Present-Day Sea Level Change Present-Day Sea Level Change Assessment and Key Uncertainties Anny Cazenave Anny Cazenave LEGOS, Toulouse

Church et al., 2004, 2006 Holgate and Woodworth, th 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

Observed rate of sea level rise: : 1.8 +/- 0.3 mm/yr : 3.3 +/- 0.4 mm/yr Acceleration? Decadal fluctuation? Influence of other processes? (e.g., recovery of Pinatubo eruption) Observed rate of sea level rise: : 1.8 +/- 0.3 mm/yr : 3.3 +/- 0.4 mm/yr Acceleration? Decadal fluctuation? Influence of other processes? (e.g., recovery of Pinatubo eruption)

Regional variability from historical tide gauges Brest New York Buenos-Aires Honolulu Time

Global coverage of altimeter satellites

Geographical distribution of sea level trends ( )

Causes of sea level change…. - Thermal expansion of sea water due to ocean warming due to ocean warming -Ocean mass change due to water mass exchange with glaciers, ice sheets and land reservoirs Causes of sea level change…. - Thermal expansion of sea water due to ocean warming due to ocean warming -Ocean mass change due to water mass exchange with glaciers, ice sheets and land reservoirs

Thermal Expansion

Ocean temperature data In situ hydrographic profiles

World Ocean Temperature Data Bases ‘ Global ’ time series of ocean temperature data at different depths: 1. Levitus et al. (2005) m : global yearly grids for m : global 5-year grids for m : global 5-year grids for Ishii et al. (2006) m : global monthly grids for Willis et al. (2004)/Lyman et al. (2006) m : yearly data for m : yearly data for Guinehut et al. (2006)-ARMOR- 4. Guinehut et al. (2006)-ARMOR m : yearly data for Domingues et al. (2006 ) m: World Ocean Temperature Data Bases ‘ Global ’ time series of ocean temperature data at different depths: 1. Levitus et al. (2005) m : global yearly grids for m : global 5-year grids for m : global 5-year grids for Ishii et al. (2006) m : global monthly grids for Willis et al. (2004)/Lyman et al. (2006) m : yearly data for m : yearly data for Guinehut et al. (2006)-ARMOR- 4. Guinehut et al. (2006)-ARMOR m : yearly data for Domingues et al. (2006 ) m: In situ + altimetry

Thermal budget in the Earth system Oceans (10 22 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 expansion Past few decades ~ 0.4 ±0.1 mm/yr ±0.3 mm/yr Observed sea level Thermal expansion

Thermal expansion ( ) : ±0.4 mm/yr Average rate : 1.5 ± 0.3 mm/yr Levitus 1.3 mm/yr Ishii 1.2 mm/yr Willis 1.6 mm/yr ARMOR 1.8 mm/yr

Contribution of thermal expansion ( ) Observed sea level rise : 3.3 mm/yr Thermal expansion : 0.8 mm/yr Residual : ocean mass change 2.5mm/yr

Causes of Regional Variability in Sea Level Change? Causes of Regional Variability in Sea Level Change?

Spatial patterns of steric sea level (thermal expansion) and observed sea level (satellite altimetry) trends ( ) Thermal Expansion Satellite Altimetry mm/yr

Residual sea level trends (Observed sea level by satellite altimetry minus thermal expansion) Causes…. Salinity?, Deep ocean temperature? Post-Glacial Rebound? Others?

Trend patterns : Comparison Models - Observations Topex/Poseidon ( )GECCO Model ( ) From position paper ‘Thermal Expansion ’

Are the trend patterns stationnary? ……. NO!

Thermal expansion Thermal expansion Lombard et al. (2005) Thermal expansion EOF

Land Ice

Land Ice Contribution (past few years) Dyugerov and Meier, 2005 Cogley, 2005 ……… Rignot & Thomas, 2002 Thomas et al., 2004 Krabill et al., 2004 Zwally et al., 2005 Johanessen et al., 2005 Davis et al., 2005 Rignot & Kanagaratnam, 2006 Rignot et al., 2006 Velicogna & Wahr (2005, 2006) Ramillien et al. (2006) ……….

Glaciers contribution to sea level From Position Paper ‘Cryospheric Contributions’ 0.8 +/- 0.4 mm/yr

Contribution 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. Greenland 2. Antarctica : « probable net loss but close to balance » 0.3 +/ mm/yr

Land Waters

Precipitation Evaporation Transpiratio n Rivers Lakes Ocean Soil wetness Ground waters Glaciers Wetlands Snow WATER CYCLE dW / dt = P - E - R Total land water storage Precipitation EvapotranspirationRunoff 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 : mm/yr Groundwater mining : mm/yr 14 largest lakes : mm/yr Climate-driven : -0.1 mm/yr Water vapour : mm/yr Net budget : ~ 0 But : many unknowns (irrigation,ground water, deforestation, urbanization….) From Position Paper ‘Terrestrial Waters’; Milly et al.

Sea Level Budget Recent Years Sea Level Budget Recent Years

Contribution of thermal expansion plus land ice to sea level rise ( ) ( ) mm/yr 1. +/ / / Thermal Expansion Land ice Thermal expansion plus land ice Satellite altimetry 3.3 +/- 0.4 ?

UncertaintiesUncertainties

Thermal expansion and salinity uncertainties uncertainties 1.Data coverage (southern ocean, deep ocean) 2.Data processing

Land ice and land waters uncertainties uncertainties 1.Ice sheets mass balance 2.Continental waters 3.Anthropogenic effects (dams, ground water removal, irrigation)

NEAR FUTURE PERSPECTIVES NEAR FUTURE PERSPECTIVES ARGO GRACE Swath altimetry Thermal expasion + salinity  Thermal expasion + salinity Land waters (climate + human activities)  Land waters (climate + human activities)  Ice sheets mass balance  Ocean mass change + thermal expansion ALTIMETRY for measuring sea level Long sea level time series  Long sea level time series Surface Waters monitoring  Surface Waters monitoring

30 March September 2003 seasonal change 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)

Moc Hoa - T/P track 140 d= 2 Km Global rms 0.15 m d= 6 Km Global rms 0.24 m Kg Luong - ERS2 track 476 Mekonk basin (south-east Asia) Water level (cm) Satellite altimetry minus GRACE 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)

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?.…..