Rising Sea Level Observations and Causes. Anny Cazenave LEGOS-CNES, Toulouse, France

Transcription

1 Rising Sea Level Observations and Causes Anny Cazenave LEGOS-CNES, Toulouse, France AAAS Annual Meeting, Chicago, Feb.2009

2 Sea Level budget: Comparison between observed sea level and sum of climate contributions (thermal expansion, land ice, land waters) : IPCC AR : 2008: New

3 Global mean sea level rise during the 20 th century Satellite altimetry Holgate and Woodworth, 2004 Tide gauges mm/yr Church et al., 2004, 2006

4 Satellite altimetry Topex/Poseidon ( ) Jason-1 (2001- ) Jason-2 (2008- )

5 Global mean sea level between 1993 and 2008 (Topex/Poseidon and Jason-1 satellites) uncertainty ~0.4 mm/yr

6 Global mean sea level trend: error budget mm/yr 0,45 0,4 0,35 0,3 0,25 0,2 S U M 0,15 0,1 0,05 0 Orbit Wet tropo Dry tropo Sea state Topex A/B Sum TG Cal/Val

7 Recent estimates of altimetry-based sea level rise ( ) mm/yr 3,5 3 2,5 2 1,5 1 0,5 0 Colorado NASA NOAA OHIO CNES zero

8 Present-day Sea Level Rise: : mm/yr : mm/yr Acceleration? Decadal fluctuation?

9 Sea Level budget: Comparison between observed sea level and sum of climate contributions (thermal expansion, land ice, land waters) : IPCC AR4

10 Observed sea level: 3.1 +/- 0.4 mm/yr Over Thermal expansion: 1.6 +/- 0.3 mm/yr over Courtesy M. Ishii

11 Contribution of glacier melting to sea level rise Ice mass loss by glacier melting (Gt/year) 1900 today 0.8 +/- 0.4 mm/yr IPCC AR4 (Lemke et al., 2007) Contribution to sea level : /- 0.1 mm/yr ( ) Meier et al.(2007)

12 Greenland and Antarctica mass balance Ice mass loss (Gt/year) Wouters et al., 2008 Greenland contribution to sea level rise ( ) : /-0.04 mm/yr (IPCC AR4) Ice mass loss (Gt/year) Antarctica contribution to sea level rise ( ) : /-0.18 mm/yr (IPCC AR4) Ice mass loss measured by remote sensing techniques

13 3 mm/yr Sea Level Rate Sea Legel Budget IPCC AR4 Land ice and steric contributions Total climate Observed rate of rise 2 mm/yr steric 1 mm/yr Glaciers Ice sheets Waters?

14 Regional distribution of sea level trends Observed by satellite altimetry Uniform trend (of 3.3 mm/yr) removed

15 Comparison between spatial patterns in sea level trends observed by satellite altimetry and estimated by the ORCA ocean circulation model (no assimilation) ( ) Observed sea level trends by satellite altimetry Temperature Model trends Salinity Wunsch et al. (2007);Kohl & Stammer (2008); Lombard et al. (2009)

16 Sea Level budget: Comparison between observed sea level and sum of climate contributions (thermal expansion, land ice, land waters) Surprises!

17 Steric sea level now estimated by Argo

18 Observed sea level Thermal expansion Recent thermosteric sea level change (Ishii and Kimoto, 2008) Courtesy M. Ishii

19 Observed and thermosteric sea level ( ) Revised ocean heat content estimate T,S océan Curves from J. Willis, JPL

20 Global mean sea level between 1993 and 2008 (Topex/Poseidon and Jason-1 satellites) uncertainty ~0.4 mm/yr

21 Can we explain recent sea level rise by land ice loss only?

22 Space gravimetry mission «GRACE» (2002- ) Temporal variations of the gravity field Mass redistribution inside and at the surface of the Earth

23 Sea Level Rise since 2003 Observed sea level (altimetry) Rate: 2.5 +/- 0.4 mm/yr over Total ice. (GRACE ice sheets + glaciers) + waters Rate:2.2 +/- 0.3 mm/yr Ocean mass (GRACE; data from CSR) Rate: 2.1 +/- 0.5 mm/yr Composante stérique (expansion thermique + salinité)

24 Sea Level Rise since 2003 Observed sea level (altimetry) Rate: 2.5 +/- 0.4 mm/yr over Total ice. (GRACE ice sheets + glaciers) + waters Rate:2.2 +/- 0.3 mm/yr Ocean mass (GRACE; data from CSR) Rate: 2.1 +/- 0.5 mm/yr Composante stérique

25 Contribution of glacier melting to sea level rise (recent years) -Glaciers ( ): 1.0 +/ mm/yr Kaser et al. (2006) -Glaciers ( ): mm/yr Cogley (2009) -Glaciers (2006): 1.1 +/ mm/yr Meier et al. (2007)

26 Space gravity mission GRACE (2002- ) Longer mass balance time series Year 2006: 0.5 mm/yr ESL Wouters, Chambers, Schrama (2008) Trend : 179 +/- 25 Gt/yr (0.5 mm/yr ESL) Rignot et al., 2008 Ice mass loss New results for Greenland and Antarctica ice mass loss : ~1 mm/yr over

27 Land waters contribution GRACE mission (2002- ) Land waters contribution

28 March 2003 Red: water excess Blue : water deficit Equivalent water height (mm) September 2003 Equivalent water height (mm)

29 Mac Kenzie Mississippi Congo Mekong km 3 /yr GRACE-based change in land water storage ( ) Lena Yenissei MacKenzie Zambeze Nil Net water loss : - 60 ± 24 km 3 /yr mm/yr sea level rise Mississipi Congo Ramillien et al. (2008)

30 Sea level rate Sea Level Budget 2003 Land ice, water and steric contributions 3 mm/yr Total climate observed 2 mm/yr Glaciers 1 mm/yr Ice sheets Waters steric

31 Steric Sea Level ( ) (sum of ocean temperature and salinity) Altimetry minus GRACE Ocean mass: Trend : 0.4 +/ mm/yr Comparaison Niveau mer observé et Contributions climatiques Altimetry minus (ice+water): Trend: 0.3 +/ mm/yr Argo: Trend: /- 0.1mm/yr

32 Steric Sea Level ( ): contribution of each ocean Total Pacific Ocean Indian Ocean Argo: Trend: /- 0.1mm/yr Atlantic Ocean

33 Concluding remarks Sea level is still rising but causes are different: : Ocean thermal expansion 50% Land ice 40% : Land ice 80%! Ocean thermal expansion: <20%

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