Global Change and the Carbon Cycle

Michael Raupach1,3,4, Pep Canadell2 and Damian Barrett2,1,4

1CSIRO Earth Observation Centre, Canberra, Australia2CSIRO Plant Industry, Canberra, Australia

3Global Carbon Project (IGBP-IHDP-WCRP-Diversitas)4CRC for Greenhouse Accounting

Thanks: Peter Briggs, Helen Cleugh, Mac Kirby, Rachel Law, Ray Leuning, Graeme Pearman,Peter Rayner, Steve Roxburgh, Will Steffen, Cathy Trudinger, YingPing Wang

and to: AGO (Australia), NIES (Japan), and CRC for Greenhouse Accounting

APN Symposium, Canberra, 23 March 2004

Outline

Carbon in the earth system

Global carbon budget

An Australian perspective

Inertia

Greenhouse mitigation

Vulnerability

Carbon in the earth system

1. Carbon is the building block of life

Forms large, reactive molecules which store and propagate information, enabling the evolutionary emergence of complex, self-organising systems

The carbon cycle is the crossroads for all major biogeochemical cycles

2. Carbon is a key to sustainable natural resource management

3. Managing the carbon cycle is key to greenhouse gas mitigation

Atmospheric CO2: past and future

Last 420,000 years:Vostok ice core record(blue)

Last 100 years:Contemporary record(red)

Next 100 years: IPCC BAU scenario(red)

Interactions between the carbon cycle and the climate system

C cycle

Aerosols

IPCC Third Assessment (2001)

Global carbon budget

What goes in:Human contributions to enhancedatmospheric CO2

What stays or comes out:Fate of enhancedatmospheric CO2

0

1

2

3

4

5

6

7

8

9

1980-89 1990-99G

tC p

er y

ear

Industrial emissions

Land Use Emissions

0

1

2

3

4

5

6

7

8

9

1980-89 1990-99

GtC

per

yea

r Land Sink

Ocean Sink

Atmospheric Accumulation

Data from IPCC Third Assessment (2001)

Global carbon budget 1980-1999Fluxes in GtC/year (summary from Sabine et al. 2004, SCOPE-GCP)

1980s 1990s

Atmospheric C accumulation 3.3 0.1 3.2 0.2 IPCC 2001

= Emissions (fossil, cement) 5.4 0.3 6.4 0.6 IPCC 2001

+ Net ocean-air flux -1.9 0.5 -1.7 0.5 IPCC 2001

-1.8 0.8 -1.9 0.7 le Quere et al 2003

+ Net land-air flux -0.2 0.7 -1.4 0.7 IPCC 2001

-0.3 0.9 -1.2 0.8 le Quere et al 2003

Net land-air flux -0.3 0.9 -1.2 0.8= Land use change 2.0 (0.9 to 2.8) 2.2 (1.4 to 3.0) Houghton 2003

+ Residual terrestrial sink -2.3 (-4.0 to -0.3) -3.4 (-5.0 to -1.8)

= Land use change 0.6 (0.3 to 0.8) 0.9 (0.5 to 1.4) de Fries et al 2002

+ Residual terrestrial sink -0.9 (-3.0 to 0) -2.1 (-3.4 to -0.9)

Global C budget from atmospheric signals (CO2, 13C, O2)

Ocean O2 flux correction

Remote sensing

National data

Attribution of net land-air flux

SCOPE-GCP Rapid Assessment of the Carbon Cycle

Field CB, Raupach MR (eds.) (2004) The Global Carbon Cycle: Integrating Humans, Climate and the Natural World. Island Press, Washington D.C. 526 pp.

A joint initiative of

• Scientific Committee On Problems in the Environment (SCOPE)

• The Global Carbon Project (IGBP-IHDP-WCRP-Diversitas)

Interannual variability in the global C cycle

-3

-1

1

3

5

7

1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000

PgC

/yr

FOSSIL RELEASE

ATMOS. ACCUMULATION

OCEAN UPTAKE (Le Quere)

IMPLIED TERRESTRIAL UPTAKE(dd13/dt)/-0.04 + 1.3, 0.7 yr lead?

O2/N2

Roger Francey, CSIRO Atmospheric Research

The current carbon cycleSabine et al (2004, SCOPE-GCP)

Global carbon budget: conclusions

Main revision to IPCC Third Assessment (2001) is possible downward revision of C flux from land use change (from ~2 to ~1 PgC/y) from remote sensing evidence

This reduces magnitude of residual terrestrial sink (around −3 to −2 PgC/y)

Atmospheric accumulation has high interannual variability (more than ±2 PgC/y around a current mean of 3.2 PgC/y)

Most of this variability is attributable to the net land-air flux

Australian NPP, NEP and NBP

Fire, Agriculture, Nitrogen

---------------------------------------------------------

Definitions:

• Gross Primary Production:GPP = Photosynthetic assimilation

• Net Primary Production:NPP = GPP − Autotrophic

Respiration

• Net Ecosystem Production:NEP = NPP − Heterotrophic

Respiration

• Net Biome Production:NBP = NEP − Disturbance Emission

(Fire)

An Australian perspective

GPP=1

RAutoRHetDist

NPP~0.5

NEP~0.1

Assim

NBP~0

AVHRR-NDVI anomaly 1981-2003

Current version (Oct 2003) uses EOC "B-PAL" archive of AVHRR data

5 km, 8-11 day composites

Still to incorporate:

• Atmos correction

• BRDF correction

• 1-km data

Peter Briggs, Edward KingJenny Lovell, Susan Campbell, Michael Raupach, Michael ScmidtSonja Nikolova, Dean Graetz, Tim Mc Vicar

Year

1980 1985 1990 1995 2000

Ne

t E

cosy

ste

m P

rod

uct

ion

(T

g C y

r-1)

-100

0

100

200

300

400

Ne

t P

rim

ary

Pro

du

ctio

n (

Tg C

yr-

1 )

200

400

600

800

1000

Mean annual NPP and NEP for Australia

Xu and Barrett (2004) unpublished

Large interannual variability Mean annual NPP = 740 TgC yr-1 (range 470 – 1032) Mean annual NEP = 0.31 TgC yr-1 (range -81 to 118) NEP calculated without fire, so actually an estimate of NBP

Comparing predicted Australian NEP and NBP with aircraft CO2 measurements off the east coast

CO2 and NEP are in antiphase NBP has higher amplitude than NEP Fire acts as an alternative oxidation pathway

year1994 1996 1998 2000

[CO

2] g

row

th r

ate

(pp

m y

r-1)

0

1

2

3

Ne

t C

arb

on E

xchange

(T

g C m

th-1

)

-20

-10

0

10

20Aircraft [CO2] over western Pacific and Australia (Matsueda et al 2002)

NEP = GPP – Ra – Rh

NBP = GPP – Ra –Rh – Fire emissions

Xu and Barrett (2004) submitted Global Change Biology

Global NEPgC/m2/y

Model-data synthesis

Models: terrestrial biosphere

(BETHY) atmospheric

transport model

Data: remote sensing atmospheric CO2

NEE

uncertaintyPeter Rayner, CSIRO Atmospheric Research

CenW

Miami

Berry

Miami Oz

Vast

Grasp

dLdP

Olson

RFBN

Century

BiosEquil

SDGVM

HybridTriffid

VECODE

LPJ

IBIS

Roxburgh et al 2004

Estimates of Australian NPP

Global average

NPP

Evidence from: * C inventories* CO2 (Cape Grim)

Effect of agriculture on Australian Net Primary Production

Australian NPP without agricultural inputs of nutrients and water

Ratio: (NPP with agric) / (NPP without agric)

Largest local NPP changes: around x 2 Continental change in C cycle: 1.07 Continental change in N cycle: around 2Raupach, M.R., Kirby, J.M., Barrett, D.J., Briggs, P.R., Lu, H.

and Zhang, L. (2002). Balances of water, carbon, nitrogen and phosphorus in Australian landscapes: Bios Release 2.04. CD-ROM (19 April 2002). CSIRO Land and Water.

Without agriculture

16

712

8

9

10

1

4

11

2

3

5

N f

lux

(kgN

/m2/

yr)

Figure 25: Comparison of spatially averaged flux terms in the steady-state mineral N budget for 12 drainage divisions with and without European-style agriculture. N flux terms are fertilisation (+), atmospheric deposition (+), fixation (+), gaseous loss ( ), leaching ( ), and disturbance ( ).

North-East Coast (1)

Fert Dep Fix GasLoss Leach Disturb

-20

-10

0

10

20

30

40

-20

-10

0

10

20

30

Flu

x (k

g N h

a-1 y

-1)

-20

-10

0

10

20

30

-20

-10

0

10

20

30

-20

-10

0

10

20

30

Fert Dep Fix GasLoss Leach Disturb-30

-20

-10

0

10

20

30

Fert Dep Fix GasLoss Leach Disturb

-20

-10

0

10

20

30

40

-20

-10

0

10

20

30

-20

-10

0

10

20

30

-20

-10

0

10

20

30

-20

-10

0

10

20

30

Fert Dep Fix GasLoss Leach Disturb-30

-20

-10

0

10

20

30

South-East Coast (2)

Tasmania (3)

Murray-Darling (4)

South Australian Gulf (5)

South-West Coast (6)

Indian Ocean (7)

Timor Sea (8)

Gulf of Carpentaria (9)

Lake Eyre (10)

Bulloo-Bancannia (11)

Western Plateau (12)

With Agriculture

No Agriculture

With agriculture

Fert Dep Fix Gas Leach Disturb

Australian nitrogen balance and the effect of agriculture

Raupach, M.R., Kirby, J.M., Barrett, D.J., Briggs, P.R., Lu, H. and Zhang, L. (2002). Balances of water, carbon, nitrogen and phosphorus in Australian landscapes: Bios Release 2.04. CD-ROM (19 April 2002). CSIRO Land and Water.

Comparing fluxes in the Australian and global C cycles

Averagia: a land mass of the same area as Australia, but with the same biogeochemical fluxes as the global terrestrial average--------------------------------------------------------------------------------------------------------------------Flux Australia Averagia

Mean Range Mean--------------------------------------------------------------------------------------------------------------------NPP (MtC/y) −780 (−1032 to −470) −2850 (by area)

NBP (MtC/y) −0.31 (−118 to +81) −60 (by area)

NEP (MtC/y) ? (?) −105 (by area)

Fire emission (MtC/y) + 107 (+77 to +142) + 45 (by area)

Fossil-fuel C emission + 103 (small) + 21 (by population)

Rainfall (mm) 465 770

Australian C fluxes from Xu and Barrett (2004, unpublished); global values from de SCOPE-GCP 2004 (de Fries LUC)

Relative to Averagia, Australia has:• about 1/3 the NPP, but 2/3 the rainfall• negligible NBP• twice the fire emissions• over 4 times the per capita fossil fuel emission

Inertia in the coupled carbon-climate-human system

Field, Raupach and Victoria (2004, SCOPE-GCP)

Glo

bal tem

peratu

re chan

ge

CO

2 E

mis

sio

ns

(Pg

Cyr

-1)

2000 2100 2200 2300

CO

2 C

on

cen

trat

ion

(p

pm

)Inertia in the coupled carbon-climate-human system

650

650

650

IPCC Third Assessment (2001)

Inertia: conclusions

Time scales (years) for system components:

• Land-air C exchange 10 to 100

• Ocean-air C exchange 100 to 1000

• Economic development 20 to 200

• Technology to decarbonise energy 10 to 100

• Development of political will to act globally ?

• Development of institutions ?

Stabilisation (of CO2 level or temperature) requires anthropogenic C emissions to fall eventually to near zero: this will take over a century

Temperature will continue to rise slowly (few tenths of degree per century) long after CO2 stabilisation, because of long-time-scale ocean inertia

Greenhouse mitigation

Carbon gap

Potential and actual mitigation

Ancillary effects

The carbon gapEdmonds et al. (2004, SCOPE-GCP)

The carbon gap is the difference between presently projected C emissions and the emission trajectory required for stabilisation

CO

2 E

mis

sio

ns

(Pg

Cyr

-1) Effect of

technological development

Carbon gap

Matching C emissions to CO2 stabilisation pathways

• Case 1 = "Business as usual" (IS92A)• Case 2 = Case 1 with major CO2 sequestration and disposal• Case 3 = Case 2 with major energy conservation and use of non-fossil-fuel energy

2000 2020 2040 2060 2080 2100Dire

ctly

hum

an-in

duce

d C

O2

emis

sion

[GtC

y-1

]

0

5

10

15

20

25 Stabilisation trajectories1000650450

IS92a scenario CO2 target (ppm)Case123

SCOPE-GCP (2004)

Mitigation Potential = Carbon Sequestered or GHG emissions

avoided, as a fraction of technical potential mitigation

Cos

t of

car

bon

($/t

Ceq

)

Technical Potential

Baseline Potential

Environmental factors

Social and institutional factors

Economic factors

Sustainably Achievable Potential

0 1

Uptake proportion at given cost

Mitigation Potential

Effects of economic, environmental and social-institutional factors on the mitigation potential of a carbon management strategy

SCOPE-GCP (2004)

Ancillary effects: economic, environmental and socio-cultural impacts of mitigation strategies

SCOPE-GCP (2004)

Greenhouse mitigation: conclusions

Even business-as-usual projections for fossil fuel emissions include very substantial technical innovation (efficiency, reductions in fossil fuel share of energy, …)

A mix of all effective strategies is required:

• Conservation

• Non-fossil-fuel energy sources

• Land-based options (reduction in land use change, biofuels)

• Geological disposal

Achievable mitigation potential is often much less (10 to 20-% of) technical potential

Uptake of a given strategy is (presently) largely determined by ancillary benefits and costs, not greenhouse mitigation outcome

Atmospheric CO2

Warming

Fossil Fuel burning

(+)

CO2 emissions

(+)

(+)Vulnerability of

biospheric C pools

(+)

(+)

Vulnerability in the carbon cycle Vulnerability of a C pool is the risk of accelerated carbon release from that pool as

climate change occurs because of a positive feedback [d(flux)/d(climate) > 0]

Vulnerable carbon pools in the 21st century

Gruber et al. (2004, SCOPE-GCP)

Carbon in terrestrial vegetation: 650 Pg

Vulnerability of terrestrial C sink:saturation level of terrestrial C sink depends on mechanism

The global terrestrial biospheric carbon sink …

Sin

k st

reng

thwill increase and saturate in the future if the dominant mechanism is CO2 and N fertilisation (CO2 saturation around 600 ppm)

will decrease in the near future if the dominant mechanism is regrowth and fire suppression

Sin

k st

reng

th

Climate warms as predicted (eg Cox et al 2000)

Climate warms more rapidly than predicted

2% 98%Sink attribution in Eastern US for 1980 to1999 (Caspersen et al. 2000)

Vulnerability of terrestrial C sink: the fire bomb

Terrestrial C sinks: for how long and at what ultimate cost?

Swetnam et al.

Canberra, 18 January 2003

www.sentinel.csiro.au

Vulnerability in the C cycle: conclusions

Stores of ~400 PgC are at moderate risk over the next century. Release of these stores would add ~200 ppm to atmospheric CO2 concentrations.

Vulnerability increases as climate change occurs.

If CO2 fertilisation is the main mechanism for the global terrestrial sink, the sink will last for 50 to 100 years

BUT

If the global terrestrial sink is largely due to forest regrowth and fire suppression then terrestrial sinks will disappear within a few decades.

Summary

Carbon in the earth system:

• The building block of life

• A key to sustainable natural resource management

• Key to greenhouse gas mitigation

Carbon cycle science is rapidly improving our knowledge of

• The spatial and temporal patterns (dynamics) in the C cycle

• Processes, feedbacks and interactions

• The connections between biophysical C cycle and human activities.

Hilary Talbot