For as long as most people can remember, food has been getting cheaper and farming has been in decline. In 1974-2005 food prices on world markets fell by three-quarters in real terms. Food today is so cheap that the West is battling gluttony even as it scrapes piles of half-eaten leftovers into the bin. 

    That is why this year's price rise has been so extraordinary. Since the spring, wheat prices have doubled and almost every crop under the sun—maize, milk, oilseeds, you name it—is at or near a peak in nominal terms. The Economist's food-price index is higher today than at any time since it was created in 1845. Even in real terms, prices have jumped by 75% since 2005. No doubt farmers will meet higher prices with investment and more production, but dearer food is likely to persist for years. 

    But the rise in prices is also the self-inflicted result of America's reckless ethanol subsidies. This year biofuels will take a third of America's (record) maize harvest. That affects food markets directly: fill up an SUV's fuel tank with ethanol and you have used enough maize to feed a person for a year. And it affects them indirectly, as farmers switch to maize from other crops. The 30m tonnes of extra maize going to ethanol this year amounts to half the fall in the world's overall grain stocks. 

    大多数人仍能记得粮食越来越便宜，农业一直在走下坡路。从1974年到2005年，世界市场上粮食的实价掉了四分之三。今天的粮食是如此便宜以至于西方一边反对暴饮暴食，一边将成堆的只吃了一半的剩菜剩饭扔进垃圾箱。 

    这就是为什么今年的价格上涨如此的异乎寻常。自从今年春天小麦的价格已经翻番，玉米、牛奶、油菜籽等几乎所有阳光下的作物的牌价都在或接近最高点。《经济学家》的粮食价格指数已经高于自该指数1845年创立以来的任何时候。自2005年以来，粮食的实价也已经上升了75%。毫无疑问，随着粮价的上升，农民会增加投资，产量也会提高。高粮价可能会持续几年。

    粮价的上升也是美国对乙醇燃料不计后果地实行补贴所带来的自作自受的后果。今年生物燃料将消耗美国创纪录的玉米收成的三分之一。这直接影响了粮食市场：用乙醇装满一辆越野车的油箱所消耗的玉米足够一个人吃一年。间接的影响是，因为农民不种其他作物而转向种植玉米了。今年有三千万吨额外的玉米用于制造乙醇，这占据了世界总体谷物储存下降数的一半。