Oceans and climate
Caroline Katsman
Global Climate Division (KNMI)
Large-scale ocean circulation
driven at the surface, by fluxes of
(wind)
momentum
heat
fresh water
(evaporation-precipitation)
⇒ density sea water = function(T,salinity)
surface (~ 1000 m):
wind-driven circulation
deep ocean:
thermohaline circulation
This lecture
i. observing the ocean
ii. characteristics ocean circulation
iii. ocean and climate
• abrupt changes in the thermohaline
circulation
• sea level rise
Observations
hydrographic sections:
• CTD (ConductivityTemperature-Depth)
• XBT (eXpandable
BathyThermograph)
• water samples (O2, nutrients)
moored instruments
• current meters
• CTDs
Observations
satellites:
• sea surface height ⇒ currents
• sea surface temperature
• ocean color (biological activity)
autonomous instruments:
profiling floats
⇒ 2 km depth
Argo float network
Atlantic Ocean section
salinity WOCE section A16 (25 W, Atlantic Ocean)
final contact with atmosphere determines
characteristics (T,S,O2..)
T-S diagram
50 Z- 30 Z
30 Z- EQ
EQ - 60 N
Mediterranean Sea
South-Atlantic
North Atlantic
Antarctica
WOCE A16 – Atlantic Ocean
ocean circulation
wind-driven circulation
large-scale gyres
wind-driven circulation
large-scale gyres
strong currents on the western side of ocean basins
wind-driven circulation
large-scale gyres
strong currents on the western side of ocean basins
Antarctic Circumpolar Current
thermohaline circulation
currents driven by variations in ocean density (T, S)
mixing and
upwelling
spreading
z
deep
convection
EQ
• geometry basins / forcing determine convection
• characteristics ‘convective end product’ differ
⇒ specific watermasses at selected locations/depths
The ocean conveyor belt
‘The great ocean conveyor’ [Broecker, 1991]
convective watermasses
Med
NADW
AABW
NADW:
AABW:
warm (+2 °C)
cold (-2 °C)
salty (35 ‰)
fresh (34.6 ‰)
ocean heat transport
50% of total heat transport occurs in the ocean
⇒ Atlantic Ocean
thermohaline circulation
wind-driven gyres
⇒ Pacific Ocean
small-scale instabilities
⇒ Southern Ocean
[Trenberth and Caron, 2001]
60 S
EQ
60 N
oceans & climate
abrupt changes in the
thermohaline circulation
multiple equilibria
temperature-driven
strength
circulation
T
salinity-driven
T or S
S
ratio S/T-forcing
in a warming climate
more heat
uptake
more melt
water
temperature-driven
strength
circulation
T
salinity-driven
T or S
S
possible
abrupt
change
ratio S/T-forcing
abrupt changes in the past
Younger Dryas (12-13.000 BP):
Greenland:
-15°C
Western Europe:
-5°C
⇒ linked to reduction
thermohaline circulation
abrupt changes in the future
forced collapse
T2100-T2000
abrupt changes in the future
forced collapse
T2100-T2000
forced collapse + GHG
T2100-T2000
abrupt changes in the future
Netherlands
oceans & climate
sea level rise
Global mean sea level rise
tide gauges:
18 ± 5 cm / century [1961-2003]
[source: IPCC 4AR, 2007]
Global mean sea level rise
tide gauges:
18 ± 5 cm / century [1961-2003]
satellites:
31 ± 7 cm / century
[1993-2003]
is this an acceleration
of the long-term trend
or a short-term fluctuation?
[source: IPCC 4AR, 2007]
[Univ of Colorado, 2010]
Sea level budget
observations limited in
space and time
(components + total)
mean rate of sea level rise (in mm/yr = 10 cm/cty)
[source: IPCC 4AR, 2007]
Sea level budget
increase
mean rate of sea level rise (in mm/yr = 10 cm/cty)
[source: IPCC 4AR, 2007]
Observations Dutch coast
relative sea level change
linear trend of 17-20 cm/cty [1890-2008]
no (statistically significant) acceleration
[Dillingh et al, 2010]
Local trend [1993-2007]
mm/yr (=10 cm/cty)
[University of Colorado, 2008]
Local trend [1993-2007]
larger than average rise
mm/yr (=10 cm/cty)
[University of Colorado, 2008]
Local trend [1993-2007]
strong drop in sea level
mm/yr (=10 cm/cty)
[University of Colorado, 2008]
Causes for local differences
1. (changes in) wind fields / surface pressure
Causes for local differences
1. (changes in) wind fields / surface pressure
2. (changes in) ocean currents
© NASA
Causes for local differences
1. (changes in) wind fields / surface pressure
2. (changes in) ocean currents
L
H
H
H
H
L
L
© NASA
Causes for local differences
1. (changes in) wind fields / surface pressure
2. (changes in) ocean currents
Gulf Stream
H
© NASA
Causes for local differences
1. (changes in) wind fields / surface pressure
2. (changes in) ocean currents
3. (changes in) gravity field
changing ice sheet
⇒ mass distribution
⇒ gravity field
⇒ “state of rest” ocean surface
geoid
© NASA
Self-gravitation effect
ice
sheet
gravitational pull on ocean towards large (ice)mass
Self-gravitation effect
ice
sheet
ice mass loss
⇒ melt water added to the ocean
Self-gravitation effect
sea level drop
ice
sheet
ice mass loss
⇒ melt water added to the ocean
⇒ sea level tilts
Self-gravitation effect
rise < global mean
ice
sheet
ice mass loss
⇒ melt water added to the ocean
⇒ sea level tilts
Self-gravitation effect
rise > global
mean
ice
sheet
ice mass loss
⇒ melt water added to the ocean
⇒ sea level tilts
Self-gravitation effect
ice
sheet
ice mass loss
⇒ melt water added to the ocean
⇒ sea level tilts
⇒ elastic response Earth’s crust
Local trend [1993-2007]
wind field
mm/yr (=10 cm/cty)
[University of Colorado, 2008]
Local trend [1993-2007]
ocean currents
mm/yr (=10 cm/cty)
[University of Colorado, 2008]
Local trend [1993-2007]
gravity field
(Alaskan glaciers)
mm/yr (=10 cm/cty)
[University of Colorado, 2008]
Regional projection
global
ocean expansion
glaciers
Greenland
Antarctica
Regional projection
global
local
extra local expansion
ocean expansion
ocean expansion
glaciers
glaciers
Greenland
SELF-GRAVITY
Greenland
EFFECT
Antarctica
Antarctica
land movement
Regional projection (SRES A1B)
global mean
0.47 m
[1980-1999 to 2090-2099]
Slangen et al. (Clim. Dyn., 2011)
Regional projection (SRES A1B)
GL [0.07 m]
based onGIC [0.17 m]
global
IPCCmean
4AR
0.47 mcontribution)
(SMB
AA [0.01 m]
steric [0.21 m]
Slangen et al. (Clim. Dyn., 2011)
GIA [0.0 m]
Regional projection (SRES A1B)
GL [0.07 m]
GIC [0.17 m]
global mean
0.47 m
AA [0.01 m]
steric [0.21 m]
using regionally
GIA [0.0 m]
distributed dataset
Cogley [2009]
Radić & Hock [2010]
Slangen et al. (Clim. Dyn., 2011)
Regional projection (SRES A1B)
GL [0.07 m]
GIC [0.17 m]
global mean
0.47 m
AA [0.01 m]
steric [0.21 m]
12 coupled
GIA [0.0 m]
climate models
[CMIP3 database]
Slangen et al. (Clim. Dyn., 2011)
Regional projection (SRES A1B)
GL [0.07 m]
GIC [0.17 m]
global mean
0.47 m
AA [0.01 m]
steric [0.21 m]
Slangen et al. (Clim. Dyn., 2011)
GIA [0.0 m]
Impact ice sheet contribution
0.47 m
[GL: 0.07 m, AA 0.01 m]
Slangen et al (2011)
[1980-1999 to 2090-2099]
Impact ice sheet contribution
0.47 m
[GL: 0.07 m, AA 0.01 m]
1.02 m
1.02 m
[GL: 0.22 m; AA: 0.41 m]
Slangen et al (2011)
[1980-1999 to 2090-2099]
To conclude…
The oceans plays an important role in climate
and (natural and forced) climate change,
but we still know surprisingly little about them
To conclude…
The oceans plays an important role in climate
and (natural and forced) climate change,
but we still know surprisingly little about them
“The oceans are the principal reservoir
for the storage of CO2, of heat
and of ignorance”
(Walter Munk, The Evolution of Physical Oceanography in
the Last Hundred Years, 2002)
EXTRA
Ice sheets
Largest potential & largest uncertainty
How much is melting now and why?
How much ice can potentially melt and
how fast can this happen?
Ice sheets
Largest potential & largest uncertainty
How much is melting now and why?
How much ice can potentially melt and
how fast can this happen?
more observations become available
our modeling skills are limited (at the moment)
Ice sheet contributions
Model-based contributions [IPCC 4AR]
21st century ice sheet
contribution (cm)
+6
-9
IPCC 4AR
Ice sheet contributions
Extrapolation current mass loss
scaled with global temperature [IPCC 4AR]
21st century ice sheet
contribution (cm)
+26
-10
IPCC 4AR
Ice sheet contributions
Extrapolation current mass loss
Extrapolation current acceleration of mass loss
[Rignot et al. (GRL, 2011)]
21st century ice sheet
contribution (cm)
56
IPCC 4AR
Rignot ‘11
Ice sheet contributions
Extrapolation current mass loss
Extrapolation current acceleration of mass loss
Upper limit glacier discharge based on
kinematic constraints [Pfeffer et al., 2008]
21st century ice sheet
contribution (cm)
+116
+32
IPCC 4AR
Rignot ‘11
Pfeffer ‘08
Ice sheet contributions
Extrapolation current mass loss
Extrapolation current acceleration of mass loss
Upper limit glacier discharge
Possible impacts marine ice sheet instabilities
[Katsman et al. 2011]
21st century ice sheet
contribution (cm)
+59
+16
IPCC 4AR
Rignot ‘11
Pfeffer ‘08
Katsman ‘11
Integrated flood risk
assessment
Katsman et al (Clim. Change, 2011)