I've always thought that a way to combat global warming would be to paint all the rooftops on the earth white (or silver) this would increase the albedo of the earth and reduce the temperature. I present this as a bit of a joke to my students who always think its a crazy idea but I read today that it has some serious followers although the idea is a bit more sinister. Depositing shiny metallic particles into the stratosphere is the idea, this would have the same effect as the white rooftops but is more difficult to reverse. What if the result was not as expected?