Greenland Ice Greenland Ice Sheet Sheet Sea Level Sea Level Contributions: Contributions: Recent Past and Recent Past and Future Future J. E. Box J. E. Box Byrd Polar Research Byrd Polar Research Center Center Understanding Sea-level Rise and Variability Understanding Sea-level Rise and Variability WCRP Workshop WCRP Workshop Global Earth Observation System of Systems Global Earth Observation System of Systems (GEOSS) (GEOSS) UNESCO, Place Fontenoy - Paris, France (Room UNESCO, Place Fontenoy - Paris, France (Room
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Climatological Estimates of Greenland Ice Sheet Sea Level Contributions: Recent Past and Future
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) - PowerPoint PPT Presentation
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Climatological Climatological Estimates of Estimates of
TemperatureTemperature and and AccumulationAccumulation Seasonal and Annual Seasonal and Annual
Empirical functions based on correlation of Empirical functions based on correlation of Polar MM5 24 km gridded results with:Polar MM5 24 km gridded results with:
Coastal station Coastal station temperaturetemperature records; records; Annual Annual accumulationaccumulation rates from ice cores rates from ice cores
PARCA PARCA
Outlet Glacier DischargeOutlet Glacier Discharge Annual Annual Empirical functions based on seasonal coastal Empirical functions based on seasonal coastal
temperaturetemperature correlation with correlation with outlet glacier outlet glacier dischargedischarge
Rignot, E., and P. Kanagaratnam (2006), Changes in Rignot, E., and P. Kanagaratnam (2006), Changes in the velocity structure of the Greenland Ice Sheet, the velocity structure of the Greenland Ice Sheet, Science, 311, 986-990.Science, 311, 986-990.
Temperature Temperature RecordsRecords
* 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.
WMO ID Station Name Time Span Source4202 Pituffik/Tule 1847-2005 **4220 Aasiaat/Egedesminde 1951-2005 **4250 Nuuk/Godthab 1748-2005 *
04216 / 04221 Ilulissat/Jakobshavn 1804-2005 *4320 Danmarkshavn 1951-2005 **4390 Pr. Christian Sund 1950-2005 **4360 Tasiilaq/Ammassalik 1895-2005 **
• Coastal
• Monthly, Seasonal, Annual
Polar Polar MM5MM5Polar Polar MM5MM5
- 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 in-situ 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.
long term record, such as coastal station temperatures or long term record, such as coastal station temperatures or ice core accumulation ratesice core accumulation rates
‘‘dependent’ variablesdependent’ variables Polar MM5 temperaturePolar MM5 temperature Polar MM5 accumulation ratePolar MM5 accumulation rate Polar MM5 training periodPolar MM5 training period
1988-2005, (N = 18), Currently1988-2005, (N = 18), Currently 1958-2005, (N = 48), before July 20061958-2005, (N = 48), before July 2006
Determine highest correlation rank for each grid Determine highest correlation rank for each grid cell vs explanatory datacell vs explanatory data
Store regression coefficients (slope and intercept) Store regression coefficients (slope and intercept) for the top two ranked sites for each grid cellfor the top two ranked sites for each grid cell
Use full instrumental record to reconstruct Use full instrumental record to reconstruct dependent variablesdependent variables Temperature, Accumulation, outlet glacier dischargeTemperature, Accumulation, outlet glacier discharge ice sheet temperaturesice sheet temperatures 1873-2004 available for annual means, (N = 132)1873-2004 available for annual means, (N = 132) seasonal means ultimatelyseasonal means ultimately
HypothesesHypotheses Surface Mass BalanceSurface Mass Balance
Ice cores can represent the spatial/temporal patterns of Ice cores can represent the spatial/temporal patterns of accumulation rate on annual to century timescalesaccumulation rate on annual to century timescales
Seasonal and annual temperatures explain seasonal to Seasonal and annual temperatures explain seasonal to interannual the spatial/temporal patterns of glacial melt interannual the spatial/temporal patterns of glacial melt water production and runoff water production and runoff
Glacier DischargeGlacier Discharge ““There is an ice dynamics response to short term There is an ice dynamics response to short term
(monthly to inter-annual) surface climate”(monthly to inter-annual) surface climate” Glacier discharge sensitivity to temperature is a useful Glacier discharge sensitivity to temperature is a useful
predictor of past and future solid ice flux to oceanspredictor of past and future solid ice flux to oceans Total Ice Sheet Mass Budgets and Global Eustatic Total Ice Sheet Mass Budgets and Global Eustatic
Sea Level ForcingSea Level Forcing Exploitation of significant correlations of surface mass Exploitation of significant correlations of surface mass
balance and outlet glacier discharge provide useful balance and outlet glacier discharge provide useful estimates of ice sheet sea level forcing on annual to estimates of ice sheet sea level forcing on annual to century time scalescentury time scales
Primary Secondary
Summer CorrelationSummer Correlation
Two Site Seasonal Two Site Seasonal Temperature CorrelationsTemperature Correlations
Seasonal Temperature Seasonal Temperature Reconstruction ResultsReconstruction Results
Seasonal Temperature Seasonal Temperature ReconstructionValidationReconstructionValidation
Linear Trend: +0.045 C/ decadeLinear Trend: +0.045 C/ decade, 0.6 K increase over 132 years0.6 K increase over 132 years, r =0.380r =0.380
Annual Temperature Annual Temperature ReconstructionReconstruction
1873-2004 mean: 1873-2004 mean: -13.16 C -13.16 C Linear Trend:Linear Trend: ++0.0530.053 C/ decade, 0.7 K increase over 132 years, C/ decade, 0.7 K increase over 132 years, r = r =
0.4720.472
Annual Temperature Annual Temperature ReconstructionReconstruction
RR22 = 0.380 = 0.380 A 1K global temperature anomaly suggests a -18 kmA 1K global temperature anomaly suggests a -18 km33 y y-1-1 surface mass surface mass
balancebalance Negative surface mass budget if global climate warms additional 0.33 Negative surface mass budget if global climate warms additional 0.33
KK 1994-2005 global T anomaly 0.442 K (with respect to 1961-1990) base 1994-2005 global T anomaly 0.442 K (with respect to 1961-1990) base
periodperiod 2005 global T anomaly 0.667 K (with respect to 1961-1990) base period2005 global T anomaly 0.667 K (with respect to 1961-1990) base period
Surface Mass Balance Surface Mass Balance Reconstruction (1866-2005)Reconstruction (1866-2005)
ConclusionsConclusions Warming over the recent decade produced large positive melt Warming over the recent decade produced large positive melt
anomalies, yet, climatological reconstruction suggests recent anomalies, yet, climatological reconstruction suggests recent summer melt is not unprecedented, warm summers in 1950s and summer melt is not unprecedented, warm summers in 1950s and 1930s1930s
Surface mass budget sensitivity to global temperature anomalies Surface mass budget sensitivity to global temperature anomalies suggest that the Greenland Ice Sheet surface mass budget would suggest that the Greenland Ice Sheet surface mass budget would become negative for a 1K global temperature anomaly.become negative for a 1K global temperature anomaly. 1994-2005 global temperature anomaly = 0.66 K 1994-2005 global temperature anomaly = 0.66 K Past warming trends suggest this threshold reached within Past warming trends suggest this threshold reached within
next 30-60 years.next 30-60 years. Overall ice sheet mass budget would be ~-300 kmOverall ice sheet mass budget would be ~-300 km33
yy-1-1
A model that accounts for temperature thresholds in outlet A model that accounts for temperature thresholds in outlet glacier discharge produces a ~30% larger sea level contribution glacier discharge produces a ~30% larger sea level contribution that one with discharge that is invariant with melt water fluxthat one with discharge that is invariant with melt water flux
Correlation analysis suggests a link between outlet glacier Correlation analysis suggests a link between outlet glacier discharge and air temperature discharge and air temperature Future sea level contribution should therefore be more than Future sea level contribution should therefore be more than
30% greater than recent estimates from Rignot and 30% greater than recent estimates from Rignot and Kanagaratnam (2006).Kanagaratnam (2006).
This model is very sensitive to the temperature threshold This model is very sensitive to the temperature threshold used.used.
The temperature thresholds are unknown, but can be The temperature thresholds are unknown, but can be evaluated with historic temperature and discharge data.evaluated with historic temperature and discharge data.
QuestionsQuestions
What mechanisms are most likely to What mechanisms are most likely to lead to outlet glacier surge in lead to outlet glacier surge in response to warming?response to warming?
What temperature threshold causes What temperature threshold causes outlet glacier to surge?outlet glacier to surge?