1. CLIMSENS: Constraining total
feedback of the climate system
by observations and models.
Ragnhild Bieltvedt Skeie
Terje Berntsen CICERO and University of Oslo
Gunnar Myhre CICERO
Magne Aldrin Norwegian Computer Center
Marit Holden Norwegian Computer Center

2. Climate sensitivity:
The equilibrium change in the annual mean global surface
temperature following a doubling of the atmospheric CO2
concentration.
IPCC 2007
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3. Constraining the climate
sensitivity
• “Bottom-up” approach. Perturbing the
representations of the climate feedbacks in
GCM models.
• “Observational based” approach. Using
historical observations and simple climate
models
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4. ΔQ = ΔF - λ ΔT
ΔQ: Heat flux in the system
ΔF: Radiative forcing
λ: Climate Feedback Parameter
At equilibrium: ΔQ = 0, λ = ΔF2xCO2 / ΔT2xCO2eq
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5. Detailed RF calculations:
Tropospheric ozone and aerosols ΔF
Emissions
Oslo CTM2 model
RF-calculations
IPCC 2007
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6. A simple climate model:
Energy balance model/Upwelling Diffusion Ocean
ΔQ
Structure of the model
Parametre:
Name Unit Value
Mixed layer depth m 60
2
Vertical heat diffusivity cm /sec 0.634
Polar parameter - 0.4
Vertical velocity, upwelling rate m/yr 4.0
2
Air-sea heat exchange parameter W/(m K) 16.0
2
Oceanic interhemispheric heat exchange coeff. W/(m K) 3.5
2
Atmospheric interhemispheric heat exchange coeff. W/(m K) 0.0
2
Climate sensitivity K/(Wm ) 0.8
Schlesinger et al. (1992)
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7. Observations
• Surface temperature
ΔT
• Ocean heat content
Levitus, GRL 2009
IPCC 2007
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8. Statistical model:
The data:
Surface temperature (3 data set, NH and SH averages).
Ocean heat content
Additative bias/correction for baseline
SOI index, Account for El Nino.
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9. Statistical model
Bayesian approach and a MCMC-algorithm:
1. Apriori distributions for parameters and input data.
2. Update your model with observations.
3. Get posteriori uncertainties for your model parameters
and input data. One of them is the climate sensitivity!
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10. λ
IPCC 2007
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11. What’s new?
• Improved representation of the radiative
forcing history
• Longer time period with observations
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