Peter Cox &

Pierre Friedlingstein

Status of the Carbon Cycle to be

incorporated in AOGCMs

OutlineINTRODUCTION : 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

CO2

Vostok Ice Core Recordsshowing strong correlations between Temperature and

Carbon Dioxide overthe last 400,000 years

Carbon Cycle-Climate Coupling

The Example of the Glacial Cycles

CO2 Concentration (measured at Mauna Loa on Hawaii)

Atmospheric CO2 is increasingat about half the rate of emissions

Seasonal cycle is dueto the land biosphere

Year-to-Year Variability in CO2 Growth-rate is driven byClimatic 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…..

Fossil Fuels

Total

Land-use Change

2003 Anomaly

Years after Volcanic Eruptions

El ChichonPinatubo

Mt Agung

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 climate-carbon 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

Fossil Fuel + Net Land-use

CO2 Emissions

Online

OfflineCLIMATE

OCEAN LAND

CO2

Greenhouse Effect

CO2 Uptake by Land / CO2-fertilization of plant

growth

CO2 Uptake by Ocean / CO2 buffering effect

Status of Carbon Cycle in AR4 AOGCMs (C4MIP)

Fossil Fuel + Net Land-use

CO2 Emissions

Online

OfflineCLIMATE

OCEAN LAND

CO2

Greenhouse EffectClimate Change effects on

Solubility of CO2

Vertical MixingCirculation

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 (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.

Positive CarbonCycle Feedback

Change in CO2 Emissions Partitioning in C4MIP Models

Fraction of Emissions Absorbed by the Land (1860-2100)

0

0.1

0.2

0.3

0.4

0.5

0.6

HadCM3LCIPSL-CM2C

CSM-1MPI LLNL

FRCGCUMD

UVic-2.7CLIMBERBERN-CC

Uncoupled Coupled

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

C4MIP: Robust Results and Uncertainties

All C4MIP models simulate a positive feedback larger warmingor larger reduction in emissions

Global Emissions for Climate Stabilisation

20502000

~ 8 GtC/yr in 2000

~ 3 GtC/yr by 2050

Impact of CarbonCycle 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

C4MIP: Robust Results and Uncertainties

All C4MIP models simulate a positive feedback larger warmingor 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 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 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 land-management and forest fires.

More detailed ocean ecosystem models.

Examples of AR5 Ocean Ecosystem Model (PISCES)

PO43-

Diatoms

MicroZoo

P.O.M

D.O.M

Si

IronNano-phyto

Meso Zoo

NO3-

NH4+

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 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 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 ?

Status of Carbon Cycle in TAR AOGCMs

Fossil Fuel + Net Land-use

CO2 Emissions

Online

OfflineCLIMATE

OCEAN LAND

CO2

Greenhouse Effect

CO2 Uptake by Land / CO2-fertilization of plant

growth

CO2 Uptake by Ocean / CO2 buffering effect

Status of Carbon Cycle in AR4 AOGCMs (C4MIP)

Fossil Fuel + Net Land-use

CO2 Emissions

Online

OfflineCLIMATE

OCEAN LAND

CO2

Greenhouse EffectClimate Change effects on

Solubility of CO2

Vertical MixingCirculation

Climate Change effects on plant productivity, soil

respiration

Possible Status of Carbon Cycle in AR5 AOGCMs

Fossil FuelCO2 Emissions

Online

OfflineCLIMATE

OCEAN LAND

CO2

Greenhouse Effect

Land-useChange

Iron DustDeposition

N and O3Deposition

Climate Change effects onSolubility of CO2

Vertical MixingCirculation

& Ocean Ecosystem Structure

Climate Change effects on plant productivity, soil

respiration & Fires

Riverine CO2 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 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, N-deposition, near surface O3 concentration, dust inputs to the ocean.

THE END !

LOOP The new IPSL C-C model

Net total carbon flux Fluxland + Fluxocean

[ ] ( )12.2

2 oceanland FluxFluxEMI

dt

COd −−=

Terrestrial biosphereORCHIDEE

(STOMATE activated)

MarineBiochemistry

PISCES

OceanORCA-LIM

OPA 8.2

AtmosphereLMDZ4

EMI = external forcing[Marland et al, 2005

Houghton, 2002]

Ocean flux GtC/mthLand flux GtC/mth

CouplerOASIS 2.4

ClimateAtmospheric[CO2]

CO2 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 : 1961-1990

First Order Validation• “IPCC” carbon budget (GtC/yr)

LOOP IPCC LOOP IPCC

2.7 3.3 3.3 3.2

2.0 1.8±0.8 2.0 2.2±0.4

2.8 1.6

(-0.3 to 4)

3.3 2.6

(1 to 4.3)

1980’s 1990’s

Atm

Ocean

Land

Cadule et al., in prep

Atmospheric carbon variation

Land use fossil fuel land

ocean

Second Order Validation

• Atmospheric CO2 – Offline transport over 1979-2003

Cadule et al., in prep

Cadule et al., in prep

• Seasonal cycle

• Long term trend

climate response to CO2

Friedlingstein et al., 2006IPSL-CM2_C IPSL_CM4_LOOP

C-cycle response to CO2

OCEAN

LAND

Friedlingstein et al., 2006IPSL-CM2_C IPSL_CM4_LOOP

C-cycle response to climate

OCEAN

LAND

Friedlingstein et al., 2006IPSL-CM2_C IPSL_CM4_LOOP

Why such a large uncertainty in the Land Carbon

Response to Climate ?

IPSL-CM2_C IPSL_CM4_LOOP HadCM3C

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)

PO43-

Diatoms

MicroZoo

P.O.M

D.O.M

Si

IronNano-phyto

Meso Zoo

NO3-

NH4+

Small Ones Big Ones

Aumont et al., 2003Krinner et al., 2005

The land response - IPSL

Extension of the growing

season

Increase insoil aridity

Berthelot et al., 2002

CO2 Temp

NPP Decomp

+Climate Sensitivity

Sensitivity of Soil respiration to Temp

+-

AnthropogenicEmissions

Avail N

N mineralisation

++

AnthropogenicN deposition

_

Climate

Land

Chemistry

Climate-Land Feedbacks and Forcings

The Key missing negative feedback – increased N availability in a warmer world ?

CO2 Temp

NPP

+Climate Sensitivity

-

AnthropogenicEmissions

Climate

Land

Climate-Land Feedbacks and Forcings

Anthropogenic Emissions

Trop O3

-

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?

CO2 TempPrecip

Veg Cover

NPP Decomp

+Climate Sensitivity

Sensitivity of Soil respiration to Temp

++

+

_+ -CO2

Fertilisation

AnthropogenicEmissions

Climate-Land Feedbacks and Forcings

Surface EnergyBalance

++

Regional Climate Change

?

+

+

Land-useChange

Avail N

N mineralisation

++

AnthropogenicN deposition

Anthropogenic Emissions

Trop O3

-

_

Climate

Land

Chemistry

CO2 TempPrecip

Veg Cover

NPP Decomp

+

AnthropogenicNOx emissions

Increased Tropospheric O3 and Vegetation – Feedbacks from biogenic emissions

Trop O3 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