One of the arguments packed around by your typical Climate Change Denier, which they whip out at appropriate moments, is to admit the obvious--that the last century has seen significant warming--but to blame this warming on the "Solar Cycles"--increases in sunspots, solar irradiance, whatever. However, the folks at Deltoid were, as far as I know, the first to point to this bit of recent research that debunks the Sun/GW connection. And Eli the Techno Bunny is the first to point out that it looks like the scientists behind the best-known solar based theories have thrown in the towel:
On other timescales however, Sun-climate links may remain worthy of study. "Climate change is a cocktail of many effects," says Jasper Kirkby, a physicist at CERN, the European particle physics laboratory near Geneva Switzerland, who is leading an experiment aimed a simulating the effect of cosmic rays on clouds. "Past climate changes have clearly been associated with solar activity. Even if this is not the case now, it is still important to understand how solar variability affects climate"
One of the most obvious problems behind any theory of this kind is that, if GW is caused by solar cycles, the effect should be seen throughout the length and breadth of the solar system. But, as I tell all my Denier friends, its getting colder on Ur Anus (a line I will keep using until someone admits to me that its hilarious).
PS. You can see the actual paper, rather than a popular summary, here.