What tree rings tell us about climate change

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Last year, wildfires ripped across the western United States, exacerbated by protracted drought. And this year could be even worse. So just how bad is this drought in the span of history? We can get a pretty good idea through the science of dendrochronology. Dr Daniel Griffin is a dendrochronologist at the University of Minnesota - he studies tree rings and climate change - and he told Newshour's Tim Franks more about the hidden history of tree rings. (Photo shows the tree rings of a Douglas fir. Credit: DendroElevator, University of Minnesota)