scholarly journals Greenland ice sheet albedo feedback: thermodynamics and atmospheric drivers

2012 ◽  
Vol 6 (4) ◽  
pp. 821-839 ◽  
Author(s):  
J. E. Box ◽  
X. Fettweis ◽  
J. C. Stroeve ◽  
M. Tedesco ◽  
D. K. Hall ◽  
...  
Keyword(s):  
Air Temperature ◽  
Negative Feedback ◽  
Ice Sheet ◽  
Surface Air Temperature ◽  
Greenland Ice Sheet ◽  
Dominant Factor ◽  
Water Runoff ◽  
Albedo Feedback ◽  
Ablation Area ◽  
Surface Melt

Abstract. Greenland ice sheet mass loss has accelerated in the past decade responding to combined glacier discharge and surface melt water runoff increases. During summer, absorbed solar energy, modulated at the surface primarily by albedo, is the dominant factor governing surface melt variability in the ablation area. Using satellite-derived surface albedo with calibrated regional climate modeled surface air temperature and surface downward solar irradiance, we determine the spatial dependence and quantitative impact of the ice sheet albedo feedback over 12 summer periods beginning in 2000. We find that, while albedo feedback defined by the change in net solar shortwave flux and temperature over time is positive over 97% of the ice sheet, when defined using paired annual anomalies, a second-order negative feedback is evident over 63% of the accumulation area. This negative feedback damps the accumulation area response to warming due to a positive correlation between snowfall and surface air temperature anomalies. Positive anomaly-gauged feedback concentrated in the ablation area accounts for more than half of the overall increase in melting when satellite-derived melt duration is used to define the timing when net shortwave flux is sunk into melting. Abnormally strong anticyclonic circulation, associated with a persistent summer North Atlantic Oscillation extreme since 2007, enabled three amplifying mechanisms to maximize the albedo feedback: (1) increased warm (south) air advection along the western ice sheet increased surface sensible heating that in turn enhanced snow grain metamorphic rates, further reducing albedo; (2) increased surface downward shortwave flux, leading to more surface heating and further albedo reduction; and (3) reduced snowfall rates sustained low albedo, maximizing surface solar heating, progressively lowering albedo over multiple years. The summer net infrared and solar radiation for the high elevation accumulation area approached positive values during this period. Thus, it is reasonable to expect 100% melt area over the ice sheet within another similar decade of warming.

scholarly journals Greenland ice sheet albedo feedback: thermodynamics and atmospheric drivers

2012 ◽  
Vol 6 (1) ◽  
pp. 593-634 ◽  
Author(s):  
J. E. Box ◽  
X. Fettweis ◽  
J. C. Stroeve ◽  
M. Tedesco ◽  
D. K. Hall ◽  
...  
Keyword(s):  
Solar Energy ◽  
Climate Model ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Dominant Factor ◽  
Water Runoff ◽  
Albedo Feedback ◽  
Ablation Area ◽  
Regional Climate Model Output ◽  
Surface Melt

Abstract. Greenland ice sheet mass loss has accelerated in the past decade responding to combined glacier discharge and surface melt water runoff increases. During summer, absorbed solar energy, modulated at the surface primarily by albedo, is the dominant factor governing surface melt variability in the ablation area. Using satellite observations of albedo and melt extent with calibrated regional climate model output, we determine the spatial dependence and quantitative impact of the ice sheet albedo feedback in twelve summer periods beginning in 2000. We find that while the albedo feedback is negative over 70 % of the ice sheet, concentrated in the accumulation area above 1500 m, positive feedback prevailing over the ablation area accounts for more than half of the overall increase in melting. Over the ablation area, year 2010 and 2011 absorbed solar energy was more than twice as large as in years 2000–2004. Anomalous anticyclonic circulation, associated with a persistent summer North Atlantic Oscillation extreme since 2007 enabled three amplifying mechanisms to maximize the albedo feedback: (1) increased warm (south) air advection along the western ice sheet increased surface sensible heating that in turn enhanced snow grain metamorphic rates, further reducing albedo; (2) increased surface downward solar irradiance, leading to more surface heating and further albedo reduction; and (3) reduced snowfall rates sustained low albedo, maximizing surface solar heating, progressively lowering albedo over multiple years. The summer net radiation for the high elevation accumulation area approached positive values during this period.

scholarly journals Ice sheet mass loss caused by dust and black carbon accumulation

2015 ◽  
Vol 9 (2) ◽  
pp. 2563-2596
Author(s):  
T. Goelles ◽  
C. E. Bøggild ◽  
R. Greve
Keyword(s):  
Mass Loss ◽  
Black Carbon ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Carbon Accumulation ◽  
Model Framework ◽  
Ice Dynamics ◽  
Ablation Area ◽  
Ice Surface ◽  
Surface Melt

Abstract. Albedo is the dominating factor governing surface melt variability in the ablation area of ice sheets and glaciers. Aerosols such as mineral dust and black carbon (soot) accumulate on the ice surface and cause a darker surface and therefore a lower albedo. The dominant source of these aerosols in the ablation area is melt-out of englacial material which has been transported via ice flow. The darkening effect on the ice surface is currently not included in sea level projections, and the effect is unknown. We present a model framework which includes ice dynamics, aerosol transport, aerosol accumulation and the darkening effect on ice albedo and its consequences for surface melt. The model is applied to a simplified geometry resembling the conditions of the Greenland ice sheet, and it is forced by several temperature scenarios to quantify the darkening effect of aerosols on future mass loss. The effect of aerosols depends non-linearly on the temperature rise due to the feedback between aerosol accumulation and surface melt. The effect of aerosols in the year 3000 is up to 12% of additional ice sheet volume loss in the warmest scenario.

scholarly journals The implication of nonradiative energy fluxes dominating Greenland ice sheet exceptional ablation area surface melt in 2012

2016 ◽  
Vol 43 (6) ◽  
pp. 2649-2658 ◽  
Author(s):  
Robert S. Fausto ◽  
Dirk As ◽  
Jason E. Box ◽  
William Colgan ◽  
Peter L. Langen ◽  
...  
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Energy Fluxes ◽  
Ablation Area ◽  
Surface Melt

scholarly journals Impact of the melt-albedo feedback on the future evolution of the Greenland Ice Sheet with PISM-dEBM-simple

2021 ◽  
Author(s):  
Maria Zeitz ◽  
Ronja Reese ◽  
Johanna Beckmann ◽  
Uta Krebs-Kanzow ◽  
Ricarda Winkelmann
Keyword(s):  
Energy Balance ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Surface Melting ◽  
Energy Balance Model ◽  
Balance Model ◽  
Albedo Feedback ◽  
Surface Warming ◽  
Ice Surface ◽  
Surface Melt

Abstract. Surface melting of the Greenland Ice Sheet contributes a large amount to current and future sea-level rise. Increased surface melt, algae growth, debris, and dust deposition lower the reflectivity of the ice surface and thereby increase melt rates: the so-called melt-albedo feedback describes this potentially self-sustaining increase in surface melting. Here we present a simplified version of the diurnal Energy Balance Model (dEBM-simple) which is implemented as a surface melt module in the Parallel Ice Sheet Model (PISM). dEBM-simple is a modification of diurnal Energy Balance Model (dEBM), a surface melt scheme of intermediate complexity useful for simulations over centennial to multi-millennial timescales. dEBM-simple is computationally efficient, suitable for standalone ice-sheet modeling and includes a simple representation of the melt-albedo feedback. Using dEBM-simple and PISM, we find that this feedback increases ice loss until 2300 through surface warming by 60 % for the high-emission scenario RCP8.5. With an increase of 90 %, the effect is more pronounced for lower surface warming under RCP2.6. Furthermore, assuming an immediate darkening of the ice surface over all summer months, we estimate an upper bound for this effect to be +70 % in the RCP8.5 scenario and a more than fourfold increase under RCP2.6. With dEBM-simple implemented in PISM, we find that the melt-albedo feedback is an essential contributor to mass loss in dynamic simulations of the Greenland Ice Sheet under future warming.

scholarly journals Positive degree-day factors for ablation on the Greenland ice sheet studied by energy-balance modelling

1995 ◽  
Vol 41 (137) ◽  
pp. 153-160 ◽  
Author(s):  
Roger J. Braithwaite
Keyword(s):  
Energy Balance ◽  
Air Temperature ◽  
Surface Albedo ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Balance Model ◽  
Ablation Area ◽  
Degree Day ◽  
Positive Degree ◽  
Temperature Surface

AbstractIce ablation is related to air temperature by the positive degree-day factor. Variations of the positive degree-day factor in West Greenland are studied using an energy-balance model to simulate ablation under different conditions. Degree-day factors for simulated and measured ice ablation at Nordbogletscher and Qamanârssûp sermia agree well with values around 8 mm d−1 °C−1. Degree-day factors for snow are less than half those for ice. Energy-balance modelling shows that degree-day factors vary with summer mean temperature, surface albedo and turbulence but there is only evidence of large positive degree-day factors at lower temperatures and with low albedo (0.3). The greatest effect of albedo variations (0.3–0.7) is at lower temperatures while variations in turbulence have greater effect at higher temperatures. Current models may underestimate runoff from the Greenland ice sheet by several tenths because they use a degree-day factor for melting ice that is too small for the colder parts of the ice sheet, i.e. the upper ablation area and the northerly margin.

scholarly journals The Greenland ice sheet: modelling the surface mass balance from GCM output with a new statistical downscaling technique

2013 ◽  
Vol 7 (3) ◽  
pp. 3163-3207 ◽  
Author(s):  
M. Geyer ◽  
D. Salas Y Melia ◽  
E. Brun ◽  
M. Dumont
Keyword(s):  
Mass Balance ◽  
Air Temperature ◽  
Statistical Downscaling ◽  
Ice Sheet ◽  
Coupled Model ◽  
Surface Air Temperature ◽  
Greenland Ice Sheet ◽  
Surface Mass Balance ◽  
Near Surface ◽  
Surface Mass

Abstract. The aim of this study is to derive a realistic estimation of the Surface Mass Balance (SMB) of the Greenland ice sheet (GrIS) through statistical downscaling of Global Coupled Model (GCM) outputs. To this end, climate simulations performed with the CNRM-CM5.1 Atmosphere-Ocean GCM within the CMIP5 (Coupled Model Intercomparison Project phase 5) framework are used for the period 1850–2300. From the year 2006, two different emission scenarios are considered (RCP4.5 and RCP8.5). Simulations of SMB performed with the detailed snowpack model Crocus driven by CNRM-CM5.1 surface atmospheric forcings serve as a reference. On the basis of these simulations, statistical relationships between total precipitation, snow-ratio, snowmelt, sublimation and near-surface air temperature are established. This leads to the formulation of SMB variation as a function of temperature variation. Based on this function, a downscaling technique is proposed in order to refine 150 km horizontal resolution SMB output from CNRM-CM5.1 to a 15 km resolution grid. This leads to a much better estimation of SMB along the GrIS margins, where steep topography gradients are not correctly represented at low-resolution. For the recent past (1989–2008), the integrated SMB over the GrIS is respectively 309 and 243 Gt yr–1 for raw and downscaled CNRM-CM5.1. In comparison, the Crocus snowpack model forced with ERA-Interim yields a value of 245 Gt yr–1. The major part of the remaining discrepancy between Crocus and downscaled CNRM-CM5.1 SMB is due to the different snow albedo representation. The difference between the raw and the downscaled SMB tends to increase with near-surface air temperature via an increase in snowmelt.

scholarly journals Positive degree-day factors for ablation on the Greenland ice sheet studied by energy-balance modelling

1995 ◽  
Vol 41 (137) ◽  
pp. 153-160 ◽  
Author(s):  
Roger J. Braithwaite
Keyword(s):  
Energy Balance ◽  
Air Temperature ◽  
Surface Albedo ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Balance Model ◽  
Ablation Area ◽  
Degree Day ◽  
Positive Degree ◽  
Temperature Surface

AbstractIce ablation is related to air temperature by the positive degree-day factor. Variations of the positive degree-day factor in West Greenland are studied using an energy-balance model to simulate ablation under different conditions. Degree-day factors for simulated and measured ice ablation at Nordbogletscher and Qamanârssûp sermia agree well with values around 8 mm d−1°C−1. Degree-day factors for snow are less than half those for ice. Energy-balance modelling shows that degree-day factors vary with summer mean temperature, surface albedo and turbulence but there is only evidence of large positive degree-day factors at lower temperatures and with low albedo (0.3). The greatest effect of albedo variations (0.3–0.7) is at lower temperatures while variations in turbulence have greater effect at higher temperatures. Current models may underestimate runoff from the Greenland ice sheet by several tenths because they use a degree-day factor for melting ice that is too small for the colder parts of the ice sheet, i.e. the upper ablation area and the northerly margin.

scholarly journals Response of the Energy Balance on the Margin of the Greenland Ice Sheet to Temperature Changes

1990 ◽  
Vol 36 (123) ◽  
pp. 217-221 ◽  
Author(s):  
Roger J. Braithwaite ◽  
Ole B. Olesen
Keyword(s):  
Heat Flux ◽  
Energy Balance ◽  
Air Temperature ◽  
Sensible Heat Flux ◽  
Ice Sheet ◽  
Temperature Response ◽  
Greenland Ice Sheet ◽  
Energy Balance Model ◽  
Balance Model ◽  
Sensible Heat

AbstractDaily ice ablation on two outlet glaciers from the Greenland ice sheet, Nordbogletscher (1979–83) and Qamanârssûp sermia (1980–86), is related to air temperature by a linear regression equation. Analysis of this ablation-temperature equation with the help of a simple energy-balance model shows that sensible-heat flux has the greatest temperature response and accounts for about one-half of the temperature response of ablation. Net radiation accounts for about one-quarter of the temperature response of ablation, and latent-heat flux and errors account for the remainder. The temperature response of sensible-heat flux at QQamanârssûp sermia is greater than at Nordbogletscher mainly due to higher average wind speeds. The association of high winds with high temperatures during Föhn events further increases sensible-heat flux. The energy-balance model shows that ablation from a snow surface is only about half that from an ice surface at the same air temperature.

scholarly journals Seasonal variability in the dynamics of marine-terminating outlet glaciers in Greenland

2010 ◽  
Vol 56 (198) ◽  
pp. 601-613 ◽  
Author(s):  
Ian M. Howat ◽  
Jason E. Box ◽  
Yushin Ahn ◽  
Adam Herrington ◽  
Ellyn M. McFadden
Keyword(s):  
Ice Sheet ◽  
Drainage System ◽  
Surface Air Temperature ◽  
Greenland Ice Sheet ◽  
Flow Speed ◽  
High Temporal Resolution ◽  
Sea Ice Concentration ◽  
Seasonal Behavior ◽  
Near Surface ◽  
Front Position

AbstractRecent studies indicate that the dynamics of fast-flowing, marine-terminating outlet glaciers of the Greenland ice sheet may be sensitive to climate and ocean forcing on sub-annual timescales. Observations of seasonal behavior of these glaciers at such high temporal resolution, however, are currently few. Here we present observations of front position, flow speed, near-surface air temperature and ocean conditions for six large marine-terminating glaciers in the Uummannaq region of West Greenland, to investigate controls on short-term glacier dynamics. As proposed by other studies, we find that seasonal front advance and retreat correlates with the formation and disappearance of an ice melange. Our data suggest that high sea-surface temperature, anomalously low sea-ice concentration and reduced melange formation in early 2003 have triggered multi-year retreat of several glaciers in the study area, which is consistent with other regions in Greenland. Of the stable glaciers, only Rink Isbræ exhibits a seasonal speed variation that correlates with variations in front position, with the others undergoing mid-summer deceleration that indicates the effects of subglacial meltwater discharge and drainage system evolution. Drainage of supraglacial lakes and water-filled crevasses results in substantial decreases in speed (40–60%) on fast-flowing glaciers. Our results demonstrate that attempts to model ice-sheet evolution must take into account short-timescale flow dynamics resulting from drainage events and oceanographic conditions.

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