Photo: Daniel Griffen, University of Minnesota (right)

From — The wildfires that torched California last fall came right on the heels of another calamity, a five-year drought that was finally washed away in early 2017. Much ink has been spilled trying to pin these extreme weather patterns on human-caused climate change, but such debates raise an even more basic question: how “extreme” are these events? Was this drought really that rare in notoriously arid California?

The answer is tricky. To make a well-educated guess at how often prolonged droughts have occurred in California’s past we would need centuries, if not a millennium, of climate data. Unfortunately, humans haven’t been measuring precipitation and temperature for that long. But thankfully, someone else has.

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