Two Roots of IPCC’s Errors

by Kyoji Kimoto (e-mail kyoji@mirane.co.jp)

1. Model studies by Manabe et al.

Climate sensitivity is 0.5K from the global energy budget of the earth, and it is 0.8K from the data analysis of Pinatubo eruption. However, IPCC claims that most probable value is 3K with the range of 2.0-4.5K. The following two roots exist for IPCC’s overestimation of climate sensitivity:

(1) Cess’s mathematical error in 1976 being followed by many researchers (see the previous post IPCC’s overestimation of climate sensitivity.)

(2) Overestimation by 1D RCM study in [Manabe et al. 1964/67](see Figure1)

Their results are compared with observational data as follows:

a. Lapse rate: fixed lapse rate of 6.5K/km (moist adiabatic lapse rate is more adequate-see Figure2)

b. Planck response: 1.3K (0.54K is more likely-see the previous post)

c. Climate sensitivity: 2.4K with water vapor feedback (0.5K is more likely-see the previous post)

d. CO2 contribution in the greenhouse effect of 33K: over 10K (3.3-6.7K is more likely -see [Newell et al., 1979;Barrett,2005])

2. Overestimation due to a fixed lapse rate of 6.5K/km adopted by Manabe

As shown in Figure 2, Manabe et al. adopted a fixed lapse rate of 6.5K/km for a convective adjustment in 1D radiative-convective model (RCM) study [Manabe et al.,1964/67]. In this scheme, the surface temperature rise (dTs) is equal to the temperature rise of tropopause (dTt) due to CO2 doubling as shown in the upper panel of Figure 3.

In contrast, Ramanathan et al. pointed out that moist adiabatic lapse rate is more adequate parameterization for lower troposphere [Ramanathan et al., 1978]. In this system, dTs is around 50% of dTt as shown in the lower panel of Figure 3 [Hummel et al., 1981; Lindzen et al., 2000]. When moist adiabatic lapse rate is applied to Manabe et al.’s data, the following results will be obtained with 50% decrease due to lapse rate scheme change:

Planck response:    Manabe 1.3K  after amendment 0.65K

Climate sensitivity:  Manabe 2.4K  after amendment 1.2K

These results are fairly close to the Group C of Table 2 in the previous post IPCC’s overestimation of climate sensitivity.

Figure1. History of model studies

Figure2. Various lapse rate scheme (adapted from Hummel et al.1981)

Figure3. Influence of lapse rate scheme on dTs

References

Barrett J., 2005: Greenhouse molecules, their spectra and function in the atmosphere. ENERGY & ENVIRONMENT, Vol. 16, 1037-1045

Hummel J.R. et al., 1981: Comparison of radiative-convective models with constant and pressure-dependent lapse rate. Tellus, Vol.33, 254-261

Kerr R.A., 2004: Three Degree of Consensus. SCIENCE Vol.305, 932-934

Lindzen et al, 2000: The Greenhouse Effect (PDF is in his home page)

Manabe S. et al., 1964: Thermal Equilibrium of the Atmosphere with a Convective Adjustment. J. Atmospheric Sciences, Vol.21, 361-385

Manabe S. et al., 1967: Thermal Equilibrium of the Atmosphere with a Given Distribution of Relative Humidity. J. Atmospheric Sciences, Vol.24, 241-259

Manabe S. et al., 1975: The Effects of Doubling the CO2 Concentration on the Climate of a General Circulation Model. J. Atmospheric Sciences, Vol.32, 3-15

Newell R.E. et al., 1979: Questions Concerning the Possible Influence of Anthropogenic CO2 on Atmospheric Temperature. J. Applied Meteorology, Vol.18, 822-825

Ramanathan V. et al., 1978: Climate Modeling Through Radiative-Convective Models. Reviews of Geophysics and Spacephysics, Vol.16,465-489

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