Overall Results - Climate Change: Identification and Projections - page 95

Above all, it can be noted that the estimated sensitivities to solar
irradiance are up to ten or twenty times higher than the maximum values
assumed by the IPCC

− 2

°C/Wm For instance, let us examine the range
of estimates which result from Ljungqvist (Figure 8.2(b)). The 5 th and 6 th
segments result from the two TSI proxies spliced with lean0 , and the 7 th and
8 th with timv15 . The two pairs estimated are in a ratio of around 1:3, and the
ranges are mutually incompatible. The existence and the level of the ER
background correction are therefore in question, and we have no
recommendation to make in this regard.

( . 62 ).

Finally, two points can be drawn out.
- Firstly, of the 16 combinations, only the final two, both based on Jones
and Mann, and only under the condition of ER background correction,
indicate a sensitivity to solar activity which is compatible with a sensitivity
reduced to the energy factor only;
- Secondly, the selection of the irradiance reconstruction only has a small
effect on the estimate of climate sensitivity S clim , as well as on the real
contribution of solar activity to recent warming. Indeed, Figure 8.3 shows
the contributions related to the two Ljungqvist combinations with lean0 and
timv15 . Despite the sensitivities of S irr being in a ratio of 3:1, the orders of
magnitude of the contributions are the same, thanks to amplitudes of
irradiance reconstructions being in the inverse ratio.

0.8

Observations
Contr ibutions TSI

0.6

0.4

0.2

0

-0.2

-0.4

-0.6

-0.8

800 1000 1200 1400 1600 1800 2000

Figure 8.3. Sensitivity of contributions of solar activity
to irradiance reconstructions