southern ocean physical controls on the the southern ocean … · the cdis reservoir, particularly...
TRANSCRIPT
eddy stirring
south north
CO2 Feair-seagas transfer
trace metalsupply
depth
biologicalfalloutrespiration/
regeneration
DIC+
N +Fe -
diapycnalmixing
DIC+
N +Fe -
DIC-
N -Fe +
Physical Controls on the Air‐Sea Partitioning of CO2
Ric Williams (Liverpool)
Thanks to Mick Follows (MIT), Jon Lauderdale (MIT), Phil Goodwin (Southampton), Andy Ridgwell (Bristol), Alessandro Tagliabue (Liverpool), and other collaborators.
• how much heat & CO2 is being sequestered?
• what are the controlling mechanisms?
• what are the wider climate implications?
Challenges for the community
MeridionalOverturning in theSouthern Ocean
Andy Hogg
The SouthernOcean
Upper Cell(i) Theory
(ii) Observations
(iii) Models
(iv) Complications
Lower Cell(i) The Basics
(ii) Observations
(iii) Models
(iv) Complications
Conclusions
The Southern Ocean
MODE / INTERMEDIATE WATER
EKMAN TRANSPORT
DEEP WATER
SOUTH AMERICAANTARCTICA
BUOYANCY LOSS
WESTERLIES
BUOYANCY GAIN
EDDIES
ACC
BOTTOM WATER
Image from Morrison et al., 2015: "Upwelling in the Southern Ocean." Phys. Today.
I “Wind-driven” Antarctic Circumpolar Current (ACC)I Upper & lower overturning cellsI Buoyancy fluxes also drive circulation
eddy stirring
south north
CO2 Feair-seagas transfer
trace metalsupply
depth
biologicalfalloutrespiration/
regeneration
DIC+
N +Fe -
diapycnalmixing
DIC+
N +Fe -
DIC-
N -Fe +
1. Mechanisms
2. Frameworks
3. Effect of residual circulation
4. Global implications
Lecture overview
Physical Controls on the Air‐Sea Partitioning of CO2
Ric Williams (Liverpool)
Thanks to Mick Follows (MIT), Jon Lauderdale (MIT), Phil Goodwin (Southampton), Andy Ridgwell (Bristol), Alessandro Tagliabue (Liverpool), and other collaborators.
MeridionalOverturning in theSouthern Ocean
Andy Hogg
The SouthernOcean
Upper Cell(i) Theory
(ii) Observations
(iii) Models
(iv) Complications
Lower Cell(i) The Basics
(ii) Observations
(iii) Models
(iv) Complications
Conclusions
The Southern Ocean
MODE / INTERMEDIATE WATER
EKMAN TRANSPORT
DEEP WATER
SOUTH AMERICAANTARCTICA
BUOYANCY LOSS
WESTERLIES
BUOYANCY GAIN
EDDIES
ACC
BOTTOM WATER
Image from Morrison et al., 2015: "Upwelling in the Southern Ocean." Phys. Today.
I “Wind-driven” Antarctic Circumpolar Current (ACC)I Upper & lower overturning cellsI Buoyancy fluxes also drive circulation
atmosphere
ocean
reactions in seawater
1. Mechanisms
carbonate chemistry
buffer factor
atmosphere
ocean
air-sea exchange
air-sea exchange timescale
month 1/10 170
1. Mechanisms
Kg air-sea transfer velocity h mixed layer depth
physicsrate limiting processes on annual timescale:
subduction into main thermoclineentrainment into winter mixed layerresulting annual air-sea uptake
fine-scale dynamical processes only important in modifying these processes
atmosphere
mixedlayer
ocean interior
uptakeoutgassing
CO2 CO2 CO2 CO2
warming cooling
atmosphere
mixerlayer
ocean interior
biologicalfallout
biologicaldrawdown
(a) physical transport and solubility (b) physical transport and biology
entrainment ofcarbon-rich waters
respiration and regeneration
physical transfer from surface to interior
physical transfer from interior to surface
1. Mechanisms
biology
biological drawdown can respond to fine-scale delivery of nutrients & trace metals
affects DIC profile
atmosphere
mixedlayer
ocean interior
uptakeoutgassing
CO2 CO2 CO2 CO2
warming cooling
atmosphere
mixerlayer
ocean interior
biologicalfallout
biologicaldrawdown
(a) physical transport and solubility (b) physical transport and biology
entrainment ofcarbon-rich waters
respiration and regeneration
physical transfer from surface to interior
physical transfer from interior to surface
1. Mechanisms
Prevailing view:biological response is not directly important for the anthropogenic response, but is crucial for glacial-interglacial cycles.
physics biology
see first order opposing signs in the physical & biological responses
atmosphere
mixedlayer
ocean interior
uptakeoutgassing
CO2 CO2 CO2 CO2
warming cooling
atmosphere
mixerlayer
ocean interior
biologicalfallout
biologicaldrawdown
(a) physical transport and solubility (b) physical transport and biology
entrainment ofcarbon-rich waters
respiration and regeneration
physical transfer from surface to interior
physical transfer from interior to surface
1. Mechanisms
thermocline
N
N pre
N =N pre+ N reg
atmosphere
mixed layer preformed & regenerated
in mixed layer
in ocean interior
2. Frameworks
efficiency of the biology
Ito & Follows (2005)
Tagliabue)et)al.)(2014,)Nature)Geoscience))
preformed +regenerated +benthic - scavenged
Dissolved free iron flux to surface dominated by winter entrainment
Tagliabue)et)al.)(2014,)GRL))
Supply of preformed & benthic Fe to the Southern Ocean
preformed
benthic
2. Frameworks Dissolved free iron
saturated
in mixed layer
disequilibrium
2. Frameworks Dissolved inorganic carbon, DIC
= Csat + Cdis
thermoclineC pre
atmosphere
mixed layerC pre= C sat +!C
C
DIC dis
in ocean interior thermocline
DIC
C pre
DIC=C pre+ C reg
atmosphere
mixed layer
2. Frameworks Dissolved inorganic carbon, DIC
Csat + Cdis + Csoft + Ccarb
saturated soft tissueregenerated
carbonatetissueregenerated
disequilibrium
DIC = Cpre + Creg
Hsurface heat loss/
density gainsurface heat gain/
density loss
eastward winds
diapycnalmixing
eddy stirring
Ekman transport
eddy transport
upper limb of overturning
dept
h
south north
lower limb ofoverturning
eddy stirring
south north
CO2 Feair-seagas transfer
trace metalsupply
depth
biologicalfalloutrespiration/
regeneration
DIC+
N +Fe -
diapycnalmixing
DIC+
N +Fe -
DIC-
N -Fe +
3. Residual circulation
• air-sea carbon uptake affected by how far surface waters are away from saturation
• air-sea carbon anomalies eroded on annual & longer timescales
• expect opposing preformed & regenerated nutrient responses
Consider effect of changes in residual circulation
Hsurface heat loss/
density gainsurface heat gain/
density loss
eastward winds
diapycnalmixing
eddy stirring
Ekman transport
eddy transport
upper limb of overturning
dept
h
south north
lower limb ofoverturning
ψres=ψEul+ψeddy,,(ψeddy≈KGMSi),
3. Residual circulation
MIT model 2.8ox2.8o, fixed KGM in eddy closure, integrated 5000 years with online biogeochemistry(Lauderdale et al., 2013, Climate Dynamics)
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generally stronger ψres=ψEul+ψeddy,,(ψeddy≈KGMSi),generally thicker subtropical thermocline
preformed carbon anomalyincreases via greater subduction
stronger westerly wind
regenerated carbon anomaly decreases, as more nutrients are subducted �
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increases via greater subduction
stronger westerly wind 3. Residual circulation
�Cpre
from T, S & Alk decreases from warmer thermocline
increases due to shorter residence time
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Wind-driven changes in the Southern Ocean carbon reservoirs 21
Fig. 12 Zonally-averaged Atlantic Ocean anomaly (mmol C m�3) of the Cdis reservoir for (a) increased, (b) decreased,
(c) northward-shifted and (d) southward-shifted westerly winds.
back into the deep ocean in regions of bottom water formation in the Southern Ocean, resulting in a306
relatively large increase in �Cdis in the abyss.307
When these anomalies are integrated (Table 2), the deep ocean changes dominate the net anomaly in308
the Cdis reservoir, particularly for southward shifted winds.309
3.4 Summary of the relationship between carbon components and ocean physics310
The close relationship between changes in atmospheric CO2 and the Southern Ocean residual circulation311
reveals a strong control by ocean physics (Figure 2b). A mechanistic view of the changes in the carbon312
components is obtained by applying the carbon framework to the model experiments. Changes in residual313
circulation explain 83% of the variance in the total saturated pool of DIC, including changes resulting314
from atmospheric CO2 and potential temperature, salinity and alkalinity anomalies. When considered315
separately, the relationship between the residual circulation and �Csat(✓,S,Apre) is fairly close for all316
experiments, controlled by ventilated changes in pycnocline depth. For southward-shifted winds of 10�,317
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27 experiments: variety of winds, GM values, limited buoyancy forcing changes
R2=0.89
stronger residual cell, greater atmospheric CO2
eddy stirring
south north
CO2 Feair-seagas transfer
trace metalsupply
depth
biologicalfalloutrespiration/
regeneration
DIC+
N +Fe -
diapycnalmixing
DIC+
N +Fe -
DIC-
N -Fe +
Residual circulation (Sv)
Atmospheric CO2 (ppm)
(Lauderdale et al., 2013, Climate Dynamics)
3. Residual circulation
0 30
260
300
Consistent with paleo argument: enhanced upwelling driving last deglacial (Anderson et al., 2009)
Glo
bal c
arbo
n an
omal
y (G
tC)
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-125.00
-100.00
-75.00
-50.00
-25.00
0.00
25.00
50.00
75.00
100.00
125.00
150.00L2
013
Cons
tant
KG
M
F200
5 Va
riabl
e KG
M
HMM
2011
Var
iabl
e KG
M
V199
7 Va
riabl
e KG
M
L201
3 Co
nsta
nt K
GM
F200
5 Va
riabl
e KG
M
HMM
2011
Var
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M
V199
7 Va
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M
L201
3 Co
nsta
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GM
F200
5 Va
riabl
e KG
M
HMM
2011
Var
iabl
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M
V199
7 Va
riabl
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M
L201
3 Co
nsta
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GM
F200
5 Va
riabl
e KG
M
HMM
2011
Var
iabl
e KG
M
V199
7 Va
riabl
e KG
M
Atmospheric CO2 Preformed Carbon Regenerated Carbon
Increased SH Winds
Decreased SH Winds
North-shifted Winds
South-shifted Winds
Glo
bal c
arbo
n an
omal
y (G
tC)
-150.00
-125.00
-100.00
-75.00
-50.00
-25.00
0.00
25.00
50.00
75.00
100.00
125.00
150.00
L201
3 Co
nsta
nt K
GM
F200
5 Va
riabl
e KG
M
HMM
2011
Var
iabl
e KG
M
V199
7 Va
riabl
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M
L201
3 Co
nsta
nt K
GM
F200
5 Va
riabl
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M
HMM
2011
Var
iabl
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M
V199
7 Va
riabl
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M
L201
3 Co
nsta
nt K
GM
F200
5 Va
riabl
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M
HMM
2011
Var
iabl
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M
V199
7 Va
riabl
e KG
M
L201
3 Co
nsta
nt K
GM
F200
5 Va
riabl
e KG
M
HMM
2011
Var
iabl
e KG
M
V199
7 Va
riabl
e KG
M
Atmospheric CO2 Preformed Carbon Regenerated Carbon
Increased SH Winds
Decreased SH Winds
North-shifted Winds
South-shifted Winds
Glo
bal c
arbo
n an
omal
y (G
tC)
-150.00
-125.00
-100.00
-75.00
-50.00
-25.00
0.00
25.00
50.00
75.00
100.00
125.00
150.00
L201
3 Co
nsta
nt K
GM
F200
5 Va
riabl
e KG
M
HMM
2011
Var
iabl
e KG
M
V199
7 Va
riabl
e KG
M
L201
3 Co
nsta
nt K
GM
F200
5 Va
riabl
e KG
M
HMM
2011
Var
iabl
e KG
M
V199
7 Va
riabl
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M
L201
3 Co
nsta
nt K
GM
F200
5 Va
riabl
e KG
M
HMM
2011
Var
iabl
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M
V199
7 Va
riabl
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M
L201
3 Co
nsta
nt K
GM
F200
5 Va
riabl
e KG
M
HMM
2011
Var
iabl
e KG
M
V199
7 Va
riabl
e KG
M
Atmospheric CO2 Preformed Carbon Regenerated Carbon
Increased SH Winds
Decreased SH Winds
North-shifted Winds
South-shifted Winds
weaker winds
stronger winds
Carbon anomaly (PgC)
Glo
bal c
arbo
n an
omal
y (G
tC)
-150.00-125.00-100.00
-75.00-50.00-25.00
0.0025.0050.0075.00
100.00125.00150.00
Incr
ease
d Ta
ux
Decr
ease
d Ta
ux
North
-shi
fted
Taux
Sout
h-sh
ifted
Tau
x
Incr
ease
d Ta
ux
Decr
ease
d Ta
ux
North
-shi
fted
Taux
Sout
h-sh
ifted
Tau
x
Incr
ease
d Ta
ux
Decr
ease
d Ta
ux
North
-shi
fted
Taux
Sout
h-sh
ifted
Tau
x
Incr
ease
d Ta
ux
Decr
ease
d Ta
ux
North
-shi
fted
Taux
Sout
h-sh
ifted
Tau
x
Atmospheric CO2 Preformed Carbon Regenerated Carbon
Constant KGMLauderdale et al
(2013)
Variable KGMFerreira et al
(2005)
Variable KGMHoffman &
Morales Maqueda (2011)
Variable KGMVisbeck et al
(1997)
Glo
bal c
arbo
n an
omal
y (G
tC)
-150.00-125.00-100.00
-75.00-50.00-25.00
0.0025.0050.0075.00
100.00125.00150.00
Incr
ease
d Ta
ux
Decr
ease
d Ta
ux
North
-shi
fted
Taux
Sout
h-sh
ifted
Tau
x
Incr
ease
d Ta
ux
Decr
ease
d Ta
ux
North
-shi
fted
Taux
Sout
h-sh
ifted
Tau
x
Incr
ease
d Ta
ux
Decr
ease
d Ta
ux
North
-shi
fted
Taux
Sout
h-sh
ifted
Tau
x
Incr
ease
d Ta
ux
Decr
ease
d Ta
ux
North
-shi
fted
Taux
Sout
h-sh
ifted
Tau
x
Atmospheric CO2 Preformed Carbon Regenerated Carbon
Constant KGMLauderdale et al
(2013)
Variable KGMFerreira et al
(2005)
Variable KGMHoffman &
Morales Maqueda (2011)
Variable KGMVisbeck et al
(1997)
Glo
bal c
arbo
n an
omal
y (G
tC)
-150.00-125.00-100.00
-75.00-50.00-25.00
0.0025.0050.0075.00
100.00125.00150.00
Incr
ease
d Ta
ux
Decr
ease
d Ta
ux
North
-shi
fted
Taux
Sout
h-sh
ifted
Tau
x
Incr
ease
d Ta
ux
Decr
ease
d Ta
ux
North
-shi
fted
Taux
Sout
h-sh
ifted
Tau
x
Incr
ease
d Ta
ux
Decr
ease
d Ta
ux
North
-shi
fted
Taux
Sout
h-sh
ifted
Tau
x
Incr
ease
d Ta
ux
Decr
ease
d Ta
ux
North
-shi
fted
Taux
Sout
h-sh
ifted
Tau
x
Atmospheric CO2 Preformed Carbon Regenerated Carbon
Constant KGMLauderdale et al
(2013)
Variable KGMFerreira et al
(2005)
Variable KGMHoffman &
Morales Maqueda (2011)
Variable KGMVisbeck et al
(1997)
wind changes & different eddy closures
• atmospheric CO2 increase due to contraction of regenerated carbon pool
see Jon Lauderdale poster
3. Residual circulation
• opposing sign of regenerated and preformed carbon anomalies
Eddy KGM closures:constant Hoffman & Morales Maqueda (2011)Ferreira et al. (2005)Visbeck et al. (1997)
Glo
bal c
arbo
n an
omal
y (G
tC)
-150.00
-125.00
-100.00
-75.00
-50.00
-25.00
0.00
25.00
50.00
75.00
100.00
125.00
150.00
L201
3 Co
nsta
nt K
GM
F200
5 Va
riabl
e KG
M
HMM
2011
Var
iabl
e KG
M
V199
7 Va
riabl
e KG
M
L201
3 Co
nsta
nt K
GM
F200
5 Va
riabl
e KG
M
HMM
2011
Var
iabl
e KG
M
V199
7 Va
riabl
e KG
M
L201
3 Co
nsta
nt K
GM
F200
5 Va
riabl
e KG
M
HMM
2011
Var
iabl
e KG
M
V199
7 Va
riabl
e KG
M
L201
3 Co
nsta
nt K
GM
F200
5 Va
riabl
e KG
M
HMM
2011
Var
iabl
e KG
M
V199
7 Va
riabl
e KG
M
Atmospheric CO2 Preformed Carbon Regenerated Carbon
Increased SH Winds
Decreased SH Winds
North-shifted Winds
South-shifted Winds
northward shift
Glo
bal c
arbo
n an
omal
y (G
tC)
-150.00
-125.00
-100.00
-75.00
-50.00
-25.00
0.00
25.00
50.00
75.00
100.00
125.00
150.00
L201
3 Co
nsta
nt K
GM
F200
5 Va
riabl
e KG
M
HMM
2011
Var
iabl
e KG
M
V199
7 Va
riabl
e KG
M
L201
3 Co
nsta
nt K
GM
F200
5 Va
riabl
e KG
M
HMM
2011
Var
iabl
e KG
M
V199
7 Va
riabl
e KG
M
L201
3 Co
nsta
nt K
GM
F200
5 Va
riabl
e KG
M
HMM
2011
Var
iabl
e KG
M
V199
7 Va
riabl
e KG
M
L201
3 Co
nsta
nt K
GM
F200
5 Va
riabl
e KG
M
HMM
2011
Var
iabl
e KG
M
V199
7 Va
riabl
e KG
M
Atmospheric CO2 Preformed Carbon Regenerated Carbon
Increased SH Winds
Decreased SH Winds
North-shifted Winds
South-shifted Winds
Glo
bal c
arbo
n an
omal
y (G
tC)
-150.00
-125.00
-100.00
-75.00
-50.00
-25.00
0.00
25.00
50.00
75.00
100.00
125.00
150.00
L201
3 Co
nsta
nt K
GM
F200
5 Va
riabl
e KG
M
HMM
2011
Var
iabl
e KG
M
V199
7 Va
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M
L201
3 Co
nsta
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F200
5 Va
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HMM
2011
Var
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V199
7 Va
riabl
e KG
M
L201
3 Co
nsta
nt K
GM
F200
5 Va
riabl
e KG
M
HMM
2011
Var
iabl
e KG
M
V199
7 Va
riabl
e KG
M
L201
3 Co
nsta
nt K
GM
F200
5 Va
riabl
e KG
M
HMM
2011
Var
iabl
e KG
M
V199
7 Va
riabl
e KG
M
Atmospheric CO2 Preformed Carbon Regenerated Carbon
Increased SH Winds
Decreased SH Winds
North-shifted Winds
South-shifted Winds
Carbon anomaly (PgC)
southwardshift
see Jon Lauderdale poster
3. Residual circulation
• opposing sign of regenerated and preformed carbon anomalies
• atmospheric CO2 increase due to contraction of preformed carbon pool
Glo
bal c
arbo
n an
omal
y (G
tC)
-150.00-125.00-100.00
-75.00-50.00-25.00
0.0025.0050.0075.00
100.00125.00150.00
Incr
ease
d Ta
ux
Decr
ease
d Ta
ux
North
-shi
fted
Taux
Sout
h-sh
ifted
Tau
x
Incr
ease
d Ta
ux
Decr
ease
d Ta
ux
North
-shi
fted
Taux
Sout
h-sh
ifted
Tau
x
Incr
ease
d Ta
ux
Decr
ease
d Ta
ux
North
-shi
fted
Taux
Sout
h-sh
ifted
Tau
x
Incr
ease
d Ta
ux
Decr
ease
d Ta
ux
North
-shi
fted
Taux
Sout
h-sh
ifted
Tau
x
Atmospheric CO2 Preformed Carbon Regenerated Carbon
Constant KGMLauderdale et al
(2013)
Variable KGMFerreira et al
(2005)
Variable KGMHoffman &
Morales Maqueda (2011)
Variable KGMVisbeck et al
(1997)
Glo
bal c
arbo
n an
omal
y (G
tC)
-150.00-125.00-100.00
-75.00-50.00-25.00
0.0025.0050.0075.00
100.00125.00150.00
Incr
ease
d Ta
ux
Decr
ease
d Ta
ux
North
-shi
fted
Taux
Sout
h-sh
ifted
Tau
x
Incr
ease
d Ta
ux
Decr
ease
d Ta
ux
North
-shi
fted
Taux
Sout
h-sh
ifted
Tau
x
Incr
ease
d Ta
ux
Decr
ease
d Ta
ux
North
-shi
fted
Taux
Sout
h-sh
ifted
Tau
x
Incr
ease
d Ta
ux
Decr
ease
d Ta
ux
North
-shi
fted
Taux
Sout
h-sh
ifted
Tau
x
Atmospheric CO2 Preformed Carbon Regenerated Carbon
Constant KGMLauderdale et al
(2013)
Variable KGMFerreira et al
(2005)
Variable KGMHoffman &
Morales Maqueda (2011)
Variable KGMVisbeck et al
(1997)
Glo
bal c
arbo
n an
omal
y (G
tC)
-150.00-125.00-100.00
-75.00-50.00-25.00
0.0025.0050.0075.00
100.00125.00150.00
Incr
ease
d Ta
ux
Decr
ease
d Ta
ux
North
-shi
fted
Taux
Sout
h-sh
ifted
Tau
x
Incr
ease
d Ta
ux
Decr
ease
d Ta
ux
North
-shi
fted
Taux
Sout
h-sh
ifted
Tau
x
Incr
ease
d Ta
ux
Decr
ease
d Ta
ux
North
-shi
fted
Taux
Sout
h-sh
ifted
Tau
x
Incr
ease
d Ta
ux
Decr
ease
d Ta
ux
North
-shi
fted
Taux
Sout
h-sh
ifted
Tau
x
Atmospheric CO2 Preformed Carbon Regenerated Carbon
Constant KGMLauderdale et al
(2013)
Variable KGMFerreira et al
(2005)
Variable KGMHoffman &
Morales Maqueda (2011)
Variable KGMVisbeck et al
(1997)
Eddy KGM closures:constant Hoffman & Morales Maqueda (2011)Ferreira et al. (2005)Visbeck et al. (1997)
wind changes & different eddy closures
4. Global implications
Southern Ocean probably playing a crucial role:• sequestering heat• sequestering anthropogenic CO2
Ultimately important for global climate change
terrestrial(2000 PgC)
fossilfuels
(accessible4000 PgC)
atmosphere (600 PgC)
ocean heatuptake
radiative forcingfrom CO2
surface warming
carbon emissions
ocean(38000 PgC)
ocean CO uptake
2
How does global warming link to carbon emissions?
2. Warming from CO2
1. IPCC context
3. Long term SST response (~500y)
4. Short term SST response (multi decades)
Work with Phil Goodwin (Southampton) & Andy Ridgwell (Bristol)
Wednesday, 28 January 15
IPCC (2013)
NATURE CLIMATE CHANGE | VOL 3 | DECEMBER 2013 | www.nature.com/natureclimatechange 1013
interview
■ The IPCC Working Group I AR5 has recently been released. What is the most important finding?I think the most important !nding is in the last part of the Summary for Policymakers, regarding the cumulative carbon budget (that is, the total emissions since the late 1800s) and the linear relationship to the temperature response of the climate system (Fig. 1). Cumulative emissions will largely determine the increases in global surface temperature and the e#ects of climate change will persist for many centuries even if emissions are stopped. For the !rst time, we present this evidence — which is !rmly anchored in the science of a complex system — to policymakers. It is a compelling way to make a policy relevant statement: a speci!c temperature target implies a limited carbon budget. $is has direct implications for policy, as limiting climate change will require sustained and substantial reductions in greenhouse gas emissions.
■ In your view, has public interest in climate change decreased? Why?$e decreased public attention on climate started some time ago. People have been confronted with other serious issues — particularly in the last 5 years or so — such as the !nancial crisis, migration and associated problems that are a#ecting people’s living conditions. What is important to realise is that climate change also a#ects conditions of living in a fundamental way, but does not always manifest across regions in the same manner. Take precipitation, for example: there are areas where it is becoming much drier, and others where they say “Oh we don’t su#er from drought, but we have our frequent %oods”. Regional climate challenges are becoming evident to people, but they are not as immediate an impact as these other problems that people have to deal with daily.
■ What is your role as co-chair and how did the experience differ from your previous IPCC positions as a draft author of a summary report and a leading author?$e role of co-chair is very di#erent. I have been a coordinating lead author of chapters in the third and fourth assessment
reports (TAR and AR4). In 2008 I was elected to co-chair. Together with my Chinese colleague Dahe Qin, we took responsibility for the production of the Working Group I (WGI) contribution to AR5, which means the basic assessment report, the technical summaries and the Summary for Policymakers. Obviously this is together with authors and a technical support unit (which is customarily funded by the government of the developed country co-chair), who assist the co-chair and lead authors to organize and steer the process.
■ After AR4 it was discovered that non-peer reviewed publications had been cited. What measures were put in place to ensure that the best science was used in the latest report?Working Group I bases its assessment primarily on peer-reviewed literature, but other scienti!c literature is also admissible, for example, information on speci!c regional issues. We instructed the lead authors right from the beginning to centre our assessment !rmly in the scienti!c community. It is not enough to have 10 or 12 lead authors per chapter; it’s important that you mobilize the scienti!c community through the inclusion of contributing authors. $is is a long tradition in WGI and in my view, one of the elements that ensures we have an additional mechanism for error correction
before we publish. In other words, we realise that the expertise of an elected lead author team is not fully comprehensive, with knowledge of every little detail. A humble author team needs to realize that it has some gaps and bring in other experts from outside. We recommended this at every lead author meeting, and I have personal experience of how to bring in further expertise at this scale. Colleagues are very willing to contribute a !gure, a paragraph, check speci!c parts of the assessment and so on — we have collaborated with more than 600 scientists, who will be listed in the report as contributing authors. Having said that, I cannot guarantee that there won’t be any errors. It is a human endeavour, so there may be mistakes that we have overlooked but we have a clear protocol for addressing necessary corrections.
■ Are there research and knowledge gaps that need to be addressed?It is not our task to identify and point to research gaps or to suggest that governments direct funding to speci!c areas. However, when you make a comprehensive assessment of the current science you can easily identify areas where you would like to have more science and more progress — !elds where the state of knowledge does not provide conclusions with more than medium con!dence, there is an absence of best estimates or there are projected ranges that you would like reduced.
I can name a few areas, which are already evident from the chapter structure that we identi!ed and outlined for this report. $ere is still large uncertainty in the understanding of clouds and aerosols, although it doesn’t impact globally on the stringency of the overall message we deliver in the Summary for Policymakers. But we would prefer much lower uncertainties. Another issue concerns the availability, coverage and quality of precipitation measurements. $is is a big limitation as we don’t have a su&cient number of observations to properly assess model simulations of changes in the water cycle, and the detection and attribution of climate change.
State of the scienceThe Intergovernmental Panel on Climate Change (IPCC) released its fifth assessment report (AR5) on the physical science of climate change on 27th September this year. Nature Climate Change speaks to the co-chair of the working group responsible for the report, Thomas Stocker.
UN
IVER
SITY
OF
BERN
, AD
RIA
N M
OSE
R
© 2013 Macmillan Publishers Limited. All rights reserved
most important finding is the linear temperature response to total emissions
Prof. Tom Stocker, co-chair of IPCC AR5 (2013):
1. IPCC context
nearly insensitive to emission scenario
Wednesday, 28 January 15
surface temperature anomaly, (oC) since 1870
cumulative carbon emission, Iem (PgC) since 1870
�T
global surfacetemperature
change
change in cumulative
carbon emissions
�T =✓
@T
@Iem
◆�Iem
global surfacetemperature
change
change in cumulative
carbon emissions
warming dependence on radiative forcing, Rfrom CO2
radiative forcing R
dependence on carbon
emissions, Iem
�T =✓
@T
@R
◆ ✓@R
@Iem
◆�Iem
global surfacetemperature
change
change in cumulative
carbon emissions
forcing R dependence on carbon emissions
=0.5 to 1.2 K(W m-2)-1
normalised ocean heat uptake (relative to R)
�T =✓
@T
@R
◆ ✓@R
@Iem
◆�Iem
constants:
time-varying variables:
warming dependence on forcing, R
from CO2
climate parameter=5.35 Wm-2
= 3500PgC
normalised ocean carbon undersaturation (relative to Iem)
radiative forcing from CO2
buffered ocean+atmos C inventory
Goodwin et al. (2015) Nature Geoscience
atmosphere
(a) change in surface warming only due to ocean heat uptake
(b) change in radiative forcing only due to ocean carbon uptakelater response after emissionsinital response from emissions
inital response from emissions later response after emissions
(assume unchanged)
less excess CO in atmosphere
more excess CO in ocean
2
ocean heat uptake
surface ocean
interior ocean
radiative forcingfrom CO2
increased
surface warming
2
increased surface warming
reduced ocean heat uptake
radiative forcing
excess CO in atmosphere2
ocean undersaturated in excess CO
from COradiative forcingincreased
radiative forcingreduced
ocean CO uptake 2ocean CO
uptake2
2from CO
from CO2
22
surface warming increases in time due to weakening ocean heat uptake
how does surface warming vary in time?
atmosphere
(a) change in surface warming only due to ocean heat uptake
(b) change in radiative forcing only due to ocean carbon uptakelater response after emissionsinital response from emissions
inital response from emissions later response after emissions
(assume unchanged)
less excess CO in atmosphere
more excess CO in ocean
2
ocean heat uptake
surface ocean
interior ocean
radiative forcingfrom CO2
increased
surface warming
2
increased surface warming
reduced ocean heat uptake
radiative forcing
excess CO in atmosphere2
ocean undersaturated in excess CO
from COradiative forcingincreased
radiative forcingreduced
ocean CO uptake 2ocean CO
uptake2
2from CO
from CO2
22
radiative forcing decreases in time due to ocean carbon uptake
how does radiative forcing from CO2 vary in time?
test in a coarse-resolution atmosphere-ocean model (GENIE) with coupled circulation & biogeochemistry
cumulative carbon emissions, Iem (PgC)500 1000 1500 2000 2500 3000
0
0.5
T (K
) erro
r
500 1000 1500 2000 2500 30000
1
2
3
4
5
T (
K)
(b) discrepancy of surface warming (model minus theory)
(a) 21st century surface warming from theory
!!
B1 IMAGEA1T MESSAGEB2 MESSAGEA1 AIMA2 ASFA1G MINICAM
tem
pera
ture
chan
ge
RCP 4.5RCP 6.0RCP 8.5
response from year 2000 to 2100 driven by IPCC
scenarios
(Goodwin et al., 2015, Nature Geoscience)
why the similar transient response?
T
heat uptake in deep ocean
thermal response anthropogenic carbon response
radiative forcingatmosphere
ocean
R
N
(a) initial response to carbon emissions on decadal timescales
(b) upper ocean equilibrates with the atmosphere after decades to centuries
(c) deep ocean equilibrates with the atmosphere after many centuries
ocean heat uptake
!
T
deep ocean heat uptake
radiative forcingatmosphere
ocean
R
!
upper ocean heat uptake ceases
T
radiative forcingatmosphere
ocean
R
climate response!
upper ocean heat uptake ceases
deep ocean heat uptake ceases
atmosphere
ocean
2excess CO increased from emissions
ocean uptake of CO
upper ocean undersaturated
deep ocean undersaturated
atmosphere
ocean
2excess CO relative to the deep ocean
upper ocean saturated
deep ocean under saturated
atmosphere
ocean
upper ocean saturated
deep ocean saturated
CO in equilibrium with ocean2
high DIC
high DIC
higher DIC
low DIC
cold
cold
cool
warm
warmer
warmer
moderate DIC
moderate DIC
2
high latitude uptake of CO2
heat uptake in deep ocean deep ocean undersaturated
equator N. high latitudeS. high latitude
dept
h thermocline
surface warming
high latitude warming
ocean uptake of CO ceases2
Nclimate response
climate responseT
heat uptake in deep ocean
thermal response anthropogenic carbon response
radiative forcingatmosphere
ocean
R
N
(a) initial response to carbon emissions on decadal timescales
(b) upper ocean equilibrates with the atmosphere after decades to centuries
(c) deep ocean equilibrates with the atmosphere after many centuries
ocean heat uptake
!
T
deep ocean heat uptake
radiative forcingatmosphere
ocean
R
!
upper ocean heat uptake ceases
T
radiative forcingatmosphere
ocean
R
climate response!
upper ocean heat uptake ceases
deep ocean heat uptake ceases
atmosphere
ocean
2excess CO increased from emissions
ocean uptake of CO
upper ocean undersaturated
deep ocean undersaturated
atmosphere
ocean
2excess CO relative to the deep ocean
upper ocean saturated
deep ocean under saturated
atmosphere
ocean
upper ocean saturated
deep ocean saturated
CO in equilibrium with ocean2
high DIC
high DIC
higher DIC
low DIC
cold
cold
cool
warm
warmer
warmer
moderate DIC
moderate DIC
2
high latitude uptake of CO2
heat uptake in deep ocean deep ocean undersaturated
equator N. high latitudeS. high latitude
dept
h thermocline
surface warming
high latitude warming
ocean uptake of CO ceases2
Nclimate response
climate response
heat & carbon sequestration mainly achieved via ventilation process
heat & carbon sequestration can though differ via air-sea timescales & biology ....
6. Challenges
Hsurface heat loss/
density gainsurface heat gain/
density loss
eastward winds
diapycnalmixing
eddy stirring
Ekman transport
eddy transport
upper limb of overturning
dept
h
south north
lower limb ofoverturning
eddy stirring
south north
CO2 Feair-seagas transfer
trace metalsupply
depth
biologicalfalloutrespiration/
regeneration
DIC+
N +Fe -
diapycnalmixing
DIC+
N +Fe -
DIC-
N -Fe +
1. Southern Ocean likely to be crucial in sequestering heat & carbon
rate limiting processes unclear, probably: subduction into main thermocline entrainment into winter mixed layer mismatch drives annual air-sea transfer
2. Residual circulation crucial for communication with the rest of ocean: stronger residual circulation increases atmospheric CO2.
link to carbon transport is unclearalso role of deep cell is unclear
3. Global climate implications from ocean heat & carbon drawdown
Partly compensating due to ventilation Mismatch in heat & carbon uptake likely to be important
cumulative carbon emissions, Iem (PgC)500 1000 1500 2000 2500 3000
0
0.5
T (K
) erro
r
500 1000 1500 2000 2500 30000
1
2
3
4
5
T (
K)
(b) discrepancy of surface warming (model minus theory)
(a) 21st century surface warming from theory
!!
B1 IMAGEA1T MESSAGEB2 MESSAGEA1 AIMA2 ASFA1G MINICAM
tem
pera
ture
chan
ge
RCP 4.5RCP 6.0RCP 8.5
cumulative carbon emissions, Iem (PgC)500 1000 1500 2000 2500 3000
0
0.5T
(K) e
rror
500 1000 1500 2000 2500 30000
1
2
3
4
5
T (
K)
(b) discrepancy of surface warming (model minus theory)
(a) 21st century surface warming from theory
!!
B1 IMAGEA1T MESSAGEB2 MESSAGEA1 AIMA2 ASFA1G MINICAM
tem
pera
ture
chan
ge
RCP 4.5RCP 6.0RCP 8.5