or “On The Surface Of The Moon, a Four-billion-year Record of Solar Activity Awaits Us”
[UPDATE : More evidence of the "imprint" of solar wind into lunar soil]
In her 2007 article “The Sun and the Earth’s Climate” published in “Living Reviews in solar physics” (Living Rev. Solar Phys. 4, (2007), http://www.livingreviews.org/lrsp-2007-2 cited on Sep 25, 2009), Professor Joanna D. Haigh writes in the Conclusions:
One important issue is to establish the magnitude of any secular trends in total solar irradiance (TSI). This may be achieved by careful analysis and understanding of the satellite instruments [and] continued [with] current and new satellites. For longer periods it requires a more fundamental understanding of how solar magnetic activity relates to TSI. This would not only facilitate more reliable centennial-scale reconstructions of TSI, from e.g. sunspot records, but also advance understanding of how cosmogenic isotope records may be interpreted as historical TSI.
Actually, there is another source of information for the history of solar activity, and it could open possibilities of discovery and understanding of an almost unheard-of scale.
I am talking about the surface of the Moon.
As per my notes about my (yes, peer-reviewed!) 2005 article “W.W.W. MOON? The why, what and when of a permanent manned lunar colony” (Journal of the British Interplanetary Society. 58(3-4):131-7):
The [...] lunar soil’s regolith contains also an at-least-billion-year-long record of the solar activity    that would help a lot in the understanding of the behaviour and evolution of our star. Just as well, buried regolith deposits are expected to preserve traces of the very young Sun .
These are the references for the above
 H Y Mc Sween, Jr., ‘Stardust to Planets‘, St. Martin’s Press, 1993, p136
 P D Spudis, ‘The Once and Future Moon‘, Smithsonian, 1996, p196
 P D Spudis, ‘The Once and Future Moon‘, Smithsonian, 1996, p106
 P D Spudis, ‘The Once and Future Moon‘, Smithsonian, 1996, p115
One doesn’t need to be a hardcore skeptic or AGW believer to understand the enormous worth of getting such information, awaiting us at a distance that can be covered in a mere 3 days.