If you've flown across Nebraska, Kansas or western Texas on a clear day, you've seen them: geometrically arranged circles of green and brown on the landscape, typically half a mile in diameter. They're the result of pivot irrigation, in which long pipes-on-wheels rotate slowly around a central point, spreading water across cornfields.
Yet most of those fields are doomed. The water that nourishes them eventually will run low.
As we all know, Americans are living longer. Women especially.
But here's what you may not know: French, German, Swedish, Italian, Japanese, British, Dutch and Canadian women are living longer too, but their lives are getting longer faster than ours. Take a look at this from the National Academy of Sciences.