Present-Day Sea Level Change Present-Day Sea Level Change Assessment and Key UncertaintiesAssessment and Key Uncertainties

Anny CazenaveAnny CazenaveLEGOS, ToulouseLEGOS, Toulouse

Church et al., 2004, 2006

Holgate and Woodworth, 2004

2020thth century sea level rise century sea level rise

Satellite altimetry

1.8 +/- 0.3 mm/yr

Rate of rise : 3.0 +/-0.4 mm/yr With PGR correction : 3.3 +/- 0.4 mm/yr

Global mean sea level from Topex/Poseidon altimetry

1993-2005

Observed rate of sea level rise:Observed rate of sea level rise:

1950-20001950-2000 : 1.8 : 1.8 +/-+/- 0.30.3 mm/yr mm/yr1993-20051993-2005 : 3.3 : 3.3 +/- 0.4+/- 0.4 mm/yr mm/yr

Acceleration?Acceleration?Decadal fluctuation?Decadal fluctuation?Influence of other processes?Influence of other processes?(e.g., recovery of Pinatubo eruption)(e.g., recovery of Pinatubo eruption)

Observed rate of sea level rise:Observed rate of sea level rise:

1950-20001950-2000 : 1.8 : 1.8 +/-+/- 0.30.3 mm/yr mm/yr1993-20051993-2005 : 3.3 : 3.3 +/- 0.4+/- 0.4 mm/yr mm/yr

Acceleration?Acceleration?Decadal fluctuation?Decadal fluctuation?Influence of other processes?Influence of other processes?(e.g., recovery of Pinatubo eruption)(e.g., recovery of Pinatubo eruption)

Regional variability Regional variability from historical tide gaugesfrom historical tide gauges

Brest

New York

Buenos-Aires

1900 2000

Honolulu

Time

Global coverage of altimeter satellitesGlobal coverage of altimeter satellites

Geographical distribution of sea level Geographical distribution of sea level trends (1993-2005)trends (1993-2005)

Causes of sea level change….Causes of sea level change….

- - Thermal expansion of sea waterThermal expansion of sea water due to ocean warmingdue to ocean warming

-Ocean mass change due to water -Ocean mass change due to water mass exchange with glaciers, ice mass exchange with glaciers, ice sheets and land reservoirssheets and land reservoirs

Causes of sea level change….Causes of sea level change….

- - Thermal expansion of sea waterThermal expansion of sea water due to ocean warmingdue to ocean warming

-Ocean mass change due to water -Ocean mass change due to water mass exchange with glaciers, ice mass exchange with glaciers, ice sheets and land reservoirssheets and land reservoirs

Thermal ExpansionThermal ExpansionThermal ExpansionThermal Expansion

Ocean temperature data 1950-2005Ocean temperature data 1950-2005

In situ In situ hydrographic hydrographic

profilesprofiles

World Ocean Temperature Data Bases‘ Global ’ time series of ocean temperature data

at different depths:

1. Levitus et al. (2005) 1. Levitus et al. (2005) 0-700 m : global yearly grids for 1955-20030-700 m : global yearly grids for 1955-2003

0-3000 m : global 5-year grids for 1955-19980-3000 m : global 5-year grids for 1955-1998

2. Ishii et al. (2006)2. Ishii et al. (2006)0-700 m : global monthly grids for 1950-20050-700 m : global monthly grids for 1950-2005

3. Willis et al. (2004)/Lyman et al. (2006)3. Willis et al. (2004)/Lyman et al. (2006) 0-750 m : yearly data for 1993-20030-750 m : yearly data for 1993-2003

4. Guinehut et al. (2006)-ARMOR-4. Guinehut et al. (2006)-ARMOR-0-700 m : yearly data for 1993-20030-700 m : yearly data for 1993-2003

5.5. Domingues et al. (2006Domingues et al. (2006))0-750 m: 1993-2005 0-750 m: 1993-2005

World Ocean Temperature Data Bases‘ Global ’ time series of ocean temperature data

at different depths:

1. Levitus et al. (2005) 1. Levitus et al. (2005) 0-700 m : global yearly grids for 1955-20030-700 m : global yearly grids for 1955-2003

0-3000 m : global 5-year grids for 1955-19980-3000 m : global 5-year grids for 1955-1998

2. Ishii et al. (2006)2. Ishii et al. (2006)0-700 m : global monthly grids for 1950-20050-700 m : global monthly grids for 1950-2005

3. Willis et al. (2004)/Lyman et al. (2006)3. Willis et al. (2004)/Lyman et al. (2006) 0-750 m : yearly data for 1993-20030-750 m : yearly data for 1993-2003

4. Guinehut et al. (2006)-ARMOR-4. Guinehut et al. (2006)-ARMOR-0-700 m : yearly data for 1993-20030-700 m : yearly data for 1993-2003

5.5. Domingues et al. (2006Domingues et al. (2006))0-750 m: 1993-2005 0-750 m: 1993-2005

In situ+

altimetry

Thermal budget in the Earth systemThermal budget in the Earth system

Oceans

(1022 J)

Land warming

Glaciers melting

Atmosphere warming

Past 50 years

Sea ice melting

Ocean warming

From Levitus et al. (2005)

Observed sea level and thermal expansionObserved sea level and thermal expansionPast few decadesPast few decades

~ 0.4 ±0.1 mm/yr

+ 1.8 ±0.3 mm/yr

Observed sea levelObserved sea level

Thermal expansion

Thermal expansion (1993-2003)Thermal expansion (1993-2003)

: + 3.1 ±0.4 mm/yr

Average rate : 1.5 ± 0.3 mm/yr

Levitus 1.3 mm/yrIshii 1.2 mm/yrWillis 1.6 mm/yrARMOR 1.8 mm/yr

Contribution of thermal expansion (1993-2005)Contribution of thermal expansion (1993-2005)Contribution of thermal expansion (1993-2005)Contribution of thermal expansion (1993-2005)

Observed sea level rise : 3.3 mm/yr

Thermal expansion : 0.8 mm/yr

Residual : ocean mass change2.5mm/yr

Causes of Regional VariabilityCauses of Regional Variabilityin Sea Level Change?in Sea Level Change?

Causes of Regional VariabilityCauses of Regional Variabilityin Sea Level Change?in Sea Level Change?

Spatial patterns of steric sea level (thermal expansion) and observed sea level (satellite altimetry) trends

(1993-2005)

Thermal Expansion Satellite Altimetry

mm/yr mm/yr

mm/yr

Residual sea level trends Residual sea level trends (Observed sea level by satellite altimetry (Observed sea level by satellite altimetry

minus thermal expansion)minus thermal expansion)------------------------------

Causes…. Salinity?, Deep ocean temperature?Causes…. Salinity?, Deep ocean temperature?Post-Glacial Rebound? Others?Post-Glacial Rebound? Others?

1993-2005

Trend patterns :Comparison Models - Observations

Topex/Poseidon (1993-2001)GECCO Model (1992-2001)

From position paper ‘Thermal Expansion’

Are the trend patterns Are the trend patterns stationnary?stationnary?

Are the trend patterns Are the trend patterns stationnary?stationnary?

…………. NO!. NO!

Thermal expansion

1993-2003

Thermal expansion

1955-2003

Lombard et al. (2005)

Thermal expansion

1955-2003

EOF1 1955-2003

Land IceLand Ice Land IceLand Ice

Land Ice Contribution Land Ice Contribution (past few years)(past few years)

Dyugerov and Meier, 2005Cogley, 2005

………

Rignot & Thomas, 2002Thomas et al., 2004Krabill et al., 2004Zwally et al., 2005Johanessen et al., 2005Davis et al., 2005Rignot & Kanagaratnam, 2006Rignot et al., 2006Velicogna & Wahr (2005, 2006)Ramillien et al. (2006)……….

Glaciers contribution to sea levelGlaciers contribution to sea level

From Position Paper ‘Cryospheric Contributions’

0.8 +/- 0.4 mm/yr

Contribution of Ice sheets to Sea LevelContribution of Ice sheets to Sea Level

From Position Paper ‘Cryospheric Contributions’

Zwally et al. (2005)Krabill et al. (2004)Thomas et al. (2006)Vellicogna and Wahr (2005)Ramillien et al. (2006)Rignot & Kanagaratnam (2006)

1. Greenland1. Greenland

2. Antarctica : « probable net loss but close to balance » 2. Antarctica : « probable net loss but close to balance »

0.3 +/- 0.15 mm/yr

Land WatersLand WatersLand WatersLand Waters

Precipitation

Evaporation Transpiration

Rivers

Lakes

OceanSoil wetness

Ground waters

Glaciers

Wetlands

Snow

WATER CYCLE

dW / dt = P - E - RdW / dt = P - E - R

Total land water storage Precipitation Evapotranspiration Runoff

Water Balance Equation

Ngo-Duc et al. (2005)

ORCHIDEE model

Land water Storage (climate-driven) contribution

Milly et al. (2003)

LaD model

Detrended thermal expansion

Land Water Contribution (Climatic + Anthropogenic) (recent decades)

• Reservoir filling : - 0.25 mm/yr• Groundwater mining : + 0.25 mm/yr• 14 largest lakes : + 0.15 mm/yr• Climate-driven : -0.1 mm/yr • Water vapour : - 0.05 mm/yr

• Net budget : ~ 0

But : many unknowns (irrigation,ground water, deforestation, urbanization….)

From Position Paper ‘Terrestrial Waters’; Milly et al.

Sea Level BudgetSea Level Budget--------------------------------Recent YearsRecent Years

Sea Level BudgetSea Level Budget--------------------------------Recent YearsRecent Years

Contribution of thermal expansion plus land ice to sea level riseContribution of thermal expansion plus land ice to sea level rise

(1993-2005)(1993-2005)mm/yr

1. +/- 0.5

1.1 +/- 0.6

2.2 +/- 0.8

4.3.2.1.0.-1.

Thermal Expansion

Land ice

Thermal expansion plus land ice

Satellite altimetry 3.3 +/- 0.4

?

UncertaintiesUncertaintiesUncertaintiesUncertainties

Thermal expansion and salinityThermal expansion and salinity uncertaintiesuncertainties

1.Data coverage (southern ocean, deep ocean)

2.Data processing

Land ice and land watersLand ice and land waters uncertaintiesuncertainties

1. Ice sheets mass balance2.Continental waters3.Anthropogenic effects (dams, ground

water removal, irrigation)

NEAR FUTURE PERSPECTIVES NEAR FUTURE PERSPECTIVES

ARGO

GRACE

Swath altimetry

Thermal expasion + salinityThermal expasion + salinity

Land waters (climate + human activities)Land waters (climate + human activities) Ice sheets mass balanceIce sheets mass balance Ocean mass change + thermal expansionOcean mass change + thermal expansion

ALTIMETRYALTIMETRYfor measuringfor measuringsea levelsea level

Long sea level time seriesLong sea level time series

Surface Waters monitoringSurface Waters monitoring

30 March 2003

30 September 2003

seasonalchange

Change in land water storage (climatic + anthropogenic) from GRACE

Resolution : 400 km

Water height equivalent (mm/yr)

Change in land water storage (climatic + anthropogenic) from GRACE :

Trend over a 3-year time span (mid-2002 to mid-2005)

Satellite altimetry minus GRACE

THERMAL EXPANSION (Steric Sea Level)THERMAL EXPANSION (Steric Sea Level)

In situ ocean temperature data

Lombard et al., 2006 Also, Chambers et al., 2004; Chambers et al., 2006

Monitoring of surface waters by satellite altimetry

Lake water level monitoring by satellite altimetry

(Irak) (Asia)

(Africa) (Africa)

Remaining puzzling questions

• Sea level rise : recent acceleration?• Cause of thermal expansion differences among data

sets (recent years)? • Cause of ocean cooling since 2004 and discrepancy

with satellite altimetry observations?• Sea level budget for the last 13 years not closed;

Cause?• ocean temperature-based thermal expansion?• Are fingerprints of PGR and present-day ice melt

detectable?

• .…..