Global Change and the Carbon Cycle

1
Global Change and the Carbon Cycle
Michael Raupach1,3,4, Pep Canadell2 and Damian
Barrett2,1,4 1CSIRO Earth Observation Centre,
Canberra, Australia 2CSIRO 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 Wangand
to AGO (Australia), NIES (Japan), and CRC for
Greenhouse Accounting APN Symposium, Canberra,
23 March 2004
2
Outline

• Carbon in the earth system
• Global carbon budget
• An Australian perspective
• Inertia
• Greenhouse mitigation
• Vulnerability

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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

4
Atmospheric CO2 past and future

• Last 420,000 yearsVostok ice core record(blue)
• Last 100 yearsContemporary record(red)
• Next 100 years IPCC BAU scenario(red)

5
Interactions between the carbon cycle and the
climate system
C cycle
Aerosols
IPCC Third Assessment (2001)
6
Global carbon budget

• What goes inHuman contributions to
  enhancedatmospheric CO2
• What stays or comes outFate of
  enhancedatmospheric CO2

Data from IPCC Third Assessment (2001)
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Global carbon budget 1980-1999Fluxes in GtC/year
(summary from Sabine et al. 2004, SCOPE-GCP)

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

• 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

Ocean O2 flux correction

• Attribution of net land-air flux

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)
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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-Diversi
  tas)

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Interannual variability in the global C cycle
Roger Francey, CSIRO Atmospheric Research
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The current carbon cycle Sabine et al (2004,
SCOPE-GCP)
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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

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An Australian perspective

• 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)

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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

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Mean annual NPP and NEP for Australia

• 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

Xu and Barrett (2004) unpublished
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Comparing predicted Australian NEP and NBP with
aircraft CO2 measurements off the east coast
Aircraft CO2 over western Pacific and Australia
(Matsueda et al 2002)
NEP GPP Ra Rh
NBP GPP Ra Rh Fire emissions

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

Xu and Barrett (2004) submitted Global Change
Biology
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Global NEPgC/m2/y

• Model-data synthesis
• Models
• terrestrial biosphere (BETHY)
• atmospheric transport model
• Data
• remote sensing
• atmospheric CO2

NEE
uncertainty
Peter Rayner, CSIRO Atmospheric Research
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Estimates of Australian NPP
Global average NPP
Evidence from C inventories CO2 (Cape Grim)
Roxburgh et al 2004
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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 2

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.
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Australian nitrogen balance and the effect of
agriculture

• Without agriculture

With agriculture
N flux (kgN/m2/yr)
Fert Dep Fix Gas Leach Disturb
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.
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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

• 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

Australian C fluxes from Xu and Barrett (2004,
unpublished) global values from de SCOPE-GCP
2004 (de Fries LUC)
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Inertia in the coupled carbon-climate-human system
Field, Raupach and Victoria (2004, SCOPE-GCP)
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Inertia in the coupled carbon-climate-human system
CO2 Emissions (PgCyr-1)
650
Global temperature change
650
CO2 Concentration (ppm)
650
IPCC Third Assessment (2001)
2000 2100 2200
2300

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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

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Greenhouse mitigation

• Carbon gap
• Potential and actual mitigation
• Ancillary effects

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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

Effect of technological development
CO2 Emissions (PgCyr-1)
Carbon gap
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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

SCOPE-GCP (2004)
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Mitigation Potential

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

SCOPE-GCP (2004)
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Ancillary effects economic, environmental and
socio-cultural impacts of mitigation
strategies
SCOPE-GCP (2004)
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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

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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) gt 0

Fossil Fuel burning
()
Atmospheric CO2
()
Warming
()
()
Vulnerability of biospheric C pools
()
CO2 emissions
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Vulnerable carbon pools in the 21st century
Carbon in terrestrial vegetation 650 Pg
Gruber et al. (2004, SCOPE-GCP)
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Vulnerability of terrestrial C sinksaturation
level of terrestrial C sink depends on mechanism

• The global terrestrial biospheric carbon sink

will 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
Climate warms more rapidly than predicted
Climate warms as predicted (eg Cox et al 2000)
2 98 Sink attribution in Eastern US
for 1980 to1999 (Caspersen et al. 2000)
33
Vulnerability of terrestrial C sink the fire
bomb

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

Swetnam et al.
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Canberra, 18 January 2003
35
www.sentinel.csiro.au
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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 yearsBUTIf the global
  terrestrial sink is largely due to forest
  regrowth and fire suppression then terrestrial
  sinks will disappear within a few decades.

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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.

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• Hilary Talbot