This insensitivity means that they can be planted widely across latitudes, and also can be planted more than once per year under appropriate climatic conditions. These varieties are also tremendously responsive to fertilizer and to water. The green Revolution undoubtedly helped to improve nutrition throughout the world. We focus here on grain as it provides more than half of humanities' daily calories. Figure 4, below, illustrates changes in total global grain production over time.
Some natural factors contribute to some of the precipitous drops in world grain production.
We also have seen that cultivated acreage has decreased in recent years. The next section takes a brief look at some resource limitations that contribute to these trends.