This week's Nature has a short review article about the effect of variations in the Sun's luminosity on Earth's climate. In fact, most of the article is about trying to understand the Sun's luminosity and the solar physics at work. In the end, I think the important thing to glean is that there is a well-known 11-year sunspot cycle, and sunspots are cooler than the solar surface. However, when there are lots of sunspots, the sun is actually a bit brighter than normal because of faculae and the "magnetic network" of bright thermal "leaks," that let more energy escape the solar surface. All the evidence points to variations is luminosity (brightness or energy flux) being due almost entirely to magnetic field variations. Not so surprising perhaps. More surprising is that as hard as people try to find secular variability in the luminosity, it doesn't seem to change much. Even less surprising is that the variations that are observed, and inferred from proxies, should have a minimal influence on Earth's climate. This, despite global warming denialists always talking about "solar variability" as if it were a well-known, well understood phenomenon.
Here's something that hardly ever gets said out loud: climate scientists know at least as much about climate as solar physicists know about the sun. There, I said it. The two fields are covered in very different ways in popular press, though. Why? My little theory goes like this: People (general public, policymakers, media) can associate solar physics with astrophysics, which is like physics, which they (usually) didn't understand when they took it in high school/college compared; climate science, on the other hand, is not like physics (to them), and maybe it is more like meteorology, which is like the weather report, which is always wrong (right? Actually, no, but that is the perception.) So there is this tendency to not believe the "climate scientists" or "climatologists" (an even worse term) when they publish a new result, and this skepticism is amplified because there are so often controversial policy consequences/implications that bring out more vocal opposition and "fair and balanced" sort of treatment in the media. Contrast that with findings about the sun or stars or astronomy in general, which is mostly covered as amazing and important new scientific facts (unless it has to do with defining planets!). So that sort of sums up my pet theory.