.1017/s0260305500015664 ◽

1995 ◽

Vol 21 ◽

pp. 96-102 ◽

Cited By ~ 3

Author(s):

I. Marsiat

Keyword(s):

Mass Balance ◽

Northern Hemisphere ◽

Land Surface ◽

Climate Models ◽

Climate Model ◽

Ice Sheet ◽

Ice Age ◽

Surface Model ◽

Glacial Cycle ◽

Ice Volume

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Investigating the evolution of major Northern Hemisphere ice sheets during the last glacial-interglacial cycle

Climate of the Past ◽

10.5194/cp-5-329-2009 ◽

2009 ◽

Vol 5 (3) ◽

pp. 329-345 ◽

Cited By ~ 62

Author(s):

S. Bonelli ◽

S. Charbit ◽

M. Kageyama ◽

M.-N. Woillez ◽

G. Ramstein ◽

...

Keyword(s):

Northern Hemisphere ◽

Climate Model ◽

Ice Sheets ◽

Ice Sheet ◽

Co2 Concentration ◽

Atmospheric Co2 ◽

Glacial Cycle ◽

Last Glacial ◽

Atmospheric Co2 Concentration ◽

The Last Glacial

Abstract. A 2.5-dimensional climate model of intermediate complexity, CLIMBER-2, fully coupled with the GREMLINS 3-D thermo-mechanical ice sheet model is used to simulate the evolution of major Northern Hemisphere ice sheets during the last glacial-interglacial cycle and to investigate the ice sheets responses to both insolation and atmospheric CO2 concentration. This model reproduces the main phases of advance and retreat of Northern Hemisphere ice sheets during the last glacial cycle, although the amplitude of these variations is less pronounced than those based on sea level reconstructions. At the last glacial maximum, the simulated ice volume is 52.5×1015 m3 and the spatial distribution of both the American and Eurasian ice complexes is in reasonable agreement with observations, with the exception of the marine parts of these former ice sheets. A set of sensitivity studies has also been performed to assess the sensitivity of the Northern Hemisphere ice sheets to both insolation and atmospheric CO2. Our results suggest that the decrease of summer insolation is the main factor responsible for the early build up of the North American ice sheet around 120 kyr BP, in agreement with benthic foraminifera δ18O signals. In contrast, low insolation and low atmospheric CO2 concentration are both necessary to trigger a long-lasting glaciation over Eurasia.

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Analysis of the surface mass balance for deglacial climate simulations

The Cryosphere ◽

10.5194/tc-15-1131-2021 ◽

2021 ◽

Vol 15 (2) ◽

pp. 1131-1156

Author(s):

Marie-Luise Kapsch ◽

Uwe Mikolajewicz ◽

Florian A. Ziemen ◽

Christian B. Rodehacke ◽

Clemens Schannwell

Keyword(s):

Mass Balance ◽

Northern Hemisphere ◽

Climate Models ◽

Ice Sheet ◽

Meridional Overturning Circulation ◽

Balance Model ◽

Surface Mass Balance ◽

Max Planck ◽

Equilibrium Line Altitude ◽

Surface Mass

Abstract. A realistic simulation of the surface mass balance (SMB) is essential for simulating past and future ice-sheet changes. As most state-of-the-art Earth system models (ESMs) are not capable of realistically representing processes determining the SMB, most studies of the SMB are limited to observations and regional climate models and cover the last century and near future only. Using transient simulations with the Max Planck Institute ESM in combination with an energy balance model (EBM), we extend previous research and study changes in the SMB and equilibrium line altitude (ELA) for the Northern Hemisphere ice sheets throughout the last deglaciation. The EBM is used to calculate and downscale the SMB onto a higher spatial resolution than the native ESM grid and allows for the resolution of SMB variations due to topographic gradients not resolved by the ESM. An evaluation for historical climate conditions (1980–2010) shows that derived SMBs compare well with SMBs from regional modeling. Throughout the deglaciation, changes in insolation dominate the Greenland SMB. The increase in insolation and associated warming early in the deglaciation result in an ELA and SMB increase. The SMB increase is caused by compensating effects of melt and accumulation: the warming of the atmosphere leads to an increase in melt at low elevations along the ice-sheet margins, while it results in an increase in accumulation at higher levels as a warmer atmosphere precipitates more. After 13 ka, the increase in melt begins to dominate, and the SMB decreases. The decline in Northern Hemisphere summer insolation after 9 ka leads to an increasing SMB and decreasing ELA. Superimposed on these long-term changes are centennial-scale episodes of abrupt SMB and ELA decreases related to slowdowns of the Atlantic meridional overturning circulation (AMOC) that lead to a cooling over most of the Northern Hemisphere.

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Coupling of climate models and ice sheet models by surface mass balance gradients: application to the Greenland Ice Sheet

The Cryosphere ◽

10.5194/tc-6-255-2012 ◽

2012 ◽

Vol 6 (2) ◽

pp. 255-272 ◽

Cited By ~ 45

Author(s):

M. M. Helsen ◽

R. S. W. van de Wal ◽

M. R. van den Broeke ◽

W. J. van de Berg ◽

J. Oerlemans

Keyword(s):

Mass Balance ◽

Climate Models ◽

Climate Model ◽

Regional Climate ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Lapse Rate ◽

Surface Mass Balance ◽

Surface Mass ◽

Temperature Lapse Rate

Abstract. It is notoriously difficult to couple surface mass balance (SMB) results from climate models to the changing geometry of an ice sheet model. This problem is traditionally avoided by using only accumulation from a climate model, and parameterizing the meltwater run-off as a function of temperature, which is often related to surface elevation (Hs). In this study, we propose a new strategy to calculate SMB, to allow a direct adjustment of SMB to a change in ice sheet topography and/or a change in climate forcing. This method is based on elevational gradients in the SMB field as computed by a regional climate model. Separate linear relations are derived for ablation and accumulation, using pairs of Hs and SMB within a minimum search radius. The continuously adjusting SMB forcing is consistent with climate model forcing fields, also for initially non-glaciated areas in the peripheral areas of an ice sheet. When applied to an asynchronous coupled ice sheet – climate model setup, this method circumvents traditional temperature lapse rate assumptions. Here we apply it to the Greenland Ice Sheet (GrIS). Experiments using both steady-state forcing and glacial-interglacial forcing result in realistic ice sheet reconstructions.

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A data-driven approach for assessing ice-sheet mass balance in space and time

Annals of Glaciology ◽

10.3189/2015aog70a021 ◽

2015 ◽

Vol 56 (70) ◽

pp. 175-183 ◽

Cited By ~ 7

Author(s):

Andrew Zammit-Mangion ◽

Jonathan L. Bamber ◽

Nana W. Schoen ◽

Jonathan C. Rougier

Keyword(s):

Mass Balance ◽

Climate Models ◽

Climate Model ◽

Numerical Models ◽

Regional Climate ◽

Ice Sheet ◽

Surface Mass ◽

Smoothing Methods ◽

Combination Methods ◽

Wide Range

AbstractCombinations of various numerical models and datasets with diverse observation characteristics have been used to assess the mass evolution of ice sheets. As a consequence, a wide range of estimates have been produced using markedly different methodologies, data, approximation methods and model assumptions. Current attempts to reconcile these estimates using simple combination methods are unsatisfactory, as common sources of errors across different methodologies may not be accurately quantified (e.g. systematic biases in models). Here we provide a general approach which deals with this issue by considering all data sources simultaneously, and, crucially, by reducing the dependence on numerical models. The methodology is based on exploiting the different space–time characteristics of the relevant ice-sheet processes, and using statistical smoothing methods to establish the causes of the observed change. In omitting direct dependence on numerical models, the methodology provides a novel means for assessing glacio-isostatic adjustment and climate models alike, using remote-sensing datasets. This is particularly advantageous in Antarctica, where in situ measurements are difficult to obtain. We illustrate the methodology by using it to infer Antarctica’s mass trend from 2003 to 2009 and produce surface mass-balance anomaly estimates to validate the RACMO2.1 regional climate model.

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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

<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>

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Reconstruction and Disintegration of Ice Sheets for the Climap 18000 And 125000 Years b.p. Experiments: Results

Journal of Glaciology ◽

10.3189/s0022143000015069 ◽

1979 ◽

Vol 24 (90) ◽

pp. 495-496

Author(s):

G. H. Denton ◽

T. J. Hughes ◽

J. L. Fastook ◽

D. H. Schilling ◽

C. S. Lingle

Keyword(s):

Northern Hemisphere ◽

Land Surface ◽

Ice Sheets ◽

Ice Sheet ◽

Recursive Formula ◽

Ice Age ◽

Flow Lines ◽

Bed Topography ◽

Surface Areas ◽

Basal Shear

AbstractLate-Wisconsin ice sheets were reconstructed for the CLIMAP 18000 years b.p. experiment. This experiment modeled the ice-age steady-state climate using boundary conditions that differed from present ones mainly in Earth-surface albedos, sea-surface areas, and land-surface topography. These required determinations of the area, volume, and elevation of Late Wisconsin ice sheets. An initial-value finite-difference numerical model for ice-sheet reconstruction was developed from a recursive formula which gave ice thickness for known variations of bed topography and theoretical variations of basal shear stress. Ice thicknesses were calculated in 50 km to 100 km steps along flow lines from margins to domes of late-Wisconsin ice sheets. We assumed that terrestrial margins were along the furthermost moraines, marine margins were along the present 500 m bathymetric contour, domes were centers of maximum post-glacial isostatic rebound, and flow lines were along glacial lineations (eskers, striations, drumlins, etc.) connecting margins to domes. At various locations ice-sheet margins were verified by dated moraines for terrestrial margins and Egga-type moraines for marine margins. Ice-sheet elevations and thicknesses were contoured from profiles reconstructed for 40 Antarctic flow lines and 137 Northern Hemisphere flow lines for a maximum ice-sheet extent, and 86 Northern Hemisphere flow lines for a minimum ice-sheet extent.

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Soil moisture–atmosphere feedback dominates land carbon uptake variability

Nature ◽

10.1038/s41586-021-03325-5 ◽

2021 ◽

Vol 592 (7852) ◽

pp. 65-69

Author(s):

Vincent Humphrey ◽

Alexis Berg ◽

Philippe Ciais ◽

Pierre Gentine ◽

Martin Jung ◽

...

Keyword(s):

Soil Moisture ◽

Land Surface ◽

Climate Models ◽

Climate Model ◽

Dominant Role ◽

Vapour Pressure Deficit ◽

Terrestrial Ecosystems ◽

Surface Model ◽

Carbon Uptake ◽

Model Simulations

AbstractYear-to-year changes in carbon uptake by terrestrial ecosystems have an essential role in determining atmospheric carbon dioxide concentrations1. It remains uncertain to what extent temperature and water availability can explain these variations at the global scale2–5. Here we use factorial climate model simulations6 and show that variability in soil moisture drives 90 per cent of the inter-annual variability in global land carbon uptake, mainly through its impact on photosynthesis. We find that most of this ecosystem response occurs indirectly as soil moisture–atmosphere feedback amplifies temperature and humidity anomalies and enhances the direct effects of soil water stress. The strength of this feedback mechanism explains why coupled climate models indicate that soil moisture has a dominant role4, which is not readily apparent from land surface model simulations and observational analyses2,5. These findings highlight the need to account for feedback between soil and atmospheric dryness when estimating the response of the carbon cycle to climatic change globally5,7, as well as when conducting field-scale investigations of the response of the ecosystem to droughts8,9. Our results show that most of the global variability in modelled land carbon uptake is driven by temperature and vapour pressure deficit effects that are controlled by soil moisture.

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Remapping of Greenland ice sheet surface mass balance anomalies for large ensemble sea-level change projections

The Cryosphere ◽

10.5194/tc-14-1747-2020 ◽

2020 ◽

Vol 14 (6) ◽

pp. 1747-1762 ◽

Cited By ~ 2

Author(s):

Heiko Goelzer ◽

Brice P. Y. Noël ◽

Tamsin L. Edwards ◽

Xavier Fettweis ◽

Jonathan M. Gregory ◽

...

Keyword(s):

Mass Balance ◽

Sea Level ◽

Climate Models ◽

Climate Model ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Sea Level Change ◽

Surface Mass Balance ◽

Surface Mass ◽

Level Change

Abstract. Future sea-level change projections with process-based stand-alone ice sheet models are typically driven with surface mass balance (SMB) forcing derived from climate models. In this work we address the problems arising from a mismatch of the modelled ice sheet geometry with the geometry used by the climate model. We present a method for applying SMB forcing from climate models to a wide range of Greenland ice sheet models with varying and temporally evolving geometries. In order to achieve that, we translate a given SMB anomaly field as a function of absolute location to a function of surface elevation for 25 regional drainage basins, which can then be applied to different modelled ice sheet geometries. The key feature of the approach is the non-locality of this remapping process. The method reproduces the original forcing data closely when remapped to the original geometry. When remapped to different modelled geometries it produces a physically meaningful forcing with smooth and continuous SMB anomalies across basin divides. The method considerably reduces non-physical biases that would arise by applying the SMB anomaly derived for the climate model geometry directly to a large range of modelled ice sheet model geometries.

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The phase space of last glacial inception for the Northern Hemisphere from coupled ice and climate modelling

10.5194/cp-2020-1 ◽

2020 ◽

Cited By ~ 1

Author(s):

Taimaz Bahadory ◽

Lev Tarasov ◽

Heather Andres

Keyword(s):

North America ◽

Northern Hemisphere ◽

Climate Model ◽

Ice Sheet ◽

Future Climate Change ◽

Climate Modelling ◽

Ice Growth ◽

Last Glacial ◽

Ice Volume ◽

Denmark Strait

Abstract. We present an ensemble of Last Glacial Inception (LGI) simulations for the Northern Hemisphere that largely captures inferred ice volume changes within proxy uncertainties. This ensemble was performed with LCice 1.0, a coupled ice sheet and climate model, varying parameters of both climate and ice sheet components, as well as the coupling between them. Certain characteristics of the spatio-temporal pattern of ice growth and subsequent retreat in both North America (NA) and Eurasia (EA) are sensitive to parameter changes, especially with respect to regional rates of ice growth and retreat. We find that the initial inception of ice over NA and EA is best characterized by the nucleation of ice at high latitude and high elevation sites. Subsequent spreading and merger along with large-scale conversion of snow fields dominate in different sectors. The latter plays an important role in the merging of eastern and western ice regions in NA. The inception peak ice volume in the ensemble occurs approximately at 111 ka and therefore lags the summer 60° N insolation minimum by more than 3 kyr. Ice volumes consistently peak earlier over EA than NA. The inception peak in North America is characterized by a merged Laurentide and Cordilleran ice sheet, with Davis Strait covered in ice in 80 % of simulations. Ice also bridges Greenland and Iceland in all runs by 114 ka and therefore blocks Denmark Strait. This latter feature would thereby divert the East Greenland Current and Denmark Strait overflow and thereby potentially have a significant impact on ocean circulation. The Eurasian ice sheet at its inception peak varies across ensemble runs between a continuous ice sheet to multiple smaller ice caps. In both continents, the colder high latitudes (Ellsmere and Svalbard) tend to grow ice through the entire simulation (to 102 ka), while lower latitudes lose ice after 110 ka. We find temperature decreases over the initial phases of the inception lead to the expansion of NA ice sheet area, and that subsequent precipitation increases contribute to its thickening. EA ice sheet area also expands with decreasing temperatures, but sea ice limits any increases in precipitation, leading to an earlier retreat away from the EA maximum ice sheet volume. We also examine the extent to which the capture of both LGI ice growth and retreat constrains the coupled ice/climate model sensitivity to changing atmospheric pCO2. For a standard transient climate response experiment (1 % increase in pCO2 until doubled), warming ranges between 0.6–2.0 °C for our initial set of 500 simulations without LGI constraint. The warming is reduced to 0.7–1.4 °C for the 55 member ensemble that captures both LGI ice growth and retreat. This therefore underlines the potential value of fully coupled ice/climate modelling of last glacial inception to constrain future climate change.

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