W.T. Pfeffer INSTAAR and Civil, Environmental, and Architectural Engineering, University of Colorado with thanks to Balaji Rajagopalan, Civil, Environmental, and Architectural Engineering, University of Colorado Christina Hulbe and Scott Waibel, Portland State University, Portland, Oregon Projected Sea Level Extremes and Uncertainties in the 21st Century US CLIVAR/NCAR ASP Researcher Colloquium 14 June 2011 Illulissat, Greenland, 2007 W.T. Pfeffer

INSTAAR Univ. of Colorado 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 year scales. Events of primary interest to glaciologists are extreme events occurring on 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 IPCC AR Sea Level Projection: Less than 1 m, but with caveats concerning ‘dynamics’ 0.18 m 0.59 m Absence of accelerated ice sheet discharge from projections noted in AR4

INSTAAR Univ. of Colorado Components of Sea Level Rise (SLR) 1. Thermal Expansion a.Upper ocean (top 700 m) b.Deep ocean 2. New Water Mass a.Antarctica b.Greenland c.Glaciers and Ice Caps (GIC) d.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) Global May dominate locally

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

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

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

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

INSTAAR Univ. of Colorado SL budget closes to mm yr -1 (16%) for SL budget closes to mm yr -1 (2%) for from Cazenave and Llovel, 2010

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

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

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

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Rignot and Kanagaratnam (2006) assessment of Greenland Ice Sheet mass loss rate by calving discharge. Mass loss rate increased from 90 to 220 km 3 /year between 1996 and Rapid Dynamics observed in Greenland in 2006 (included in AR4 discussion)

INSTAAR Univ. of Colorado Moving from AR4 (2007) to AR5 (2014): Meier et al, Glaciers Dominate 21 st Century Sea Level Rise, Science, Project at current rate of change 2. Project at current rate Projected SLR (mm) to 2100 by Extrapolation Glaciers and Ice Caps current acceleration held fixed 240 ± 128 current rate held fixed 104 ± 25 Greenland current acceleration held fixed 245 ± 106 current rate held fixed 47 ± 8 Antarctica current acceleration held fixed 75 ± 50? current rate held fixed 16 ± 5 Total Global current acceleration held fixed 560 ± 230? current rate held fixed 167 ± 44 observations projections Hedging the hazard of extrapolation by calculating two bracketing cases

INSTAAR Univ. of Colorado 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 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 Pfeffer et al, Kinematic Constraints on 21 st Century Sea Level Rise, Science, Scenarios (SLR in mm)

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

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

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

INSTAAR Univ. of Colorado Rignot et al, 2011 Rignot projected Sea Level Rise to 2050 (cm) Antarctica & Greenland15± 2 Glaciers and Ice Caps 8 ± 4 (using Meier et al 2007) Thermal Expansion 9 ± 3 (using IPCC AR4) Total Sea Level Rise by ± 5

INSTAAR Univ. of Colorado YearGR SMBGR DGR MBMsigmaYearAnt SMBAnt DAnt MBMsigma Rignot et al 2011 Data

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

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

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

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

INSTAAR Univ. of Colorado 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

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Time 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 scale of transitional/transient process But… 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. Stationarity

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

INSTAAR Univ. of Colorado 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 Where’s the Joker?

INSTAAR Univ. of Colorado