The War of the Graphs - Climate Change: Identification and Projections - page 33

The war of the graphs is not limited solely to temperature reconstructions.
It is also played out in the field of solar irradiance reconstructions. It is
known that the IPCC recognizes the contribution of solar activity, but only in
the reduced form of net TSI. This goes some way to explaining the medieval
warm period, without contributing too heavily towards the 20 th Century
warming, which would harm the CO 2 -centred hypothesis if its contribution
were greater. With this in mind, anything that can emphasize medieval solar
activity and reduce its significance in the 20 th Century is very
welcome. Therefore, Delaygue and Bard [DEL 10] note that “[their]
results suggest that the recent solar activity is not exceptionally high for the
last millennium”. Indeed, we discover (Figure 2.11) that between 740 and
750 a local maximum briefly reached 20 th Century values 9 . More overtly, in
an EBM simulation study, T. Crowley [CRO 00] announced that he had
completed a set of two reconstructions of irradiances by “an estimation
of 14 C using fluctuations in 10 Be. The justification of the inclusion of this
latter index is that none of the first two datasets leads to a medieval solar
maximum which is comparable to the current day”. Justification or merely
“cherry picking”?
It is also known that the IPCC systematically refers to the date 1750 as
representative of the pre-industrial era. By chance (?), this date is right in the
middle of a local maximum reading of solar activity, between the minimums
of Maunder (1700) and Dalton (1800). The variation shown by
radiative forcing compared to the modern era is thereby significantly reduced.
The effect is emphasized further by adjusting the calculation using the closest
cyclical minimums to 1750 and 2011, claiming that these minimums are the
most “stable”. Thus, the IPCC can produce a variation of radiative forcing
since the pre-industrial era of between 0 and 0.1 Wm −2 , reduced further by the
AR4 report, where the figure was located between 0 and 0.3 Wm -2 . A glance at
the Shapiro reconstruction (Figure 2.10) therefore leaves the reader puzzled,
with min/max variations reaching 6 Wm -2 . Given the factor 0.7/4 to reach net
irradiance, the result is variations in solar radiative forcing of over 1 Wm -2 .
This distortion leads the IPCC to place question marks over this reconstruction
(AR5, sections 2.2.1.2, 2.2.1.3 and 5.3.5.3 10 ).
9 ER background correction also has a contribution to make on this issue.
10 “Simulations with an EMIC using a much stronger solar forcing (0.44% TSI increase from
LMM to present, Shapiro et al ., 2011) appear to be incompatible with most temperature
reconstructions (Feulner, 2011)”.