THINKING ABOUT when Iceland’s next big volcanic eruption hits. “Among the problems: dangerous gases in air flight corridors. But crop failures strike me as a bigger concern. . . . In my view the human race has been lucky in terms of the severity of geological phenomena since the late 19th century. During the 19th century many more severe natural events occurred than was the case in the 20th. We might be overdue.”

That’s right — whether you’re talking solar megaflares, volcano eruptions, little ice ages, or whatever, the 20th Century was unusually benign compared to the 19th. That’s affected our perception of what’s “normal” — and, hence, worth preparing for — and probably in an unfortunate way.