Status of the Carbon Cycle to be incorporated in AOGCMs

1. Status of the Carbon Cycle to be incorporated in AOGCMs Peter Cox & Pierre Friedlingstein

2. Outline INTRODUCTION : • Rationale for including the carbon cycle in AOGCMs : Carbon-Cycle Climate Interactions. CURRENT STATUS OF CARBON CYCLE IN AOGCMs: • Coupled-Climate Carbon Cycle Model Intercomparison Project (C4MIP). • Robust findings and key uncertainties. • Missing processes. POSSIBLE STATUS OF CARBON CYCLE IN AOGCMS BY AR5: • Modelling of CO2 emissions from land-use and land-management. • More detailed ocean ecosystem models • Interactive nitrogen cycling on land. • Links to changes in atmospheric chemistry and aerosols ? • Implications for AR5 scenarios. CONCLUSIONS

3. Currently only about half of human emissions of CO2 remain in the atmosphere - the ocean and land ecosystems appear to be absorbing the remainder. The Carbon Cycle and Climate Change Atmospheric Increase = 3.2 +/- 0.1 GtC/yr (50%) Emissions (fossil fuel, cement) = 6.4 +/- 0.4 GtC/yr (100%) Ocean-atmosphere flux = -1.7 +/- 0.5 GtC/yr (27%) Land-atmosphere flux = -1.4 +/- 0.7 GtC/yr (22%) Estimated Global Carbon Balance for 1990s (IPCC TAR)

4. Currently only about half of human emissions of CO2 remain in the atmosphere - the ocean and land ecosystems appear to be absorbing the remainder. Atmosphere-land and atmosphere-ocean fluxes of CO2 are sensitive to climate. The Carbon Cycle and Climate Change

5. Temperature Carbon Cycle-Climate Coupling The Example of the Glacial Cycles CO2 Vostok Ice Core Records showing strong correlations between Temperature and Carbon Dioxide over the last 400,000 years

6. CO2 Concentration (measured at Mauna Loa on Hawaii) Atmospheric CO2 is increasing at about half the rate of emissions Seasonal cycle is due to the land biosphere

7. Year-to-Year Variability in CO2 Growth-rate is driven by Climatic Anomalies (e.g. El Nino, Volcanoes)

8. CO2 growth-rate anomalies are normally well correlated with El Nino (+ve anomalies) and La Nina (-ve anomalies) …… except after major volcanoes… …..or in the last few years ??

9. CO2 Growth-Rate is Sensitive to Climatic Anomalies….. 2003 Anomaly Total Fossil Fuels Years after Volcanic Eruptions Land-use Change Mt Agung El Chichon Pinatubo

10. Currently only about half of human emissions of CO2 remain in the atmosphere - the ocean and land ecosystems appear to be absorbing the remainder. Atmosphere-land and atmosphere-ocean fluxes of CO2 are sensitive to climate. To date most GCMs have used prescribed atmospheric CO2 and therefore neglect climate-carbon cycle feedbacks. The Carbon Cycle and Climate Change

11. Currently only about half of human emissions of CO2 remain in the atmosphere - the ocean and land ecosystems appear to be absorbing the remainder. Atmosphere-land and atmosphere-ocean fluxes of CO2 are sensitive to climate. Most GCMs prescribe atmospheric CO2 and therefore neglect climate-carbon cycle feedbacks. How important might these be for future climate change? The Carbon Cycle and Climate Change

12. Status of Carbon Cycle in TAR AOGCMs Online CLIMATE Offline Greenhouse Effect CO2 CO2 Uptake by Ocean / CO2 buffering effect CO2 Uptake by Land / CO2-fertilization of plant growth OCEAN LAND Fossil Fuel + Net Land-use CO2 Emissions

13. Status of Carbon Cycle in AR4 AOGCMs (C4MIP) Online CLIMATE Offline Greenhouse Effect Climate Change effects on Solubility of CO2 Vertical Mixing Circulation Climate Change effects on plant productivity, soil respiration CO2 OCEAN LAND Fossil Fuel + Net Land-use CO2 Emissions

14. Hadley Centre climate-carbon GCM simulation shows climate change suppressing land carbon uptake…..

15. IGBP/GAIM (AIMES) - WCRP/WGCM coordinated activity to explore the coupled climate carbon cycle feedback 11 Coupled Climate-Carbon models (7 AOGCMs) have now been used to simulate 21st century climate and CO2 under similar scenarios. Models agree that effects of climate change on the carbon cycle will lead to more CO2 in the atmosphere (positive climate-carbon cycle feedback). But magnitude of this effect, and primary cause, vary between models  Coupled Climate Carbon Cycle Intercomparison Project (C4MIP)

16. C4MIP Models – extra CO2 due to climate effects on the carbon cycle All models simulate a positive feedback, but with very different magnitudes.

17. Change in CO2 Emissions Partitioning in C4MIP Models Positive Carbon Cycle Feedback

18. C4MIP Models indicate that Climate Change will hinder CO2 uptake by the land, but the size of this effect is uncertain

19. All C4MIP models simulate a positive feedback larger warming or larger reduction in emissions C4MIP: Robust Results and Uncertainties

20. GlobalEmissions for Climate Stabilisation 2000 2050 ~ 8 GtC/yr in 2000 ~ 3 GtC/yr by 2050

21. Impact of Climate-Carbon Cycle Feedbacks on Integrated Permissible Emissions Impact of Carbon Cycle Feedbacks Single model: urgently need to provide updated stabilisation permissible emissions scenarios with error bars covering full climate-carbon system!

22. All C4MIP models simulate a positive feedback larger warming or larger reduction in emissions Uncertainty in the 21st century CO2 (range: 750 – 1000 ppm) Large uncertainty on the feedback (20 to 220 ppm) Feedback analysis to attribute uncertainty C4MIP: Robust Results and Uncertainties

23. Contributions to uncertainty in future CO2 concentration (from C4MIP models) IPCC, AR4

24. Response of land NPP to climate (includes uncertainties in hydrological changes) Transient climate sensitivity to CO2 Response of soil (heterotrophic) respiration to climate. However, rate of increase of CO2 also depends on responses of land and especially ocean uptake to CO2. C4MIP: Key Uncertainties in Climate-Carbon Feedback

25. Possible Status of Carbon Cycle in AOGCMs by AR5 • More complete model validation/use of observational constraints. • Modelling of CO2 emissions from land-use and land-management and forest fires.

26. Land use

27. Statistical Dynamics approach to large-scale Vegetation Dynamics Including age-class distributions Explicit simulation of rainforest regrowth on multiple patches Moment Equations for Statistics of Vegetation State Morecroft et al., 2001

28. Interactive Forest Fire • Currently implemented in ORCHIDEE • will allow to estimate role of fire on CO2 • will allow to estimate impact of climate change on fire and feedback on climate • Emissions of CH4, NOx,… Thonicke, et al., 2005

29. Possible Status of Carbon Cycle in AOGCMs by AR5 • More complete model validation/use of observational constraints. • Modelling of CO2 emissions from land-use and land-management and forest fires. • More detailed ocean ecosystem models.

30. PO43- Diatoms NH4+ Si Nano-phyto NO3- Iron MicroZoo D.O.M Meso Zoo P.O.M Small Ones Big Ones Examples of AR5 Ocean Ecosystem Model (PISCES) Aumont et al., 2003

31. Possible Status of Carbon Cycle in AOGCMs by AR5 • More complete model validation/use of observational constraints. • Modelling of CO2 emissions from land-use and land-management and forest fires. • More detailed ocean ecosystem models. • Interactive nitrogen cycling on land.

32. Nitrogen Deposition is already significant and will increase Millennium Ecosystem Assessment, 2005

33. Possible Status of Carbon Cycle in AOGCMs by AR5 • More complete model validation/use of observational constraints. • Modelling of CO2 emissions from land-use and land-management and forest fires. • More detailed ocean ecosystem models. • Interactive nitrogen cycling on land. • Links to changes in atmospheric chemistry and aerosols ?

34. Status of Carbon Cycle in TAR AOGCMs Online CLIMATE Offline Greenhouse Effect CO2 CO2 Uptake by Ocean / CO2 buffering effect CO2 Uptake by Land / CO2-fertilization of plant growth OCEAN LAND Fossil Fuel + Net Land-use CO2 Emissions

35. Status of Carbon Cycle in AR4 AOGCMs (C4MIP) Online CLIMATE Offline Greenhouse Effect Climate Change effects on Solubility of CO2 Vertical Mixing Circulation Climate Change effects on plant productivity, soil respiration CO2 OCEAN LAND Fossil Fuel + Net Land-use CO2 Emissions

36. Possible Status of Carbon Cycle in AR5 AOGCMs Online CLIMATE Offline Greenhouse Effect Climate Change effects on Solubility of CO2 Vertical Mixing Circulation & Ocean Ecosystem Structure Climate Change effects on plant productivity, soil respiration & Fires CO2 Riverine CO2 fluxes OCEAN LAND Iron Dust Deposition Fossil Fuel CO2 Emissions Land-use Change N and O3 Deposition

37. Conclusions I • Climate and carbon cycle are tightly coupled, so the carbon cycle must be part of Earth System Models. • First generation coupled-climate carbon cycle models all suggest that climate change will increase the fraction of CO2 emissions that are airborne. • There are major uncertainties in the size of this positive climate-carbon feedback (leading to an extra 20-200ppmv by 2100 under the A2 emissions scenario, with a mean of 90+/-50 ppmv). • This uncertainty also impacts on the CO2 emissions consistent with stabilisation at a given concentration.

38. Conclusions 2 • By AR5 climate-carbon cycle models are likely to include a number of processes that were missing in the first generation C4MIP models, including: • Interactive calculation of net land-use emissions. • More complex ocean ecosystem models. • Interactive N-cycling on the land. • Riverive carbon fluxes from land to ocean • This places new demands on driving scenarios that need to include consistent land-use change/management, N-deposition, near surface O3 concentration, dust inputs to the ocean.

39. THE END !

40. Climate Atmospheric [CO2] AtmosphereLMDZ4 OceanORCA-LIMOPA 8.2 Coupler OASIS 2.4 ∆t = physic time step ∆t = 1day CO2 concentrationre-calculated each month MarineBiochemistry PISCES Terrestrial biosphereORCHIDEE(STOMATE activated) Carbon Land flux GtC/mth Ocean flux GtC/mth EMI = external forcing [Marland et al, 2005 Houghton, 2002] Net total carbon flux Fluxland + Fluxocean LOOP The new IPSL C-C model Cadule et al., in prep

41. Global mean surface temperature anomalies Base period : 1961-1990 Zero Order Validation Cadule et al., in prep

42. fossil fuel Atmospheric carbon variation land Land use ocean First Order Validation • “IPCC” carbon budget (GtC/yr) 1990’s 1980’s Atm Ocean Land Cadule et al., in prep

43. Second Order Validation • Atmospheric CO2 • Offline transport over 1979-2003 Cadule et al., in prep

44. Seasonal cycle • Long term trend Cadule et al., in prep

45. aclimate response to CO2 Friedlingstein et al., 2006 IPSL-CM2_C IPSL_CM4_LOOP

46. bC-cycle response to CO2 LAND OCEAN Friedlingstein et al., 2006 IPSL-CM2_C IPSL_CM4_LOOP

47. gC-cycle response to climate LAND OCEAN Friedlingstein et al., 2006 IPSL-CM2_C IPSL_CM4_LOOP

48. Why such a large uncertainty in the Land Carbon Response to Climate ?

49. IPSL-CM2_C IPSL_CM4_LOOP HadCM3C REGIONAL LAND RESPONSE TO CLIMATE

50. Improving the carbon cycle • Coupled C-C run with fires and land-use • Include nitrogen cycle