Credulity can be expensive. So don't believe everything you hear. It's a good lesson to teach in this modern era in which the communications revolution allows scores of hopeful persuaders to bid for our attention daily, trying to sell us a product, a service, their qualifications for public office or the proposition that our very lives depend on taking their advice. Opinion shapers have learned that their chances of getting attention increases in proportion to the size of the catastrophe they promise if we don't heed their warnings. Thus, in our modern era, we learn that unless we act now, the entire planet and all the life it bears is at risk. Their claims are bolstered by those magic words: "scientists say." This book asserts that the record of such claims shows that they should be taken with a large spoonful of skepticism. Credulity not only can cost a great deal of money, but in some notable cases it has cost lives.