Food scientists at Cornell University have produced a strain of broccoli that thrives in hot environments, which may make it possible for states with stiflingly hot summers to grow the vegetable. California, where cool coastal fog is perfect for growing standard broccoli, currently produces more than 90 percent of the broccoli grown in the United States. If California were to disappear, what would the American diet be like? Expensive and grainy. California produces a sizable majority of many American fruits, vegetables, and nuts: 99 percent of artichokes, 99 percent of walnuts, 97 percent of kiwis, 97 percent of plums, 95...