rising sea level observations and causes
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Rising Sea Level Rising Sea Level
Observations and CausesObservations and Causes
Anny Cazenave LEGOS-CNES, Toulouse, France
AAAS Annual Meeting, Chicago, Feb.2009
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Sea Level budget:Sea Level budget:Comparison between observed sea level Comparison between observed sea level and sum of climate contributionsand sum of climate contributions(thermal expansion, land ice, land waters) (thermal expansion, land ice, land waters)
•• 19931993--2003: IPCC AR42003: IPCC AR4•• 20032003--2008: New2008: New
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Church et al., 2004, 2006
Holgate and Woodworth, 2004
Global mean sea level rise during the 20Global mean sea level rise during the 20thth centurycentury
Satellite altimetry
1.6-1.8 mm/yrTide gauges
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Satellite altimetry
Jason-2 (2008- )
Topex/Poseidon(1992-2006) Jason-1
(2001- )
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Global mean sea level between 1993 and 2008 (Topex/Poseidon and Jason-1 satellites)
uncertainty ~0.4 mm/yr
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0
0,05
0,1
0,15
0,2
0,25
0,3
0,35
0,4
0,45
Orbit Wet tropo Dry tropo Sea state TopexA/B
Sum TGCal/Val
Global mean sea level trend: error budget
mm/yr
SUM
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0
0,5
1
1,5
2
2,5
3
3,5
Colorado NASA NOAA OHIO CNES zero
Recent estimates of altimetry-based sea level rise (1993-2008)
mm/yr
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PresentPresent--day Sea Level Rise:day Sea Level Rise:
19501950--2000: 1.72000: 1.7--1.8 mm/yr1.8 mm/yr19931993--2008: 3.02008: 3.0--3.53.5 mm/yrmm/yr
Acceleration?Acceleration?Decadal fluctuation?Decadal fluctuation?
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Sea Level budget:Sea Level budget:Comparison between observed sea level Comparison between observed sea level and sum of climate contributionsand sum of climate contributions(thermal expansion, land ice, land waters) (thermal expansion, land ice, land waters)
•• 19931993--2003: IPCC AR42003: IPCC AR4
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Courtesy M. Ishii
Thermal expansion: 1.6 +/- 0.3 mm/yrover 1993-2003
Observed sea level:3.1 +/- 0.4 mm/yrOver 1993-2003
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Contribution of glacier meltingContribution of glacier meltingto sea level riseto sea level rise
0.8 +/- 0.4 mm/yr
IPCC AR4 (Lemke et al., 2007)Contribution to sea level :
0.77 +/- 0.1 mm/yr (1993-2003)
Ice mass loss by glacier melting (Gt/year)
1900
today
Meier et al.(2007)
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Greenland and Antarctica mass balance
Ice mass loss measured by remote sensing techniques
Greenland contributionto sea level rise(1993-2003) :
0.21 +/-0.04 mm/yr (IPCC AR4)
Ice mass loss (Gt/year)
Wouters et al., 2008
Antarctica contributionto sea level rise(1993-2003) :
0.21 +/-0.18 mm/yr (IPCC AR4)
Ice mass loss (Gt/year)
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Sea Legel Budget Sea Legel Budget 19931993--20032003IPCC AR4IPCC AR4
Land ice and steric contributions Land ice and steric contributions
Glaciers
Ice sheets
1 mm/yr
Waters?
steric
Total
climate
Observed rate of rise
3 mm/yr
2 mm/yr
Sea LevelRate
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Regional distribution of sea level trends
1993-2008
Observed by satellite altimetry
Uniform trend (of 3.3 mm/yr)removed
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Temperature
Salinity
Comparison between spatial patterns in sea level trends Comparison between spatial patterns in sea level trends observed by satellite altimetry and observed by satellite altimetry and
estimated by the ORCA ocean circulation model (no assimilation) estimated by the ORCA ocean circulation model (no assimilation) (1993(1993--2001)2001)
Observed sea level trendsby satellite altimetry
Model trends
Wunsch et al. (2007);Kohl & Stammer (2008); Lombard et al. (2009)
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Sea Level budget:Sea Level budget:Comparison between observed sea level Comparison between observed sea level and sum of climate contributionsand sum of climate contributions(thermal expansion, land ice, land waters) (thermal expansion, land ice, land waters)
20032003--20082008 Surprises!
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Steric sea level now estimated by Argo
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Recent thermosteric sea level change (Ishii and Kimoto, 2008)
Courtesy M. Ishii
Thermal expansion
Observed sea level
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Revised ocean heat content estimateRevised ocean heat content estimate
Curves from J. Willis, JPL
T,S océan
Observed and thermosteric sea level (2003-2008)
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Global mean sea level between 1993 and 2008 (Topex/Poseidon and Jason-1 satellites)
uncertainty ~0.4 mm/yr
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Can we explain recent sea level rise Can we explain recent sea level rise by land ice loss only?by land ice loss only?
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Space gravimetry mission « GRACE » (2002- )�Temporal variations of the gravity field���� Mass redistribution inside and at the surface of the Earth
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Observed sea level(altimetry)
Ocean mass(GRACE; data from CSR)
Rate: 2.1 +/- 0.5 mm/yr
Total ice.(GRACE ice sheets
+ glaciers) + watersRate:2.2 +/- 0.3 mm/yr
Composante stérique (expansion thermique + salinité)
Sea Level Rise since 2003
Rate: 2.5 +/- 0.4 mm/yrover 2003-2008
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Observed sea level(altimetry)
Ocean mass(GRACE; data from CSR)
Rate: 2.1 +/- 0.5 mm/yr
Total ice.(GRACE ice sheets
+ glaciers) + watersRate:2.2 +/- 0.3 mm/yr
Composante stérique
Sea Level Rise since 2003
Rate: 2.5 +/- 0.4 mm/yrover 2003-2008
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Contribution of glacier meltingto sea level rise (recent years)
-Glaciers (2001-2004): 1.0 +/- 0.19 mm/yrKaser et al. (2006)
-Glaciers (2001-2005): 1.1-1.4 mm/yrCogley (2009)
-Glaciers (2006): 1.1 +/- 0.24 mm/yrMeier et al. (2007)
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Space gravity mission GRACE (2002- )���� Longer mass balance time series
New results for Greenland and Antarctica ice mass loss : ~1 mm/yr over 2003-2008
Wouters , Chambers, Schrama (2008)
Trend : 179 +/- 25 Gt/yr(0.5 mm/yr ESL)
Rignot et al., 2008
Ice mass loss
Year 2006:
0.5 mm/yr ESL
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Land waters contributionLand waterscontribution
GRACE mission (2002- )
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March 2003
September 2003
Equivalent water height (mm)
Equivalent water height (mm)
Red: water excessBlue : water deficit
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12
34
56
78
910
1112
-100
-80
-60
-40
-20
0
20
40
60
Mississippi Congo MekongMac Kenzie
Lena
Yenissei
MacKenzie
Zambeze
Nil
Mississipi
Congo
km3/yr
Net water loss :- 60 ± 24 km3/yr
+ 0.2 mm/yr sea level rise
GRACE-based change in land water storage (2002-2007 )
Ramillien et al. (2008)
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Sea Level Budget Sea Level Budget 20032003--20082008Land ice, water and steric contributions Land ice, water and steric contributions
Glaciers
Ice sheets
1 mm/yr
Waters steric
Total climate observed
3 mm/yr
2 mm/yr
Sea levelrate
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Comparaison Niveau mer observé et
Contributions climatiques
Argo: Trend: 0.37 +/- 0.1mm/yr
Altimetry minus GRACE Ocean mass:
Altimetry minus (ice+water): Trend: 0.3 +/- 0.15 mm/yr
Steric Sea Level (2003-2008)(sum of ocean temperature and salinity)
Trend : 0.4 +/- 0.15 mm/yr
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Argo: Trend: 0.37 +/- 0.1mm/yr
Steric Sea Level (2003-2008):contribution of each ocean
Pacific Ocean
Indian Ocean
Atlantic Ocean
Total
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Concluding remarks
Sea level is still rising but causes are different:
1993-2003 : Ocean thermal expansion 50%Land ice 40%
2003-2008 : Land ice 80%!
Ocean thermal expansion: <20%
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