The Anthropogenic Global Warming Hypothesis is important these days because power hungry collectivist politicians and eco-activists want to use their claims that man is about to bring about the end of mankind to enact laws that will end Western Civilization. This was the stated goal of Maurice Strong when he was working to establish the UN IPCC. Those promoting the idea of global warming use proxies of past temperature to support claims that it is much hotter today than in the past. Tree ring data were widely used for this purpose. Personally I have always doubted that tree ring data would be useful as a temperature proxy because of the many factors besides temperature that influence tree growth rates. I also doubt the NASA/GISS temperature data set that politicians use to support AGW claims because it is an outlier from other data sets, and also because, frankly, of the influence of James Hansen. Anthony Watts has done a comprehensive study of proxy temperature data sets, and the results cast doubt on the validity of tree ring data, and on the NASA/GISS data set.