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

Quasi-inversion estimation of permissible CO2 emission

toward stabilization

Toru Miyama（ Frontier Research Center for Global Change ）

2007 October 11

Forward Casting(conventional projection)

“What if ?”

Temp. riseCO2 emission CO2 in air

Backward Casting (Inverse)(social/political needs)

“How ?”

??

PermissibleCO2 emission

Temperaturetarget

~2oC?

CO2 stabilization

CO2 emission= Nature uptake

Climate-change Carbon-cycle Feedback

Anthropogenic

CO2 emission

Uptake by ocean and land

CO2increase

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 CO2 uptake results in more CO2 concentration, and hence higher temperature (Climate-change Carbon-cycle feedback is positive.) • Therefore, further CO2 emission cut would be needed for the same CO2 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. 2007 ）

Climate model with carbon cycle model

CO2 stabilizationscenario (given)

Projection of climateby the model

Projection of CO2 land/ocean uptake under the influence ofclimate change and given CO2 concentration

dt

d

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 cond

itions as ones for year 1850• Time integration

– 250 years spin-up under year 1850 conditions– Integration from 1850 to 2300 under given CO2 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

CO2 concentration CO2 for radiation

SP550

coupledSP550 SP550

SP550

uncoupledSP550 constant

No greenhouse effect

SP1000

coupledSP1000 SP1000

SP1000

uncoupledSP1000 constant

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 uncoupledSP550 uncoupled

SP1000 coupled

SP550 uncoupled

SP550 uncoupledSP 1000 uncoupled

SST

（ K; deviation from 282.2K) （ K; deviation from 290.15K)

•　 More CO2 , More temperature rise, in the coupled runs. •　 No temperature rise for the uncoupled runs. •　 Gradual temperature rise even after CO2 stabilization (SP550 coupled) •　 ~3oC T2 rise for SP550 coupled

Ocean/Land CO2 　 uptake (PgC/year)

SP550 SP1000TOTALOceanLand

Solid ： Coupleddashed ： Uncoupled

• CO2 uptake increases during accelerated CO2 concentration. Then, slowdown of CO2 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 CO2.

Permissible Emission = (CO2 in air)

+ Ocean/Land Uptake

dashed ： Uncoupled run

SP550 SP1000

•　 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 2300. • Climate-change Carbon-Cycle feedback reduces permissible emission. •　 Quasi-inversion estimate agrees well with fossil carbon emission during 20th century.

PgC/year

Green: Fossil carbon emission (reality)

solid:Coupled run

dt

d

Cumulative Sum from 1850 to 2300 (PgC)

Land uptake Ocean Uptake Total uptake Emission

coupled 480.7 708.3 1189 1766

uncoupled 165.4

(-65%)

599.9

(-15.3%)

765.3

(-35.6%)

1342

(-24.0%)

Land uptake Ocean uptake Total uptake Emission

coupled 455.8 1153 1608.8 3127

uncoupled -46.0

(-110.1%)

937.2

(-18.7%)

891.2

(-44.6%)

2411

(-22.9%)

SP550

SP1000

30 年移動平均なし ( 年平均のみ）Ocean Uptake Land Uptake

Total uptake Emission

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 (pCO2a-pCO2o ）

PgC/year

μatm (Global average ）

Why pCO2o is increased by feedback? pCO2o=P(T,S,TCO2,Alk)

Temperature, salinity, TCO2, alkalinitydependence

SST increaseIs important

More Temperature rise,

Reduced TCO2

Year 2100 Year 2300

Feedback in spatial distribution (“coupled run” minus “uncoupled run” ）

Accumulated CO2 fluxFrom 1850 to 2100increase

KgC/m^2

decrease

pCO2o(1850-2100 average)

pCO2o

(“coupled run” minus “uncoupled run” ）

Each contribution

T S

TCO2Alkalinity

Balance on land

Balance for total

SP550 SP1000

soil res

veg res.

total

GPP

Solid:coupledDash:uncoupled

Balance for veg

SP550 SP1000

litter fall

veg res.

total

GPP

Solid:coupledDash:uncoupled

Balance for soil

SP550 SP1000

litter fall

veg res.

total

GPP

Solid:coupledDash: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 ~3oC temperature rise. In any way, much further reduction of CO2 is necessary for final stabilization.

• Land relatively quickly adjusts to equilibrium. Furthermore, global warming could change land to CO2 source. Land would not be reliable CO2 sink in the long run..

• Because ocean needs long time to equilibrium, it can be sink of CO2 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. )

Emission concentration

forward

Quasi-inversion

Stabilization Scenario

NADW strength