Transcript Greenland ice sheet temperature reconstruction over the

Climatological Estimates of
Greenland Ice Sheet
Sea Level Contributions:
Recent Past and Future
J. E. Box
Byrd Polar Research Center
Understanding Sea-level Rise and Variability
WCRP Workshop
Global Earth Observation System of Systems (GEOSS)
UNESCO, Place Fontenoy - Paris, France (Room XII)
Spatial/Temporal Reconstructions
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Temperature and Accumulation
Seasonal and Annual
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Empirical functions based on correlation of Polar MM5 24
km gridded results with:
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Coastal station temperature records;
Annual accumulation rates from ice cores
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PARCA
Outlet Glacier Discharge
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Annual
Empirical functions based on seasonal coastal temperature
correlation with outlet glacier discharge
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Rignot, E., and P. Kanagaratnam (2006), Changes in the velocity
structure of the Greenland Ice Sheet, Science, 311, 986-990.
Temperature
Records
• Coastal
• Monthly, Seasonal, Annual
WMO ID
4202
4220
4250
04216 / 04221
4320
4390
4360
Station Name
Pituffik/Tule
Aasiaat/Egedesminde
Nuuk/Godthab
Ilulissat/Jakobshavn
Danmarkshavn
Pr. Christian Sund
Tasiilaq/Ammassalik
Time Span
1847-2005
1951-2005
1748-2005
1804-2005
1951-2005
1950-2005
1895-2005
Source
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*
*
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* Vinther, B. M., K. K. Andersen, P. D. Jones, K.
R. Briffa and J. Cappelen, Extending Greenland
Temperature Records into the late 18th Century,
doi:10.1029/2005JD006810, JGR, in press 2006.
** GISTEMP (NASA), Hansen et al.
Polar MM5
- Bromwich D.H., J. Cassano, T. Klein, G. Heinemann, K.
Hines, K. Steffen, and J. E. Box, 2001: Mesoscale
modeling of katabatic winds over Greenland with
the Polar MM5, Monthly Weather Review, 129(9),
2290-2309.
- Cassano, J., J.E. Box, D.H. Bromwich, L. Li, and K.
Steffen, 2001: Verification of Polar MM5
simulations of Greenland's atmospheric
circulation, Journal of Geophysical Research,
106(D24), 33867-33890.
- Box, J.E., D. H. Bromwich, L-S Bai, 2004: Greenland ice sheet surface mass
balance for 1991-2000: application of Polar MM5 mesoscale model and insitu data, J. Geophys. Res., Vol. 109, No. D16, D16105,
10.1029/2003JD004451
- Box, J.E., D.H. Bromwich, B.A. Veenhuis, L-S Bai, J.C. Stroeve, J.C. Rogers, K.
Steffen, T. Haran, S-H Wang, Greenland ice sheet surface mass balance
variability (1988-2004) from calibrated Polar MM5 output, J. Climate,
accepted Sept 27 2005.
Polar MM5 Domains
Polar MM5 Mass Budget Results (1988-2005)
Y
Psolid
Pliquid
E
QS
C
M
R
B
AAR
1988
629
19
70
37
522
405
302
221
0.83
1989
607
24
67
32
508
488
356
152
0.8
1990
639
19
69
31
538
544
426
112
0.77
1991
653
19
63
33
556
494
364
192
0.8
1992
633
11
64
36
533
282
201
331
0.87
1993
616
25
56
32
528
488
377
150
0.78
1994
578
22
60
36
482
423
320
162
0.8
1995
584
23
63
36
484
531
416
68
0.77
1996
679
22
58
40
580
404
299
281
0.85
1997
663
25
67
36
560
520
394
166
0.8
1998
616
26
71
36
509
635
510
-1
0.74
1999
631
23
62
33
536
470
347
189
0.81
2000
645
35
62
34
549
524
395
154
0.8
2001
681
24
60
28
593
485
367
226
0.81
2002
673
27
64
31
579
610
443
136
0.76
2003
710
37
65
32
613
628
483
130
0.77
2004
658
29
72
33
554
536
403
151
0.79
2005
699
30
82
35
583
699
545
37
0.74
Mean
641
24
64
34
543
498
377
166
0.80
Min
578
11
56
28
482
282
201
-1
0.74
Max
710
37
82
40
613
699
545
331
0.87
Range
132
26
26
12
131
417
344
332
0.13
NEW
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Box, J.E., D.H. Bromwich, B.A. Veenhuis, L-S
Bai, J.C. Stroeve, J.C. Rogers, K. Steffen, T.
Haran, S-H Wang, 2006, Greenland Ice Sheet
Surface Mass Balance Variability (1988-2004)
from Calibrated Polar MM5 Output, J. Climate,
19 (12), 2783-2800
Methods: Statistical Regression
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Explanatory (‘independent’) variables
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long term record, such as coastal station temperatures or ice core
accumulation rates
‘dependent’ variables
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Polar MM5 temperature
Polar MM5 accumulation rate
Polar MM5 training period
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1988-2005, (N = 18), Currently
1958-2005, (N = 48), before July 2006
Determine highest correlation rank for each grid cell vs
explanatory data
Store regression coefficients (slope and intercept) for the top
two ranked sites for each grid cell
Use full instrumental record to reconstruct dependent variables
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Temperature, Accumulation, outlet glacier discharge
ice sheet temperatures
1873-2004 available for annual means, (N = 132)
seasonal means ultimately
Hypotheses
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Surface Mass Balance
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Glacier Discharge
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Ice cores can represent the spatial/temporal patterns of accumulation
rate on annual to century timescales
Seasonal and annual temperatures explain seasonal to interannual the
spatial/temporal patterns of glacial melt water production and runoff
“There is an ice dynamics response to short term (monthly to interannual) surface climate”
Glacier discharge sensitivity to temperature is a useful predictor of past
and future solid ice flux to oceans
Total Ice Sheet Mass Budgets and Global Eustatic Sea Level
Forcing
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Exploitation of significant correlations of surface mass balance and
outlet glacier discharge provide useful estimates of ice sheet sea level
forcing on annual to century time scales
Summer Correlation
Primary
Secondary
Two Site Seasonal Temperature
Correlations
Seasonal Temperature Reconstruction Results
Seasonal Temperature
ReconstructionValidation
Annual Temperature Reconstruction
Linear Trend: +0.045 C/ decade, 0.6 K increase over 132 years, r =0.380
Annual Temperature Reconstruction
1873-2004 mean: -13.16 C
Linear Trend: +0.053 C/ decade, 0.7 K increase over 132 years, r = 0.472
Runoff Reconstruction (1866-2005)
Based on Greenland Summer (JJA) Temperature Vs. Polar MM5 Runoff
Surface Mass Balance Reconstruction (1866-2005)
Using summer (JJA) temperature, R2 = 0.75
Greenland Ice Sheet Mass Budget
Implications of Climate Warming
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Runoff
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Accumulation
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+102 km3 y-1 K-1 sensitivity
1988-2005 baseline = 507 km3 y-1
R2 = 0.237
Surface Mass Budget
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+384 km3 y-1 K-1 sensitivity
1988-2005 baseline = 243 Gt y-1
R2 = 0.673
A 1K global temperature anomaly suggests a runoff of 627 km3 y-1
-282 km3 y-1 K-1 sensitivity
1988-2005 baseline = 264 km3 y-1
R2 = 0.380
A 1K global temperature anomaly suggests a -18 km3 y-1 surface mass balance
Negative surface mass budget if global climate warms additional 0.33 K
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1994-2005 global T anomaly 0.442 K (with respect to 1961-1990) base period
2005 global T anomaly 0.667 K (with respect to 1961-1990) base period
Surface Mass Balance Reconstruction (1866-2005)
Using summer (JJA) temperature, R2 = 0.75
Sea Level Contribution Reconstructions: 1873-2004
D Constant 1996-2005
JJA Discharge,SMB
ANN Discharge,SMB
ANN Discharge,SMB nonlinear
(Const. D, Ann. SMB), (nonlin. D, Ann. SMB)
1920-1930: 0.66 mm y-1 , 0.82 mm y-1
1960-1970: 0.58 mm y-1 , 0.59 mm y-1
1994-2004: 0.64 mm y-1 , 0.74 mm y-1
1873-2004: 0.64 mm y-1 , 0.74 mm y-1
Conclusions
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Warming over the recent decade produced large positive melt anomalies, yet,
climatological reconstruction suggests recent summer melt is not unprecedented,
warm summers in 1950s and 1930s
Surface mass budget sensitivity to global temperature anomalies suggest that the
Greenland Ice Sheet surface mass budget would become negative for a 1K global
temperature anomaly.
 1994-2005 global temperature anomaly = 0.66 K
 Past warming trends suggest this threshold reached within next 30-60 years.
 Overall ice sheet mass budget would be ~-300 km3 y-1
A model that accounts for temperature thresholds in outlet glacier discharge
produces a ~30% larger sea level contribution that one with discharge that is
invariant with melt water flux
Correlation analysis suggests a link between outlet glacier discharge and air
temperature
 Future sea level contribution should therefore be more than 30% greater than
recent estimates from Rignot and Kanagaratnam (2006).
 This model is very sensitive to the temperature threshold used.
 The temperature thresholds are unknown, but can be evaluated with historic
temperature and discharge data.
Questions
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What mechanisms are most likely to lead to
outlet glacier surge in response to warming?
What temperature threshold causes outlet glacier
to surge?