WOCE and BEYOND Nov. 2002

WOCE and BEYOND WOCE and BEYOND Nov. 2002Nov. 2002

Sea Level Rise:Sea Level Rise:Can we explain Can we explain

what we measure?what we measure?

Anny CazenaveAnny CazenaveLEGOS-GRGS/CNESLEGOS-GRGS/CNES

Toulouse, FranceToulouse, France

- - STERIC sea level: change in STERIC sea level: change in DensityDensity

-- EUSTATIC sea level: change in EUSTATIC sea level: change in Ocean Mass Ocean Mass

Temperature Temperature SalinitySalinity

Water mass exchange Water mass exchange with continents and ice capswith continents and ice caps

-1.0 -0.5 0.5 1.0 1.5 2.00.0

0.0 1.0-1.0

mm/year

2.0 mm/year

Thermal expansion

Glaciers

Greenland (present)

Antarctica (present)

Ice sheets (long term)

Permafrost

Sedimentary deposits

TOTAL

OBSERVATIONS

Continental waters

2020thth Century Sea Level Rise, IPCC, 2001 Century Sea Level Rise, IPCC, 2001

SUMMARY OF RECENT RESULTSSUMMARY OF RECENT RESULTS

During the 1990s, sea level has been rising by During the 1990s, sea level has been rising by ~ 3 mm/yr evidence for a recent acceleration ???~ 3 mm/yr evidence for a recent acceleration ???

Steric and eustatic sea level change recognized as Steric and eustatic sea level change recognized as highly non uniform overestimate of the 20highly non uniform overestimate of the 20thth century sea level rise by tide gauges ???century sea level rise by tide gauges ???

New rates for glaciers and ice sheets recent meltingNew rates for glaciers and ice sheets recent melting

Land water mass contribution to sea level rise can Land water mass contribution to sea level rise can now be estimatednow be estimated

ObservationsObservationsofof

Present-Day Sea Level RisePresent-Day Sea Level Rise

Sea Level Rise Sea Level Rise during the 1990sduring the 1990s

fromfromSatellite AltimetrySatellite Altimetry

TOPEX/POSEIDONTOPEX/POSEIDON

SEA LEVEL TRENDS measured by SEA LEVEL TRENDS measured by TOPEX/POSEIDON (1993-2001)TOPEX/POSEIDON (1993-2001)

Trends in mm/year

Satellite Altimetry forSatellite Altimetry for Global Mean Sea Level Global Mean Sea Level

AdvantagesAdvantages• high-precisionhigh-precision• high spatio-temporal high spatio-temporal

resolutionresolution• global coverageglobal coverage• absolute absolute

measurementsmeasurements

DrawbacksDrawbacks• time series still short time series still short

(10 years)(10 years)

• no coverage of high-no coverage of high-latitude oceans (T/P latitude oceans (T/P & Jason)& Jason)

Sea Level Rise Sea Level Rise during the 20during the 20thth century century

fromfromTide GaugesTide Gauges

WORLDWIDE TIDE GAUGE NETWORK -2001-

Tide gauges used by B. Douglas (1997)Tide gauges used by B. Douglas (1997)

SAN FRANCISCOSAN FRANCISCO BRESTBREST

NEW YORKNEW YORK STOCKHOLMSTOCKHOLM

Main processes causing vertical land motions

• Tectonic deformationsTectonic deformations• Seismic activitySeismic activity• Volcanic activityVolcanic activity• Viscous deformation of the Earth’s mantleViscous deformation of the Earth’s mantle (Post Glacial Rebound)(Post Glacial Rebound)• Land subsidence due to sediments compaction, Land subsidence due to sediments compaction,

underground water extraction, etc.underground water extraction, etc.

• Surface loading due to air and water mass Surface loading due to air and water mass redistribution among atmosphere, oceans, redistribution among atmosphere, oceans, continental water reservoirs and ice capscontinental water reservoirs and ice caps

Deformation of the Earth’s mantle under ice sheet loadingDeformation of the Earth’s mantle under ice sheet loadingand POST GLACIAL REBOUNDand POST GLACIAL REBOUND

TIDE GAUGE-BASEDTIDE GAUGE-BASEDSEA LEVEL RISE SEA LEVEL RISE

FOR THE 20FOR THE 20thth CENTURY CENTURYGlobalGlobal

• 1.5 1.5 +/- 0.5 mm/yr (IPCC, 2001)+/- 0.5 mm/yr (IPCC, 2001)

• 1.711.71 +/- 0.55 mm/yr (Douglas, 2001; +/- 0.55 mm/yr (Douglas, 2001;

27 sites)27 sites)

• 1.841.84 +/- 0.35 mm/yr (Peltier, 2001; +/- 0.35 mm/yr (Peltier, 2001;

27 sites)27 sites)

• 1.51.5 +/- 0.4 mm/yr (Tamaseia et al., 2001; 23 +/- 0.4 mm/yr (Tamaseia et al., 2001; 23 sites)sites)

Tide Gauges forTide Gauges for Global Mean Sea Level Global Mean Sea Level

AdvantagesAdvantages• historical historical

information information

(back to 1900)(back to 1900)

• useful for calibrating useful for calibrating onboard altimetry onboard altimetry systemssystems

DrawbacksDrawbacks• heterogeneous and heterogeneous and

limited coveragelimited coverage• gaps in data recordsgaps in data records• land motion land motion

contaminationcontamination• data sensitive to local data sensitive to local

perturbationsperturbations

Sea level change during the last 6000 yearsSea level change during the last 6000 years

20th century

-6000 years present

From Lambeck, 2002From Lambeck, 2002

CONSTRAINTS CONSTRAINTS FROM FROM

ASTRONOMICAL/GEOPHYSICALASTRONOMICAL/GEOPHYSICAL OBSERVABLESOBSERVABLES

CONSTRAINTS CONSTRAINTS FROM FROM

ASTRONOMICAL/GEOPHYSICALASTRONOMICAL/GEOPHYSICAL OBSERVABLESOBSERVABLES

Astronomical/Geophysical ObservablesAstronomical/Geophysical Observables

Non-tidal Earth ’s rotation acceleration or Non-tidal Earth ’s rotation acceleration or length of day -LOD- deceleration: -0.6 ms/cy length of day -LOD- deceleration: -0.6 ms/cy for the past 2500 yearsfor the past 2500 years

Secular decrease of the Earth ’s dynamical Secular decrease of the Earth ’s dynamical flattening : -3x10flattening : -3x10-11-11/yr for the past 25 years/yr for the past 25 years

Secular movement of the Earth ’s rotation  Secular movement of the Earth ’s rotation  pole: 10 m/cy towards Greenland over the past pole: 10 m/cy towards Greenland over the past 100 years100 years

2J&

From Wahr and Davis, 2002 From Wahr and Davis, 2002

Length of DayLength of Day(LoD)(LoD)

variations variations for the past for the past 2500 years2500 yearsLoDLoD

JJ22

-500 year 2000

Secular decrease of the Earth ’s flattening (JSecular decrease of the Earth ’s flattening (J22))

From Cox and Chao, 2002From Cox and Chao, 2002

From Wahr and Davis, 2002 From Wahr and Davis, 2002

Length of DayLength of Day(LoD)(LoD)

variations variations for the past for the past 2500 years2500 yearsLoDLoD

JJ22

-500 year 2000

From Sabadini and Vermeersen, 2002From Sabadini and Vermeersen, 2002

Post Glacial Rebound

PGR + present-day melting

AA+G

observation

Secular Decrease of the Earth’s FlatteningSecular Decrease of the Earth’s Flattening

Long-wavelength geoidLong-wavelength geoid Sketch of the Earth’s interiorSketch of the Earth’s interior

Viscosity of the Earth’s mantleViscosity of the Earth’s mantle

Sketch of the Earth’s interiorSketch of the Earth’s interior

Lower Lower mantlemantle

CoreCore

Upper Upper mantlemantle

Viscosity profilesViscosity profiles from global from global

circulation modelscirculation models

Secular decreases ofSecular decreases ofLength of Day and Earth’s flattening Length of Day and Earth’s flattening

are not are not strong constraints on strong constraints on

present-day eustatic sea level risepresent-day eustatic sea level rise

DO WE UNDERSTAND DO WE UNDERSTAND OBSERVATIONS OBSERVATIONS

OFOFPRESENT-DAY PRESENT-DAY

SEA LEVEL RISE?SEA LEVEL RISE?

Sea Level Rise Sea Level Rise duringduring

the 1990sthe 1990s

Carte des dérives duniveau de la mer entre

1993 et 1998

en haut :Topex/Poseidon

en bas :expansion thermique

SEA LEVEL TRENDS SEA LEVEL TRENDS FOR 1993-1998FOR 1993-1998

(mm/yr)(mm/yr)

Upper map : Upper map : ObservedObserved

(Topex/Poseidon)(Topex/Poseidon)

Bottom map: Bottom map: Computed Computed

(thermal expansion)(thermal expansion)

--

Topex/Poseidon (1993-1998)Topex/Poseidon (1993-1998)

Thermal expansion (1993-1998)Thermal expansion (1993-1998)

From Cabanes et al., 2001-27 mm/yr +27

World ocean temperature data base

S. Levitus, C. Stephens, J.I. Antonov & T.P. BoyerNOAA Atlas NESDIS 40, 2000

World ocean temperature data base

S. Levitus, C. Stephens, J.I. Antonov & T.P. BoyerNOAA Atlas NESDIS 40, 2000

Global gridded time series of ocean temperature data at different depths:

• 0-500 m : yearly means for 1945-1998• 0-3000 m : 5-year means for 1945-1995

Global gridded time series of ocean temperature data at different depths:

• 0-500 m : yearly means for 1945-1998• 0-3000 m : 5-year means for 1945-1995

Topex/Poseidon sea level---Topex/Poseidon sea level---Thermal expansion----Thermal expansion----Résidual----Résidual----

From Cabanes et al., 2001

Sea level rise measured by Topex/Poseidon is mainly caused by

thermal expansion (warming) of ocean waters

Sea Level Rise Sea Level Rise duringduring

the 20the 20thth century century

-1.0 -0.5 0.5 1.0 1.5 2.00.0

0.0 1.0-1.0

mm/year

2.0 mm/year

Thermal expansion

Glaciers

Greenland (present)

Antarctica (present)

Ice sheets (long term)

Permafrost

Sedimentary deposits

TOTAL

OBSERVATIONS

Continental waters

2020thth Century Sea Level Rise, IPCC, 2001 Century Sea Level Rise, IPCC, 2001

Past CenturyPast Century Sea Level Rise:Sea Level Rise:

is the observedis the observed1.5 mm/yr rate1.5 mm/yr rate

too high?too high?OROR

are climate-related are climate-related contributions contributions

underestimated?underestimated?

Past CenturyPast Century Sea Level Rise:Sea Level Rise:

is the observedis the observed1.5 mm/yr rate1.5 mm/yr rate

too high?too high?OROR

are climate-related are climate-related contributions contributions

underestimated?underestimated?

Steric Sea Level Trends for the Upper 3000m (1955-1994)

Global Steric Sea Level (0 - 3000 m)

0.5 +/- 0.05 mm/yr

Steric contribution

(thermal expansion)

to sea level rise for 1955-1995

0.5 +/- 0.05 mm/yr

Steric sea level trends

Global mean steric sea level

From Cabanes et al., 2001

STERIC SEA LEVEL TRENDS (1955-1995)STERIC SEA LEVEL TRENDS (1955-1995)

0.5 +/- 0.05 mm/yr

1.4 +/- 0.1 mm/yr

Steric sea level Steric sea level trends map and trends map and tide gauge sites tide gauge sites used by Douglas used by Douglas

(1997)(1997)

1.3 +/- 0.1 1.3 +/- 0.1 mm/yrmm/yr

0.5 +/- 0.05 mm/yr0.5 +/- 0.05 mm/yr

From Cabanes et al., 2001

SEA LEVEL RISE (1955-1995)SEA LEVEL RISE (1955-1995)

Steric average at the 25 tide gauge sites:Steric average at the 25 tide gauge sites: 1.3 +/- 0.1 mm/yr1.3 +/- 0.1 mm/yr

Observed by tide gauges (25 sites) : Observed by tide gauges (25 sites) : 1.6 +/- 0.15 mm/yr1.6 +/- 0.15 mm/yr

Thermal expansion (global mean) : Thermal expansion (global mean) : 0.5 +/- 0.05 mm/yr0.5 +/- 0.05 mm/yr

Salinity effect (global mean) : Salinity effect (global mean) : 0.05 +/- 0.02 mm/yr0.05 +/- 0.02 mm/yr

SEA LEVEL RISE (1955-1995)SEA LEVEL RISE (1955-1995)

Steric average at the 25 tide gauge sites:Steric average at the 25 tide gauge sites: 1.3 +/- 0.1 mm/yr1.3 +/- 0.1 mm/yr

Observed by tide gauges (25 sites) : Observed by tide gauges (25 sites) : 1.6 +/- 0.15 mm/yr1.6 +/- 0.15 mm/yr

Thermal expansion (global mean) : Thermal expansion (global mean) : 0.5 +/- 0.05 mm/yr0.5 +/- 0.05 mm/yr

Salinity effect (global mean) : Salinity effect (global mean) : 0.05 +/- 0.02 mm/yr0.05 +/- 0.02 mm/yr

Map of steric sea level trends and GLOSS tide gauge network

Steric sea level:- global mean (in blue)-subsampled at GLOSS sites (in red)

The inhomogeneous distribution of historical tide gauges used to estimate the 20th century sea level rise cannot capture

the regional thermosteric variability

Tide gauge-based estimates of 20th century sea level rise too high???

EUSTATIC EUSTATIC SEA LEVEL RISESEA LEVEL RISE

(ocean mass change)(ocean mass change)

Eustatic contribution Eustatic contribution from from

land water storageland water storage(change in the global water cycle(change in the global water cycle))

Eustatic contribution Eustatic contribution from from

land water storageland water storage(change in the global water cycle(change in the global water cycle))

-1.0 -0.5 0.5 1.0 1.5 2.00.0

0.0 1.0-1.0

mm/year

2.0 mm/year

Thermal expansion

Glaciers

Greenland (present)

Antarctica (present)

Ice sheets (long term)

Permafrost

Sedimentary deposits

TOTAL

OBSERVATIONS

Continental waters

2020thth Century Sea Level Rise, IPCC, 2001 Century Sea Level Rise, IPCC, 2001

Precipitation

Evaporation

Evaporation

Transpiration

Precipitation :

RiversLakes

Oceans Soil Moisture

Ground Waters

Atmosphere

Snow Pack

Water mass balance : Water mass balance : dW/dt = P - E - RdW/dt = P - E - R

W: Water stored in soilsW: Water stored in soilsP : PrecipitationP : Precipitation

E : EvapotranspirationE : EvapotranspirationR: RunoffR: Runoff

GLOBAL HYDROLOGICAL GLOBAL HYDROLOGICAL MODELSMODELS

THE LAND DYNAMICS (LaD) MODELTHE LAND DYNAMICS (LaD) MODEL

P.C.D. Milly and A.B. ShmakinP.C.D. Milly and A.B. ShmakinNOAA/university of PrincetonNOAA/university of Princeton

J. Hydrometeorology, 2001J. Hydrometeorology, 2001

GLOBAL MODELING OF LAND WATER GLOBAL MODELING OF LAND WATER AND AND

ENERGY BALANCESENERGY BALANCES

LaD MODEL

Monthly grids of :- Snow depth- Soil moisture- Underground waters (aquifers)

for 1981-1998

LAND WATER MASS CONTRIBUTION TO SEA LEVEL CHANGELAND WATER MASS CONTRIBUTION TO SEA LEVEL CHANGELAND WATER MASS CONTRIBUTION TO SEA LEVEL CHANGE

0.13 mm/yr0.13 mm/yr

0.05 mm/yr0.05 mm/yr

0.18 mm/yr0.18 mm/yr

Soil watersSoil waters

SnowSnow

TotalTotal

Trends in land water content (1981-1998)Trends in land water content (1981-1998)

drierdrier wetterwetter - 3 mm/yr 3 mm/yr- 3 mm/yr 3 mm/yr

Trends in precipitation on land (1981-1998)

drierdrier wetterwetter

Land water mass contribution to sea level rise over 1980-2000

amounts to 0.2 mm/year

EUSTATIC CONTRIBUTION EUSTATIC CONTRIBUTION FROM FROM

MOUNTAIN GLACIERS MOUNTAIN GLACIERS ANDAND

ICE SHEETSICE SHEETS

EUSTATIC CONTRIBUTION EUSTATIC CONTRIBUTION FROM FROM

MOUNTAIN GLACIERS MOUNTAIN GLACIERS ANDAND

ICE SHEETSICE SHEETS

Eustatic contribution from mountain Eustatic contribution from mountain glaciers, ice sheets and land watersglaciers, ice sheets and land waters

MOUNTAIN GLACIERSMOUNTAIN GLACIERS : < +0.5 mm/yr : < +0.5 mm/yr

ICE SHEETSICE SHEETS : : Greenland : +0.13 mm/yr Greenland : +0.13 mm/yr (Krabill et al., 2000)(Krabill et al., 2000)

Antarctica : +0.16 +/- 0.05 mm/yr (WA) Antarctica : +0.16 +/- 0.05 mm/yr (WA) 0 +/- 0.07 mm/yr (EA)0 +/- 0.07 mm/yr (EA) total = + 0.16 mm/yrtotal = + 0.16 mm/yr

(Rignot and Thomas, 2002)(Rignot and Thomas, 2002)

LAND WATERLAND WATER :+0.2 mm/yr :+0.2 mm/yr (Milly et al., 2002)(Milly et al., 2002)

TOTAL : ~1 mm/yrTOTAL : ~1 mm/yr

From Dyurgerov and Meier, 2002From Dyurgerov and Meier, 2002

Sea level rise due to mountain glaciersSea level rise due to mountain glaciers

Eustatic contributions from mountain Eustatic contributions from mountain glaciers, ice sheets and land watersglaciers, ice sheets and land waters

MOUNTAIN GLACIERSMOUNTAIN GLACIERS : < +0.5 mm/yr : < +0.5 mm/yr

ICE SHEETSICE SHEETS : : Greenland : +0.13 mm/yr Greenland : +0.13 mm/yr (Krabill et al., 2000)(Krabill et al., 2000)

Antarctica : +0.16 +/- 0.05 mm/yr (WA) Antarctica : +0.16 +/- 0.05 mm/yr (WA) 0 +/- 0.07 mm/yr (EA)0 +/- 0.07 mm/yr (EA) total = + 0.16 mm/yrtotal = + 0.16 mm/yr

(Rignot and Thomas, 2002)(Rignot and Thomas, 2002)

LAND WATERLAND WATER :+0.2 mm/yr :+0.2 mm/yr (Milly et al., 2002)(Milly et al., 2002)

TOTAL : ~1 mm/yrTOTAL : ~1 mm/yr

since SEA LEVEL RISE of the since SEA LEVEL RISE of the 1990s is fully explained by 1990s is fully explained by

thermal expansion, there is no thermal expansion, there is no room for an additional 1 mm/yr room for an additional 1 mm/yr

eustatic contribution…..eustatic contribution…..

-1.0 -0.5 0.5 1.0 1.5 2.00.0

0.0 1.0-1.0

mm/year

2.0 mm/year

Thermal expansion

Glaciers

Greenland (present)

Antarctica (present)

Ice sheets (long term)

Permafrost

Sedimentary deposits

TOTAL

OBSERVATIONS

Continental waters

2020thth Century Sea Level Rise, IPCC, 2001 Century Sea Level Rise, IPCC, 2001

ACCELERATION OF SEA LEVEL ACCELERATION OF SEA LEVEL RISE IN THE LAST 1-2 DECADES ???RISE IN THE LAST 1-2 DECADES ???

STERIC SEA LEVEL ---------OBSERVED BY TOPEX/POSEIDON ------

1950 1990

1945 20001970

GLOBAL OCEAN - STERIC SEA LEVEL- EOF mode 1GLOBAL OCEAN - STERIC SEA LEVEL- EOF mode 1

(0-500 m(0-500 m))0-3000 m0-3000 m

1945 1970 2000

1945 20001970

ATLANTIC OCEAN - STERIC SEA LEVEL-EOF mode 1ATLANTIC OCEAN - STERIC SEA LEVEL-EOF mode 1

0-500 m0 -3000 m

1945 1970 2000

TOPEX/POSEIDONTOPEX/POSEIDONSEA LEVELSEA LEVEL

EOF mode 1EOF mode 1

1993 2003

From Dyurgerov and Meier, 2002From Dyurgerov and Meier, 2002

Sea level rise due to mountain glaciersSea level rise due to mountain glaciers

change in rate?

PERSPECTIVESPERSPECTIVES

JASON-1JASON-1

Global mean sea level from Topex/Poseidon and Jason-1Global mean sea level from Topex/Poseidon and Jason-1

Jason-1Jason-1

GRACE satellites launched on March 17, 2002

Circulation oceanique

Variations temporelles du champ de gravitéVariations temporelles du champ de gravitéTEMPORAL CHANGE OF THE GRAVITY FIELDTEMPORAL CHANGE OF THE GRAVITY FIELD

GRACE MISSION:GRACE MISSION:

Spatio-temporal gravity variationsSpatio-temporal gravity variationsResolution : 2°x2°Resolution : 2°x2°

Precision : 0.5 cm (water height)Precision : 0.5 cm (water height)Time scale : Time scale :

1 month to several years1 month to several years

GRACE MISSION:GRACE MISSION:

Spatio-temporal gravity variationsSpatio-temporal gravity variationsResolution : 2°x2°Resolution : 2°x2°

Precision : 0.5 cm (water height)Precision : 0.5 cm (water height)Time scale : Time scale :

1 month to several years1 month to several years

Precipitation

Evaporation

Evaporation

Transpiration

Precipitation :

RiversLakes

Oceans Soil Moisture

Ground Waters

Atmosphere

Snow Pack

Separation of thermalSeparation of thermal and mass contributionsand mass contributions

Sea level riseSea level riseGRACE (land)GRACE (land)

Land water Land water andand

ice sheetsice sheets mass balancemass balance

Ocean water mass changeOcean water mass change

GRACE (ocean)GRACE (ocean)

JASONJASON