Why do believers think they can predict the future?

Well, yes, it IS possible to predict the future within an acceptable margin of error. Its called "statistical ysis" and there are numerous sources from which to take meaningful data, from glacial core samples to tree rings, sedimentary layers, fossil records, meteorological records, oceanographic data, etc etc etc. Obviously you're going to find people on both sides of the argument that offer supporting evidence for their arguements, but your "NASA facts" are only for the contiguous 48 states, which is a small and inconclusive sample of what may or may not indicate a worldwide trend. NASA scientists would be the first to admit that. Temperature measurements taken all over the globe over the past 150 years have actually averaged a small increase over time, including during the last 10 years. FACT. However, just to humor you, there is not enough data to determine what the very long-term cycles have been (beyond a few million years) or what they are going to be in the future, whether the current climate is in agreement with those cycles or just a statistical abberation, or what the very long-term future may hold. If I were a betting man, I'd put my money on short-term global warming however, and there is no doubt that man has contributed to it, at least in some small way.