●A3 サイズ制作 284％プリント
Carbon cycle feedback of land ecosystems
in response to atmospheric CO2 increase
From a CMIP5 paper
by Hajima et al. (2014), J. Clim
doi: http://dx.doi.org/10.1175/JCLI-D-13-00177.1
Tomohiro Hajima , Kaoru Tachiiri , Akihiko Ito , Michio Kawamiya1,2
1
1
1:Japan Agency for Marine-Earth Science and Technology , JAPAN
2,1
2:National Institute for Environmental Studies, JAPAN
Target: CO2-Land Carbon Feedback in CMIP5-ESMs
Background: What is CO2-Land Carbon Feedback?
Background: Why CO2-Land Carbon Feedback ?
・ Negative carbon cycle feedback in land ecosystems
・Induced by CO2-fertilization effect on plant production
・One of the strongest feedback in the Earth system
・CMIP5-ESMs displayed the largest spread for the strength
> A key feedback for making precise climate projections
Gross Primary
Production
Net Primary
Production
Plant
Resp.
!&#$%%
1.0
-2 -1
!&#'%%
K ]
1.5 [W m!"#$%%
Negative
Feedbacks
!&
+2
1
/0
3%
8
7/
3%
6+
5/
8
Positive
Feedbacks
!&
+2
4
/0
-.
+,
!&
+2
1
/0
3%
8
7/
6+
5/
Climate-Carbon
Ocean
Soil
Carbon
*
()
Climate-Carbon
Land
!$#'%%
0.5
-.
Heterotroph.
Resp.
Litter
Fall
$#$%%
0.0
+,
Climate-Carbon
Feedback
$#'%%
-0.5
*
()
CO2-Carbon
Feedback
Vegetation
Carbon
&#$%%
-1.0
CO2-Carbon
Land
CO2-Carbon
Ocean
8
Fig. 2 Comparison of carbon cycle feedbacks: from Arora et al. (2013).
4
/0
Units are converted from carbon-base [PgC] to energy-base [W m-2 K-1]
by a method of Gregory et al. (2009). Bars represent Ave. ±1.65xS.D.
3%
!&
+2
Fig. 1 Terrestrial carbon cycle processes (left) and the carbon cycle feedback
(right). Blue: CO2-carbon feedback , Red: Climate-carbon feedback.
Purpose, Models, and Simulations
Purpose : To reveal the reason for the large spread by CMIP5-ESMs in CO2-Land Carbon feedback
Models
: Eight CMIP5-ESMs (MPI-ESM-LR; BCC-CSM1.1; HadGEM2-ES; IPSL-CM5A-LR; CanESM2; MIROC-ESM; CESM1-BGC; NorESM1-ME)
Simulation: Biogeochemically-coupled run
* CO2 increase by 1 [% yr-1] during 140 years, reaching to 1140 ppmv
* CO2 only impacts on Carbon cycle, not radiation processes → No global warming
* CMIP5 name esxFixClim1
Decompose the CO2- Land Carbon feedback into seven factors
→Display models’ behavior in response to CO2 increase
2.5
2
1.5
0.8
0.6
0.4
1
0.5
0.2
0
-0.5
0
-0.2
1.4
35
1.2
30
1
25
0.8
0.8
20
0.6
0.6
15
0.4
0.4
10
0.2
0.2
5
1.2
1
0
0
0
-0.2
-0.2
-5
-0.4
-0.4
-10
0.3
3
0.6
0.25
60
0.2
2
1
0
0.4
0.15
0.1
0.2
0.05
40
20
0
0
0
-0.05
-1
-0.1
MPI-ESM-LR
BCC-CSM1.1
HadGEM2-ES
IPSL-CM5A-LR
CanESM2
MIROC-ESM
CESM1-BGC
NorESM1-ME
-20
ΔCland
Δgpp ΔGPP ΔNPP ΔCveg ΔCsoil
-0.2x ΔHR xΔCland
�CL =
�CV x
�CS
�CL
�gpp x �GPP x �NPP x
�HR
ΔCO2
ΔCO2
Δgpp
ΔGPP
ΔNPP
ΔCveg
ΔCsoil
ΔHR
/�CO2
/�CO2
/�CV
/�CS
/�gpp
/�GPP
/�NPP
/�HR
ΔNPP [PgC yr ]
Fig. 4
X-axis: NPP increase from initial condition
Y-axis: CO2-Land Carbon feedback, evaluated by total ecosystem carbon increase
in Biogeochemically coupled run
-1
Fig. 3
CO2-Land carbon feedback & its decomposed seven
-0.4 factors.
Gray bars: S.D., Horizontal lines: multimodel-means.
Each factor is associated with:
ΔCland
: CO2-land carbon feedback [PgC PgC-1]
ΔCO2
Δgpp
ΔCO2
ΔGPP
Δgpp
ΔNPP
ΔGPP
ΔCveg
ΔNPP
ΔCsoil
ΔCveg
ΔHR
ΔCsoil
ΔCland
ΔHR
: Photosynthesis response [PgC yr LAI ]
-1
-1
-0.6
-1
-0.500.51
: ΔLAI [m2 m-2], assuming ΔGPP = Δgpp x ΔLAI
: Fraction of carbon that goes into biomass, not for plant respiration [-]
: Turnover rate of vegetation carbon [yr]
: Allocation of carbon within ecosystem [-]
: Soil decomposition rate per unit SOC [-]
: Turn over rate of ecosystem carbon [yr]
Simple, but important result:
NPP response strongly controls the Feedback strength
CO2-land carbon feedback
[PgC]
Main results
・CO2 increase stimulates plant growth and following carbon cycle processes
・The degrees of response in those processes vary among models
・However, the key process to control the total ecosystem response, the
CO2-land carbon feedback, is NPP.
・NPP is a very fundamental variable and hence have long been investigated
・This research highlights the importance of NPP (GPP) again, in terms of
feedbacks within the Earth system
・We propose a similar analysis in CMIP6 run, under Nitrogen limitation on
ecosystems
Another important issue: Dependency on the rate of CO2 increase
CO2-Land Carbon feedback
parameter [PgC ppmv-1]
[ppmv]
Spread shown by
- Multi-scenario
- Single-Model (MIROC)
simulations
・[Background] Previous studies suggested the strength of CO2-Land carbon feedback
depends on the emission (concentration) scenarios
・[Method] Using a single ESM, biogeochemically-coupled runs were executed
with several types of CO2 scenarios
・A feedback parameter for CO2-Land carbon feedback ( β : quantified
by ΔCland=βxΔCO2) showed an exponentially decreasing trend
against the rate of CO2 increase (symbols with black, orange, cyan, red, and blue);
indirect estimations (open symbols) also support this result
・This is because carbon storages cannot catch up with the
fast-CO2-increasing scenarios (the results now shown here)
・This suggests land carbon sink is weaker when CO2 emission is fast
(note: in the absence of global warming impact)
Spread shown by
- Single scenario (1%yr-1) ・However, the difference among scenarios will diminish when CO2
- Multi-Model
concentration is stabilized and carabon storages reach new teady states
simulations
・This would provide information on underlying mechanism of constant
Rate of CO2 increase in scenarios [ppmv yr-1]
TCRE regardless of scenario choice