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?
• .…..
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