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 Temperature and Accumulation Temperature and Accumulation Seasonal and Annual Seasonal and Annual Empirical functions based on correlation of Polar MM5 24 km gridded results with: Empirical functions based on correlation of Polar MM5 24 km gridded results with: Coastal station temperature records; Coastal station temperature records; Annual accumulation rates from ice cores Annual accumulation rates from ice cores PARCA PARCA Outlet Glacier Discharge Outlet Glacier Discharge Annual Annual Empirical functions based on seasonal coastal temperature correlation with outlet glacier discharge Empirical functions based on seasonal coastal temperature correlation with outlet glacier discharge Rignot, E., and P. Kanagaratnam (2006), Changes in the velocity structure of the Greenland Ice Sheet, Science, 311, Rignot, E., and P. Kanagaratnam (2006), Changes in the velocity structure of the Greenland Ice Sheet, Science, 311,

Temperature Records * 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: /2005JD006810, JGR, in press ** GISTEMP (NASA), Hansen et al. Coastal Monthly, Seasonal, Annual

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), 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), Box, J.E., D. H. Bromwich, L-S Bai, 2004: Greenland ice sheet surface mass balance for : application of Polar MM5 mesoscale model and in- situ data, J. Geophys. Res., Vol. 109, No. D16, D16105, /2003JD 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 ( ) from calibrated Polar MM5 output, J. Climate, accepted Sept

Polar MM5 Domains

YP solid P liquid EQSQS CMRBAAR Mean Min Max Range Polar MM5 Mass Budget Results ( )

NEW 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 ( ) from Calibrated Polar MM5 Output, J. Climate, 19 (12), 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 ( ) from Calibrated Polar MM5 Output, J. Climate, 19 (12),

Methods: Statistical Regression Explanatory (‘independent’) variables Explanatory (‘independent’) variables long term record, such as coastal station temperatures or ice core accumulation rates long term record, such as coastal station temperatures or ice core accumulation rates ‘dependent’ variables ‘dependent’ variables Polar MM5 temperature Polar MM5 temperature Polar MM5 accumulation rate Polar MM5 accumulation rate Polar MM5 training period Polar MM5 training period , (N = 18), Currently , (N = 18), Currently , (N = 48), before July , (N = 48), before July 2006 Determine highest correlation rank for each grid cell vs explanatory data 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 Store regression coefficients (slope and intercept) for the top two ranked sites for each grid cell Use full instrumental record to reconstruct dependent variables Use full instrumental record to reconstruct dependent variables Temperature, Accumulation, outlet glacier discharge Temperature, Accumulation, outlet glacier discharge ice sheet temperatures ice sheet temperatures available for annual means, (N = 132) available for annual means, (N = 132) seasonal means ultimately seasonal means ultimately

Hypotheses Surface Mass Balance Surface Mass Balance Ice cores can represent the spatial/temporal patterns of accumulation rate on annual to century timescales 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 Seasonal and annual temperatures explain seasonal to interannual the spatial/temporal patterns of glacial melt water production and runoff Glacier Discharge Glacier Discharge “There is an ice dynamics response to short term (monthly to inter- annual) surface climate” “There is an ice dynamics response to short term (monthly to inter- annual) surface climate” Glacier discharge sensitivity to temperature is a useful predictor of past and future solid ice flux to oceans 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 Total Ice Sheet Mass Budgets and Global Eustatic Sea Level Forcing 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 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

PrimarySecondary Summer Correlation

Two Site Seasonal Temperature Correlations

Seasonal Temperature Reconstruction Results

Seasonal Temperature ReconstructionValidation

Linear Trend: C/ decade0.6 K increase over 132 yearsr =0.380 Linear Trend: C/ decade, 0.6 K increase over 132 years, r =0.380 Annual Temperature Reconstruction

mean: C Linear Trend: C/ decade, 0.7 K increase over 132 years, r = Linear Trend: C/ decade, 0.7 K increase over 132 years, r = Annual Temperature Reconstruction

Runoff Reconstruction ( ) Based on Greenland Summer (JJA) Temperature Vs. Polar MM5 Runoff

Surface Mass Balance Reconstruction ( ) Using summer (JJA) temperature, R 2 = 0.75

Greenland Ice Sheet Mass Budget Implications of Climate Warming Runoff Runoff +384 km 3 y -1 K -1 sensitivity +384 km 3 y -1 K -1 sensitivity baseline = 243 Gt y baseline = 243 Gt y -1 R 2 = R 2 = A 1K global temperature anomaly suggests a runoff of 627 km 3 y -1 A 1K global temperature anomaly suggests a runoff of 627 km 3 y -1 Accumulation Accumulation +102 km 3 y -1 K -1 sensitivity +102 km 3 y -1 K -1 sensitivity baseline = 507 km 3 y baseline = 507 km 3 y -1 R 2 = R 2 = Surface Mass Budget Surface Mass Budget -282 km 3 y -1 K -1 sensitivity -282 km 3 y -1 K -1 sensitivity baseline = 264 km 3 y baseline = 264 km 3 y -1 R 2 = R 2 = A 1K global temperature anomaly suggests a -18 km 3 y -1 surface mass balance A 1K global temperature anomaly suggests a -18 km 3 y -1 surface mass balance Negative surface mass budget if global climate warms additional 0.33 K Negative surface mass budget if global climate warms additional 0.33 K global T anomaly K (with respect to ) base period global T anomaly K (with respect to ) base period 2005 global T anomaly K (with respect to ) base period 2005 global T anomaly K (with respect to ) base period

Surface Mass Balance Reconstruction ( ) Using summer (JJA) temperature, R 2 = 0.75

Sea Level Contribution Reconstructions: D Constant JJA Discharge,SMB ANN Discharge,SMB ANN Discharge,SMB nonlinear (Const. D, Ann. SMB), (nonlin. D, Ann. SMB) : 0.66 mm y -1, 0.82 mm y : 0.58 mm y -1, 0.59 mm y : 0.64 mm y -1, 0.74 mm y : 0.64 mm y -1, 0.74 mm y -1 Sea Level Contribution Reconstructions:

Conclusions 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 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. 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 global temperature anomaly = 0.66 K global temperature anomaly = 0.66 K Past warming trends suggest this threshold reached within next years. Past warming trends suggest this threshold reached within next years. Overall ice sheet mass budget would be ~-300 km 3 y -1 Overall ice sheet mass budget would be ~-300 km 3 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 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 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). 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. 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. The temperature thresholds are unknown, but can be evaluated with historic temperature and discharge data.

Questions What mechanisms are most likely to lead to outlet glacier surge in response to warming? What mechanisms are most likely to lead to outlet glacier surge in response to warming? What temperature threshold causes outlet glacier to surge? What temperature threshold causes outlet glacier to surge?