0
Recent breakthrough in including

ice sheets in climate models
and the challenges ahead
Miren Vizcaino
Dep. Geoscience and...
Greenland and Antarctic ice
Mean since 1992
sheets are losing mass 0.59 ± 0.20 mm yr
•  In response to both
atmospheric an...
Ice sheets also modify climate
(interactive) locally & globally
Through changes in
•  Snow albedo: couples atmosphere and ...
Modeling climate

ice interaction

Total mass budget= Surface Mass Balance – ice discharge to ocean
	

Precipitation
Tempe...
State of the art
•  Very few AOGCMs have been coupled to ice sheet models
(Ridley et al. 2005, Vizcaino et al. 2008,2010)
...
Challenges in coupling ice sheet
and global climate models
•  Resolution
•  Spatial: AOGCMs have resolution of ~100 km. Ic...
The SMB challenge
•  High Surface Mass Balance gradients at
ice sheet margins (steep topography)

kg m-2 yr-1

Until very ...
Ice

climate in RCMs vs. GCMs

Global climate
models

RCMs) Global
climate

Regional
climate models
Lateral
Forcing

Ice s...
Recent break-through:
first realistic SMB from global climate
model
•  Model is the Community Earth System Model (CESM)
• ...
CESM compares well (r=0.80) with in-situ
observations from N=475 stations
1960-2005 SMB from CESM downscaled at 5 km & fro...
CESM compares well with RCMs
SMB>0

1960-2005 SMB (kg m-2 yr-1)
(standard deviation in
parenthesis)

SMB = PREC-RU-SU
RU=M...
Intra-annual mass evolution compares well
with gravimetry data (GRACE)
55

7
6

CESM seasonal cycle of snowmelt, bare ice ...
The recipe for a good SMB
1.  Realistic atmospheric forcing (radiation, wind, humidity)
2.  Explicit simulation of snow pr...
57

Explicit albedo simulation
At melt season
peak (July)

Before melt
season (April)

a

b

c

0.9
0.825
0.8
0.7
0.6
0.5
...
GrIS SMB Projections up to 2100
with CESM
Following high-forcing scenario RCP8.5

Challenge the future

15
Temperature change under RCP8.5
Annual, 2080-99 minus 1980-99 (K)

Summer, 2080-99 minus 1980-99 (K)
b!
Greenland:
+4.1 K
...
Change in surface fluxes (RCP8.5)
Wm-2

2080-99 minus 1980-99

(Only significant anomalies)

albedo

• 
• 
• 
• 
• 
SWd!

...
Change in integrated SMB terms

(Gt yr-1)

SMB = PREC-RUNOFF-SUBLIMATION
RUNOFF=MELT+RAIN-Refreezing
(standard deviation i...
New equilibrium line ~500 m higher
SMB>0

1980-99!

kg m-2 yr-1

2080-99!

SMB<0

• 
• 
• 
• 

Ablation area increases fro...
Summary
•  Ice sheets are not yet interactive components of most
global climate models
•  Major challenges come from diffe...
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Miren sympo17oct13

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On 17/10/2013 TU Delft Climate Institute organised the symposium The Greenland and Antarctic ice sheets: present, future, and unknowns. This is one of the four presentations given there.
http://www.tudelft.nl/nl/actueel/agenda/event/detail/symposium-tu-delft-climate-institute-17th-october-2013/

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Transcript of "Miren sympo17oct13"

  1. 1. Recent breakthrough in including ice sheets in climate models and the challenges ahead Miren Vizcaino Dep. Geoscience and Remote Sensing, Delft University of Technology "Icebergs from Jakobshavn Isbrae”, courtesy of Mark Drinkwater, ESA Challenge the future 1
  2. 2. Greenland and Antarctic ice Mean since 1992 sheets are losing mass 0.59 ± 0.20 mm yr •  In response to both atmospheric and ocean forcing •  Several surface melt extremes over GrIS in the last two decades •  Ocean melt reduces buttressing 360 Gt= 1 mm of AIS & GIS grounded ice A Shepherd et al. Science 2012;338:1183-1189 Challenge the future 2 −1
  3. 3. Ice sheets also modify climate (interactive) locally & globally Through changes in •  Snow albedo: couples atmosphere and SMB, specially during melt season •  Topography: •  Elevation effect (thermodynamical): temperature decreases with elevation •  Local climate: katabatic winds, clouds, orographic forcing of precipitation •  Atmospheric circulation: storm-tracks, mean circulation •  Freshwater fluxes: •  Meridional Overturning Circulation •  Sea-ice formation (Bintanja et al. 2013) •  Ocean circulation in fjords and under ice shelves (meltwater feedback) •  Land cover (ice sheet area retreat/advance): affects albedo, roughness, turbulent fluxes Challenge the future 3
  4. 4. Modeling climate ice interaction Total mass budget= Surface Mass Balance – ice discharge to ocean Precipitation Temperature, radiation, wind, moisture Global climate Meltwater Ocean melt SMB Snow albedo Topography & Area Ice Flow Model Challenge the future 4
  5. 5. State of the art •  Very few AOGCMs have been coupled to ice sheet models (Ridley et al. 2005, Vizcaino et al. 2008,2010) •  Why should we include them? •  Integration of several components of climate system and their interaction (e.g. ice-ocean, ice-clouds, ice-storm track, land icesea ice) •  Representing feedbacks (e.g. albedo, elevation) •  Integration of different time-scales: •  Relating past, present and future processes in the climate system •  This helps to model validation (for instance, with “black swans” from paleo and recent observations to identify missing or misrepresented processes) Challenge the future 5
  6. 6. Challenges in coupling ice sheet and global climate models •  Resolution •  Spatial: AOGCMs have resolution of ~100 km. Ice sheet models need higher resolution (few kms and below) to resolve: •  Fast ice flow •  Atmospheric and ocean forcing: ocean melt in fjords, ocean circulation under ice shelves, orographic forcing of precipitation, melt gradients at ice sheet margins,… •  Temporal: long time scales involved in ice sheet build-up and complete decay •  Ice sheet initialization: obtaining a realistic present-day ice sheet •  well adjusted to the simulated climate (to avoid non-physical background trend) •  with memory of past climate (ice column temperature, viscosity, basal conditions) Challenge the future 6
  7. 7. The SMB challenge •  High Surface Mass Balance gradients at ice sheet margins (steep topography) kg m-2 yr-1 Until very recently: •  Climate models considered unsuitable: coarse resolution (~tens of km needed), climate biases •  Regional climate models preferred. But: •  Lateral forcing from GCMs needed •  No direct global climate-ice coupling (e.g. no meltwater-ocean feedbacks) •  Un-suited for multi-century studies (e.g. no elevation feedback) Surface mass balance (precip-su-melt) as modeled by RACMO2 Challenge the future 7
  8. 8. Ice climate in RCMs vs. GCMs Global climate models RCMs) Global climate Regional climate models Lateral Forcing Ice sheet flow & surface models Regional climate Ice sheet processes Snow albedo feedback Global GCMs) climate Ice sheet processes albedo, elevation, meltwater feedbacks Challenge the future 8
  9. 9. Recent break-through: first realistic SMB from global climate model •  Model is the Community Earth System Model (CESM) •  Results on model validation and 21st-century projections of GrIS SMB published in J. Climate Challenge the future 9
  10. 10. CESM compares well (r=0.80) with in-situ observations from N=475 stations 1960-2005 SMB from CESM downscaled at 5 km & from N=475 stations (kg m-2 yr-1) •  •  •  Accumulation rates overestimated in N interior Good match in the southern part, except in the wet SE 67 °N, west margin (“k-transect”) •  Modeled equilibrium line altitude (~1500 m) is close to observations •  Small differences over 1000 m •  Gradient is underestimated: •  Local terrain not resolved (narrow fjord framed by tundra) •  Local anomaly in bare ice albedo (“dark zone”) Vizcaino et al., 2013, J. Clim. Challenge the future 10
  11. 11. CESM compares well with RCMs SMB>0 1960-2005 SMB (kg m-2 yr-1) (standard deviation in parenthesis) SMB = PREC-RU-SU RU=MELT+RAIN-REF CESM RACMO2 Other RCMs Net SMB 359 (120) 376 (117) 288/356/287 PREC 866 (88) 723 (74) 600/696/610 MELT 568 (112) 504 (111) Refreezing 242 (25) 245 (38) RUN-OFF 457(95) 306 (86) SU 54 40 Gt yr-1 CESM, 5 km CESM 5 km r= 0.79 SMB<0 RACMO2, 5 km RACMO2 ~11 km •  •  •  •  •  (MAR/PMM5/ERA40-d) 5/108/38 Bands of precip. maxima are well reproduced Higher precip. in the interior & lower in SE Major ablation zones well captured Narrow SE ablation areas in both models Refreezing: 35% of available liquid water Challenge the future 11
  12. 12. Intra-annual mass evolution compares well with gravimetry data (GRACE) 55 7 6 CESM seasonal cycle of snowmelt, bare ice melt, refreezing, snowfall, rain, and sublimation (Gt). Snow Melt mass (Gt) 5 4 Snowfall 3 RE 2 Ice Melt 1 SU Rainfall 0 0 90 180 day cum. mass anomaly (Gt) 300 200 270 360 GRACE 100 0 -100 •  Similar maximum, minimum & amplitude, regardless of influence of climate variability & “different” periods (GRACE data starts later, in 2003 vs. CESM -200 -300 Mean (thick lines) and range (thin lines) of de-trended monthly cumulative mass anomalies (Gt) for CESM (1996-2004, blue) and GRACE (2003-2011, black). 1996 of CESM) 995 6 7 8 month 996 FIG. 9. Upper) CESM seasonal cycle of snow melt, bare ice melt, refreezing, snowfall, 997 rain and sublimation. Units are Gt. Lower) Comparison of the seasonal cycle of mass 998 anomalies between CESM (blue) and GRACE (black). Units are Gt. Thick lines represent 1 2 3 4 5 9 10 11 12 Challenge the future 12
  13. 13. The recipe for a good SMB 1.  Realistic atmospheric forcing (radiation, wind, humidity) 2.  Explicit simulation of snow processes: albedo, compaction, refreezing. •  •  SMB in CESM is calculated in land component (giving “immediate” ice-atmospheric coupling) Albedo depends on snow grain size, solar zenit angle, spectral band, snow impurities (SNICAR model) 3.  Sub-grid representation of elevation dependency of SMB ①  Atmospheric forcing (temperature, humidity) is downscaled to ice sheet grid ②  SMB is re-calculated at several fixed elevations ③  SMB maps are interpolated to ice sheet grid (horizontally & vertically) Challenge the future 13
  14. 14. 57 Explicit albedo simulation At melt season peak (July) Before melt season (April) a b c 0.9 0.825 0.8 0.7 0.6 0.5 0.2 1960-2005 mean albedos 1008 1009 CESM (global model) RACMO2 (regional model) Challenge the future 14 FIG. 11. Map of mean April (a) and July (b) albedos for 1960-2005 as simulated by
  15. 15. GrIS SMB Projections up to 2100 with CESM Following high-forcing scenario RCP8.5 Challenge the future 15
  16. 16. Temperature change under RCP8.5 Annual, 2080-99 minus 1980-99 (K) Summer, 2080-99 minus 1980-99 (K) b! Greenland: +4.1 K Global: +3.7 K 60-90°N: +7.9 K Greenland: +4.7 K •  MOC reduction reduces warming SE of Greenland •  JJA increase is highest •  In ice-free regions to N & E, due to stronger sea ice losses (>40%) along the coast •  In the interior of the ice sheet, which remains below melting point Challenge the future 16
  17. 17. Change in surface fluxes (RCP8.5) Wm-2 2080-99 minus 1980-99 (Only significant anomalies) albedo •  •  •  •  •  SWd! LWd! More incoming LW Less incoming SW due to increased cloudiness Albedo decreases Net radiation increases Turbulent flux increases albedo! Vizcaino et al., 2013, J. Clim., Part II Rnet! SHF! LHF! Challenge the future 17
  18. 18. Change in integrated SMB terms (Gt yr-1) SMB = PREC-RUNOFF-SUBLIMATION RUNOFF=MELT+RAIN-Refreezing (standard deviation in parenthesis) % indicates increase 2080-99 wrt 1980-99 Melt 1500 1980-99 SMB Gt per year -78 (143) PRECIPITATION 855 (70) 1158 (74) +35% Snowfall 728 (59) 857 (47) +18% SURFACE MELT Snowfall 500 Rain 0 SMB •  •  •  •  •  372 (100) 552 (119) 1186 (155) +215% Refreezing 240 (25) 318 (25) +33% RUN-OFF 438 (98) 1168 (168) +266% SUBLIMATION 54 (3) 60 (4) +11% Run-off 1000 -500 1980 2080-99 2000 2020 2040 year 2060 2080 SMB becomes negative Snowfall increases by 18% Melt doubles Refreezing capacity decreases 5.5 cm SLE by 2100 2100 Vizcaino et al., 2013, J. Clim., Part II Challenge the future 18
  19. 19. New equilibrium line ~500 m higher SMB>0 1980-99! kg m-2 yr-1 2080-99! SMB<0 •  •  •  •  Ablation area increases from 9% to 28% of ice sheet Max. increase of eq. line in NE (~1000 m higher) SMB increases over 2000 m Map is similar to projections from regional models Challenge the future 19
  20. 20. Summary •  Ice sheets are not yet interactive components of most global climate models •  Major challenges come from differences in spatial & temporal resolutions •  Until recently, global climate models considered unsuited to reproduce high SMB gradients, due to climate biases and insufficient resolution •  Now the first global climate model is able to simulate realistic SMB, due to realistic atmospheric simulation coupled with explicit representation of snow processes, and sub-grid representation of vertical gradients Challenge the future 20
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