Carbon emission metrics for Carbon emission metrics for climate stabilization and climate stabilization and the implications to metricsthe implications to metricsfor non-CO2 GHGsfor non-CO2 GHGs

Michio KawamiyaResearch Institute for Global ChangeJapan Agency for Marine-earth Science and Technology

Introduction: limitation of Introduction: limitation of single basket approachsingle basket approach

“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)

Forcings for these two lines have the same value of GWP.

GTP is superior when discussing stabilization

Different roles of short-lived Different roles of short-lived and long-lived agentsand long-lived agents

Short-lived: “trim” the peakLong-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 CO2 concentration has been often used as a carbon often used as a carbon emission metrics…emission metrics…

IPCC AR5 WG3 (2007) 　

… … then concentration then concentration metrics is converted to metrics is converted to socio-economic scenarios.socio-economic scenarios.

IPCC AR5 WG3 (2007) 　

CO2 emission paths to achieve CO2 concentration stabilization

Cumulative carbon emission Cumulative carbon emission as a metric for climate as a metric for climate stabilization level and stabilization level and transient climate responsetransient climate response

Matthews et al. (2009)

NotificationsNotifications

CCR = T/CE = (T/CA)(CA/CE) = αACCR: Climate-carbon response (matthews et al., 2009)α(=T/CA): Temperature rise per unit airborne carbonA(=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 CCR may be independent independent of scenarioof scenario

1%/year increase

Instanteneous x2 & x4

MIROC-ESM: a GCM-basedMIROC-ESM: a GCM-basedEarth System ModelEarth System Model

AGCM

CCSR/NIES/FRCGC

T42(~2.8ºx2.8º)

L80 (TOA:80km)

OGCM

COCO (CCSR/FRCGC)

Curvilinear grid system

(0.5-1.0)º x 1.4º

Atmosphere

Ocean Land

MIROC-AGCM

SPRINTARS (CHASER)

COCO

NPZD

MATSIRO

SEIB-DGVM

MIROC-ESM

Global warming projection Global warming projection with MIROC-ESM under RCP with MIROC-ESM under RCP scenariosscenarios

MIROC-ESM 結果Temperature Rise averaged over 2090’s relative to 1980-1999 average

Climate Carbon Response in Climate Carbon Response in MIROC-ESMMIROC-ESM

(1) With all anthropogenic forcings (2) non-CO2 GHG corrected CCR

RCP2.6

RCP6.0

RCP4.5RCP8.5

R2.6

R6.0R4.5

R8.5

Another possible cause for Another possible cause for scenario dependence of CCRscenario dependence of CCR

Global temperaturechangeO

cean

hea

t upt

ake

Scenario A

Scenario B

Scenario A Scenario B

Changes in ocean heat uptake:Q = SW + LW +SH + LH = T

Efficiency of ocean heat uptake

(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 (2) non-CO2 GHG corrected

(3) Ocean heat uptake corrected

Implications for establishing Implications for establishing metrics for short-lived and metrics for short-lived and long-lived GHGslong-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.