Food scarcity is emerging as the defining issue of the new era now unfolding, much as ideological conflict was the defining issue of the historical era that recently ended. More fundamentally, food scarcity may be the first major economic manifestation of an environmentally unsustainable global economy. An early hint of the shift to an economy of scarcity came in late April 1996, when wheat prices on the Chicago Board of Trade soared above $7 a bushel, the highest level in history and more than double the price a year earlier. Corn prices also doubled, moving above $5 a bushel, a new record. And the price of rice, the other major grain, was climbing. In this, the seventh volume in the Worldwatch Environmental Alert series, Lester Brown observes that prices were climbing because world carryover stocks of grain had fallen to 48 days of consumption, the lowest level on record. Production was falling behind demand. Brown, president of the Worldwatch Institute, argues that the continually expanding demand for food is colliding with some of the earth's natural limits, including the sustainable yield of oceanic fisheries, the sustainable yield of the aquifers that supply irrigation water, and the physiological limits of crop varieties to use fertilizer.