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Status of the Carbon Cycle to be
incorporated in AOGCMs
Peter Cox
&
Pierre Friedlingstein
Outline
INTRODUCTION :
 Rationale for including the carbon cycle in AOGCMs : Carbon-Cycle
Climate Interactions.
CURRENT STATUS OF CARBON CYCLE IN AOGCMs:
 Coupled-Climate Carbon Cycle Model Intercomparison Project (C4MIP).
 Robust findings and key uncertainties.
 Missing processes.
POSSIBLE STATUS OF CARBON CYCLE IN AOGCMS BY AR5:





Modelling of CO2 emissions from land-use and land-management.
More detailed ocean ecosystem models
Interactive nitrogen cycling on land.
Links to changes in atmospheric chemistry and aerosols ?
Implications for AR5 scenarios.
CONCLUSIONS
The Carbon Cycle and Climate Change
 Currently only about half of human emissions of CO2
remain in the atmosphere - the ocean and land
ecosystems appear to be absorbing the remainder.
Atmospheric Increase
= 3.2 +/- 0.1 GtC/yr
(50%)
Emissions (fossil fuel, cement) = 6.4 +/- 0.4 GtC/yr (100%)
Ocean-atmosphere flux
= -1.7 +/- 0.5 GtC/yr
(27%)
Land-atmosphere flux
= -1.4 +/- 0.7 GtC/yr
(22%)
Estimated Global Carbon Balance for 1990s (IPCC TAR)
The Carbon Cycle and Climate Change
 Currently only about half of human emissions of CO2
remain in the atmosphere - the ocean and land
ecosystems appear to be absorbing the remainder.
 Atmosphere-land and atmosphere-ocean fluxes of
CO2 are sensitive to climate.
Temperature
Carbon Cycle-Climate
Coupling
The Example of the
Glacial Cycles
CO2
Vostok Ice Core Records
showing strong correlations
between Temperature and
Carbon Dioxide over
the last 400,000 years
CO2 Concentration (measured at Mauna Loa on Hawaii)
Atmospheric CO2 is increasing
at about half the rate of emissions
Seasonal cycle is due
to the land biosphere
Year-to-Year Variability in CO2 Growth-rate is driven by
Climatic Anomalies (e.g. El Nino, Volcanoes)
CO2 growth-rate anomalies are
normally well correlated with
El Nino (+ve anomalies) and
La Nina (-ve anomalies)
…… except after major
volcanoes…
…..or in the last few years ??
CO2 Growth-Rate is Sensitive to Climatic Anomalies…..
2003 Anomaly
Total
Fossil Fuels
Land-use Change
Mt Agung
El Chichon
Years after
Volcanic Eruptions
Pinatubo
The Carbon Cycle and Climate Change
 Currently only about half of human emissions of CO2
remain in the atmosphere - the ocean and land
ecosystems appear to be absorbing the remainder.
 Atmosphere-land and atmosphere-ocean fluxes of
CO2 are sensitive to climate.
 To date most GCMs have used prescribed
atmospheric CO2 and therefore neglect climatecarbon cycle feedbacks.
The Carbon Cycle and Climate Change
 Currently only about half of human emissions of CO2
remain in the atmosphere - the ocean and land
ecosystems appear to be absorbing the remainder.
 Atmosphere-land and atmosphere-ocean fluxes of
CO2 are sensitive to climate.
 Most GCMs prescribe atmospheric CO2 and
therefore neglect climate-carbon cycle feedbacks.
 How important might these be for future climate
change?
Status of Carbon Cycle in TAR AOGCMs
Online
CLIMATE
Offline
Greenhouse
Effect
CO2
CO2 Uptake by Ocean /
CO2 buffering effect
CO2 Uptake by Land /
CO2-fertilization of plant
growth
OCEAN
LAND
Fossil Fuel +
Net Land-use
CO2 Emissions
Status of Carbon Cycle in AR4 AOGCMs (C4MIP)
Online
CLIMATE
Climate Change effects on
Solubility of CO2
Vertical Mixing
Circulation
Greenhouse
Effect
CO2
OCEAN
Offline
Climate Change effects on
plant productivity, soil
respiration
LAND
Fossil Fuel +
Net Land-use
CO2 Emissions
Hadley Centre climate-carbon GCM simulation shows climate
change suppressing land carbon uptake…..
Coupled Climate Carbon Cycle Intercomparison
Project (C4MIP)
• IGBP/GAIM (AIMES) - WCRP/WGCM coordinated
activity to explore the coupled climate carbon cycle
feedback
• 11 Coupled Climate-Carbon models (7 AOGCMs) have
now been used to simulate 21st century climate and CO2
under similar scenarios.
• Models agree that effects of climate change on the
carbon cycle will lead to more CO2 in the atmosphere
(positive climate-carbon cycle feedback).
• But magnitude of this effect, and primary cause, vary
between models 
C4MIP Models – extra CO2 due to climate effects on
the carbon cycle
All models simulate a positive feedback, but with very different magnitudes.
Change in CO2 Emissions Partitioning in C4MIP Models
Positive Carbon
Cycle Feedback
C4MIP Models indicate that Climate Change will hinder CO2
uptake by the land, but the size of this effect is uncertain
Fraction of Emissions Absorbed by the Land
(1860-2100)
0.6
0.5
0.4
0.3
0.2
0.1
Uncoupled
-2
.7
LI
M
BE
BE
R
R
N
-C
C
C
U
Vi
c
M
D
U
G
C
FR
C
NL
LL
M
PI
IP
S
H
ad
C
M
3L
L- C
C
M
2C
C
SM
-1
0
Coupled
C4MIP: Robust Results and Uncertainties
 All C4MIP models simulate a positive feedback
 larger warming
 or larger reduction in emissions
Global Emissions for Climate Stabilisation
2000 2050
~ 8 GtC/yr in 2000
~ 3 GtC/yr by 2050
Impact of Climate-Carbon Cycle Feedbacks on Integrated Permissible Emissions
Impact of Carbon
Cycle Feedbacks
Single model: urgently need to provide updated stabilisation permissible emissions scenarios with error bars covering full
climate-carbon system!
C4MIP: Robust Results and Uncertainties
 All C4MIP models simulate a positive feedback
 larger warming
 or larger reduction in emissions
 Uncertainty in the 21st century CO2 (range: 750 – 1000
ppm)
 Large uncertainty on the feedback (20 to 220 ppm)
 Feedback analysis to attribute uncertainty
Contributions to uncertainty in future CO2
concentration (from C4MIP models)
IPCC, AR4
C4MIP: Key Uncertainties in Climate-Carbon
Feedback
 Response of land NPP to climate (includes uncertainties
in hydrological changes)
 Transient climate sensitivity to CO2
 Response of soil (heterotrophic) respiration to climate.
 However, rate of increase of CO2 also depends on
responses of land and especially ocean uptake to CO2.
Possible Status of Carbon Cycle in AOGCMs by AR5
 More complete model validation/use of observational
constraints.
 Modelling of CO2 emissions from land-use and landmanagement and forest fires.
Land use
Statistical Dynamics approach to large-scale Vegetation Dynamics
Including age-class distributions
Explicit simulation of
rainforest regrowth
on multiple patches
Moment Equations for
Statistics of Vegetation State
Morecroft et al., 2001
Interactive Forest Fire
• Currently
implemented in
ORCHIDEE
– will allow to estimate
role of fire on CO2
– will allow to estimate
impact of climate
change on fire and
feedback on climate
– Emissions of CH4,
NOx,…
Thonicke, et al., 2005
Possible Status of Carbon Cycle in AOGCMs by AR5
 More complete model validation/use of observational
constraints.
 Modelling of CO2 emissions from land-use and landmanagement and forest fires.
 More detailed ocean ecosystem models.
Examples of AR5 Ocean Ecosystem Model
(PISCES)
NH4+
NO3
-
PO43-
Diatoms
Si
Nano-phyto
Iron
MicroZoo
D.O.M
Meso Zoo
P.O.M
Small Ones
Big Ones
Aumont et al., 2003
Possible Status of Carbon Cycle in AOGCMs by AR5
 More complete model validation/use of observational
constraints.
 Modelling of CO2 emissions from land-use and landmanagement and forest fires.
 More detailed ocean ecosystem models.
 Interactive nitrogen cycling on land.
Nitrogen Deposition is already significant
and will increase
Millennium Ecosystem Assessment, 2005
Possible Status of Carbon Cycle in AOGCMs by AR5
 More complete model validation/use of observational
constraints.
 Modelling of CO2 emissions from land-use and landmanagement and forest fires.
 More detailed ocean ecosystem models.
 Interactive nitrogen cycling on land.
 Links to changes in atmospheric chemistry and aerosols ?
Status of Carbon Cycle in TAR AOGCMs
Online
CLIMATE
Offline
Greenhouse
Effect
CO2
CO2 Uptake by Ocean /
CO2 buffering effect
CO2 Uptake by Land /
CO2-fertilization of plant
growth
OCEAN
LAND
Fossil Fuel +
Net Land-use
CO2 Emissions
Status of Carbon Cycle in AR4 AOGCMs (C4MIP)
Online
CLIMATE
Climate Change effects on
Solubility of CO2
Vertical Mixing
Circulation
Greenhouse
Effect
CO2
OCEAN
Offline
Climate Change effects on
plant productivity, soil
respiration
LAND
Fossil Fuel +
Net Land-use
CO2 Emissions
Possible Status of Carbon Cycle in AR5 AOGCMs
Online
CLIMATE
Climate Change effects on
Solubility of CO2
Vertical Mixing
Circulation
& Ocean Ecosystem
Structure
OCEAN
Iron Dust
Deposition
Greenhouse
Effect
CO2
Offline
Climate Change effects on
plant productivity, soil
respiration
& Fires
Riverine CO2
fluxes
Fossil Fuel
CO2 Emissions
LAND
Land-use
Change
N and O3
Deposition
Conclusions I
 Climate and carbon cycle are tightly coupled, so the
carbon cycle must be part of Earth System Models.
 First generation coupled-climate carbon cycle models all
suggest that climate change will increase the fraction of
CO2 emissions that are airborne.
 There are major uncertainties in the size of this positive
climate-carbon feedback (leading to an extra 20-200ppmv
by 2100 under the A2 emissions scenario, with a mean of
90+/-50 ppmv).
 This uncertainty also impacts on the CO2 emissions
consistent with stabilisation at a given concentration.
Conclusions 2
 By AR5 climate-carbon cycle models are likely to include a
number of processes that were missing in the first
generation C4MIP models, including:




Interactive calculation of net land-use emissions.
More complex ocean ecosystem models.
Interactive N-cycling on the land.
Riverive carbon fluxes from land to ocean
 This places new demands on driving scenarios that need
to include consistent land-use change/management, Ndeposition, near surface O3 concentration, dust inputs to
the ocean.
THE END !
LOOP
The new IPSL C-C model
Atmospheric
[CO2]
d CO2  EMI  Fluxland  Fluxocean 

dt
2.12
CO2 concentration
re-calculated each month
Climate
Atmosphere Coupler
LMDZ4
OASIS 2.4
∆t = physic time step
Terrestrial biosphere
ORCHIDEE
(STOMATE activated)
Ocean
ORCA-LIM
OPA 8.2
∆t = 1day
Marine
Biochemistry
PISCES
Carbon
Land flux GtC/mth
EMI = external forcing
[Marland et al, 2005
Houghton, 2002]
Ocean flux GtC/mth
Net total carbon flux
Fluxland + Fluxocean
Cadule et al., in prep
Zero Order Validation
Global mean surface temperature anomalies
Base period : 1961-1990
Cadule et al., in prep
First Order Validation
• “IPCC” carbon budget (GtC/yr)
Atmospheric carbon variation
fossil fuel
Land use
lan
d
ocean
1990’s
1980’s
LOOP
IPCC
LOOP
IPCC
Atm
2.7
3.3
3.3
3.2
Ocean
2.0
1.8±0.8
2.0
2.2±0.4
Land
2.8
1.6
(-0.3 to 4)
3.3
2.6
(1 to 4.3)
Cadule et al., in prep
Second Order Validation
• Atmospheric CO2
– Offline transport over 1979-2003
Cadule et al., in prep
• Seasonal
cycle
• Long term
trend
Cadule et al., in prep
a climate response to CO2
IPSL-CM2_C
IPSL_CM4_LOOP
Friedlingstein et al., 2006
b C-cycle response to CO2
LAND
OCEAN
IPSL-CM2_C
IPSL_CM4_LOOP
Friedlingstein et al., 2006
g C-cycle response to climate
LAND
OCEAN
IPSL-CM2_C
IPSL_CM4_LOOP
Friedlingstein et al., 2006
Why such a large uncertainty
in the Land Carbon
Response to Climate ?
REGIONAL LAND RESPONSE TO CLIMATE
IPSL-CM2_C
IPSL_CM4_LOOP
HadCM3C
Improving the carbon cycle
• Coupled C-C run with fires and land-use
• Include nitrogen cycle
Nitrogen
Motivation:
• Controls the carbon cycle
– Impact on carbon uptake
– Impact on the C-C feedback estimate
Examples of AR5 carbon cycle models
(ORCHIDEE and PISCES)
NH4+
NO3
-
PO43-
Diatoms
Si
Nano-phyto
Iron
MicroZoo
D.O.M
Meso Zoo
P.O.M
Small Ones
Krinner et al., 2005
Big Ones
Aumont et al., 2003
The land response - IPSL
Increase in
soil aridity
Extension of the
growing season
Berthelot et al., 2002
Climate-Land Feedbacks and Forcings
Anthropogenic
Emissions
Climate Sensitivity
+
CO2
Temp
Climate
Sensitivity of Soil
respiration to Temp
_
NPP
+
Decomp
Land
N mineralisation
+
The Key missing negative feedback –
increased N availability in a warmer
world ?
+
Avail N
Anthropogenic
N deposition
Chemistry
Climate-Land Feedbacks and Forcings
Anthropogenic
Emissions
Climate Sensitivity
+
CO2
The Key missing forcing factor?
Tropospheric O3 levels are projected to
increase significantly - to levels which
may be detrimental to plants (see for
example Gregg et al., 2003)
Could this suppress the land carbon sink
and accelerate global warming?
Temp
Climate
NPP
Trop O3
Anthropogenic
Emissions
Land
Climate-Land Feedbacks and Forcings
Anthropogenic
Emissions
Regional
Climate
Change
Precip
+
Surface Energy
Balance
Land-use
Change
Veg
Cover
Climate Sensitivity
?
CO2
Fertilisation
+
+
+
+
+
CO2
_
Temp
+
-
+
_
NPP
Trop O3
Anthropogenic
Emissions
Climate
Sensitivity of Soil
respiration to Temp
+
Decomp
Land
N mineralisation
+
+
Avail N
Anthropogenic
N deposition
Chemistry
Increased Tropospheric O3 and Vegetation –
Feedbacks from biogenic emissions
CO2
Precip
+
Temp
Isoprene emissions increase with
temperature
Veg
Cover
NPP
Isoprene emissions increase with
increasing vegetation cover?
+
Trop O3
Decomp
+
+
Isoprene
Isoprene increases O3 in high NOx conditions
Anthropogenic
NOx emissions
Humans now dominate the Global Nitrogen Cycle
Millennium
Ecosystem
Assessment, 2005