A GCM study on emission pathways to climate stabilization

1
A GCM study on emission pathways to climate
stabilization

• E. Roeckner, M. Giorgetta, T. Crüger, M. Esch,
  and J. Pongratz
• Max Planck Institute for Meteorology, Hamburg
• EU FP6 Integrated Project ENSEMBLES
  RT2A Climate change scenarios

2
Motivation

• United Nations Framework on Climate Change
• Article 2 ... to achieve stabilization of
  greenhouse gas concentrations in the atmosphere
  that would prevent dangerous anthropogenic
  interference with the climate system
• European ENSEMBLES project
• Agressive mitigation scenario E1 (Van Vuuren et
  al., 2007).
• Stabilize the anthropogenic radiative forcing to
  that equivalent to a CO2 concentration at around
  450 ppm during the 22nd century.
• To match the European Union 2C target.
• Questions
• What anthropogenic CO2 emissions are allowable
  for a given pathway of atmosperic CO2
  concentration?
• Where are is carbon of anthrop. sources stored in
  the system?
• What is the resulting climate change for a given
  CO2 pathway?
• What is the role of feedbacks between climate
  change and carbon cycle, e.g. for climate change
  or for feasible carbon emissions?

3
Methodology

• Method proposed for the future CMIP5 experiments,
  i.e. experiments for the 5th IPCC assessment of
  climate change (Hibbard et al., 2007)

4
Carbon cycle climate model
Anthropogenic forcing
Natural forcing
CH4, N2O, CFC conc.
Volcanic aerosol
CO2 emissions/conc.
Solar variations
Land use change
X
X
AtmosphereECHAM5 T31/L194
Momentum, Energy, H2O, CO2
OceanMPIOM 3L40 HAMOCC
LandHD JSBACH
Carbon cycle climate model
5
Experiments
Control18601000 yr
Historic1860-2005
SRES A1B
Ensembles of 5 realizations
E1 450 ppm
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E1 scenario (Van Vuuren et al., 2007)

• Equivalent CO2 concentration stabilizes at 450
  ppm
• Sulfate aerosol decreases quickly? near
  pre-industrial levels at 2100? less cooling in
  early 21st cent.
• Land use change consistent with assumptions in
  the IMAGE model

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Pre-industrial control simulation
Global annual mean surface air temperature (C)
and CO2 concentration (ppmv) Pre-industrial
conditions, thick lines 11-year running means
Surface air temperature(left scale,
C) Atmospheric CO2 concentration (right
scale, ppmv)

• Climate of undisturbed system stable over 1000
  years,no systematic drift in surface air
  temperature or CO2 concentration

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Global annual mean surface air temperature
Global annual mean surface air temperature
anomalies w.r.t. 1860-1880 (C)5 year running
means
simulated (5 realizations) observed (Brohan et
al., 2006)

• Simulated surface air temperature less variable
  than observed.
• Natural sources of variability like volcanic
  forcing or the 11 year solar cycle are excluded
  from the experiment.
• Simulated warming in 2005 slightly underestimated.

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Global annual mean CO2 emissions 1860 to 2005
CO2 emissions from fossil fuel combustion and
cement production (GtC/yr)Global annual mean
11-year running means
Implied emissions from simulations Observed
(Marland et al., 2006)

• Model allows for relatively higher emissions
  before 1930.
• Minimum in 1940s
• Similar emissions in 2000.

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Carbon release and uptake by land, 1860 2005
Carbon release from land use emissions and uptake
by land (GtC/yr), Positive land-to-atmosphere
flux Model 11-year running means,
Observed land-use emissions (Houghton,
2008) Simulated land-use emissions Simulated
net land uptake Simulated land uptake

• Simulated land use emissions smaller than
  observed, especially in 1960-2000
• Simulated land uptake sationary from 1920 to 1960.

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Simulated carbon uptake 1860 to 2005
Simulated carbon uptake (GtC/yr)11-year running
means
Simulated ocean uptake Simulated land uptake(as
on previous figure)

• Ocean carbon uptake very similar to land uptake
• Reduced uptake in 1950s

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Global surface air temperature anomalies
Global annual mean surface air temperature
anomalies w.r.t. 1860-1880 (C)
Historic 1950-2000 A1B 2001 2100 E1 2001
2100

• Initially stronger warming in E1 than in A1B
  because of faster reduction in sulfate aerosol
  loading, hence less cooling.
• Reduce warming in E1 after 2040
• Warming in 2100 4C in A1B and 2C in E1
• Climate carbon cycle feedback will differ after
  2050

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Implied CO2 emissions 1950 to 2100
Implied CO2 emissions with and without climate
carbon cycle feedback (GtC/yr)
Historic 1950 2000 A1B 2001 2100 E1 2001
2100

• Implied CO2 emissions of E1 scenario drop sharply
  after 2015 (unlike emissions for A1B scenario)
• Implied emissions are reduced by feedback of
  climate warming on the carbon cycleIn 2100 -2
  GtC/yr in E1 and -4.5 GtC/yr in A1B
• Implied emissions of E1 close to 0 in 2100 (still
  positive).

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Accumulated C emissions Coupled Uncoupled
Reduction in accumulated C emissions by climate
carbon cycle coupling (GtC)(11-year running
means)
Historic 1860 2000 A1B 2001 2100 E1 2001
2100

• Climate carbon cycle feedback reduces implied
  carbon emissions until 2100 by 180 (E1) to 280
  (A1B) GtC.

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Conclusions

• The E1 450ppm CO2(equiv) scenario fulfills the EU
  climate policy goal of limiting the temperature
  increase to a maximum of 2C.
• In the 2050s (2090s) the allowable CO2 emissions
  for E1 are about 65 (17) of those of the
  1990s.
• As in previous studies, a positive climate-carbon
  cycle feedback is simulated.
• Climate warming reduces the ability of both land
  and ocean to take up anthropogenic carbon.
• Climate carbon cycle feedback reduces the
  allowable emissions by about 2 GtC/yr in the E1
  scenario, accumulating to 170 GtC until 2100.
• Uncertainty to be estimated from multi-model
  ensemble used in ENSEMBLES project.

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• END

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Carbon uptake by ocean and land 1960-2000
Fraction of simulated fossil fuel emissions ()
Remaining in the atmosphere Absorbed by
ocean Aborbed by land

• 50 of simulated fossil fuel emissons remain in
  the atmosphere
• In 2000 simulated ocean uptake 2 x simulated
  land uptake

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Fig.12
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Fig.13
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Surface C uptake Coupled uncoupled

• Regions with negative differences take up less
  carbon under global warming conditions and
  contribute to a positive feedback between climate
  and carbon cycle.

Stabilization scenario E1 (2080 to 2100)
IPCC SRES scenario A1B (2080 to 2100)
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Table 1
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Table 2