the record of sea level change from satellite measurements: what have we learned?
TRANSCRIPT
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What Have We Learned?
Bowie Lecture Fall AGU 2005
R. S. NeremR. S. NeremColorado Center for Astrodynamics ResearchColorado Center for Astrodynamics Research
Cooperative Institute for Research in Environmental SciencesCooperative Institute for Research in Environmental SciencesUniversity of Colorado at BoulderUniversity of Colorado at Boulder
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Many Thanks!Many Thanks!
“Unselfish Cooperation in Research”
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Global Surface Temperature Global Surface Temperature AnomaliesAnomalies
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GISS [Hansen et al., 2005]
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Global Climate Model PredictionsGlobal Climate Model Predictions
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Year [Suzuki et al., 2005]
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Global Climate Model PredictionsGlobal Climate Model Predictions
[Suzuki et al., 2005]
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Earth’s Heat Balance (1955-1998)Earth’s Heat Balance (1955-1998)
Estimates of Earth's heat balance components (1022 J) for the 1955-1998 period.
[Levitus et al., 2005]
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Effects of Sea Level RiseEffects of Sea Level Rise
1 meter 2 meters
4 meters 8 meters GFDL
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The Bathtub Sea Level ModelThe Bathtub Sea Level Model
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The Bathtub Sea Level ModelThe Bathtub Sea Level Model
+
-
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Sea Level MeasurementsSea Level Measurements
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Causes of Sea Level ChangeCauses of Sea Level Change
Inflow Bathtub Outflow
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Causes of Sea Level ChangeCauses of Sea Level Change
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Causes of Sea Level ChangeCauses of Sea Level Change• Thermal Expansion (~ 1 meter potential)Thermal Expansion (~ 1 meter potential)• Water Exchange with Continents Water Exchange with Continents (potential)(potential)– Greenland Ice Greenland Ice (7 (7 meters)meters)
– Antarctic Ice Antarctic Ice (60 (60 meters)meters)
– Mountain Glaciers Mountain Glaciers (0.5 (0.5 meter)meter)
– Terrestrial Water Storage Variations Terrestrial Water Storage Variations (< (< 0.5 meter)0.5 meter)
– Other (halosteric, etc.)Other (halosteric, etc.)
€
ΔSLTotal = ΔSLThermosteric + ΔSLGreenland + ΔSLAntarctica
+ ΔSLGlaciers + ΔSLStorage + ΔSLOther
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GRAVITY
REBOUND
Satellite Measurements of Sea Level Satellite Measurements of Sea Level ChangeChange
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Glacial Isostatic AdjustmentGlacial Isostatic Adjustment
[James et al., 2005]
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Glacial Isostatic AdjustmentGlacial Isostatic Adjustment
-7.0 -2.0 -1.5 -1.0 -0.5 0 0.5 1.0 1.5 2.0 25.0 Present-Day Radial Deformation (mm/year)
[Milne, 2005]
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Sea Level Change BudgetSea Level Change Budget
€
ΔSLTotal = ΔSLThermosteric + ΔSLGreenland + ΔSLAntarctica
+ ΔSLGlaciers + ΔSLStorage + ΔSLOther
Total Sea LevelTotal Sea Level
Last Decade (mm/year)
20th Century (mm/year)
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Past Sea Level ChangesPast Sea Level Changes
Alley et al. [2005]
Avg 10 mm/yrPeak 50 mm/yr
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PSMSL Sea Level Records > 10 yearsPSMSL Sea Level Records > 10 years
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PSMSL Sea Level Records > 50 yearsPSMSL Sea Level Records > 50 years
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Tide Gauge Sea Level MeasurementsTide Gauge Sea Level Measurements
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Rate ~ 1.8 mm/year
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Tide Gauge Sea Level MeasurementsTide Gauge Sea Level Measurements• The rate of sea level The rate of sea level change over the 20th change over the 20th century is generally century is generally taken as 1.8 mm/year taken as 1.8 mm/year [e.g. [e.g. DouglasDouglas, 1991]., 1991].
• Suggestions of a tide Suggestions of a tide gauge geographic sampling gauge geographic sampling bias [bias [Cabanes et alCabanes et al., ., 2001] appear to have been 2001] appear to have been resolved [resolved [Miller and Miller and DouglasDouglas, 2004], though , 2004], though spatial sampling is still spatial sampling is still a concern.a concern.
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TOPEX/PoseidonTOPEX/Poseidonand Jasonand Jason
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The Jason MissionThe Jason Mission
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Tide Gauges versus Satellite Tide Gauges versus Satellite AltimetryAltimetry
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TOPEX/Poseidon and JasonTOPEX/Poseidon and Jason10-day Groundtrack10-day Groundtrack
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TOPEX Sea Level: January 1998TOPEX Sea Level: January 1998
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TOPEX/Poseidon: In the beginning……TOPEX/Poseidon: In the beginning……
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Correlation = +0.5
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Nerem, R. S., “Global Mean Sea Level Variations from TOPEX/POSEIDON Altimeter Data,” Science, Vol. 268, pp. 708-710, May 5, 1995.Nerem, R. S., Global Mean Sea Level Change: Correction, Science, Letters to the Editor, Vol. 275, p. 1053, February 21, 1997.
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Tide Gauges Available for Altimeter Tide Gauges Available for Altimeter CalibrationCalibration
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TOPEX Tide Gauge CalibrationTOPEX Tide Gauge Calibration
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TOPEX and Jason Tide Gauge TOPEX and Jason Tide Gauge CalibrationsCalibrations
TOPEX
Jason
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GPS ANTENNA (JPL)WVR (JPL)
BUBBLER (NOAA)ACOUSTIC (NOAA)
EQUIP SHED
MET SENSORS
Point Arguello, CA
+ 54 m
+ 27 m
+ 6 m
LASERSENSOR (CU)
Platform Harvest Calibration SitePlatform Harvest Calibration Site
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Global Mean Sea Level VariationsGlobal Mean Sea Level Variations
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Global Mean Sea Level VariationsGlobal Mean Sea Level Variations
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Global Mean Sea Level VariationsGlobal Mean Sea Level Variations
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Seasonal variations removed
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Global Mean Sea Level VariationsGlobal Mean Sea Level Variations
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Seasonal variations removedGIA correction applied (0.3 mm/year)
Rate = 3.2 ± 0.4 mm/year
http://sealevel.colorado.edu
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Sea Level Change BudgetSea Level Change Budget
€
ΔSLTotal = ΔSLThermosteric + ΔSLGreenland + ΔSLAntarctica
+ ΔSLGlaciers + ΔSLStorage + ΔSLOther
Thermal ExpansionThermal Expansion3.2
1.8
Last Decade (mm/year)
20th Century (mm/year)
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Thermosteric Sea Level ChangeThermosteric Sea Level Change
[Levitus et al., 2005; Antonov et al., 2005]
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Rate = 0.4 mm/year (1955-2004)
Rate = 1.2 - 1.6 mm/year (1993-2004)
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Decadal Variability Due to Volcanic Decadal Variability Due to Volcanic Forcing?Forcing?
[Church et al., 2005]
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Total (Altimetry) Thermosteric
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Total versus Thermosteric Sea Level Total versus Thermosteric Sea Level ChangeChange
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Total (Altimetry) Thermosteric
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3.2 mm/year
1.2 mm/year
[Willis et al., 2005]
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Global Sea Level Trends: 1993-2005Global Sea Level Trends: 1993-2005
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Global Sea Level TrendsGlobal Sea Level Trends
Altimetry
Climate Model(MIROC)
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Sea Level Variations versus Sea Level Variations versus LatitudeLatitude
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Sea Level Change versus LatitudeSea Level Change versus Latitude
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Total Sea Level (TOPEX/Jason)Thermosteric (Willis)
Latitude
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Sea Level Change BudgetSea Level Change Budget
€
ΔSLTotal = ΔSLThermosteric + ΔSLGreenland + ΔSLAntarctica
+ ΔSLGlaciers + ΔSLStorage + ΔSLOther
Greenland and Antarctica Ice MeltGreenland and Antarctica Ice Melt3.2
1.8
1.2
0.4
Last Decade (mm/year)
20th Century (mm/year)
Mountain Glaciers and Water StorageMountain Glaciers and Water Storage
Water mass redistribution changes the Earth’s gravity field
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GRACEGRACEGravity Recovery and Climate Gravity Recovery and Climate
ExperimentExperiment
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GRACE Surface Water Mass VariationsGRACE Surface Water Mass Variations
Swenson, Leuliette, Nerem, 2005
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GRACE Global Ocean MassGRACE Global Ocean Mass
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GRACEAltimeter - Steric
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Detrended
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The Global Water CycleThe Global Water Cycle
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Ocean/Continents Mass Change from Ocean/Continents Mass Change from GRACEGRACE
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Continents Ocean
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GRACE Continental Water Mass GRACE Continental Water Mass EstimatesEstimates
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AfricaEurasiaNorth AmericaSouth America
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GRACE Ocean Water Mass EstimatesGRACE Ocean Water Mass Estimates
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AtlanticIndianPacific
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GRACE Surface Water - South AmericaGRACE Surface Water - South America
[Lemoine et al., 2005]
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Contribution of Amazon to Sea Level Contribution of Amazon to Sea Level ChangeChange
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Global OceanAmazon Contribution
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GRACE Geoid Change Trend: 2002-2005GRACE Geoid Change Trend: 2002-2005
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Sea Level Change BudgetSea Level Change Budget
€
ΔSLTotal = ΔSLThermosteric + ΔSLGreenland + ΔSLAntarctica
+ ΔSLGlaciers + ΔSLStorage + ΔSLOther
Greenland and Antarctica Ice MeltGreenland and Antarctica Ice Melt3.2
1.8
1.2
0.4
Last Decade (mm/year)
20th Century (mm/year)
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Polar Ice and Sea Level ChangePolar Ice and Sea Level Change
[Mitrovica et al., 2001]1.20 1.10 1.00 0.90 0.80 0.70 0.60 0.50 0.40 0.30 0.20 0.10 0.0
Antarctica
Greenland
• Polar ice Polar ice gravitationally gravitationally attracts the ocean attracts the ocean waterwater
• Melting of ice causes Melting of ice causes regional fall of sea regional fall of sea level in the vicinity level in the vicinity of the ice sheetof the ice sheet
• Patterns fit to tide Patterns fit to tide gauge observations:gauge observations:
€
ΔSLGreenland = 0.6 mm/yearΔSLAntarctica + ΔSLThermosteric
= 0.6 −1.0 mm/year
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The Sea Level “Enigma”The Sea Level “Enigma”
• Observed sea level rise over the 20th century is Observed sea level rise over the 20th century is ~1.8 mm/year.~1.8 mm/year.
• Approximately 0.4 mm/year is attributed to thermal Approximately 0.4 mm/year is attributed to thermal expansion, leaving ~1.4 mm/year to be attributed expansion, leaving ~1.4 mm/year to be attributed to other sources (most likely melting ice)to other sources (most likely melting ice)
• The Earth’s rotation is very sensitive to melting The Earth’s rotation is very sensitive to melting large ice sheets and glaciers, but also to Glacial large ice sheets and glaciers, but also to Glacial Isostatic Adjustment.Isostatic Adjustment.
• Observations of changes in the Earth’s rotation Observations of changes in the Earth’s rotation appear to be well described by models of Glacial appear to be well described by models of Glacial Isostatic Adjustment (GIA), and thus little room Isostatic Adjustment (GIA), and thus little room is left for a contribution from melting ice.is left for a contribution from melting ice.
Munk, W., Twentieth century sea level: An engima,Proc. Nat. Acad. Sci., 99, 6550-6555, 2002.
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Sea Level “Enigma”Sea Level “Enigma”
Ancient Eclipse Data
Drift of Rotation Pole Oblateness Variations
Satellite Laser Ranging
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Earth’s Rotational StabilityEarth’s Rotational Stability
[Mitrovica et al., 2005]
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Sea Level Enigma: Recent Sea Level Enigma: Recent DevelopmentsDevelopments
• Improved theory for Earth’s Improved theory for Earth’s rotational stability rotational stability significantly changes the GIA significantly changes the GIA modeling predictions.modeling predictions.
• Revised estimates of the Revised estimates of the Earth’s oblateness variations Earth’s oblateness variations are now available, which are now available, which include uncertainties in the include uncertainties in the knowledge of the 18.6 year knowledge of the 18.6 year tide.tide.
• Better estimates of the Better estimates of the rotation pole drift are now rotation pole drift are now available.available.
• These developments now require These developments now require a 20th century contribution a 20th century contribution from melting ice of ~1 mm/year from melting ice of ~1 mm/year in order to explain the Earth in order to explain the Earth rotation observations.rotation observations.
[Mitrovica et al., 2005]
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Salinity Changes - Ocean FresheningSalinity Changes - Ocean Freshening
[Munk, 2003]
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Greenland Ice ContributionsGreenland Ice Contributions
[Johannessen et al., 2005][Rignot and Kanagaratnam, 2005]
InSAR: 0.23-0.55 mm/yr
[Krabill et al., 2004]
Laser Alt: 0.25 mm/yr Radar Alt: Accumulation
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Greenland Melt ExtentGreenland Melt Extent
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Antarctic Ice Mass Flux from InSARAntarctic Ice Mass Flux from InSAR
Rapid coastal thinning in Bellinghausen and Amundsen sectors of West Antarctica-177±30 km3/yr
Interior thickening and peripheral thinning in East Antarctica+9±30 km3/yr
SLR 0.4 to 0.6 mm/yr
-114 km3/yr
-37±20 km3/yr
+33 km3/yr
-38 km3/yr+48 km3/yr
-2 km3/yr
+5 km3/yr
-22 km3/yr
-3 km3/yr
+5 km3/yr
-2 km3/yr
-56 km3/yr
-2 km3/yr
+21 km3/yr
-4 km3/yr
-33 km3/yr
-4 km3/yr
-49±20 km3/yr
Peninsula: loss in Graham land, gain in Palmer land.
[Rignot, 2005]
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Antarctic Ice Changes from Radar Antarctic Ice Changes from Radar AltimetryAltimetry
Interior thickening in East Antarctica - coastal thinning or near balance of coastal East Antarctica (-0.12 mm/yr SLR).
Rapid thinning in Amundsen/Belliingshausen sea sectors of West Antarctica.
[Davis et al., 2005]
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Ice Height from Radar Altimeter Ice Height from Radar Altimeter MeasurementsMeasurements
[Zwally et al., 2005]
Greenland Margins ~ -0.12 mm/yearGreenland Interior ~ +0.14 mm/yearWAIS ~ -0.12 mm/yearEAIS ~ +0.04 mm/year
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Greenland Mass Variability from Greenland Mass Variability from GRACEGRACE
[Velicogna and Wahr, 2005]
0.45 ± .06 mm/year
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Antarctica Ice Mass Change from Antarctica Ice Mass Change from GRACEGRACE
[Velicogna and Wahr, 2005]
0.44 ± .23 mm/year
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Ice Mass Variability from GRACEIce Mass Variability from GRACE
[Luthcke et al., 2005]
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Preliminary ICESat Preliminary ICESat ResultsResults
dh/dt Laser 3a (10/7 - 11/7, 2004) -
Laser 2a (9/25 - 11/18, 2003)
[Luthcke et al., 2005]
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Sea Level Change BudgetSea Level Change Budget
€
ΔSLTotal = ΔSLThermosteric + ΔSLGreenland + ΔSLAntarctica
+ ΔSLGlaciers + ΔSLStorage + ΔSLOther
Melting of Mountain GlaciersMelting of Mountain Glaciers
3.2
1.8
Last Decade (mm/year)
20th Century (mm/year)
1.2
0.4
0.4
0.2
0.5
0.3
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GPS Crustal Uplift in AlaskaGPS Crustal Uplift in Alaska
[Larsen et al., 2005]
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Alaska Glacier Mass Changes from Alaska Glacier Mass Changes from GRACEGRACE
[Tamisiea et al., 2005]
Sea Level Contribution of 0.3 mm/year over 2002-2004
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Ice Volume Changes in PatagoniaIce Volume Changes in Patagonia1975 - 1995 - 20001975 - 1995 - 2000
ΔMSL = 0.04 mm/year (1975 - 1990s)ΔMSL = 0.1 mm/year (1995-2000)
[Rignot et al., 2003]
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Mountain Glaciers: Contribution to Mountain Glaciers: Contribution to Sea LevelSea Level
0
5
10
15
20
25
1960 1970 1980 1990 2000 2010Year
[Dyurgerov and Meier, 2005]
0
5
10
15
20
25
1960 1970 1980 1990 2000 2010Year
1961-2003: 0.5 mm/year
1994-2003: 0.9 mm/year
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Sea Level Change BudgetSea Level Change Budget
€
ΔSLTotal = ΔSLThermosteric + ΔSLGreenland + ΔSLAntarctica
+ ΔSLGlaciers + ΔSLStorage + ΔSLOther
Land Water StorageLand Water Storage
3.2
1.8
Last Decade (mm/year)
20th Century (mm/year)
1.2
0.4
0.4
0.2
0.5
0.3
0.9
0.4
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Sea Level Change BudgetSea Level Change Budget
€
ΔSLTotal = ΔSLThermosteric + ΔSLGreenland + ΔSLAntarctica + ΔSLGlaciers + ΔSLStorage + ΔSLOther
3.0 = 1.2 0.4 0.5 0.9 ? ?
1.4 = 0.4 0.2 0.3 0.5 ? ?
20th Century: 1.8 mm/year (observed)
Last Decade: 3.2 mm/year (observed)
Last Decade (mm/year)
20th Century (mm/year)
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What Have We Learned?What Have We Learned?• The “enigma” of 20th century sea level change has The “enigma” of 20th century sea level change has been largely resolved and a larger contribution from been largely resolved and a larger contribution from melting ice is now allowed (~1 mm/year).melting ice is now allowed (~1 mm/year).
• Satellite altimetry has observed an average increase Satellite altimetry has observed an average increase in sea level of 3.2 mm/year over 1993-2005, which in sea level of 3.2 mm/year over 1993-2005, which probably reflects an acceleration versus the 20th probably reflects an acceleration versus the 20th century rate (~1.8 mm/year).century rate (~1.8 mm/year).
• Roughly half the current rise may be attributed to Roughly half the current rise may be attributed to thermal expansion and half to the addition of water thermal expansion and half to the addition of water to the oceans (likely from melting of mountain to the oceans (likely from melting of mountain glaciers and polar ice).glaciers and polar ice).
• Although there are uncertainties in the sea level Although there are uncertainties in the sea level contribution from present-day melting of the ice contribution from present-day melting of the ice sheets and mountain glaciers, there is a growing sheets and mountain glaciers, there is a growing body of evidence that the contribution is large body of evidence that the contribution is large (~1.5-2 mm/year) and accelerating.(~1.5-2 mm/year) and accelerating.
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Satellite Missions Studying Sea Level Satellite Missions Studying Sea Level ChangeChange
Planned/Pending approval
In orbit Approved
00 01 02 03 04 05 06 07 08 09 10 11 12 13 14
JASON-2/OSTM
TOPEX/POSEIDON
JASON-1
Envisat RA-2
Medium accuracy RA (SSH) from high-inclination orbit
High accuracy RA (SSH) from mid-inclination orbit
CRYOSAT-2/LRM
OceanSat-3 AltiKaERS-2 RA
GMES S-3
ICESAT
Geosat Follow-On NPOESS
GRACE GRACE follow-on
Laser Altimetry (ice)
Temporal Gravity (ocean mass) ICESAT-2 ?
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Future Greenland Ice ChangesFuture Greenland Ice Changes
Alley et al. [2005]
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Stay Above Sea Level!Stay Above Sea Level!
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Thanks and Happy Holidays!Thanks and Happy Holidays!