Quasi-inversion estimation of permissible CO 2 emission toward s tabilization

1. Quasi-inversion estimation of permissible CO2 emission toward stabilization Toru Miyama （Frontier Research Center for Global Change） 2007 October 11

2. CO2 in air Temp. rise Forward Casting(conventional projection) “What if ?” CO2 emission

3. Permissible CO2 emission CO2 stabilization Temperature target ?? ~2oC? CO2 emission = Nature uptake Backward Casting (Inverse)(social/political needs) “How ?”

4. Climate-change Carbon-cycle Feedback Anthropogenic CO2 emission CO2 increase in air Uptake by ocean and land • 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

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

6. Climate model with carbon cycle model CO2 stabilization scenario (given) Projection of climate by the model Projection of CO2 land/ocean uptake under the influence of climate change and given CO2 concentration “Quasi-inverse estimation” Permissible Emission = (CO2 in air) + Ocean/Land Uptake Proposed for AR5 （Hibbard et al. 2007）

7. Method and Model

8. 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

9. 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 CO2 scenario CO2 concentration time-series (ppm) SP1000 （1000ppm at mid-24 century） SP550 （550ppm at mid-22 century） year

10. 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

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

12. Global-average T2/SST time-series SST T2 SP1000 coupled SP1000 coupled SP550 coupled SP550 uncoupled SP1000 uncoupled SP550 uncoupled SP550 uncoupled SP 1000 uncoupled （K; deviation from 282.2K) （K; deviation from 290.15K) • More CO2 , More temperature rise, in the coupledruns. • No temperature rise for the uncoupled runs. • Gradual temperature rise even after CO2 stabilization (SP550 coupled) • ~3oC T2 rise for SP550 coupled

13. Ocean/Land CO2uptake (PgC/year) SP1000 SP550 Solid：Coupled dashed：Uncoupled TOTAL Ocean Land • 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.

14. Permissible Emission = (CO2 in air) + Ocean/Land Uptake PgC/year SP550 SP1000 dashed： Uncoupled run solid: Coupled run Green: Fossil carbon emission (reality) • Stabilization of CO2 and the accompanying natureadjustment 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.

15. Cumulative Sum from 1850 to 2300 (PgC) SP550 SP1000

16. 30年移動平均なし(年平均のみ）

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

18. Feedback to CO2 flux (global total)(“coupled run” minus “uncoupled run”） CO2 flux＝E (pCO2a-pCO2o） μatm (Global average） PgC/year

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

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

21. (“coupled run” minus “uncoupled run”） pCO2o Each contribution S T Alkalinity TCO2

22. Balance on land

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

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

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

26. 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.

27. 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. ) forward Emission concentration Quasi-inversion Stabilization Scenario

28. NADW strength