Presumed Parameters - Climate Change: Identification and Projections - page 58

5.3. Coefficient of radiative forcing α 1

The AR5, section 8.3.2.1, states: “Using the formula from Table 3 of
Myhre et al . (1998) […], the CO 2 Radiative Forcing from 1750 to 2011 is
1.82 (1.63 to 2.01) Wm -2 . The uncertainty is dominated by the radiative
transfer modelling which is assessed to be 10%”. Curiously, these assertions
are not assigned a level of confidence - that we personally feel should be
positioned at the lowest level (see section 5.8).

Figure 5.1. Taken from Myrhe (1998)

This table (Figure 5.1) confirms that forcing by CO 2 follows a
logarithmic law, and specifies the value of the coefficient of radiative
forcing:

− 2

α = 5 35 Wm

1

For a doubling of CO 2 , by multiplying

α

by log(2), we obtain a radiative

1

− 2

forcing of Wm . This value is taken up in AR3, AR4 and AR5, and has

not changed since 1998.

3

5.4. The climate feedback coefficient λ

G

The climate feedback coefficient affects the denominator of λ

G

expressions . Hence the interest in investigating its inverse: global

sensitivity to radiative forcing :

S = α / λ

i i G

− 1

S

= λ

G