Global Glacier and Ice Cap contributions to Sea Level Rise W.T. Pfeffer*, INSTAAR/University of...

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, 2004 W.T. Pfeffer

*with contributions from AMAP/SWIPA Glacier and Ice Cap working group, Mark Dyurgerov, Mark Meier

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.Antarcticab.Greenlandc.Glaciers and Ice Caps (GIC)d.Terrestrial storage

1. Ground water2. Surface water

a. Reservoir storage

3. Relative (local)

a. Dynamics (winds/currents)b. Gravitationalc. Isostatic reboundd. Coastal subsidence

1. Infrastructure loading2. SLR loading3. Upstream sediment trapping4. 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.

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…

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

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

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 103 km2

(Shumski, 1969) Mainland only: 132 x 103 km2

(Hock et al, 2009) Ant. Peninsula only: 116 x 103 km2 (Rignot et al 2008)

WGI-XF Data set: biased toward small land-terminating glaciers

e.g. WGI-XF missing Bering Glacier, Alaska Devon Ice Cap, Canada Flade Isblink, GreenlandGenerally, observations missing in Greenland, Antarctica, USA:

not analyzed

unmeasured

unmeasuredunmeasured

>> 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

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, 1960-2008)” in prep.

From data compilation of Dyurgerov and Meier, 2005

Global assessmentrelies on records from ca. 300 glaciers out of ~400,000 total.

Number of monitored glaciers is declining.

Glacier and Ice Cap mass loss summary Global (current 2005)

402± 95 GT/yr in 2006

Glacier and Ice Cap mass loss summary for Arctic only (current 2009)

Glacier and Ice Cap mass loss summary (current 2009)

SWIPA 5C in Review

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

•Other recent developments:

Antarctic Glaciers and Ice Caps SLE contribution 1961-2004 = 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)

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. 80-110 GT/yr

402 ± 95 GT/yr (2006)

UPDATE: 379 ± ~38 GT/yr (1993-2006)Dyurgerov, “Reanalysis of Glacier Changes Between the IGY and IPY, 1960-2008)” in prep.

Individual Ice/Eustatic Components:

Greenland mass loss summary (current 2009)

1995 1997 1999 2001 2003 2005 2007 20090

ass lo

Data fromMeier et al 2007

Mernild et al 2009 (modeled)

Rignot et al 2008 Velicognia 2009

30 GT/y2(Velicognia)

17 GT/y2 (Used here)

Individual Ice/Eustatic Components:

Antarctica mass loss summary (current 2009)

1995 1997 1999 2001 2003 2005 2007 2009-100

ass lo

E.Antarctica

W.AntarcticafromMeier et al 2007

All AntarcticafromRignot et al 2008

All AntarcticafromVelicognia 2009

26 GT/y2(Velicogna)

8.5 GT/y2 (Used here)

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 was645 GT/yr = 1.8 mm/yr(Meier et al 2007)

(*Dyurgerov in prep result)

The future: Projection of SLR rates forward to 2100 by extrapolation of present-day rates(assuming mass balance acceleration remains constant)

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

Examine range of mass balance acceleration:

Greenland -30 ± 11 GT/y2

Antarctica -26 ± 14 GT/y2

GIC -12 ± 6 GT/y20.41 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

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

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

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.

Illulissat, Greenland, 2007 W.T. Pfeffer

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.

Projection of net SLR forward to 2100 by extrapolation of present-day (last ca. 5-10 years) forward without dynamics

No Dynamic Projection – this is strictly empirical projection of observed present-day rates forward to 2100

0.41 m SLE

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

Components of Sea Level Rise (SLR) - Relative Contributions

Significant uncertainties apply to all components

Urgency of response varies with rate of environmental change

What are rates A & B?

Rate A may be ~20th C rate;B much harder to estimate

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 50-100 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

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.

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.

Global Glacier and Ice Cap contributions to Sea Level Rise W.T. Pfeffer*, INSTAAR/University of...

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