Last spring, Bill and I were sifting through the aftermath of a big agricultural experiment up at the greenhouse. We had been growing sweet potatoes under the greenhouse gas levels predicted for the next several hundred years, the levels that we’re likely to see if we, as a society, do nothing about carbon emissions. The potatoes grew bigger as carbon dioxide increased. This was not a surprise. We also saw that these big potatoes were less nutritious, much lower in protein content, no matter how much fertilizer we gave them. This was a bit of a surprise. It is also bad news, because the
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