# Presentation: 302228

## Sea Level Rise:

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

**Sea Level Rise:**
**Can we explain **
**what we measure?**
**Anny Cazenave**
**LEGOS-GRGS/CNES**
**Toulouse, France**

## Slide 2

## - STERIC sea level:    change in  Density

**- ****STERIC sea level:    change in  ****Density**
**-**** EUSTATIC sea level:  change  in ****Ocean Mass **

**Temperature         Salinity**

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

## 20th Century Sea Level Rise,  IPCC, 2001

**-1.0**

**-0.5**

** ****0.5**

**1.0**

**1.5**

**2.0**

**0.0**

**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**

**20****th**** Century Sea Level Rise,  IPCC, 2001**

## SUMMARY OF RECENT RESULTS

******  ****During the 1990s, sea level has been rising by **
**~ 3 mm/yr        evidence for a  recent acceleration ???**
******  ****Steric and eustatic sea level change recognized as highly non uniform          overestimate of the 20****th**** century sea level rise by tide gauges ???**
** **
******  ****New rates for glaciers and ice sheets recent melting**
****** **** ****Land water mass contribution to sea level rise can now be estimated**

## Observations

**Observations**
**of**
**Present-Day Sea Level Rise**

## Sea Level Rise 

**during the 1990s**
** ****from**
**Satellite Altimetry**

## TOPEX/POSEIDON

**TOPEX/POSEIDON**

## Slide 9

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

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

**Trends in mm/year**

## Satellite Altimetry for Global Mean Sea Level

_**Advantages**_
**high-precision**
**high spatio-temporal resolution**
**global coverage**
**absolute measurements**

_**Drawbacks**_
**time series still short (10 years)**
**no coverage of high-latitude oceans (T/P & Jason)**

## Sea Level Rise 

**during the 20****th**** century**
** ****from**
**Tide Gauges**

## WORLDWIDE TIDE GAUGE NETWORK -2001-

**WORLDWIDE TIDE GAUGE NETWORK -2001-**

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

## SAN FRANCISCO

**SAN FRANCISCO**

**BREST**

**NEW YORK**

**STOCKHOLM**

## Main processes causing vertical land motions

**Tectonic deformations**
**Seismic activity**
**Volcanic activity**
**Viscous deformation of the Earth’s mantle**
**    ****(Post Glacial Rebound)**
**Land subsidence due to sediments compaction, underground water extraction, etc.**

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

## Deformation of the Earth’s mantle under ice sheet loading

**and POST GLACIAL REBOUND**

## TIDE GAUGE-BASEDSEA LEVEL RISE FOR THE 20th CENTURYGlobal

**1.5 ****+/- 0.5 mm/yr (IPCC, 2001)**
**1.71**** +/- 0.55 mm/yr (Douglas, 2001; **
**   ****27 sites)**
**1.84**** +/- 0.35 mm/yr (Peltier, 2001;**
**   ****27 sites)**
**1.5**** +/- 0.4 mm/yr (Tamaseia et al., 2001; 23 sites)**

## Tide Gauges for Global Mean Sea Level

_**Advantages**_
**historical information **
**   ****(back to 1900)**
**useful for calibrating onboard altimetry systems**

_**Drawbacks**_
**heterogeneous and limited coverage**
**gaps in data records**
**land motion contamination**
**data sensitive to local perturbations**

## Sea level change during the last 6000 years

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

**20****th**** century**

**    ****-6000 years****                                              ****present**

**From Lambeck, 2002**

## CONSTRAINTS 

**FROM **
**ASTRONOMICAL/GEOPHYSICAL**
** ****OBSERVABLES**

## Astronomical/Geophysical Observables

** **
******   ****Non-tidal Earth ’s rotation acceleration or length of day -LOD- deceleration: -0.6 ms/cy for the past 2500 years**
****** ****  ****Secular decrease of the Earth ’s dynamical flattening     : -3x10****-11****/yr for the past 25 years**
****** **** ****Secular movement of the Earth ’s rotation  pole: 10 m/cy towards Greenland over the past 100 years**

## Length of Day

**Length of Day**
**(LoD)**
**variations **
**for the past **
**2500 years**

**LoD**

**J****2**

**-500**

**year**

**2000**

## Secular decrease of the Earth ’s flattening (J2)

**Secular decrease of the Earth ’s flattening (J****2****)**

**From Cox and Chao, 2002**

## Length of Day

**Length of Day**
**(LoD)**
**variations **
**for the past **
**2500 years**

**LoD**

**J****2**

**-500**

**year**

**2000**

## Slide 26

## Secular Decrease of the Earth’s Flattening

**Post Glacial**
** ****Rebound**

**PGR + present-day melting**

** ****A**

**A+G**

**observation**

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

## Long-wavelength geoid

**Long-wavelength geoid**

**Sketch of the Earth’s interior**

**Viscosity of the Earth’s mantle**

## Sketch of the Earth’s interior

**Sketch of the Earth’s interior**

**Lower mantle**

**           ****Core**

**Upper **
**mantle**

**Viscosity profiles**
** ****from global circulation models**

## Secular decreases of

**Secular decreases of**
**Length of Day and Earth’s flattening **
**are not **
**strong constraints on **
**present-day eustatic sea level rise**

## DO WE UNDERSTAND OBSERVATIONS 

**DO WE UNDERSTAND OBSERVATIONS **
**OF**
**PRESENT-DAY **
**SEA LEVEL RISE?**

## Sea Level Rise 

**Sea Level Rise **
**during**
** ****the 1990s**
** **

## SEA LEVEL TRENDS 

**SEA LEVEL TRENDS **
**FOR 1993-1998**
**(mm/yr)**
**Upper map : **
**Observed**
** ****(Topex/Poseidon)**
**Bottom map: **
**Computed **
**(thermal expansion)**

**-**

**Topex/Poseidon (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. Boyer**
**NOAA 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**

## Topex/Poseidon sea level---

**Topex/Poseidon sea level---**
**Thermal expansion----**
**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 **
**during**
** ****the 20****th**** century**
** **

## 20th Century Sea Level Rise,  IPCC, 2001

**-1.0**

**-0.5**

** ****0.5**

**1.0**

**1.5**

**2.0**

**0.0**

**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**

**20****th**** Century Sea Level Rise,  IPCC, 2001**

## Past Century

** ****Sea Level Rise:**
**is the observed**
**1.5 mm/yr rate**
**too high?**
**OR**
**are climate-related **
**contributions **
**underestimated?**

## Steric  contribution

**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)**

## Steric sea level trends map and tide gauge sites used by Douglas (1997)

**0.5 +/- 0.05 mm/yr**

**1.4 +/- 0.1 mm/yr**

**Steric sea level trends map and tide gauge sites used by Douglas (1997)**

** ****1.3 +/- 0.1 mm/yr**

**0.5 +/- 0.05 mm/yr**

**From Cabanes et al., 2001**

## SEA LEVEL RISE (1955-1995)

****** ****Steric average at the 25 tide gauge sites:**
**                     **_**1.3 +/- 0.1 mm/yr**_
****** ****Observed by tide gauges (25 sites) : **_**1.6 +/- 0.15 mm/yr**_
******Thermal expansion (global mean) : **_**0.5 +/-  0.05 mm/yr**_
******Salinity effect (global mean) : **
**0.05 +/- 0.02 mm/yr**

## Map of steric sea level trends and GLOSS tide gauge network 

**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**
** ****20****th**** century sea level rise too high???**

## EUSTATIC 

**SEA LEVEL RISE**
**(ocean mass change)**

## Eustatic contribution 

**from **
**land water storage**
**(change in the global water cycle****)**

## 20th Century Sea Level Rise,  IPCC, 2001

**-1.0**

**-0.5**

** ****0.5**

**1.0**

**1.5**

**2.0**

**0.0**

**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**

**20****th**** Century Sea Level Rise,  IPCC, 2001**

## Precipitation 

**Precipitation **

**Evaporation**

**Evaporation**

**Transpiration**

**Precipitation : **

**Rivers**

**Lakes**

**Oceans**

** ****Soil Moisture**

** ****Ground Waters**

**Atmosphere**

**Snow Pack**

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

**Water mass balance : ****dW/dt = P - E - R**
**            ****W: Water stored in soils**
**P : Precipitation**
**           ****E : Evapotranspiration**
**R: Runoff**

**GLOBAL HYDROLOGICAL **
**MODELS**

- 

## 

**THE LAND DYNAMICS (LaD) MODEL**
**P.C.D. Milly and A.B. Shmakin**
**NOAA/university of Princeton**
**J. Hydrometeorology, 2001**
**                **

**GLOBAL MODELING OF LAND WATER **
**AND **
**ENERGY BALANCES**

## LaD MODEL

**Monthly grids of :**
**- Snow depth**
**- Soil moisture**
**- Underground waters (aquifers)**
**for 1981-1998**

## 0.13 mm/yr

**0.13 mm/yr**

**0.05 mm/yr**

** ****0.18 mm/yr**

**Soil waters**

**Snow**

**Total**

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

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

**drier**** **                                   **wetter**

**                ****- 3 mm/yr                                                    3 mm/yr**

## drier                                        wetter

**Trends in precipitation on land (1981-1998)**

**drier**** **                                       **wetter**

## Land water mass contribution

** ****to sea level rise over 1980-2000**
** ****amounts to**
** ****0.2 mm/year**

## EUSTATIC CONTRIBUTION 

**FROM **
**MOUNTAIN GLACIERS **
**AND**
** ****ICE SHEETS**

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

** **
******   **_**MOUNTAIN GLACIERS**_** : < +0.5 mm/yr**
****** ****  **_**ICE SHEETS**_** :  **
**     ****Greenland : +0.13 mm/yr ****(Krabill et al., 2000)**
**     ****Antarctica : +0.16 +/- 0.05 mm/yr (WA) **
**                             ****0 +/- 0.07 mm/yr (EA)**
**                              ****total = + 0.16 mm/yr**
**(Rignot and Thomas, 2002)**
** ********  **_**LAND WATER**_** :+0.2 mm/yr    ****(Milly et al., 2002)**
**TOTAL : ~1 mm/yr**

## Sea level rise due to mountain glaciers

**From Dyurgerov and Meier, 2002**

**Sea level rise due to mountain glaciers**

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

** **
******   **_**MOUNTAIN GLACIERS**_** : < +0.5 mm/yr**
****** ****  **_**ICE SHEETS**_** :  **
**     ****Greenland : +0.13 mm/yr ****(Krabill et al., 2000)**
**     ****Antarctica : +0.16 +/- 0.05 mm/yr (WA) **
**                             ****0 +/- 0.07 mm/yr (EA)**
**                              ****total = + 0.16 mm/yr**
**(Rignot and Thomas, 2002)**
** ********  **_**LAND WATER**_** :+0.2 mm/yr    ****(Milly et al., 2002)**
**TOTAL : ~1 mm/yr**

## since SEA LEVEL RISE of the 1990s is fully explained by thermal expansion, there is no room for an additional 1 mm/yr eustatic contribution.....

**since SEA LEVEL RISE of the 1990s is fully explained by thermal expansion, there is no room for an additional 1 mm/yr eustatic contribution.....**

- THE NEW ENIGMA

## 20th Century Sea Level Rise,  IPCC, 2001

**-1.0**

**-0.5**

** ****0.5**

**1.0**

**1.5**

**2.0**

**0.0**

**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**

**20****th**** Century Sea Level Rise,  IPCC, 2001**

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

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

## STERIC SEA LEVEL ---------

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

**1950**

**1990**

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

**2000**

**1970**

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

**(0-500 m****)**

**0-3000 m**

**1945**

**1970**

**2000**

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

**2000**

**1970**

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

**0-500 m**

**0 -3000 m**

**1945**

**1970**

**2000**

## TOPEX/POSEIDON

**TOPEX/POSEIDON**
**SEA LEVEL**
**EOF mode 1**

**   ****1993                                           2003**

## Sea level rise due to mountain glaciers

**From Dyurgerov and Meier, 2002**

**Sea level rise due to mountain glaciers**

**c****hange in rate?**

## PERSPECTIVES

## JASON-1

**JASON-1**

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

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

**Jason-1**

## GRACE satellites launched on March 17, 2002

## TEMPORAL CHANGE OF THE GRAVITY FIELD

**TEMPORAL CHANGE OF THE GRAVITY FIELD**

##  GRACE MISSION:

** ****GRACE MISSION:**
**Spatio-temporal gravity variations**
**Resolution : 2°x2°**
**Precision : 0.5 cm (water height)**
**Time scale : **
**1 month to several years**

## Precipitation 

**Precipitation **

**Evaporation**

**Evaporation**

**Transpiration**

**Precipitation : **

**Rivers**

**Lakes**

**Oceans**

** ****Soil Moisture**

** ****Ground Waters**

**Atmosphere**

**Snow Pack**

## Slide 76

## Sea level rise

**Separation of thermal**
** ****and mass contributions**

**Sea level rise**

**GRACE (land)**
**Land water **
**and**
** ****ice sheets**
** ****mass balance**

**Ocean water mass change**

**GRACE (ocean)**

**JASON**

## The End