Quasi-inversion estimation of permissible CO 2 emission toward stabilization Toru Miyama （ Frontier Research Center for Global Change ） 2007 October 11

Forward Casting (conventional projection) “What if ?” Temp. rise CO 2 emission CO 2 in air

Backward Casting (Inverse) (social/political needs) “How ?” ?? Permissible CO 2 emission Temperature target ~2 o C? CO 2 stabilization CO 2 emission = Nature uptake

Climate-change Carbon-cycle Feedback Anthropogenic CO 2 emission Uptake by ocean and land CO2 increase in air Part (about half at present) of anthropogenic CO2 is absorbed by nature (ocean and land). The rest remains in atmosphere. Climate change projections with carbon-cycle models tell that nature uptake would decrease more or less due to temperature rise. Reduced CO 2 uptake results in more CO 2 concentration, and hence higher temperature (Climate-change Carbon-cycle feedback is positive.) Therefore, further CO2 emission cut would be needed for the same CO 2 stabilization target under the influence of Climate- change Carbon-cycle feedback

Invitation to “Cool Earth 50” By ex-PM Abe (May 24, 2007) Half emission Same level as nature uptake stabilization

“Quasi-inverse estimation” Permissible Emission = (CO2 in air) + Ocean/Land Uptake Proposed for AR5 （ Hibbard et al ） Climate model with carbon cycle model CO 2 stabilization scenario (given) Projection of climate by the model Projection of CO 2 land/ocean uptake under the influence of climate change and given CO2 concentration

Method and Model

Integrated Earth System Model MIROC “-KISSME” Ocean: NPZD biology model （ Oschlies,2001 ） + carbon cycle recommended by OCMIP. Land: Sim-CYCLE model (Ito and Oikawa, 2002). Intermediate Climate-change Carbon-cycle feedback strength among AR4 models

Model integration CO2 stabilization scenario (Knutti et al. 2005) Other forcings –Other greenhouse gasses 、 aerosol 、 vegetation index: the same conditions as ones for year 1850 Time integration –250 years spin-up under year 1850 conditions –Integration from 1850 to 2300 under given CO 2 scenario CO2 concentration time-series (ppm) SP550 （ 550ppm at mid-22 century ） year SP1000 （ 1000ppm at mid-24 century ）

Climate-change Carbon-cycle Feedback To test influence of Climate-change Carbon-cycle Feedback, 2 runs with/without greenhouse effect are performed for each scenario (SP550, SP1000). 2x2=4 runs in total CO 2 concentration CO 2 for radiation SP550 coupled SP550 uncoupled SP550constant No greenhouse effect SP1000 coupled SP1000 uncoupled SP1000constant No greenhouse effect

Results 30 year running average to remove seasonal/ interannual /decadal variation

Global-average T2/SST time-series SP1000 coupled SP550 coupled T2 SP1000 uncoupled SP550 uncoupled SP1000 coupled SP550 uncoupled SP 1000 uncoupled SST （ K; deviation from 282.2K) （ K; deviation from K) More CO 2, More temperature rise, in the coupled runs. No temperature rise for the uncoupled runs. Gradual temperature rise even after CO 2 stabilization (SP550 coupled) ~3 o C T2 rise for SP550 coupled

Ocean/Land CO 2 uptake (PgC/year) SP550 SP1000 TOTAL Ocean Land Solid ： Coupled dashed ： Uncoupled CO2 uptake increases during accelerated CO 2 concentration. Then, slowdown of CO 2 rise reduces uptake toward equilibrium. Ocean needs longer time for equilibrium than land. Eventually ocean uptake dominates in total uptake. Climate-Change Carbon-Cycle Feedback reduces uptake. Especially influence to land uptake is significant. In SP1000 coupled run, Land becomes net source of CO 2.

Permissible Emission = (CO2 in air) + Ocean/Land Uptake dashed ： Uncoupled run SP550SP1000 Stabilization of CO2 and the accompanying nature adjustment toward equilibrium force reduction of permissible emission. Slow adjustment of ocean allows anthropogenic emission even at year Climate-change Carbon-Cycle feedback reduces permissible emission. Quasi-inversion estimate agrees well with fossil carbon emission during 20 th century. PgC/year Green: Fossil carbon emission (reality) solid: Coupled run

Cumulative Sum from 1850 to 2300 (PgC) Land uptakeOcean Uptake Total uptakeEmission coupled uncoupled165.4 (-65%) (-15.3%) (-35.6%) 1342 (-24.0%) Land uptakeOcean uptakeTotal uptake Emission coupled uncoupled-46.0 (-110.1%) (-18.7%) (-44.6%) 2411 (-22.9%) SP550 SP1000

30 年移動平均なし ( 年平均のみ） Ocean UptakeLand Uptake Total uptakeEmission

Climate-change Carbon-cycle feedback in ocean SP550 as an example “Coupled run” minus “uncoupled run”

Feedback to CO2 flux (global total) (“coupled run” minus “uncoupled run” ） CO2 flux ＝ E (pCO 2 a-pCO 2 o ） PgC/year μatm (Global average ）

Why pCO2o is increased by feedback? pCO2o=P(T,S,TCO 2,Alk) Temperature, salinity, TCO2, alkalinity dependence SST increase Is important More Temperature rise, Reduced TCO2 Year 2100 Year 2300

Feedback in spatial distribution (“coupled run” minus “uncoupled run” ） Accumulated CO2 flux From 1850 to 2100 increase KgC/m^2 decrease pCO2o ( average)

pCO 2 o (“coupled run” minus “uncoupled run” ） Each contribution T S TCO 2 Alkalinity

Balance on land

Balance for total SP550SP1000 soil res veg res. total GPP Solid:coupled Dash:uncoupled

Balance for veg SP550SP1000 litter fall veg res. total GPP Solid:coupled Dash:uncoupled

Balance for soil SP550SP1000 litter fall veg res. total GPP Solid:coupled Dash:uncoupled

Summary Climate-change Carbon-cycle feedback reduces permissible emission. Total reduction of the accumulated CO2 emission to 2300 is about 20%. If SP550 is the target, 50% reduction until year 2050 is not necessary. However, it results in ~3 o C temperature rise. In any way, much further reduction of CO 2 is necessary for final stabilization. Land relatively quickly adjusts to equilibrium. Furthermore, global warming could change land to CO 2 source. Land would not be reliable CO 2 sink in the long run.. Because ocean needs long time to equilibrium, it can be sink of CO 2 for long time. Climate-change Carbon-cycle is positive, but relatively small.

Discussions Other green gasses, aerosols, land use change must be considered (Any stabilization target?). SP550 might be too relaxed target. Forward experiments with 50% Greenhouse gas until 2050 are being considered (with Masui/Hijioka-san in NIES. ) Emissionconcentration forward Quasi-inversion Stabilization Scenario

NADW strength