Global Glacier and Ice Cap contributions to Sea Level Rise W.T. Pfeffer*, INSTAAR/University of Colorado INSTAAR Univ. of Colorado Calving and subglacial flood, Columbia Glacier, Alaska, 2004W.T. Pfeffer *with contributions from AMAP/SWIPA Glacier and Ice Cap working group, Mark Dyurgerov, Mark Meier

INSTAAR Univ. of Colorado Components of Sea Level Rise (SLR) - Relative Contributions 1. Steric (thermal expansion) a.Upper ocean (top 700 m) b.Lower ocean) 2.Eustatic (new water) a.Antarctica b.Greenland c.Glaciers and Ice Caps (GIC) d.Terrestrial storage 1.Ground water 2.Surface water a. Reservoir storage 3. Relative (local) a. Dynamics (winds/currents) b. Gravitational c. Isostatic rebound d. Coastal subsidence 1. Infrastructure loading 2. SLR loading 3. Upstream sediment trapping 4. Groundwater depletion from Domingues et al, Nature 2008 Objective: Assess current eustatic SLE contributions from all sources with meaningful uncertainties, and forecast future SLE on useful time scales (decades-century) with meaningful uncertainties.

INSTAAR Univ. of Colorado Glacier and Ice Cap regions (from Radic and Hock in press) Current work: SWIPA glacier and ice cap module (AMAP) Radic and Hock (in press) improved estimates of global GIC volume. and others…

INSTAAR Univ. of Colorado Glacier and Ice Cap global area is poorly constrained: SLE (m) Global GIC volume “known” to within ~22 cm SLE Earlier evaluations did not consider GIC surrounding Greenland and Antarctica from Dyurgerov and Meier, 2005

INSTAAR Univ. of Colorado Glacier and Ice Cap volume summary (current 2009) Glacier and Ice Cap regional volumes (from Radic and Hock in press) factor 1/k adjusts for missing data

INSTAAR Univ. of Colorado Glacier and Ice Cap mass loss summary (current 2009) Glacier and Ice Cap regions (from Radic and Hock in press) Data (area) sources: Inventoried regions: WGI-XF Greenland: Weng (1995) > de Woul (2008) Antarctica*: Shumski (1969), Dyurgerov and Meier (2005), Hock et al (2009) Other uninventoried regions: GGHYDRO 2.3 (Cogley, 2003) *Antarctic total : 169 x 10 3 km 2 (Shumski, 1969) Mainland only: 132 x 10 3 km 2 (Hock et al, 2009) Ant. Peninsula only: 116 x 10 3 km 2 (Rignot et al 2008)

INSTAAR Univ. of Colorado WGI-XF Data set: biased toward small land-terminating glaciers e.g. WGI-XF missing Bering Glacier, Alaska Devon Ice Cap, Canada Flade Isblink, Greenland Generally, observations missing in Greenland, Antarctica, USA: not analyzed unmeasured >> Major uncertainties in most basic inventory items: e.g. area, volume >> Nearly complete lack of knowledge of properties needed for modeling e.g. topography, velocities, bed topography, size/location of outlets, etc

INSTAAR Univ. of Colorado Global mass balance of GIC: No new comprehensive assessment since Dyurgerov and Meier, 2005* *but see Dyurgerov, “Reanalysis of Glacier Changes Between the IGY and IPY, )” in prep. From data compilation of Dyurgerov and Meier, 2005 Global assessment relies on records from ca. 300 glaciers out of ~400,000 total. Number of monitored glaciers is declining.

INSTAAR Univ. of Colorado Glacier and Ice Cap mass loss summary Global (current 2005) 402± 95 GT/yr in 2006

INSTAAR Univ. of Colorado Glacier and Ice Cap mass loss summary for Arctic only (current 2009)

INSTAAR Univ. of Colorado Glacier and Ice Cap mass loss summary (current 2009) SWIPA 5C in Review

INSTAAR Univ. of Colorado GRACE gravity from Peltier, 2009 showing Greenland and Alaska mass loss rates, corrected for isostacy.

INSTAAR Univ. of Colorado Other recent developments: Antarctic Glaciers and Ice Caps SLE contribution = 0.79 ± 0.34 mm/yr (Hock et al, 2009) Global GIC committed future SLE contribution ~ 0.18 m even with further climate change (Bahr et al, 2009) Calving flux from GIS very poorly known but is ~30-40% of total mass loss where observed (Svalbard, Russian Arctic)

INSTAAR Univ. of Colorado Glaciers and Ice Caps: No comprehensive summation* since Meier et al (2007): -402 ± 95 GT/yr (for 2006) Newer observations (2008) for Alaska show ca GT/yr 402 ± 95 GT/yr (2006) UPDATE: 379 ± ~38 GT/yr ( ) Dyurgerov, “Reanalysis of Glacier Changes Between the IGY and IPY, )” in prep.

INSTAAR Univ. of Colorado Individual Ice/Eustatic Components: Greenland mass loss summary (current 2009)

INSTAAR Univ. of Colorado Individual Ice/Eustatic Components: Antarctica mass loss summary (current 2009)

INSTAAR Univ. of Colorado Relative contributions (current 2009) from Meier et al 2007 with updates from Rignot (2008 a,b) and others % SLR updated GIC: 402±95 GT/yr 46% Greenland: 267±38 GT/yr 31 % Antarctica: 196±30 GT/yr 23 % TOTAL: 865 GT/yr = 2.4 mm/yr SLR previous total was 645 GT/yr = 1.8 mm/yr (Meier et al 2007) (*Dyurgerov in prep result)

INSTAAR Univ. of Colorado The future: Projection of SLR rates forward to 2100 by extrapolation of present-day rates (assuming mass balance acceleration remains constant) 14 GT/yr 2

INSTAAR Univ. of Colorado Projection of SLR rates forward to 2100 by extrapolation of present-day (last ca. 5 years) forward with dynamics Projected dynamics (Pfeffer et al 2008): Eustatic: ~ 0.52 to 1.71 m with dynamic projection Total SLR w/ nominal 0.30 m steric component: ~0.82 to 2.01 m by 2100 Projected contributions to 2100: Greenland.44 m 41% (V) Antarctica.38 m 36% (V) GIC.25 m 25% (M) TOTAL 1.06 m

INSTAAR Univ. of Colorado Projection of SLR rates forward to 2100 by extrapolation of present-day (last ca. 5 years) forward with dynamics Examine range of mass balance acceleration: Greenland -30 ± 11 GT/y 2 Antarctica -26 ± 14 GT/y 2 GIC -12 ± 6 GT/y m SLE 0.28 m SLE 0.14 m SLE 0.55 m SLE Using Velicogna 2009 values for Greenland and Antarctica, Meier et al 2007 values for GIC GIC Ant. Gld.

INSTAAR Univ. of Colorado One complication: West Antarctica Loss of Ross and/or Filchner- Ronne ice shelves is not imminent, but possible in next century, by submarine melt. Forecast including dynamic response changes in this case. But see recent work by Powell et al on timing of Pliocene W. Ant. collapse

INSTAAR Univ. of Colorado Summary: Present day SLE contributions, next-century projected contributions, and uncertainties for Greenland, Antarctica, and GIC are all ~comparable and significant. GIC observational record is improving in some respects (e.g. GRACE, small-scale airborne altimetry) but at risk of being extinguished in other respects (e.g. mass balance components, velocities

INSTAAR Univ. of Colorado Recommendations for GIC: 1. Complete GLIMS inventory, continue/expand GIC mass balance measurement programs. 2. NEED DATA TO GO INTO GLIMS: Glacier outlines esp. in Antarctica and Patagonia. 3. Update/revamp WGI to include full range of GIC. Significant data missing from Antarctica, North America, Russian Arctic, Patagonia and High Asian Arctic 4. Remote sensing data needed: Altimetry, InSAR: location/speed of outlets, Airborne/shipborne soundings: bathymetry in front of outlets, depth sounding in outlets, microwave observations: snow facies, etc. 5. Groundtruth: Velocity, mass balance observations.

INSTAAR Univ. of Colorado Illulissat, Greenland, 2007 W.T. Pfeffer

INSTAAR Univ. of Colorado Over-prediction of future sea level rise may be as expensive as under-prediction: 1. For very large SLR predictions, planners start applying triage: Which 20% will be saved, and which 80% will be sacrificed? 2. Strong tendency to devalue land placed on seaward side of limit of inundation. Incentive for long-term investment falls without positive defensive action, but forecast will likely come first. Over-prediction of future sea level rise may more expensive than under-prediction.

INSTAAR Univ. of Colorado

Projection of net SLR forward to 2100 by extrapolation of present-day (last ca years) forward without dynamics No Dynamic Projection – this is strictly empirical projection of observed present- day rates forward to 2100 Sea level equivalent (m) m SLE

INSTAAR Univ. of Colorado Projection of SLR rates forward to 2100 by extrapolation of present-day (last ca. 5 years) forward with dynamics Estimated SLR to 2100 with dynamics using Pfeffer et al 2008, high- and low- range estimates. Dynamic response applies to all categories: GIC, Greenland, and Antarctica

INSTAAR Univ. of Colorado Components of Sea Level Rise (SLR) - Relative Contributions Significant uncertainties apply to all components

INSTAAR Univ. of Colorado Urgency of response varies with rate of environmental change A B What are rates A & B? Rate A may be ~20 th C rate; B much harder to estimate

INSTAAR Univ. of Colorado Cost of uncertainty (value of reducing uncertainty) varies over time What are time scales C and D? C: Possibly ~ 1 year (reducing uncertainty in sea level forecast on much shorter time scales isn’t useful). D: Possibly years (reducing uncertainty in sea level forecast 500 years from now isn’t politically/economically usable). Long-term determinations not useful in the absence of medium- short term determinations

INSTAAR Univ. of Colorado Uncertainty in predictions of future Ice Sheet and Glacier/Ice Cap response GIC rate uncertainty is initially greater than Greenland or Antarctic rate uncertainty, but will become less at some point in the future (> 50 years) as GIC volume diminishes.

INSTAAR Univ. of Colorado Uncertainty in predictions of future Ice Sheet and Glacier/Ice Cap response GIC net contribution will be surpassed by Greenland and Antarctic contribution at some point in the future (> 50 years) as GIC volume and loss rate diminishes. But all magnitudes are significant within the century time scale.