A favorite trick of Hansen, Hayhoe, Dessler, et. al is to start their Mann-made warming trends in the 1970s. This is a wonderful trick, because they also tell us that the 1970s were artificially cooled by man-made cooling.
The cooling between 1940 and 1970 was likely a result of industrial pollution that produced sunlight-blocking aerosols, a phenomenon known as global dimming. As industry ramped up across the globe, much air pollution was being spewed out of smoke stacks along with carbon dioxide.
Global Warming: Fiction: Scientists in the 1970s Were Predicting a Coming Ice Age
Hansen uses the 1970s as his baseline for normal temperatures, and his crew also tells us that 1970s temperatures were not normal because of aerosols.
So the rules are, use the 1970s when convenient for obtaining funding, and chuck them when inconvenient.
