They provide approximately 60 percent of the calories and 50 percent of the protein consumed by the human race. The legumes provide about 20 percent of the world's protein. Then balance of calories, protein and essential vitamins and minerals is obtained from tuber and root crops and various fruits, nuts and vegetables. Food animals, deriving their food either directly or indirectly from plants, provide 20 percent of the protein with 5 percent coming from fish. For agriculture, climate must be managed both as a resource to be used wisely on the one hand or a hazard to be dealt with on the other.
Food production is very much a function of climate, which in itself is unpredictable.
In fact, the principal characteristic of climate is variability. Predictive climate changes derived from computer simulations are far from accurate and may be deceptive even with the most advanced modeling. Volcanoes, cloud cover, regional characteristics and changing of atmospheric components cannot, if they ever will, be successfully factored into an accurate climate model. From the perspective of food security, the stability of agricultural production is as important, if not more so, than the magnitude of output. Extremes in weather, rather than averages, affect agriculture.