Sea Level Rise
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Sea Level Raises
The Earth is Warming
Annual Global Mean Surface Temperatures 0.8 0.6 0.4
∆°C
0.2 0
-0.2 -0.4 -0.6 1880
1900
1920
1940 1960 Year
1980
2000
[Hansen et al., 2005]
What Causes Sea Level to Change?
The Bathtub Sea Level Model Precipitation over Oceans Runoff from Continents
+ Evaporation from Oceans Precipitation over Continents
What is Global Mean Sea Level Change?
• “Global Mean Sea Level
Change” is the change in the average height of the oceans over the entire globe at a single point in time. • Sea level change at a specific location in the ocean may be higher or lower than the global mean because of differences in ocean temperature and other effects. • Usually measured in units of millimeters (mm): 25.4 mm = 1 in • Does not include ocean tides,
Land Movement Can Affect Sea Level Locally InSAR Image of Subsidence in New Orleans
[Dixon et al., 2006]
mm/yr
Measurements of Sea Level Change GRAVITY
Tide Gauge Sea Level Measurements
Tide Gauges with Greater Than 10 Years of Measuremen
Tide Gauges with Greater Than 50 Years of Measuremen
150
Tide Gauge Observations 3.2 mm/year
100 2.0 mm/year ∆MSL (mm)
50 0.8 mm/year 0
50 Average Rate ~ 1.8 mm/year 100
1880
1900
1920
1940 Year
1960
1980
2000
[Church and White, 2006]
Satellite Altimeters TOPEX/Poseidon 1992-2005
Jason-1 2001 - ?
OSTM/Jason-2 2008
Global Mean Sea Level from Satellite Altimetry Average Rate = 3.5 mm/year (1993-2006)
1997-1998 El Nino
[Mitchum and Nerem, 2007
Sea Level Change is Not the Same Everywhere Average Sea Level Rise over 1993-2006
mm/yr
Sea Level Change Potential Contributions Thermal Expansion: ~1 meter
Mountain Glaciers: 0.5 meters
Greenland Ice Melt: 7 meters
Antarctic Ice Melt: 60 meters Land Water Storage: < 0.5 meters
Thermal Expansion: Contribution to Sea Level 20 Rate = 0.4 mm/year (1955-2004)
15 Rate = 1.2 - 1.6 mm/year (1993-2004)
∆MSL (mm)
10 5 Mt. Pinatubo
0 5
10 15
1960
1970
1980 Year
1990
2000
[Levitus et al., 2005; Antonov et al., 2005
Mountain Glaciers: Contribution to Sea Level 25
∆MSL (mm)
20
1961-2003: 0.5 mm/year 1994-2003: 0.9 mm/year
15
10
5
0 1960
1970
1980
1990 Year
2000
2010
[Dyurgerov and Meier, 2005]
Greenland Ice Mass Loss from GRACE 300
362 Gt = 1 mm GMSL 200
Gt/year
100 0
100 200 300 -140 Gt/year = 0.4 mm/year GMSL
400 2003.5
2004
2004.5
2005 Year
2005.5
2006
2006.5
Credit: Roger Braithwaite
[Luthcke et al., 2006]
Greenland Melt Extent
Antarctic Ice Mass Flux from InSAR SLR 0.4 to 0.6 mm/yr
-4 km3/yr
-2 km3/yr
-2 km3/yr
+5 km3/yr
-37±20 km3/yr
-2 km3/yr
-3 km3/yr
-49±20 km3/yr
+48 km3/yr -38 km3/yr
-4 km3/yr
-114 km3/yr -22 km3/yr -56 km3/yr
+33 km3/yr
-33 km3/yr
+21 km3/yr
+5 km3/yr
[Rignot, 2005]
Sea Level Budget (IPCC, mm/year) 1993-2003
1961-2003
Thermal Expansion
1.6 ± 0.5
0.4 ± 0.1
+
Mountain Glaciers
0.8 ± 0.2
0.5 ± 0.2
+
Greenland Ice Melt
0.2 ± 0.1
0.1 ± 0.1
+
Antarctic Ice Melt
0.2 ± 0.3
0.1 ± 0.4
?
?
Land Water Storage
=Total of Observed Contributions2.8 ± 0.7 Observed Sea Level Change3.1 ± 0.7
1.1 ± 0.5 1.8 ± 0.5
Is Sea Level Rise Accelerating?
• Short answer: probably • The satellite sea level record is too short (~14 years) to rule out that the recent rise is due to natural decadal variability. • This is only likely to be resolved by having a longer satellite data record (~30 years). • The decline in satellite programs in recent years has put this in jeopardy.
Sea Level Observations versus Predictions Satellite Observations Tide Gauge Observations
Climate Model Predictions (IPCC 3rd Assessment, 2001)
[Rahmstorf et al., 2007]
What to Expect in the Future
• Future sea level
•
•
5 predictions are .8° uncertain because of uncertainties in the contributions of 1 Greenland and .4° Antarctica. The IPCC 4th Assessment projects 0.28 - 0.59 m of sea level rise by 2100, but [Rahmstorf, 2007] did not exclude higher rates. In fact, a recent study Even if greenhouse gases were stabilized now, suggests higher substantial sea rates level rise would continue for several (0.5 - 1.4 m by 2100). centuries because of inertia in the climate system (~ 0.1
Summary
• Observations of sea level change are consistent
with how we expect sea level to respond in a warming climate. • Sea level rose faster in the last decade than the 20th century average. • Whether the current rate of rise is accelerating can only be resolved with longer satellite time series. • Presently, ocean warming, melting of mountain glaciers, and melting of the polar ice caps are contributing in roughly equal amounts to the observed rise. • The largest uncertainty in future sea level rise projections is the contribution of Greenland and Antarctica.
Greenland Ice Mass Loss Estimates Luthcke et al. [2006] Krabill et al. [2004] Zwally et al. [2005] Rignot et al. [2006] Velicogna and Wahr [2005] Ramillien et al. [2006] Chen et al. [2006] Velicogna and Wahr [2006]
Mass Loss 362 Gt = 1 mm GMSL
[Cazenave, 2006]
Antarctic Ice Mass Loss Estimates Rignot and Thomas [2002] Zwally et al. [2005] Davis et al. [2005] Velicogna and Wahr [2006] Chen et al. [2006] Ramillien et al. [2006]
362 Gt = 1 mm GMSL
[Cazenave, 2006]
Sea Level Budget (1993-2006) Thermal Expansion: 1.2 - 1.6 mm/year
+
Mountain Glaciers: ~0.6 - 1.0 mm/year
+
Greenland Ice Melt: ~0.2 - 0.5 mm/year
+
Antarctic Ice Melt: ~0.2 - 0.4 mm/year Land Water Storage: ?
=
Total: 2.2 - 3.5 mm/yearObserved by Satellites
Alaska Glacier Mass Changes from GRACE
Sea Level Contribution of 0.3 mm/year over 2002-2004
[Tamisiea et al., 2005]
Effects of Sea Level Rise
1 meter
2 meters
4
8
G
The Earth is Warming
Annual Global Mean Surface Temperatures 0.8 0.6 0.4
∆°C
0.2 0
-0.2 -0.4 -0.6 1880
1900
1920
1940 1960 Year
1980
2000
[Hansen et al., 2005]
What Causes Sea Level to Change?
The Bathtub Sea Level Model Precipitation over Oceans Runoff from Continents
+ Evaporation from Oceans Precipitation over Continents
What is Global Mean Sea Level Change?
• “Global Mean Sea Level
Change” is the change in the average height of the oceans over the entire globe at a single point in time. • Sea level change at a specific location in the ocean may be higher or lower than the global mean because of differences in ocean temperature and other effects. • Usually measured in units of millimeters (mm): 25.4 mm = 1 in • Does not include ocean tides,
Land Movement Can Affect Sea Level Locally InSAR Image of Subsidence in New Orleans
[Dixon et al., 2006]
mm/yr
Measurements of Sea Level Change GRAVITY
Tide Gauge Sea Level Measurements
Tide Gauges with Greater Than 10 Years of Measuremen
Tide Gauges with Greater Than 50 Years of Measuremen
150
Tide Gauge Observations 3.2 mm/year
100 2.0 mm/year ∆MSL (mm)
50 0.8 mm/year 0
50 Average Rate ~ 1.8 mm/year 100
1880
1900
1920
1940 Year
1960
1980
2000
[Church and White, 2006]
Satellite Altimeters TOPEX/Poseidon 1992-2005
Jason-1 2001 - ?
OSTM/Jason-2 2008
Global Mean Sea Level from Satellite Altimetry Average Rate = 3.5 mm/year (1993-2006)
1997-1998 El Nino
[Mitchum and Nerem, 2007
Sea Level Change is Not the Same Everywhere Average Sea Level Rise over 1993-2006
mm/yr
Sea Level Change Potential Contributions Thermal Expansion: ~1 meter
Mountain Glaciers: 0.5 meters
Greenland Ice Melt: 7 meters
Antarctic Ice Melt: 60 meters Land Water Storage: < 0.5 meters
Thermal Expansion: Contribution to Sea Level 20 Rate = 0.4 mm/year (1955-2004)
15 Rate = 1.2 - 1.6 mm/year (1993-2004)
∆MSL (mm)
10 5 Mt. Pinatubo
0 5
10 15
1960
1970
1980 Year
1990
2000
[Levitus et al., 2005; Antonov et al., 2005
Mountain Glaciers: Contribution to Sea Level 25
∆MSL (mm)
20
1961-2003: 0.5 mm/year 1994-2003: 0.9 mm/year
15
10
5
0 1960
1970
1980
1990 Year
2000
2010
[Dyurgerov and Meier, 2005]
Greenland Ice Mass Loss from GRACE 300
362 Gt = 1 mm GMSL 200
Gt/year
100 0
100 200 300 -140 Gt/year = 0.4 mm/year GMSL
400 2003.5
2004
2004.5
2005 Year
2005.5
2006
2006.5
Credit: Roger Braithwaite
[Luthcke et al., 2006]
Greenland Melt Extent
Antarctic Ice Mass Flux from InSAR SLR 0.4 to 0.6 mm/yr
-4 km3/yr
-2 km3/yr
-2 km3/yr
+5 km3/yr
-37±20 km3/yr
-2 km3/yr
-3 km3/yr
-49±20 km3/yr
+48 km3/yr -38 km3/yr
-4 km3/yr
-114 km3/yr -22 km3/yr -56 km3/yr
+33 km3/yr
-33 km3/yr
+21 km3/yr
+5 km3/yr
[Rignot, 2005]
Sea Level Budget (IPCC, mm/year) 1993-2003
1961-2003
Thermal Expansion
1.6 ± 0.5
0.4 ± 0.1
+
Mountain Glaciers
0.8 ± 0.2
0.5 ± 0.2
+
Greenland Ice Melt
0.2 ± 0.1
0.1 ± 0.1
+
Antarctic Ice Melt
0.2 ± 0.3
0.1 ± 0.4
?
?
Land Water Storage
=Total of Observed Contributions2.8 ± 0.7 Observed Sea Level Change3.1 ± 0.7
1.1 ± 0.5 1.8 ± 0.5
Is Sea Level Rise Accelerating?
• Short answer: probably • The satellite sea level record is too short (~14 years) to rule out that the recent rise is due to natural decadal variability. • This is only likely to be resolved by having a longer satellite data record (~30 years). • The decline in satellite programs in recent years has put this in jeopardy.
Sea Level Observations versus Predictions Satellite Observations Tide Gauge Observations
Climate Model Predictions (IPCC 3rd Assessment, 2001)
[Rahmstorf et al., 2007]
What to Expect in the Future
• Future sea level
•
•
5 predictions are .8° uncertain because of uncertainties in the contributions of 1 Greenland and .4° Antarctica. The IPCC 4th Assessment projects 0.28 - 0.59 m of sea level rise by 2100, but [Rahmstorf, 2007] did not exclude higher rates. In fact, a recent study Even if greenhouse gases were stabilized now, suggests higher substantial sea rates level rise would continue for several (0.5 - 1.4 m by 2100). centuries because of inertia in the climate system (~ 0.1
Summary
• Observations of sea level change are consistent
with how we expect sea level to respond in a warming climate. • Sea level rose faster in the last decade than the 20th century average. • Whether the current rate of rise is accelerating can only be resolved with longer satellite time series. • Presently, ocean warming, melting of mountain glaciers, and melting of the polar ice caps are contributing in roughly equal amounts to the observed rise. • The largest uncertainty in future sea level rise projections is the contribution of Greenland and Antarctica.
Greenland Ice Mass Loss Estimates Luthcke et al. [2006] Krabill et al. [2004] Zwally et al. [2005] Rignot et al. [2006] Velicogna and Wahr [2005] Ramillien et al. [2006] Chen et al. [2006] Velicogna and Wahr [2006]
Mass Loss 362 Gt = 1 mm GMSL
[Cazenave, 2006]
Antarctic Ice Mass Loss Estimates Rignot and Thomas [2002] Zwally et al. [2005] Davis et al. [2005] Velicogna and Wahr [2006] Chen et al. [2006] Ramillien et al. [2006]
362 Gt = 1 mm GMSL
[Cazenave, 2006]
Sea Level Budget (1993-2006) Thermal Expansion: 1.2 - 1.6 mm/year
+
Mountain Glaciers: ~0.6 - 1.0 mm/year
+
Greenland Ice Melt: ~0.2 - 0.5 mm/year
+
Antarctic Ice Melt: ~0.2 - 0.4 mm/year Land Water Storage: ?
=
Total: 2.2 - 3.5 mm/yearObserved by Satellites
Alaska Glacier Mass Changes from GRACE
Sea Level Contribution of 0.3 mm/year over 2002-2004
[Tamisiea et al., 2005]
Effects of Sea Level Rise
1 meter
2 meters
4
8
G
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