Transcript Present-Day Sea Level Change Assessment and Key Uncertainties Anny Cazenave LEGOS, Toulouse 20th century sea level rise Satellite altimetry Holgate and Woodworth, 2004 1.8 +/- 0.3

Present-Day Sea Level Change
Assessment and Key Uncertainties
Anny Cazenave
LEGOS, Toulouse
20th century sea level rise
Satellite altimetry
Holgate and Woodworth, 2004
1.8 +/- 0.3 mm/yr
Church et al., 2004, 2006
Global mean sea level from Topex/Poseidon altimetry
Rate of rise : 3.0 +/-0.4 mm/yr
With PGR correction : 3.3 +/- 0.4 mm/yr
1993-2005
Observed rate of sea level rise:
1950-2000 : 1.8 +/- 0.3 mm/yr
1993-2005 : 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
New York
Brest
Honolulu
Buenos-Aires
1900
Time
2000
Global coverage of altimeter satellites
Geographical distribution of sea level trends
(1993-2005)
Causes of sea level change….
- Thermal expansion of sea water
due to ocean warming
-Ocean mass change due to water
mass exchange with glaciers, ice
sheets and land reservoirs
Thermal Expansion
Ocean temperature data
1950-2005
In situ
hydrographic
profiles
World Ocean Temperature Data Bases
‘ Global ’ time series of ocean temperature data
at different depths:
1. Levitus et al. (2005)
0-700 m : global yearly grids for 1955-2003
0-3000 m : global 5-year grids for 1955-1998
2. Ishii et al. (2006)
0-700 m : global monthly grids for 1950-2005
3. Willis et al. (2004)/Lyman et al. (2006)
In situ
+
altimetry
0-750 m : yearly data for 1993-2003
4. Guinehut et al. (2006)-ARMOR0-700 m : yearly data for 1993-2003
5. Domingues et al. (2006)
0-750 m: 1993-2005
Thermal budget in the Earth system
Past 50 years
(1022 J)
Oceans
Land warming
Glaciers melting
Ocean
warming
Atmosphere warming
Sea ice melting
From Levitus et al. (2005)
Observed sea level and thermal expansion
Past few decades
Observed sea level
+ 1.8
±0.3
mm/yr
Thermal expansion
~ 0.4
±0.1
mm/yr
Thermal expansion (1993-2003)
:
+ 3.1
±0.4
mm/yr
Levitus
Ishii
Willis
ARMOR
1.3 mm/yr
1.2 mm/yr
1.6 mm/yr
1.8 mm/yr
Contribution of thermal expansion (1993-2005)
Residual : ocean mass change
2.5mm/yr
Causes of Regional Variability
in Sea Level Change?
Spatial patterns of steric sea level (thermal expansion)
and observed sea level (satellite altimetry) trends
(1993-2005)
mm/yr
mm/yr
mm/yr
Satellite Altimetry
Thermal Expansion
Residual sea level trends
(Observed sea level by satellite altimetry
minus thermal expansion)
--------------1993-2005
Causes…. Salinity?, Deep ocean temperature?
Post-Glacial Rebound? Others?
Trend patterns :
Comparison Models - Observations
GECCO Model (1992-2001)
From position paper ‘Thermal Expansion’
Topex/Poseidon (1993-2001)
Are the trend patterns
stationnary?
……. NO!
Thermal expansion
Thermal expansion
1955-2003
1993-2003
EOF1 1955-2003
Thermal expansion
1955-2003
Lombard et al. (2005)
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
0.8
+/- 0.4
mm/yr
From Position Paper ‘Cryospheric Contributions’
Contribution of Ice sheets to Sea Level
1. Greenland
Zwally et al. (2005)
Krabill et al. (2004)
Thomas et al. (2006)
Vellicogna and Wahr (2005)
Ramillien et al. (2006)
Rignot & Kanagaratnam (2006)
0.3
+/- 0.15
mm/yr
2. Antarctica : « probable net loss but close to balance »
From Position Paper ‘Cryospheric Contributions’
Land Waters
WATER CYCLE
Precipitation
Glaciers
Evaporation
Snow
Transpiration
Lakes
Wetlands
Ocean
Rivers
Soil wetness
Ground waters
Water Balance Equation
dW / dt
Total land water storage
=
P - E - R
Precipitation
Evapotranspiration
Runoff
Land water Storage (climate-driven) contribution
Milly et al.
(2003)
LaD model
Ngo-Duc et al.
(2005)
ORCHIDEE 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 Budget
---------------Recent Years
Contribution of thermal expansion plus land ice to sea level rise
(1993-2005)
-1.
0.
1.
Thermal Expansion
2.
3.
4.
1. +/- 0.5
1.1
Land ice
+/- 0.6
Thermal expansion
plus land ice
2.2 +/- 0.8
?
Satellite altimetry
3.3 +/- 0.4
mm/yr
Uncertainties
Thermal expansion and salinity
uncertainties
1. Data coverage (southern ocean,
deep ocean)
2. Data processing
Land ice and land waters
uncertainties
1. Ice sheets mass balance
2. Continental waters
3. Anthropogenic effects (dams,
ground water removal, irrigation)
NEAR FUTURE PERSPECTIVES
ALTIMETRY
for measuring
sea level
ARGO
 Long sea level time series
 Thermal expasion + salinity
 Land waters (climate + human activities)
GRACE
Swath altimetry
 Ice sheets mass balance
 Ocean mass change + thermal expansion
 Surface Waters monitoring
Change in land water storage (climatic + anthropogenic)
from GRACE
seasonal
change
30 March 2003
30 September 2003
Resolution : 400 km
Change in land water storage (climatic + anthropogenic)
from GRACE :
Trend over a 3-year time span (mid-2002 to mid-2005)
Water height equivalent (mm/yr)
THERMAL EXPANSION (Steric Sea Level)
Satellite altimetry minus GRACE
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)
(Africa)
(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?
• .…..