the record of sea level change from satellite measurements: what have we learned?

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40 The Record of Sea Level Changefrom Satellite Measurements:

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

Many Thanks!Many Thanks!

“Unselfish Cooperation in Research”

Global Surface Temperature Global Surface Temperature AnomaliesAnomalies

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1880 1900 1920 1940 1960 1980 2000Year

GISS [Hansen et al., 2005]

Global Climate Model PredictionsGlobal Climate Model Predictions

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0.25

0.3

2000 2020 2040 2060 2080 2100

1pctto2x

a1b

commit

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a2

Year [Suzuki et al., 2005]

Global Climate Model PredictionsGlobal Climate Model Predictions

[Suzuki et al., 2005]

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]

Effects of Sea Level RiseEffects of Sea Level Rise

1 meter 2 meters

4 meters 8 meters GFDL

The Bathtub Sea Level ModelThe Bathtub Sea Level Model

The Bathtub Sea Level ModelThe Bathtub Sea Level Model

+

-

Sea Level MeasurementsSea Level Measurements

Causes of Sea Level ChangeCauses of Sea Level Change

Inflow Bathtub Outflow

Causes of Sea Level ChangeCauses of Sea Level Change

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.)

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ΔSLTotal = ΔSLThermosteric + ΔSLGreenland + ΔSLAntarctica

+ ΔSLGlaciers + ΔSLStorage + ΔSLOther

GRAVITY

REBOUND

Satellite Measurements of Sea Level Satellite Measurements of Sea Level ChangeChange

Glacial Isostatic AdjustmentGlacial Isostatic Adjustment

[James et al., 2005]

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]

Sea Level Change BudgetSea Level Change Budget

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Total Sea LevelTotal Sea Level

Last Decade (mm/year)

20th Century (mm/year)

Past Sea Level ChangesPast Sea Level Changes

Alley et al. [2005]

Avg 10 mm/yrPeak 50 mm/yr

PSMSL Sea Level Records > 10 yearsPSMSL Sea Level Records > 10 years

PSMSL Sea Level Records > 50 yearsPSMSL Sea Level Records > 50 years

Tide Gauge Sea Level MeasurementsTide Gauge Sea Level Measurements

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Rate ~ 1.8 mm/year

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.

TOPEX/PoseidonTOPEX/Poseidonand Jasonand Jason

The Jason MissionThe Jason Mission

QuickTime™ and aCinepak decompressor

are needed to see this picture.

Tide Gauges versus Satellite Tide Gauges versus Satellite AltimetryAltimetry

TOPEX/Poseidon and JasonTOPEX/Poseidon and Jason10-day Groundtrack10-day Groundtrack

TOPEX Sea Level: January 1998TOPEX Sea Level: January 1998

TOPEX/Poseidon: In the beginning……TOPEX/Poseidon: In the beginning……

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1993 1993.5 1994 1994.5 1995

ΔMSLΔSST

Year

Correlation = +0.5

Rate = +3.9 ± 0.8 mm/year

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.

Tide Gauges Available for Altimeter Tide Gauges Available for Altimeter CalibrationCalibration

TOPEX Tide Gauge CalibrationTOPEX Tide Gauge Calibration

TOPEX and Jason Tide Gauge TOPEX and Jason Tide Gauge CalibrationsCalibrations

TOPEX

Jason

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

Global Mean Sea Level VariationsGlobal Mean Sea Level Variations

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TOPEX/PoseidonJason

Year

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Seasonal variations removed


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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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Thermal ExpansionThermal Expansion3.2

1.8



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Thermosteric Sea Level ChangeThermosteric Sea Level Change

[Levitus et al., 2005; Antonov et al., 2005]

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1960 1970 1980 1990 2000Year

Rate = 0.4 mm/year (1955-2004)

Rate = 1.2 - 1.6 mm/year (1993-2004)

Decadal Variability Due to Volcanic Decadal Variability Due to Volcanic Forcing?Forcing?

[Church et al., 2005]

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1992 1994 1996 1998 2000 2002 2004 2006

Total (Altimetry) Thermosteric

Year

Total versus Thermosteric Sea Level Total versus Thermosteric Sea Level ChangeChange

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1992 1994 1996 1998 2000 2002 2004 2006

Total (Altimetry) Thermosteric

Year

3.2 mm/year

1.2 mm/year

[Willis et al., 2005]

Global Sea Level Trends: 1993-2005Global Sea Level Trends: 1993-2005

Global Sea Level TrendsGlobal Sea Level Trends

Altimetry

Climate Model(MIROC)

Sea Level Variations versus Sea Level Variations versus LatitudeLatitude

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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Greenland and Antarctica Ice MeltGreenland and Antarctica Ice Melt3.2

1.8

1.2

0.4



Mountain Glaciers and Water StorageMountain Glaciers and Water Storage

Water mass redistribution changes the Earth’s gravity field

GRACEGRACEGravity Recovery and Climate Gravity Recovery and Climate

ExperimentExperiment



GRACE Surface Water Mass VariationsGRACE Surface Water Mass Variations

Swenson, Leuliette, Nerem, 2005



GRACE Global Ocean MassGRACE Global Ocean Mass

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GRACEAltimeter - Steric

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Detrended

The Global Water CycleThe Global Water Cycle

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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2002.5 2003 2003.5 2004 2004.5 2005 2005.5

AtlanticIndianPacific

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GRACE Surface Water - South AmericaGRACE Surface Water - South America

[Lemoine et al., 2005]



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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Greenland and Antarctica Ice MeltGreenland and Antarctica Ice Melt3.2

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1.2

0.4



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:

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ΔSLGreenland = 0.6 mm/yearΔSLAntarctica + ΔSLThermosteric

= 0.6 −1.0 mm/year

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.

Sea Level “Enigma”Sea Level “Enigma”

Ancient Eclipse Data

Drift of Rotation Pole Oblateness Variations

Satellite Laser Ranging



Earth’s Rotational StabilityEarth’s Rotational Stability

[Mitrovica et al., 2005]

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]

Salinity Changes - Ocean FresheningSalinity Changes - Ocean Freshening

[Munk, 2003]

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

Greenland Melt ExtentGreenland Melt Extent

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]

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]

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

Greenland Mass Variability from Greenland Mass Variability from GRACEGRACE

[Velicogna and Wahr, 2005]

0.45 ± .06 mm/year

Antarctica Ice Mass Change from Antarctica Ice Mass Change from GRACEGRACE

[Velicogna and Wahr, 2005]

0.44 ± .23 mm/year

Ice Mass Variability from GRACEIce Mass Variability from GRACE

[Luthcke et al., 2005]

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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Melting of Mountain GlaciersMelting of Mountain Glaciers

3.2

1.8



1.2

0.4

0.4

0.2

0.5

0.3

GPS Crustal Uplift in AlaskaGPS Crustal Uplift in Alaska

[Larsen et al., 2005]

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

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]

Mountain Glaciers: Contribution to Mountain Glaciers: Contribution to Sea LevelSea Level

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[Dyurgerov and Meier, 2005]

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1961-2003: 0.5 mm/year

1994-2003: 0.9 mm/year


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Land Water StorageLand Water Storage

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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)



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.

Satellite Missions Studying Sea Level Satellite Missions Studying Sea Level ChangeChange

Planned/Pending approval

In orbit Approved

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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 ?

Future Greenland Ice ChangesFuture Greenland Ice Changes

Alley et al. [2005]

Stay Above Sea Level!Stay Above Sea Level!

Thanks and Happy Holidays!Thanks and Happy Holidays!

the record of sea level change from satellite measurements: what have we learned?

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