The darkening of the Greenland ice sheet: trends, drivers and projections (1981–2100)

Abstract. The surface energy balance and meltwater production of the Greenland ice sheet (GrIS) are modulated by snow and ice albedo through the amount of absorbed solar radiation. Here we show, using spaceborne multispectral data collected during the three decades from 1981 to 2012, that summertime surface albedo over the GrIS decreased at a statistically significant (99 %) rate of 0.02 decade-1 between 1996 and 2012. The negative trend is confined to the regions of the GrIS that undergo melting in summer with the dry-snow zone showing no trend. The period 1981–1996 showed no statistically significant trend. The analysis of the outputs of a regional climate model indicates that the drivers of the observed albedo decrease is imputable to a combination of increased near-surface temperatures, which enhanced melt and promoted growth in snow grain size and the expansion of bare ice areas, as well as by trends in light-absorbing impurities on the snow and ice surfaces. Neither aerosol models nor in situ observations indicate increasing trends in impurities in the atmosphere over Greenland, suggesting that their apparent increase in snow and ice might be related to the exposure of a "dark band" of dirty ice and to the consolidation of impurities at the surface with melt. Albedo projections through the end of the century under different warming scenarios consistently point to continued darkening, with albedo anomalies in 2100 averaged over the whole ice sheet lower than in 2000 by 0.08, driven solely by a warming climate. Future darkening is likely underestimated because of known underestimates in projected melting and because the model albedo scheme does not currently include light-absorbing impurities and the effect of biological activity, which themselves have a positive feedback, leading to increased melting, grain growth and darkening.

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The darkening of the Greenland ice sheet: trends, drivers, and projections (1981–2100)

The Cryosphere ◽

10.5194/tc-10-477-2016 ◽

2016 ◽

Vol 10 (2) ◽

pp. 477-496 ◽

Cited By ~ 81

Author(s):

Marco Tedesco ◽

Sarah Doherty ◽

Xavier Fettweis ◽

Patrick Alexander ◽

Jeyavinoth Jeyaratnam ◽

...

Keyword(s):

Ice Sheet ◽

Greenland Ice Sheet ◽

Aerosol Deposition ◽

Near Surface ◽

Multispectral Data ◽

Warming Climate ◽

Air Temperatures ◽

Increasing Trends ◽

Snow And Ice

Abstract. The surface energy balance and meltwater production of the Greenland ice sheet (GrIS) are modulated by snow and ice albedo through the amount of absorbed solar radiation. Here we show, using space-borne multispectral data collected during the 3 decades from 1981 to 2012, that summertime surface albedo over the GrIS decreased at a statistically significant (99 %) rate of 0.02 decade−1 between 1996 and 2012. Over the same period, albedo modelled by the Modèle Atmosphérique Régionale (MAR) also shows a decrease, though at a lower rate ( ∼ −0.01 decade−1) than that obtained from space-borne data. We suggest that the discrepancy between modelled and measured albedo trends can be explained by the absence in the model of processes associated with the presence of light-absorbing impurities. The negative trend in observed albedo is confined to the regions of the GrIS that undergo melting in summer, with the dry-snow zone showing no trend. The period 1981–1996 also showed no statistically significant trend over the whole GrIS. Analysis of MAR outputs indicates that the observed albedo decrease is attributable to the combined effects of increased near-surface air temperatures, which enhanced melt and promoted growth in snow grain size and the expansion of bare ice areas, and to trends in light-absorbing impurities (LAI) on the snow and ice surfaces. Neither aerosol models nor in situ and remote sensing observations indicate increasing trends in LAI in the atmosphere over Greenland. Similarly, an analysis of the number of fires and BC emissions from fires points to the absence of trends for such quantities. This suggests that the apparent increase of LAI in snow and ice might be related to the exposure of a "dark band" of dirty ice and to increased consolidation of LAI at the surface with melt, not to increased aerosol deposition. Albedo projections through to the end of the century under different warming scenarios consistently point to continued darkening, with albedo anomalies averaged over the whole ice sheet lower by 0.08 in 2100 than in 2000, driven solely by a warming climate. Future darkening is likely underestimated because of known underestimates in modelled melting (as seen in hindcasts) and because the model albedo scheme does not currently include the effects of LAI, which have a positive feedback on albedo decline through increased melting, grain growth, and darkening.

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Evaluation of a new snow albedo scheme in RACMO2 for the Greenland ice sheet

10.5194/egusphere-egu2020-15261 ◽

2020 ◽

Author(s):

Christiaan van Dalum ◽

Willem Jan van de Berg ◽

Stef Lhermitte ◽

Michiel van den Broeke

Keyword(s):

Climate Models ◽

Climate Model ◽

Regional Climate ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Atmospheric Conditions ◽

Surface Mass ◽

Snow Albedo ◽

In Situ Data ◽

Snow And Ice

<p>Snow and ice albedo schemes in present day climate models often lack a sophisticated radiation penetration scheme and are limited to a broadband albedo. In this study, we evaluate a new snow albedo scheme in the regional climate model RACMO2 that uses the two-stream radiative transfer in snow model TARTES and the spectral-to-narrowband albedo module SNOWBAL for the Greenland ice sheet. Additionally, the bare ice albedo parameterization has been updated. The snow and ice albedo output of the updated version of RACMO2, referred to as RACMO2.3p3, is evaluated using PROMICE and K-transect in-situ data and MODIS remote-sensing observations. Generally, the RACMO2.3p3 albedo is in very good agreement with satellite observations, leading to a domain-averaged bias of only -0.012. Some discrepancies are, however, observed for regions close to the ice margin. Compared to the previous iteration RACMO2.3p2, the albedo of RACMO2.3p3 is considerably higher in the bare ice zone during the ablation season, as atmospheric conditions now alter the bare ice albedo. For most other regions, however, the albedo of RACMO2.3p3 is lower due to spectral effects, radiation penetration, snow metamorphism or a delayed firn-ice transition. Furthermore, a white-out effect during cloudy conditions is captured and the snow albedo shows a low sensitivity to low soot concentrations. The surface mass balance of RACMO2.3p3 compares well with observations. Subsurface heating, however, now leads to increased melt and refreezing in south Greenland, changing the snow structure.</p>

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River inundation suggests ice-sheet runoff retention

Journal of Glaciology ◽

10.3189/2015jog15j012 ◽

2015 ◽

Vol 61 (228) ◽

pp. 776-788 ◽

Cited By ~ 10

Author(s):

Irina Overeem ◽

Benjamin Hudson ◽

Ethan Welty ◽

Andreas Mikkelsen ◽

Jonathan Bamber ◽

...

Keyword(s):

River Discharge ◽

Climate Model ◽

Regional Climate ◽

Ice Sheet ◽

Indirect Evidence ◽

Greenland Ice Sheet ◽

Warming Trend ◽

Global Ocean ◽

Total Discharge

AbstractThe Greenland ice sheet is experiencing dramatic melt that is likely to continue with rapid Arctic warming. However, the proportion of meltwater stored before reaching the global ocean remains difficult to quantify. We use NASA MODIS surface reflectance data to estimate river discharge from two West Greenland rivers – the Watson River near Kangerlussuaq and the Naujat Kuat River near Nuuk – over the summers of 2000–12. By comparison with in situ river discharge observations, ‘inundation–discharge’ relations were constructed for both rivers. MODIS-based total annual discharges agree well with total discharge estimated from in situ observations (86% of summer discharge in 2009 to 96% in 2011 at the Watson River, and 106% of total discharge in 2011 to 104% in 2012 at the Naujat Kuat River). We find, however, that a time-lapse camera, deployed at the Watson River in summer 2012, better captures the variations in observed discharge, benefiting from fewer data gaps due to clouds. The MODIS-derived estimates indicate that summer discharge has not significantly increased over the last decade, despite a strong warming trend. Also, meltwater runoff estimates derived from the regional climate model RACMO2/GR for the drainage basins are higher than our reconstructions of river discharge. These results provide indirect evidence for a considerable component of water storage within the glacio-hydrological system.

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Estimating the Greenland ice sheet surface mass balance contribution to future sea level rise using the regional atmospheric climate model MAR

The Cryosphere ◽

10.5194/tc-7-469-2013 ◽

2013 ◽

Vol 7 (2) ◽

pp. 469-489 ◽

Cited By ~ 224

Author(s):

X. Fettweis ◽

B. Franco ◽

M. Tedesco ◽

J. H. van Angelen ◽

J. T. M. Lenaerts ◽

...

Keyword(s):

Mass Balance ◽

Sea Level Rise ◽

Sea Level ◽

Climate Model ◽

Regional Climate ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Surface Mass Balance ◽

Near Surface ◽

Surface Mass

Abstract. To estimate the sea level rise (SLR) originating from changes in surface mass balance (SMB) of the Greenland ice sheet (GrIS), we present 21st century climate projections obtained with the regional climate model MAR (Modèle Atmosphérique Régional), forced by output of three CMIP5 (Coupled Model Intercomparison Project Phase 5) general circulation models (GCMs). Our results indicate that in a warmer climate, mass gain from increased winter snowfall over the GrIS does not compensate mass loss through increased meltwater run-off in summer. Despite the large spread in the projected near-surface warming, all the MAR projections show similar non-linear increase of GrIS surface melt volume because no change is projected in the general atmospheric circulation over Greenland. By coarsely estimating the GrIS SMB changes from GCM output, we show that the uncertainty from the GCM-based forcing represents about half of the projected SMB changes. In 2100, the CMIP5 ensemble mean projects a GrIS SMB decrease equivalent to a mean SLR of &plus;4 &pm; 2 cm and &plus;9 &pm; 4 cm for the RCP (Representative Concentration Pathways) 4.5 and RCP 8.5 scenarios respectively. These estimates do not consider the positive melt–elevation feedback, although sensitivity experiments using perturbed ice sheet topographies consistent with the projected SMB changes demonstrate that this is a significant feedback, and highlight the importance of coupling regional climate models to an ice sheet model. Such a coupling will allow the assessment of future response of both surface processes and ice-dynamic changes to rising temperatures, as well as their mutual feedbacks.

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Impact of updated radiative transfer scheme in snow and ice in RACMO2.3p3 on the surface mass and energy budget of the Greenland ice sheet

The Cryosphere ◽

10.5194/tc-15-1823-2021 ◽

2021 ◽

Vol 15 (4) ◽

pp. 1823-1844

Author(s):

Christiaan T. van Dalum ◽

Willem Jan van de Berg ◽

Michiel R. van den Broeke

Keyword(s):

Radiative Transfer ◽

Energy Budget ◽

Climate Model ◽

Regional Climate ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Internal Heating ◽

Transfer Scheme ◽

Surface Mass ◽

Snow And Ice

Abstract. Radiative transfer in snow and ice is often not modeled explicitly in regional climate models. In this study, we evaluate a new englacial radiative transfer scheme and assess the surface mass and energy budget for the Greenland ice sheet in the latest version of the regional climate model RACMO2, version 2.3p3. We also evaluate the modeled (sub)surface temperature and melt, as radiation penetration now enables internal heating. The results are compared to the previous model version and are evaluated against stake measurements and automatic weather station data of the K-transect and PROMICE projects. In addition, subsurface snow temperature profiles are compared at the K-transect, Summit, and southeast Greenland. The surface mass balance is in good agreement with observations, with a mean bias of −31 mm w.e. yr−1 (−2.67 %), and only changes considerably with respect to the previous RACMO2 version around the ice margins and near the percolation zone. Melt and refreezing, on the other hand, are changed more substantially in various regions due to the changed albedo representation, subsurface energy absorption, and meltwater percolation. Internal heating leads to higher snow temperatures in summer, in agreement with observations, and introduces a shallow layer of subsurface melt. Hence, this study shows the consequences and necessity of radiative transfer in snow and ice for regional climate modeling of the Greenland ice sheet.

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Drifting snow climate of the Greenland ice sheet: a study with a regional climate model

The Cryosphere Discussions ◽

10.5194/tcd-6-1611-2012 ◽

2012 ◽

Vol 6 (3) ◽

pp. 1611-1635 ◽

Cited By ~ 2

Author(s):

J. T. M. Lenaerts ◽

M. R. van den Broeke ◽

J. H. van Angelen ◽

E. van Meijgaard ◽

S. J. Déry

Keyword(s):

Wind Speed ◽

Regional Climate Model ◽

Climate Model ◽

Regional Climate ◽

Regional Scale ◽

Winter Season ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Near Surface ◽

Drifting Snow

Abstract. This paper presents the drifting snow climate of the Greenland ice sheet, using output from a high-resolution (~11 km) regional climate model (RACMO2). Because reliable direct observations of drifting snow do not exist, we evaluate the modeled near-surface climate instead, using Automatic Weather Station (AWS) observations from the K-transect and find that RACMO2 realistically simulates near-surface wind speed and relative humidity, two variables that are important for drifting snow. Integrated over the ice sheet, drifting snow sublimation (SUds) equals 24 ± 3 Gt yr−1, and is significantly larger than surface sublimation (SUs, 16 ± 2 Gt yr−1). SUds strongly varies between seasons, and is only important in winter, when surface sublimation and runoff are small. A rapid transition exists between the winter season, when snowfall and SUds are important, and the summer season, when snowmelt is significant, which increases surface snow density and thereby limits drifting snow processes. Drifting snow erosion (ERds) is only important on a regional scale. In recent decades, following decreasing wind speed and rising near-surface temperatures, SUds exhibits a negative trend (0.1 ± 0.1 Gt yr−1), which is compensated by an increase in SUs of similar magnitude.

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Climate of the Greenland ice sheet using a high-resolution climate model – Part 2: Near-surface climate and energy balance

The Cryosphere Discussions ◽

10.5194/tcd-4-603-2010 ◽

2010 ◽

Vol 4 (2) ◽

pp. 603-639 ◽

Cited By ~ 4

Author(s):

J. Ettema ◽

M. R. van den Broeke ◽

E. van Meijgaard ◽

W. J. van de Berg

Keyword(s):

High Resolution ◽

Large Scale ◽

Climate Model ◽

Regional Climate ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Katabatic Wind ◽

Surface Cooling ◽

Near Surface ◽

Surface Climate

Abstract. The near-surface climate of the Greenland ice sheet is characterized by persistent katabatic winds and quasi-permanent temperature deficit. Using a high resolution (11 km) regional climate model allows for detailed study of the spatial variability in these phenomena and the underlying atmospheric processes. The near-surface temperature distribution over the ice sheet is clearly affected by elevation, latitude, large scale advection, meso-scale topographic features and the occurrence of summer melt. The lowest annual temperatures of −30.5 °C are found north of the highest elevations of the GrIS, whereas the lowest southern margins are warmest (−3.5 °C). Over the ice sheet, a persistent katabatic wind system develops due to radiative surface cooling and the gently slope of the surface. The strongest wind speeds are seen in the northeast where the strong large scale winds, low cloud cover and concave surface force a continuous supply of cold air, which enhances the katabatic forcing. The radiative cooling of the surface is controlled by the net longwave emission and transport of heat towards the surface by turbulence. In summer this mechanism is much weaker, leading to less horizontal variability in near-surface temperatures and wind speed.

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Brief communication: Interest of a regional climate model against ERA5 to simulate the near-surface climate of the Greenland ice sheet

10.5194/tc-2019-96 ◽

2019 ◽

Author(s):

Alison Delhasse ◽

Christoph Kittel ◽

Charles Amory ◽

Stefan Hofer ◽

Xavier Fettweis

Keyword(s):

Climate Models ◽

Climate Model ◽

Regional Climate ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Regional Climate Models ◽

Near Surface ◽

Weather Forecasts ◽

Surface Climate ◽

Medium Range

Abstract. The ERA5 reanalysis, recently made available by the European Centre for Medium-Range Weather Forecasts (ECMWF), is a new reanalysis product at a higher resolution which will replace ERA-Interim, considered to be the best reanalysis over Greenland until now. However, so far very little is known about the performance of ERA5 when compared to ERA-Interim over the Greenland Ice Sheet (GrIS). This study shows (1) that ERA5 improves not significantly the ERA-Interim comparison with near-surface climate observations over GrIS, (2) polar regional climate models (e.g. MAR) are still a useful tool to study the GrIS climate compared to ERA5, in particular in summer, and (3) that MAR results are not sensitive to the forcing used at its lateral boundaries (ERA5 or ERA-Interim).

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Drifting snow climate of the Greenland ice sheet: a study with a regional climate model

The Cryosphere ◽

10.5194/tc-6-891-2012 ◽

2012 ◽

Vol 6 (4) ◽

pp. 891-899 ◽

Cited By ~ 49

Author(s):

J. T. M. Lenaerts ◽

M. R. van den Broeke ◽

J. H. van Angelen ◽

E. van Meijgaard ◽

S. J. Déry

Keyword(s):

Wind Speed ◽

Regional Climate Model ◽

Climate Model ◽

Regional Climate ◽

Regional Scale ◽

Winter Season ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Near Surface ◽

Drifting Snow

Abstract. This paper presents the drifting snow climate of the Greenland ice sheet, using output from a high-resolution (∼11 km) regional climate model. Because reliable direct observations of drifting snow do not exist, we evaluate the modeled near-surface climate instead, using automatic weather station (AWS) observations from the K-transect and find that RACMO2 realistically simulates near-surface wind speed and relative humidity, two variables that are important for drifting snow. Integrated over the ice sheet, drifting snow sublimation (SUds) equals 24 &pm; 3 Gt yr−1, and is significantly larger than surface sublimation (SUs, 16 &pm; 2 Gt yr−1). SUds strongly varies between seasons, and is only important in winter, when surface sublimation and runoff are small. A rapid transition exists between the winter season, when snowfall and SUds are important, and the summer season, when snowmelt is significant, which increases surface snow density and thereby limits drifting snow processes. Drifting snow erosion (ERds) is only important on a regional scale. In recent decades, following decreasing wind speed and rising near-surface temperatures, SUds exhibits a negative trend (0.1 &pm; 0.1 Gt yr−1), which is compensated by an increase in SUs of similar magnitude.

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