Why it was the European Warm Period
and the Very Little Ice Age

Recently, Eli got tangled in a toodo at Tamino's (where are the bouncers when you need them) with one Leif Svalgaard, who looks at solar insolation for a living. Eli played but a small role in the proceeding. To make the story very short (and indeed it went on more and more and more and almost lead the mild mannered T to close up the comments)

Svalgaard propounds (go read Tamino) that there is no difference in solar insolation between solar cycle minima extending back to the year dot, and the year dot includes our beloved Maunder minima. Eli went and RTF AR4 on this, and indeed the solar gang has changed its tune, not as far as Svalgaard, but certainly a major change from the TAR.

The magnitude of the long-term trend in solar irradiance remains uncertain. A reassessment of the stellar data (Hall and Lockwood, 2004) has been unable to confirm or refute the analysis by Baliunas and Jastrow (1990) that implied significant long-term solar irradiance changes, and also underpinned some of the earlier reconstructions (see Section 2.7). Several new studies (Lean et al., 2002; Foster, 2004; Foukal et al., 2004; Y.M. Wang et al., 2005) suggest that long-term irradiance changes were notably less than in earlier reconstructions (Hoyt and Schatten, 1993; Lean et al., 1995; Lockwood and Stamper, 1999; Bard et al., 2000; Fligge and Solanki, 2000; Lean, 2000) that were employed in a number of TAR climate change simulations and in many of the simulations shown in Figure 6.13d.

In the previous reconstructions, the 17th-century ‘Maunder Minimum’ total irradiance was 0.15 to 0.65% (irradiance change about 2.0 to 8.7 W/m^2; radiative forcing about 0.36 to 1.55 W/m^2) below the present-day mean (Figure 6.13b). Most of the recent studies (with the exception of Solanki and Krivova, 2003) calculate a reduction of only around 0.1% (irradiance change of the order of –1 W/m^2, radiative forcing of –0.2 W/m^2; section 2.7). Following these results, the magnitude of the radiative forcing used in Chapter 9 for the Maunder Minimum period is relatively small (–0.2 W/m^2 relative to today).

Which if true (and this is going to be very short) leads one to the conclusion that the little ice age was very little and very local and may have had a lot more to do with volcanic activity then much else. Leaving us with the European Warm Period. There they won't even go out on a large tree trunk (Section 2.7 of WGI)

Prior to direct telescopic measurements of sunspots, which commenced around 1610, knowledge of solar activity is inferred indirectly from the 14C and 10Be cosmogenic isotope record in tree rings and ice cores, respectively, which exhibit solar related cycles near 90, 200 and 2,300 years. Some studies of cosmogenic isotopes (Jirikowic and Damon, 1994) and spectral analysis of the sunspot record (Rigozo et al., 2001) suggest that solar activity during the 12th-century Medieval Solar Maximum was comparable to the present Modern Solar Maximum. Recent work attempts to account for the chain of physical processes in which solar magnetic fi elds modulate the heliosphere, in turn altering the penetration of the galactic cosmic rays, the flux of which produces the cosmogenic isotopes that are subsequently deposited in the terrestrial system following additional transport and chemical processes. An initial effort reported exceptionally high levels of solar activity in the past 70 years, relative to the preceding 8,000 years (Solanki et al., 2004). In contrast, when differences among isotopes records are taken into account and the 14C record corrected for fossil fuel burning, current levels of solar activity are found to be historically high, but not exceptionally so (Muscheler et al., 2007).

Which leaves us precisely here