Presumed Parameters - Climate Change: Identification and Projections - page 59

Given that , it would be necessary to establish the joint S G = S

1 /

α

1

probability of S 1 and

in order to obtain the range of uncertainty of the
quotient. But since the relative uncertainties relating to S 1
(

α

1

are much greater than those for (

± 10%

),

1.4427 °< < CS 8.6562 ° C )

α

1 1

it allows us to simply divide the limits of S 1 by : α

1

− 2 − 2

0.27 ° CWm / < S < 1.62 ° CWm /

G

Reversing and reordering gives the limits on : λ

G

0.62 Wm

− 2

/ °< < C λ 3.7 Wm

− 2

/ ° C

G

We are particularly interested in the upper limit of S G . By referring to the
initial statement on climate sensitivity, we can write:

( likelihood 90 - 100 %).

S <° 1. 6 2 C / Wm −

2

G

5.5. Sensitivity to irradiance S 2

− 2

net , the forcing coefficient for solar

Since irradiance is evaluated in

Wm

activity , restricted to the energy factor only, is by definition equal to 1.

α

2

λ −

1

Given that , the range for sensitivity to net irradiance is therefore S = α

2 G 2

identical to that of :

S

G

0.27 ° CWm /

− 2

< S < 1.62 ° CWm /

− 2

2

We are particularly interested in the upper limit and we can therefore
state, in compliance with IPCC terminology:

It is very unlikely that sensitivity to net irradiance is higher than
2 −

. 1 62 ° C / Wm

The IPCC did not explicitly make this assertion, but it can be inferred
from the ranges indicated for S 1 and

, reviewed, corrected and confirmed
by successive IPCC reports, as well as the ratios of

α

1

− 1

, which
themselves arise from the fundamental concepts of the IPCC: radiative
forcings, energy balance and global climate feedback.

S = λ α

i G i