Long article: linked above. Here's the intro: In February 2007, depending on what newspaper you read, you might have seen an article detailing a "controversial new theory" of global warming. The idea was that variations in cosmic rays penetrating the Earth's atmosphere would change the amount of cloud cover, in turn changing our planet's reflectivity, and so the temperature at its surface. This, it was said, could be the reason why temperatures have been seen to be varying so much over the Earth's history, and why they are rising now. The theory was detailed in a book, The Chilling Stars,...