To the Editor: Yet another climate denier letter displaying a scientific illiteracy that is a sad indictment of our educational system: "Humans didn't cause global warming" in the Feb 11 edition of The Sanford Herald. All you have to do is Google "Scientific American global warming" to find out that global warming is an undisputed scientific fact. Climate scientists know all about previous periods of climate change, that's basic high school science class stuff. They were all caused by something. Scientists call that something a "forcing." They have established that this time the forcing is not any of the previous...