Leif Svalgaard says: April 5, 2011 at 7:54 pm
This is well-trodden ground. Nothing new to add, just the same old, tired arguments. Perhaps a note on EUV: as you can see here (slide 13)
the energy in the EUV band [and other UV bands] is very tiny; many orders of magnitude less than what shines down on our heads each day. So a larger solar cycle variation of EUV does not make any significant difference in the energy budget.
Leif Svalgaard says: April 6, 2011 at 10:16 am
It is not clear what his [Courtillot] theory is. I have come across two claims he makes: 1) the Earth’s magnetic field determines climate, and 2) cosmic rays determines climate. Now, it is of no use to discuss this if the influences are minor [because we are interested in the major drivers], so the issue is not if some subtle influence can be found by suitable massaging/filtering/torturing/misrepresentation etc of the [often dubious data and more dubious proxies], but whether such influence is large enough that is swamps anything else [otherwise we need no worry, e.g. if AGW is really larger than the solar influence, then who cares about the Sun]. The cosmic ray issue is clouded [no pun!] by the fact that the cosmic ray intensity is primarily controlled by the intensity of the Earth’s magnetic field, and not by the Sun [ignoring galactic changes, supernovae, aliens, etc]: http://www.leif.org/research/CosmicRays-GeoDipole.jpg the little wiggles are solar related, the big swing is not. Anyway, what should matter is what the GCR intensity actually is in the troposphere where clouds are formed and not what causes the GCRs. We do not have good measurements of GCRs before the 1950s [the early measurements back to the 1930s have uncertain calibration], but there have been no long-term changes in GCRs since then [the solar cycle changes are only a few percent anyway], e.g.
. Also, solar activity [and the solar wind and magnetic flux, etc] right now is on par with what it was in the 19th century [ http://www.leif.org/research/2009JA015069.pdf , Figure 10], yet the climate is claimed to be significantly warmer now, contrary to what we would expect from a cosmic ray variation. So, for me, there is precious little observational evidence for the GCR theory.