Carbon emission metrics for climate stabilization and the

Carbon emission metrics for climate stabilization and the implications to metrics for non-CO 2 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+640 Gt. C” and “ 1280 Gt. C, 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

CO 2 concentration has been often used as a carbon emission metrics… IPCC AR 5 WG 3 (2007)　

… then concentration metrics is converted to socio-economic scenarios. CO 2 emission paths to achieve CO 2 concentration stabilization IPCC AR 5 WG 3 (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 x 2 & x 4

MIROC-ESM: a GCM-based Earth System Model AGCM CCSR/NIES/FRCGC T 42(~2. 8ºx 2. 8º) MIROC-ESM L 80 (TOA: 80 km) 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 RCP 2. 6 RCP 4. 5 RCP 8. 5 RCP 6. 0 (2) non-CO 2 GHG corrected CCR R 2. 6 R 4. 5 R 6. 0 R 8. 5

Another possible cause for scenario dependence of CCR Efficiency of ocean heat uptake Ocean heat uptake Scenario A Scenario B Changes in ocean heat uptake: DQ = DSW + DLW +DSH + DLH = k DT Global temperature change Scenario A Scenario B Atmosphere Ocean

(3) Ocean-heat-uptake (OHU) corrected CCR is moderately scenario dependent in our case, but can be corrected in terms of OHU.

Airborne CO 2 is again not a good metrics… (1) With all anthropogenic forcings (3) Ocean heat uptake corrected (2) non-CO 2 GHG corrected

Implications for establishing metrics for short-lived and longlived 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.