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CLI MSENS: Con st r a in in g t o t a lf eedback o f t he cl im a te sys temby ob ser va t i ons and m odels.

Ragnh i ld B iel t ved t Sk e ie

Terje Berntsen CICERO and University of OsloGunnar Myhre CICEROMagne Aldrin Norwegian Computer CenterMarit Holden Norwegian Computer Center

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Cl im a t e sen si t i v i t y :The equ i l i b r i um change i n t he annua l m ean g loba l su r facet e m p e ra t u re f o l l o w i n g a d o u b l i n g o f t h e at m o sp h e r i c CO2concen t ra t i on .

IPCC 2007

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Const r a i n i ng t he cl im at e

sens i t i v i t y

Bottom-up approach. Perturbing the

representations of the climate feedbacks inGCM models.

Observational based approach. Using

historical observations and simple climatemodels

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Q = F - T

Q: Heat flux in the system

F: Radiative forcing

: Climate Feedback Parameter

At equilibrium: Q = 0, = F2xCO2/ T2xCO2eq

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Det a i led RF ca lcu la t ion s:Tr oposph er ic ozon e and aer oso ls

Emissions

Oslo CTM2 model

RF-calculations

IPCC 2007

F

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A sim p le cl im at e m odel :Energy balance model/Upwelling Diffusion Ocean

StructureofthemodelParametre:

Schlesinger et al. (1992)

Name Unit Value

Mixed layer depth m 60Vertical heat diffusivity cm /sec 0.634Polar parameter - 0.4Vertical velocity, upwelling rate m/yr 4.0Air-sea heat exchange parameter W/(m

2K) 16.0

Oceanic interhemispheric heat exchange coeff. W/(m K) 3.5Atmospheric interhemispheric heat exchange coeff. W/(m K) 0.0Climate sensitivity K/(Wm ) 0.8

Q

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Observa t i ons

Surface temperature

Ocean heat content

Levitus, GRL 2009

T

IPCC 2007

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St a t i st i ca l m ode l :

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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St a t i st i ca l m ode l

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 parametersand input data. One of them is the climate sensitivity!

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IPCC 2007

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W h at s n ew ?

Improved representation of the radiative

forcing history

Longer time period with observations