There is plenty of evidence that our sun's activity cycles have quite a lot to do with our climate, with observations over the past 5,000 years seemingly backing up a number of theories that sunspot cycles can have a profound effect on our world's weather.
Even over the past 1,000 years it can be shown that the number of sunspots appearing on the sun's surface gives us a pretty good indication of activity, with more sunspots heralding warmer temperatures and less (or none) bringing cooler temperatures.
Work done by Dr. Henrik Svensmark has shown that the Roman and Medieval Warm Periods coincided with lengthy periods of high sunspot numbers and the Little Ice Ages (approximately 1300 to 1550 AD and 1650 to 1750AD) coincided with lengthy periods of minimal sunspot numbers, the so-called Maunder and Dalton Minimums. (I linked to Svensmark's Wikipedia page as most of his works, papers, and videos are linked from there.) Svensmark has managed to tie together solar activity and its effects on gamma radiation and cloud formation. (I won't go into all of it here, but I have covered it before.)
Now we find out our sun may be going into an extended quiet period – a minimum – like those seen during the Little Ice Ages. If Svensmark is right this may mean we're going to see extended periods of colder than normal weather that may last decades.
Waiting for solar fireworks to reach a grand finale next year? Um, sorry, looks like you already missed them. Structures in the sun's corona indicate that the peak in our star's latest cycle of activity has been and gone, at least in its northern hemisphere.If such a thing does happen, it will give us a better idea of what effect the sun and CO2 has on our climate. I'm willing to bet that many of the AGW faithful are going to find out their favorite villain, anthropogenic CO2, has had little effect on climate and that the changes seen in our most recent history have been driven primarily by solar activity.
The southern hemisphere, meanwhile, is on a sluggish rise to solar maximum and may not hit its peak until 2014.
This bizarre asymmetry strengthens a theory that has been bubbling among sun watchers for the past few years: our star is headed for hibernation. Having the sun's outbursts turned off for a while would provide a better baseline for studying how they influence Earth's climate.
The next few decades are going to be interesting.