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

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 (C 4 MIP).  Robust findings and key uncertainties.  Missing processes. POSSIBLE STATUS OF CARBON CYCLE IN AOGCMS BY AR5:  Modelling of CO 2 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 CO 2 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 = /- 0.5 GtC/yr (27%) Land-atmosphere flux = /- 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 CO 2 remain in the atmosphere - the ocean and land ecosystems appear to be absorbing the remainder.  Atmosphere-land and atmosphere-ocean fluxes of CO 2 are sensitive to climate.

Temperature CO 2 Vostok Ice Core Records showing strong correlations between Temperature and Carbon Dioxide over the last 400,000 years Carbon Cycle-Climate Coupling The Example of the Glacial Cycles

CO 2 Concentration (measured at Mauna Loa on Hawaii) Atmospheric CO 2 is increasing at about half the rate of emissions Seasonal cycle is due to the land biosphere

Year-to-Year Variability in CO 2 Growth-rate is driven by Climatic Anomalies (e.g. El Nino, Volcanoes)

CO 2 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 ??

CO 2 Growth-Rate is Sensitive to Climatic Anomalies….. Fossil Fuels Total Land-use Change 2003 Anomaly Years after Volcanic Eruptions El Chichon Pinatubo Mt Agung

The Carbon Cycle and Climate Change  Currently only about half of human emissions of CO 2 remain in the atmosphere - the ocean and land ecosystems appear to be absorbing the remainder.  Atmosphere-land and atmosphere-ocean fluxes of CO 2 are sensitive to climate.  To date most GCMs have used prescribed atmospheric CO 2 and therefore neglect climate- carbon cycle feedbacks.

The Carbon Cycle and Climate Change  Currently only about half of human emissions of CO 2 remain in the atmosphere - the ocean and land ecosystems appear to be absorbing the remainder.  Atmosphere-land and atmosphere-ocean fluxes of CO 2 are sensitive to climate.  Most GCMs prescribe atmospheric CO 2 and therefore neglect climate-carbon cycle feedbacks.  How important might these be for future climate change?

Status of Carbon Cycle in TAR AOGCMs Fossil Fuel + Net Land-use CO 2 Emissions Online Offline CLIMATE OCEAN LAND CO 2 Greenhouse Effect CO 2 Uptake by Land / CO 2 -fertilization of plant growth CO 2 Uptake by Ocean / CO 2 buffering effect

Status of Carbon Cycle in AR4 AOGCMs (C 4 MIP) Fossil Fuel + Net Land-use CO 2 Emissions Online Offline CLIMATE OCEAN LAND CO 2 Greenhouse Effect Climate Change effects on Solubility of CO 2 Vertical Mixing Circulation Climate Change effects on plant productivity, soil respiration

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

Coupled Climate Carbon Cycle Intercomparison Project (C 4 MIP) 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 21 st century climate and CO 2 under similar scenarios. Models agree that effects of climate change on the carbon cycle will lead to more CO 2 in the atmosphere (positive climate-carbon cycle feedback). But magnitude of this effect, and primary cause, vary between models 

C 4 MIP Models – extra CO 2 due to climate effects on the carbon cycle All models simulate a positive feedback, but with very different magnitudes.

Positive Carbon Cycle Feedback Change in CO 2 Emissions Partitioning in C 4 MIP Models

C 4 MIP Models indicate that Climate Change will hinder CO 2 uptake by the land, but the size of this effect is uncertain

C 4 MIP: Robust Results and Uncertainties  All C 4 MIP models simulate a positive feedback  larger warming  or larger reduction in emissions

Global Emissions for Climate Stabilisation ~ 8 GtC/yr in 2000 ~ 3 GtC/yr by 2050

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

C 4 MIP: Robust Results and Uncertainties  All C 4 MIP models simulate a positive feedback  larger warming  or larger reduction in emissions  Uncertainty in the 21st century CO 2 (range: 750 – 1000 ppm)  Large uncertainty on the feedback (20 to 220 ppm)  Feedback analysis to attribute uncertainty

Contributions to uncertainty in future CO 2 concentration (from C 4 MIP models) IPCC, AR4

C 4 MIP: Key Uncertainties in Climate-Carbon Feedback  Response of land NPP to climate (includes uncertainties in hydrological changes)  Transient climate sensitivity to CO 2  Response of soil (heterotrophic) respiration to climate.  However, rate of increase of CO 2 also depends on responses of land and especially ocean uptake to CO 2.

Possible Status of Carbon Cycle in AOGCMs by AR5  More complete model validation/use of observational constraints.  Modelling of CO 2 emissions from land-use and land- management and forest fires.

Land use

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

Interactive Forest Fire Currently implemented in ORCHIDEE –will allow to estimate role of fire on CO 2 –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 CO 2 emissions from land-use and land- management and forest fires.  More detailed ocean ecosystem models.

Examples of AR5 Ocean Ecosystem Model (PISCES) PO 4 3- Diatoms MicroZoo P.O.M D.O.M Si Iron Nano-phyto Meso Zoo NO 3 - NH 4 + Small OnesBig Ones Aumont et al., 2003

Possible Status of Carbon Cycle in AOGCMs by AR5  More complete model validation/use of observational constraints.  Modelling of CO 2 emissions from land-use and land- management 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 CO 2 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 ?

Status of Carbon Cycle in TAR AOGCMs Fossil Fuel + Net Land-use CO 2 Emissions Online Offline CLIMATE OCEAN LAND CO 2 Greenhouse Effect CO 2 Uptake by Land / CO 2 -fertilization of plant growth CO 2 Uptake by Ocean / CO 2 buffering effect

Status of Carbon Cycle in AR4 AOGCMs (C 4 MIP) Fossil Fuel + Net Land-use CO 2 Emissions Online Offline CLIMATE OCEAN LAND CO 2 Greenhouse Effect Climate Change effects on Solubility of CO 2 Vertical Mixing Circulation Climate Change effects on plant productivity, soil respiration

Possible Status of Carbon Cycle in AR5 AOGCMs Fossil Fuel CO 2 Emissions Online Offline CLIMATE OCEAN LAND CO 2 Greenhouse Effect Land-use Change Iron Dust Deposition N and O3 Deposition Climate Change effects on Solubility of CO 2 Vertical Mixing Circulation & Ocean Ecosystem Structure Climate Change effects on plant productivity, soil respiration & Fires Riverine CO 2 fluxes

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 ppmv by 2100 under the A2 emissions scenario, with a mean of 90+/-50 ppmv).  This uncertainty also impacts on the CO 2 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, N- deposition, near surface O3 concentration, dust inputs to the ocean.

THE END !

LOOP The new IPSL C-C model Net total carbon flux Flux land + Flux ocean Terrestrial biosphere ORCHIDEE (STOMATE activated) Marine Biochemistry PISCES Ocean ORCA-LIM OPA 8.2 Atmosphere LMDZ4 EMI = external forcing [Marland et al, 2005 Houghton, 2002] Ocean flux GtC/mth Land flux GtC/mth Coupler OASIS 2.4 Climate Atmospheric [CO 2 ] CO 2 concentration re-calculated each month ∆t = 1day Carbon ∆t = physic time step Cadule et al., in prep

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

First Order Validation “IPCC” carbon budget (GtC/yr) LOOPIPCCLOOPIPCC ± ± (-0.3 to 4) (1 to 4.3) 1980’s 1990’s Atm Ocean Land Cadule et al., in prep Atmospheric carbon variation Land use fossil fuellan d ocean

Second Order Validation Atmospheric CO2 –Offline transport over Cadule et al., in prep

Seasonal cycle Long term trend

 climate response to CO 2 Friedlingstein et al., 2006 IPSL-CM2_CIPSL_CM4_LOOP

 C-cycle response to CO 2 OCEAN LAND Friedlingstein et al., 2006 IPSL-CM2_CIPSL_CM4_LOOP

 C-cycle response to climate OCEAN LAND Friedlingstein et al., 2006 IPSL-CM2_CIPSL_CM4_LOOP

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

IPSL-CM2_CIPSL_CM4_LOOPHadCM3C REGIONAL LAND RESPONSE TO CLIMATE

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) PO 4 3- Diatoms MicroZoo P.O.M D.O.M Si Iron Nano-phyto Meso Zoo NO 3 - NH 4 + Small OnesBig Ones Aumont et al., 2003 Krinner et al., 2005

The land response - IPSL Extension of the growing season Increase in soil aridity Berthelot et al., 2002

CO 2 Temp NPPDecomp + Climate Sensitivity Sensitivity of Soil respiration to Temp + - Anthropogenic Emissions Avail N N mineralisation + + Anthropogenic N deposition _ Climate Land Chemistry Climate-Land Feedbacks and Forcings The Key missing negative feedback – increased N availability in a warmer world ?

CO 2 Temp NPP + Climate Sensitivity - Anthropogenic Emissions Climate Land Climate-Land Feedbacks and Forcings Anthropogenic Emissions Trop O3 - The Key missing forcing factor? Tropospheric O 3 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?

CO 2 TempPrecip Veg Cover NPPDecomp + Climate Sensitivity Sensitivity of Soil respiration to Temp _ + - CO 2 Fertilisation Anthropogenic Emissions Climate-Land Feedbacks and Forcings Surface Energy Balance + + Regional Climate Change ? + + Land-use Change Avail N N mineralisation + + Anthropogenic N deposition Anthropogenic Emissions Trop O3 - _ Climate Land Chemistry

CO 2 TempPrecip Veg Cover NPPDecomp + Anthropogenic NOx emissions Increased Tropospheric O3 and Vegetation – Feedbacks from biogenic emissions Trop O 3 Isoprene + Isoprene emissions increase with temperature + Isoprene increases O3 in high NOx conditions + Isoprene emissions increase with increasing vegetation cover?

Humans now dominate the Global Nitrogen Cycle Millennium Ecosystem Assessment, 2005