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Status of the Carbon Cycle to be incorporated in AOGCMs Peter Cox & Pierre Friedlingstein 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 The Carbon Cycle and Climate Change Currently only about half of human emissions of CO2 remain in the atmosphere - the ocean and land ecosystems appear to be absorbing the remainder. 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) The Carbon Cycle and Climate Change 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. 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 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 Year-to-Year Variability in CO2 Growth-rate is driven by Climatic Anomalies (e.g. El Nino, Volcanoes) 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 ?? CO2 Growth-Rate is Sensitive to Climatic Anomalies….. 2003 Anomaly Total Fossil Fuels Land-use Change Mt Agung El Chichon Years after Volcanic Eruptions Pinatubo The Carbon Cycle and Climate Change 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 climatecarbon cycle feedbacks. The Carbon Cycle and Climate Change 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? 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 Status of Carbon Cycle in AR4 AOGCMs (C4MIP) Online CLIMATE Climate Change effects on Solubility of CO2 Vertical Mixing Circulation Greenhouse Effect CO2 OCEAN Offline Climate Change effects on plant productivity, soil respiration LAND Fossil Fuel + Net Land-use CO2 Emissions Hadley Centre climate-carbon GCM simulation shows climate change suppressing land carbon uptake….. Coupled Climate Carbon Cycle Intercomparison Project (C4MIP) • 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 C4MIP Models – extra CO2 due to climate effects on the carbon cycle All models simulate a positive feedback, but with very different magnitudes. Change in CO2 Emissions Partitioning in C4MIP Models Positive Carbon Cycle Feedback C4MIP Models indicate that Climate Change will hinder CO2 uptake by the land, but the size of this effect is uncertain Fraction of Emissions Absorbed by the Land (1860-2100) 0.6 0.5 0.4 0.3 0.2 0.1 Uncoupled -2 .7 LI M BE BE R R N -C C C U Vi c M D U G C FR C NL LL M PI IP S H ad C M 3L L- C C M 2C C SM -1 0 Coupled C4MIP: Robust Results and Uncertainties All C4MIP models simulate a positive feedback larger warming or larger reduction in emissions Global Emissions for Climate Stabilisation 2000 2050 ~ 8 GtC/yr in 2000 ~ 3 GtC/yr by 2050 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! C4MIP: Robust Results and Uncertainties 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 Contributions to uncertainty in future CO2 concentration (from C4MIP models) IPCC, AR4 C4MIP: Key Uncertainties in Climate-Carbon Feedback 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. 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 landmanagement and forest fires. Land use 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 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 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 landmanagement and forest fires. More detailed ocean ecosystem models. Examples of AR5 Ocean Ecosystem Model (PISCES) NH4+ NO3 - PO43- Diatoms Si Nano-phyto Iron MicroZoo D.O.M Meso Zoo P.O.M Small Ones Big Ones Aumont et al., 2003 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 landmanagement and forest fires. More detailed ocean ecosystem models. Interactive nitrogen cycling on land. Nitrogen Deposition is already significant and will increase Millennium Ecosystem Assessment, 2005 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 landmanagement and forest fires. More detailed ocean ecosystem models. Interactive nitrogen cycling on land. Links to changes in atmospheric chemistry and aerosols ? 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 Status of Carbon Cycle in AR4 AOGCMs (C4MIP) Online CLIMATE Climate Change effects on Solubility of CO2 Vertical Mixing Circulation Greenhouse Effect CO2 OCEAN Offline Climate Change effects on plant productivity, soil respiration LAND Fossil Fuel + Net Land-use CO2 Emissions Possible Status of Carbon Cycle in AR5 AOGCMs Online CLIMATE Climate Change effects on Solubility of CO2 Vertical Mixing Circulation & Ocean Ecosystem Structure OCEAN Iron Dust Deposition Greenhouse Effect CO2 Offline Climate Change effects on plant productivity, soil respiration & Fires Riverine CO2 fluxes Fossil Fuel CO2 Emissions LAND Land-use Change N and O3 Deposition 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. 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, Ndeposition, near surface O3 concentration, dust inputs to the ocean. THE END ! LOOP The new IPSL C-C model Atmospheric [CO2] d CO2 EMI Fluxland Fluxocean dt 2.12 CO2 concentration re-calculated each month Climate Atmosphere Coupler LMDZ4 OASIS 2.4 ∆t = physic time step Terrestrial biosphere ORCHIDEE (STOMATE activated) Ocean ORCA-LIM OPA 8.2 ∆t = 1day Marine Biochemistry PISCES Carbon Land flux GtC/mth EMI = external forcing [Marland et al, 2005 Houghton, 2002] Ocean flux GtC/mth Net total carbon flux Fluxland + Fluxocean Cadule et al., in prep Zero Order Validation Global mean surface temperature anomalies Base period : 1961-1990 Cadule et al., in prep First Order Validation • “IPCC” carbon budget (GtC/yr) Atmospheric carbon variation fossil fuel Land use lan d ocean 1990’s 1980’s LOOP IPCC LOOP IPCC Atm 2.7 3.3 3.3 3.2 Ocean 2.0 1.8±0.8 2.0 2.2±0.4 Land 2.8 1.6 (-0.3 to 4) 3.3 2.6 (1 to 4.3) Cadule et al., in prep Second Order Validation • Atmospheric CO2 – Offline transport over 1979-2003 Cadule et al., in prep • Seasonal cycle • Long term trend Cadule et al., in prep a climate response to CO2 IPSL-CM2_C IPSL_CM4_LOOP Friedlingstein et al., 2006 b C-cycle response to CO2 LAND OCEAN IPSL-CM2_C IPSL_CM4_LOOP Friedlingstein et al., 2006 g C-cycle response to climate LAND OCEAN IPSL-CM2_C IPSL_CM4_LOOP Friedlingstein et al., 2006 Why such a large uncertainty in the Land Carbon Response to Climate ? REGIONAL LAND RESPONSE TO CLIMATE IPSL-CM2_C IPSL_CM4_LOOP HadCM3C Improving the carbon cycle • Coupled C-C run with fires and land-use • Include nitrogen cycle Nitrogen Motivation: • Controls the carbon cycle – Impact on carbon uptake – Impact on the C-C feedback estimate Examples of AR5 carbon cycle models (ORCHIDEE and PISCES) NH4+ NO3 - PO43- Diatoms Si Nano-phyto Iron MicroZoo D.O.M Meso Zoo P.O.M Small Ones Krinner et al., 2005 Big Ones Aumont et al., 2003 The land response - IPSL Increase in soil aridity Extension of the growing season Berthelot et al., 2002 Climate-Land Feedbacks and Forcings Anthropogenic Emissions Climate Sensitivity + CO2 Temp Climate Sensitivity of Soil respiration to Temp _ NPP + Decomp Land N mineralisation + The Key missing negative feedback – increased N availability in a warmer world ? + Avail N Anthropogenic N deposition Chemistry Climate-Land Feedbacks and Forcings Anthropogenic Emissions Climate Sensitivity + CO2 The Key missing forcing factor? Tropospheric O3 levels are projected to increase significantly - to levels which may be detrimental to plants (see for example Gregg et al., 2003) Could this suppress the land carbon sink and accelerate global warming? Temp Climate NPP Trop O3 Anthropogenic Emissions Land Climate-Land Feedbacks and Forcings Anthropogenic Emissions Regional Climate Change Precip + Surface Energy Balance Land-use Change Veg Cover Climate Sensitivity ? CO2 Fertilisation + + + + + CO2 _ Temp + - + _ NPP Trop O3 Anthropogenic Emissions Climate Sensitivity of Soil respiration to Temp + Decomp Land N mineralisation + + Avail N Anthropogenic N deposition Chemistry Increased Tropospheric O3 and Vegetation – Feedbacks from biogenic emissions CO2 Precip + Temp Isoprene emissions increase with temperature Veg Cover NPP Isoprene emissions increase with increasing vegetation cover? + Trop O3 Decomp + + Isoprene Isoprene increases O3 in high NOx conditions Anthropogenic NOx emissions Humans now dominate the Global Nitrogen Cycle Millennium Ecosystem Assessment, 2005