What's with the Hockey Stick? I'd be Happy with Tomorrow Morning's Forecast

Ok so I camped out this weekend and the weather prospects were looking good. Sunny, 20% POP with a max of 1mm rain. Naturally, thundershowers hit and it poured all night. But I can understand. Weather is a complex phenomenon, and the output is based on the interaction between so many complex factors, we just can't measure things accurately enough to keep us dry all the time. If it's so obvious that skilled meteorologists using all their pimped-out sensors and satellites can't give you a very good same-day forecast than you get by looking out the window and hitting up Google Earth, how come some scientists are so sure they can tell us what the weather was like a thousand years ago? These guys who came up with the contreversial hockey stick curve supposedly determined the yearly average temperature every day for the past thousand years by measuring tree rings and ice plugs. Come on. If we can't predict the future, why are we so good a REdicting the past? Why is it that intelligent people think that they can accurately calculate the state of a complex system hundreds of years ago based on today's sketchy half-assed data, when the best information science can get us today is pretty much worthless in telling us what the state of the same system will be mere hours into the future? Is the future an open book and the past written in stone? Or are both just models of alternative space-time configurations that our minds construct with the sensory information available at any one time???