Variability of Solar Spectral Irradiance II

I once had a spirited debate with my brother about climate change. I paraphrased Al Gore and took the view that unabated pollution is causing global warming and thus, climate change. He countered by saying that there is a growing scientific evidence that points solely to the sun as the main culprit.

I just saw a Nat Geo feature on this one. Indeed, it has been shown, through isotope analysis and carbon dating, that significant changes in the earth's climate over thousands of years were strongly correlated with cycles and patterns in the sun's radiance or solar energy. There's no question that greenhouse gases are warming the planet, but clearly, the sun's activities have something to do with it as well.

This is still frontier territory, as physicists still grapple with a lot of issues involving UV rays, solar wind and others causing long-term effects on the earth's climate, and I realize that Ambrose, who's in Germany as part of a team investigating this phenomenon, is right on track.