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Projected Sea Level Extremes and Uncertainties in the 21st Century

Projected Sea Level Extremes and Uncertainties in the 21st Century.

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Projected Sea Level Extremes and Uncertainties in the 21st Century

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  1. Projected Sea Level Extremes and Uncertainties in the 21st Century W.T. PfefferINSTAAR and Civil, Environmental, and Architectural Engineering, University of Coloradowith thanks toBalaji Rajagopalan , Civil, Environmental, and Architectural Engineering, University of ColoradoChristina Hulbe and Scott Waibel, Portland State University, Portland, Oregon Illulissat, Greenland, 2007 W.T. Pfeffer US CLIVAR/NCAR ASP Researcher Colloquium 14 June 2011

  2. Some issues in making projections of future sea level rise (SLR): • Methods of projection: Deterministic numerical models are virtually the exclusive option being pursued, and they don’t work very well (yet). What are the alternatives? • Time scales: Planners, policy makers, etc. are primarily concerned with 10-100 year scales. Events of primary interest to glaciologists are extreme events occurring on 100-1000 year scales. • Uncertainties: Handled extremely casually so far; much more careful and thorough treatment is urgently needed. • End users (policy makers, planners, risk managers, coastal engineers) need information on SLR delivered on decade-by-decade basis as PDFs. We are not there yet. INSTAAR Univ. of Colorado

  3. 0.59 m Absence of accelerated ice sheet discharge from projections noted in AR4 0.18 m IPCC AR4 2007 Sea Level Projection: Less than 1 m, but with caveats concerning ‘dynamics’ INSTAAR Univ. of Colorado

  4. 1. Thermal Expansion • Upper ocean (top 700 m) • Deep ocean • 2. New Water Mass • Antarctica • Greenland • Glaciers and Ice Caps (GIC) • Other terrestrial storage • 3. Relative (local) • a. Dynamics (winds/currents) • b. Gravitational • c. Glacio-isostatic rebound (GIA) • d. Coastal subsidence • 1. Infrastructure loading • 2. SLR loading • 3. Upstream sediment trapping • 4. Groundwater depletion • (very long-term components, e.g. tectonics, are not considered here) Components of Sea Level Rise (SLR) Global May dominate locally INSTAAR Univ. of Colorado

  5. Mountain Glaciers and Ice Caps Greenland and Antarctica Terrestrial Storage Thermal expansion Present day components of SLR from Domingues et al, 2008 INSTAAR Univ. of Colorado

  6. Mass Loss 1992-2008 from Cazenave and Llovel, Annual Review of Marine Science, 2010 INSTAAR Univ. of Colorado

  7. Mass Loss 1992-2008 from Cazenave and Llovel, Annual Review of Marine Science, 2010 Mass Loss 1992-2008 from Cazenave and Llovel, Annual Review of Marine Science, 2010 INSTAAR Univ. of Colorado

  8. Antarctic Range Greenland Range Compilation figure courtesy Georg Kaser INSTAAR Univ. of Colorado

  9. from Cazenave and Llovel, 2010 SL budget closes to -0.05 mm yr-1 (2%) for 2003-2007 SL budget closes to +0.46 mm yr-1 (16%) for 1993-2007 INSTAAR Univ. of Colorado

  10. Future SLR: Projections from IPCC 4th Assessment (AR4, 2007): IPCC AR4 2007 Sea Level Projection, including ‘scaled-up’ projection to approximate effects of dynamics INSTAAR Univ. of Colorado

  11. “Dynamics”always acts in glacier mass balance Dynamics: Response to change in mass balance isn’t instantaneous W.T. Pfeffer Institute of Arctic and Alpine ResearchDepartment of Civil, Environmental, and Architectural EngineeringUniversity of Colorado at Boulder

  12. “Rapid” or “Disequilibrium” dynamics is the unpredictable part of the glacier/ice sheet component “Dynamics”: Glacier is not operating toward a geometry in equilibrium with its mass balance environment W.T. Pfeffer Institute of Arctic and Alpine ResearchDepartment of Civil, Environmental, and Architectural EngineeringUniversity of Colorado at Boulder

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  14. Rapid Dynamics observed in Greenland in 2006 (included in AR4 discussion) Rignot and Kanagaratnam (2006) assessment of Greenland Ice Sheet mass loss rate by calving discharge. Mass loss rate increased from 90 to 220 km3/year between 1996 and 2006. INSTAAR Univ. of Colorado

  15. Moving from AR4 (2007) to AR5 (2014): Meier et al, Glaciers Dominate 21st Century Sea Level Rise, Science, 2007 1. Project at current rate of change 2. Project at current rate observations projections Hedging the hazard of extrapolation by calculating two bracketing cases INSTAAR Univ. of Colorado

  16. Reaction to the rediscovery of rapid dynamics: big sea level rise “forecasts”. Never published as a definitive statement by the sea level rise community, but taken seriously by designers and policy makers anyway. INSTAAR Univ. of Colorado

  17. Pfeffer et al, Kinematic Constraints on 21st Century Sea Level Rise, Science, 2008 Response to hypothesized “2 m from Greenland by 2100”: Is this even possible? Simple calculations independent of unproven physics suggest global total SLR limited to no more than ~2m by 2100. INSTAAR Univ. of Colorado 3 Scenarios (SLR in mm)

  18. For better of worse, extrapolation in various forms has become a widely used tool for estimating land ice contributions to SLR during the next century, despite strong evidence that processes driving land ice mass loss is non-stationary. If we’re going to do this what uncertainties are involved? INSTAAR Univ. of Colorado

  19. Rignot et al 2011, Greenland mass loss INSTAAR Univ. of Colorado

  20. Rignot et al 2011, Greenland mass loss INSTAAR Univ. of Colorado

  21. Rignot et al 2011, Combined mass loss, Greenland and Antarctica INSTAAR Univ. of Colorado

  22. Rignot et al, 2011 INSTAAR Univ. of Colorado

  23. Rignot et al 2011 Data INSTAAR Univ. of Colorado

  24. SLE by 2100: 14.2 ± 5.5 cm Projected SLR from Rignot data using GLM methods – Greenland INSTAAR Univ. of Colorado

  25. SLE by 2100: 25.0 ± 16.5 cm Projected SLR from Rignot data using GLM methods – Antarctica 1992-2009 INSTAAR Univ. of Colorado

  26. SLE by 2100: 11.0 ± 13.0 cm Effect of dropping first 2 years of 17 year data series Projected SLR from Rignot data using GLM methods – Antarctica 1994-2009 INSTAAR Univ. of Colorado

  27. Using GLM Greenland + Antarctica SLE by 2100: 20.7 ± 5.6 cm Projected SLR from Rignot data using GLM methods – Antarctica + Greenland Rignot et al’s projection for Greenland + Antarctica: by 2100: 56 ± 3 cm INSTAAR Univ. of Colorado

  28. Add estimate for Thermal Expansion Total Global Land Ice (Ice Sheets + Glaciers and Ice Caps) + Thermal Expansion contribution to Sea Level by using GLM: 2100: 40.5 ± 2 cm Rignot et al projection 2100: 56 ± 5 cm Ice Sheets only INSTAAR Univ. of Colorado

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  30. Without getting bogged down down in the deterministic morass, how do time scales of dynamics work? This is a question that could be asked. It has not. Time scale of transitional/transient process Mass Loss Rate (<0) Stationary process: continued acceleration Transitional process: stabilizes at new steady state Transient process: returns to initial state after period of fast change Time Stationarity INSTAAR Univ. of Colorado But…

  31. Treatment of SLR primarily as management of uncertainty (Planners, designers, etc want PDFs, not modeled time series). This requires evaluation of all components, not just leading terms Glaciological community has been mostly locked into investigations of the ‘fat tail’: high-impact/low probability events. Probability of Occurrence Fat Tails and Skinny Bodies? 1 m? 2 m? Total SLR by certain date (2100)

  32. What are the weaknesses in projecting sea level rise? 1. We need an alternative to fully deterministic numerical models. 2. We need better assessments of uncertainty. 3. We need better determination of near-term (decadal) behavior. 4. We need more geographically complete and efficient (faster updating) observational systems. INSTAAR Univ. of Colorado

  33. Where’s the Joker? INSTAAR Univ. of Colorado

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