Carbon emission metrics and its relevance to

Carbon emission metrics for climate
stabilization and the implications to
metrics
for non-CO2 GHGs
Michio Kawamiya
Research Institute for Global Change
Japan Agency for Marine-earth Science and
Technology
Introduction: limitation of single
basket approach
Forcings for these two lines have
the same value of GWP.
“Methane+640GtC” and “1280GtC,
No Methane” have the same forcing
in terms of GWP.
-> “Single basket approach” does
not work for discussing stabilization
levels. (Eby et al., 2009; Solomon et
al., 2011)
GTP is superior when
discussing stabilization
Different roles of short-lived and
long-lived agents
Short-lived: “trim” the peak
 Long-lived: determine the stabilization level

“Two-basket approach” is proposed
( Solomon et al., 2011)
-> GTP for short-lived agents
Cumulative emission for long-lived agents
CO2 concentration has been often
used as a carbon emission
metrics…
IPCC AR5 WG3 (2007)
… then concentration metrics is
converted to socio-economic
scenarios.
CO2 emission paths to achieve CO2 concentration
stabilization
IPCC AR5 WG3 (2007)
Cumulative carbon emission as a
metric for climate stabilization level
and transient climate response
Matthews et al. (2009)
Notifications
CCR = T/CE = (T/CA)(CA/CE) = αA
CCR: Climate-carbon response (matthews et al., 2009)
α(=T/CA): Temperature rise per unit airborne carbon
A(=CA/CE): Airborne fraction
Cf. Climate sensitivity: λ=T/F
F: Radiative forcing
CCR may be regarded as “earth system sensitivity”, with the
forcing being anthropogenic carbon emission rather than
radiative forcing.
CCR may be
independent of
scenario
1%/year increase
Instanteneous x2 & x4
MIROC-ESM: a GCM-based
Earth System Model
AGCM
CCSR/NIES/FRCGC
T42(~2.8ºx2.8º)
MIROC-ESM
L80 (TOA:80km)
Atmosphere
OGCM
MIROC-AGCM
SPRINTARS (CHASER)
Ocean
Land
COCO
MATSIRO
NPZD
SEIB-DGVM
COCO (CCSR/FRCGC)
Curvilinear grid system
(0.5-1.0)º x 1.4º
Global warming projection with
MIROC-ESM under RCP scenarios
MIROC-ESM結果
Temperature Rise averaged over 2090’s relative to
1980-1999 average
Climate Carbon Response in
MIROC-ESM
(1) With all anthropogenic forcings
RCP2.6
RCP4.5
RCP8.5
RCP6.0
(2) non-CO2 GHG corrected CCR
R2.6
R4.5
R6.0
R8.5
Another possible cause for scenario
dependence of CCR
Efficiency of ocean heat uptake
Ocean heat uptake
Scenario A
Changes in ocean heat uptake:
DQ = DSW + DLW
+DSH + DLH
= k DT
Scenario B
Global temperature
change
Scenario A
Scenario B
Atmosphere
Atmosphere
Ocean
Ocean
(3) Ocean-heat-uptake (OHU) corrected CCR
CCR is moderately scenario dependent in our case, but can be
corrected in terms of OHU.
Airborne CO2 is again not a good metrics…
(1) With all anthropogenic forcings
(3) Ocean heat uptake corrected
(2) non-CO2 GHG corrected
Implications for establishing metrics
for short-lived and long-lived GHGs
It is important to recognize the difference between
short-lived and long-lived GHGs with the same GWP,
in particular for discussing climate stabilization.
 For stabilization issues, cumulative emission (CE) of
long-lived GHGs may be more desirable than
concentration.
 There may be a moderate scenario dependence of
CE, especially for fast scenarios due to that of ocean
heat uptake (OHU).
 Constraining OHU efficiency may improve the validity
of CE as a metrics.


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