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
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W.T. PfefferINSTAAR and Civil, Environmental, and Architectural Engineering, University of Colorado
with thanks toBalaji Rajagopalan , Civil, Environmental, and Architectural Engineering, University of ColoradoChristina Hulbe and Scott Waibel, Portland State University, Portland, Oregon
Projected Sea Level Extremes and Uncertainties in the 21st Century
US CLIVAR/NCAR ASP Researcher Colloquium14 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 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
IPCC AR4 2007 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
(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 expansionTerrestrial Storage
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Mass Loss 1992-2008from Cazenave and Llovel, Annual Review of Marine Science, 2010
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Mass Loss 1992-2008from Cazenave and Llovel, Annual Review of Marine Science, 2010Mass Loss 1992-2008
from Cazenave and Llovel, Annual Review of Marine Science, 2010
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Antarctic Range
Greenland Range
Compilation figure courtesy Georg Kaser
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SL budget closes to +0.46 mm yr-1 (16%) for 1993-2007
SL budget closes to -0.05 mm yr-1 (2%) for 2003-2007
from Cazenave and Llovel, 2010
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IPCC AR4 2007 Sea Level Projection, including ‘scaled-up’ projection to approximate effects of dynamics
Future SLR: Projections from IPCC 4th Assessment (AR4, 2007):
W.T. Pfeffer Institute of Arctic and Alpine ResearchDepartment of Civil, Environmental, and Architectural EngineeringUniversity 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 ResearchDepartment of Civil, Environmental, and Architectural EngineeringUniversity of Colorado at Boulder
“Dynamics”: Glacier is not operating toward a geometry in equilibriumwith its mass balance environment
“Rapid” or “Disequilibrium” dynamics is the unpredictable part of the glacier/ice sheet component
INSTAAR Univ. of Colorado
INSTAAR Univ. of Colorado
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.
Rapid Dynamics observed in Greenland in 2006 (included in AR4 discussion)
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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
Projected SLR (mm) to 2100 by Extrapolation
Glaciers and Ice Caps
current acceleration held fixed 240 ± 128current rate held fixed 104 ± 25
Greenlandcurrent acceleration held fixed 245 ± 106
current rate held fixed 47 ± 8
Antarcticacurrent acceleration held fixed 75 ± 50?
current rate held fixed 16 ± 5
Total Globalcurrent acceleration held fixed 560 ± 230?
current rate held fixed 167 ± 44
observations projections
Hedging the hazard of extrapolation by calculating two bracketing cases
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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 2100.
Pfeffer et al, Kinematic Constraints on 21st Century Sea Level Rise, Science, 2008
3 Scenarios (SLR in mm)
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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?
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Rignot et al 2011, Greenland mass loss
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Rignot et al 2011, Greenland mass loss
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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 & Greenland 15± 2
Glaciers and Ice Caps 8 ± 4 (using Meier et al 2007)
Thermal Expansion 9 ± 3 (using IPCC AR4)
Total Sea Level Rise by 2050
32 ± 5
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Year GR SMB GR D GR MBM sigma Year Ant SMB Ant D Ant MBM sigma1992 486.9157292 513.6 -26.7 51 1992 2211.979938 2024.705477 187.2744612 91
Projected SLR from Rignot data using GLM methods – Greenland
SLE by 2100:14.2 ± 5.5 cm
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Projected SLR from Rignot data using GLM methods – Antarctica1992-2009
SLE by 2100:25.0 ± 16.5 cm
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Projected SLR from Rignot data using GLM methods – Antarctica1994-2009
SLE by 2100:11.0 ± 13.0 cm
Effect of dropping first 2 years of 17 year data series
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Projected SLR from Rignot data using GLM methods – Antarctica + Greenland
Rignot et al’s projection for Greenland + Antarctica: by 2100: 56 ± 3 cm
Using GLMGreenland + AntarcticaSLE by 2100:
20.7 ± 5.6 cm
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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
INSTAAR Univ. of Colorado
Time
Mas
s Lo
ss R
ate
(<0)
Stationary process: continued accelerationTransitional process: stabilizes at new steady stateTransient 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).
Pro
babi
lity
of
Occ
urre
nce
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 andSkinny 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.
