SEA LEVEL over the altimetry era
Global and Regional Anny Cazenave and William Llovel, LEGOS, Toulouse Michael Ablain, CLS, Toulouse
Global mean sea level evolution since 1870
Satellite altimetry era
Coupled climate models IPCC, 2007
Historical data (Church&White, 2006)
cm
Altimetry-derived global mean sea level Univ. Colorado ; Rate 3.36 mm/yr GSFC/NASA; Rate 3.25 mm/yr CLS-LEGOS, Rate 3.25 mm/yr Mean rate : 3.3 mm/yr Uncertainty : 0.4 mm/yr
Topex/Poseidon, Jason-1, Jason-2
Global mean sea level trend: error budget mm/yr
0,45 0,4 0,35
S U M
0,3 0,25 0,2 0,15 0,1 0,05 0 Orbit Wet tropo Dry tropo Sea state Topex A/B
Sum
Tide TGGauges
Cal/Val
Sea level is not rising uniformly! Geographical distribution of sea level trends (1993-2009)
Independent check of the current rate of sea level rise Study of the sea level budget: -contributions of ocean thermal expansion - contribution of land ice melt + land waters
Ocean temperature and salinity measurements
Figure 5.A.1
Until ~ 2003
Since ~2003: Argo
Thermal budget of the climate system (last 50 years) Heat content (1022 J) Oceans
15
~ 80% of heat
excess in the climate system is stored in the oceans
10
5
Land
Atmosphere
After Levitus et al., 2005
Steric sea level (1993-2009)
Argo data from different groups
Ocean temperature data from Levitus et al
Global mean sea level 1993-2009
Rate : 3.3 +/- 0.4 mm/yr
Altimetry-based sea level Observed sea level minus thermal expansion = Ocean mass change Mean residual trend: ~ 2.2 mm/yr
Thermal expansion mean trend : 1.1 +/- 0.3 mm/yr Ishii & Kimoto, 2009
Levitus et al., 2009 (XbT and Argo bias corrected)
Land ice contribution to sea level
Greenland Columbia glacier (Alaska) Antarctica
Contribution of glacier melting to sea level rise Sea level equivalent Rate of ice mass loss by glacier melting (Gt/year) From Meier et al.(2007)
1900
•1993-2003: 0. 8 +/(IPCC AR4)
0.11 mm/yr
•2001-2004 : 1. +/- 0.2 mm/yr (Kaser et al. , 2006) •2001-2005: 1.1-1.4 mm/yr (Cogley, 2009) •2006: 1.1 +/- 0.24 mm/yr Meier et al. (2007)
Mean contribution of glaciers melting to sea level rise (1993-2009) ~ 1 mm/yr
Ice sheet mass balance and contribution to recent years sea level rise
Radar and Laser Altimetry
INSAR
Space gravimetry GRACE mission since 2002
Monitoring the ice sheet mass balance from space
Ice sheet mass balance from GRACE (2002-2009) GRACE satellites
Mass loss as a function of time
Greenland
Antarctica
-230 +/- 33 Gt/yr 0.6 mm/yr 2002
-140+/- 75 Gt/yr + 0.4 mm/yr 2010
2002
2010 Llovel et al., 2010 (GRGS data)
Annual ice mass loss - Greenland 1993
1997
2001
0
Gt/year
-100
-200
Altimetry InSAR
GRACE
-300 Mean contribution over 1993-2009 : ~0.5 mm/yr
2005
2009
Annual ice mass loss : Antarctica 1993
1997
2001
2005
0
Gt/year
-100
-200
Altimetry InSAR GRACE
-300
Mean contribution over 1993-2009: ~0.4 mm/yr
2009
Global water cycle
Global land water storage change From GRACE (2002-2009)
GRACE-based water storage trend 2002-2009 (km3/yr)
Water gain
Net trend : + 80 +/- 40 km3/yr Sea level equivalent : -0.2 +/- 0.1 mm/yr
Water loss
Llovel et al., 2010
Sea Level Budget
Sea Level Budget 1993-2003 (IPCC AR4 results)
Sea level rate
Total climatic
3 mm/yr
2 mm/yr
Land ice loss
Thermal expansion
Ice sheets 1 mm/yr Glaciers
Land Waters ?
Observed sea level rise
Sea Level Budget 1993-2009 (Land ice plus thermal expansion)
Sea level rate
Total climatic
3 mm/yr
Land ice loss
2 mm/yr Ice sheets
Thermal expansion
1 mm/yr Glaciers Land Waters
Observed sea level rise
Global mean sea level (1993-2009)
Observed sea level by satellite altimetry Sum of climate related- contributions
Mass change (land ice trends/GRACE)
Steric sea level
Global mean sea level 1993-2009
Observed sea level (altimetry)
Sum of climate-related contributions
Residuals
Altimery-derived global mean sea level (detrended) –blue curveLand water storage change (in equivalent sea level) from the ISBA/TRIP hydrological model (CNRM) –green curve-
Regional sea level variability
Spatial trend patterns….(1993-2008)
Observed by satellite altimetry (mean uniform trend of 3.3 mm/yr removed)
Thermal expansion (temperature and salinity data from Levitus et al. 2009)
27 Llovel et al (2010)
Comparison between spatial patterns in sea level trends: Observed by satellite altimetry and estimated by the NEMO ocean circulation model (no assimilation) (1993-2001) Observed sea level trends by satellite altimetry
Temperature
Salinity Model trends
Wunsch et al. 2007; Kohl & Stammer 2008; Lombard et al. 2009
EXPANSION THERMIQUE
Spatial trend patterns Altimetry era
Observations (satellite altimetry)
minus
= ?
Thermal expansion (Levitus et al., 2009)
•Salinity? -Gravitational effects? •Circulation? •Others? > 30
Gravitationnal effects on regional sea level due to ongoing (future) land ice melt Antarctica melting
Greenland melting
Glacier melting
In mm/yr if melting rate corresponds to 1 mm/yr equivalent sea level rise
Mitrovica, 2009; Milne et al., 2009
What are the main challenges for the next few years?
Vermeer and Rahmstorf, 2009
Future Sea Level Rise Rahmstorf, 2007
Projections 1m ------------------------------------------------------------------
Grinsted et al., 2009
?
Today
Observations
IPC
007 2 C
What do we need? I. Continuity of observations
(multi-decade-long records)
(Altimetry/sea level; Argo/Temperature & salinity; GRACE/mass changes; Glaciers and Ice sheets mass changes) II. Increase modeling efforts • Integrated sea level studies (2-D; past decades) • Consensus results on best GIA corrections • Coupled climate model projections (21st century) - Ice sheet dynamics - Regional/decadal variability
Sea level budget 2003-2009 3 mm/an
Total mass + steric
Compilation of published results of land ice loss
Ocean mass from GRACE
2 mm/an G+A
1 mm/an
Steric (Argo) Mean of 3 recent Glaciers estimates
GIA = -1.9 mm/yr GIA= -1.2 mm/yr
Land waters
Observed sea level rise
GIA trend expressed in terms of equivalent water height
GIA ocean Peltier (2009) = ~ -1.9 mm/yr Paulson (2007) = ~ -1 mm/yr
