Environmental consequences of agriculture

Agriculture increases the carrying capacity, but this increase comes at a price. It has already been stated that humans have often replaced the natural vegetation with crops and pasturage. Even when we disregard the large-scale developments in the 19th and 20th centuries, especially the extension of arable land into steppe and desert areas by way of irrigation and the use of fertilizer, we can still say that the landscape of Eurasia is in large parts human-made. Of course, this differs from region to region: thus, large parts of Central Asia and of the taiga forests remained to some extent untouched. But elsewhere, humans modified their environment, almost always in harmful ways.

A decreasing complexity of an ecosystem, for instance, a decreasing number of plants or animals, usually implies an increasing instability of the system. Even attempts to improve soil quality, such as fertilizing, can have such effects, but one should think above all of deforestation in order to clear land for cultivation or pasturage (permanently or for so-called shifting cultivation), or to obtain wood or charcoal. Overgrazing can stop a forest from regenerating. Deforestation and overgrazing can lead to soil erosion by wind and water, and this in turn can deregulate water systems, and so on. There are other mechanisms of soil degradation as well: drainage leading to oxidation and settling, as in peat bogs in northern Europe, or salinization because of irrigation as along the Tigris, Euphrates, and Nile. Desertification or flooding can be the ultimate consequences.

Not all environmental damage should be laid at the door of agriculture. Humankind has always been introducing pollutants into the environment. In the context of the ancient

World, one should not only think of the smoke of heating and cooking fires, waste water, and refuse, but also about the by-products of mining and smelting. Lead was a by-product of silver mining and silver extraction, and mercury and arsenic were used in certain manufactures. An increase in the levels of atmospheric lead during the Roman Empire is visible in measurements taken from drill cores of polar ice or of lake sediments.