The Role of Climate Change and Ecology in History

A popular activity of historians and nonhistorians alike has long been to try to associate historical developments with changes in the climate and ecology of different regions. Historical models known as climate determinism” and “ecological theory” attempt to relate historical developments to changes in the natural environment, which have been seen as influencing both the rise and fall of civilizations, In Mesopotamia, for example, it has been suggested that cool and dry conditions led to the beginning of civilization ca.3000 B.CE. and that a hot and dry period around 500 B.CE led to the decline of Mesopotamian civilization. In between, various other ecological conditions, such as deforestation, soil exhaustion.overpopulation, and even human-caused climate change, have been adduced to explain nearly every major social, economic, and political change.

But complex models that hypothesize long-term and far-reaching effects of climate and ecology on history have problems. One is that, so far, no one quite agrees as to just when the cooler, warmer, drier, or more humid periods were. One model has the Sahara drying out in the fourth millennium B.c.E. and leading to an influx of population into the Nile River valley, whereas another has the Sahara being much more humid at the same time. Another problem is misconceptions about the results of climate change on certain kinds of economies. For example, it has been suggested that lessened rainfall brought an economic decline in lower Mesopotamia because this area was particularly vulnerable to lower rainfall amounts; but given that all of the crops were irrigated, the economy in fact would have been quite insensitive to the amount of rainfall, which never was sufficient for extensive farming in the first place. In a like manner, overgrazing and deforestation are blamed for the decline of societies that already had altered their economies to cope with just these issues-for example, by planting salt-tolerant barley instead of wheat when the soil became salinated.

Another problem is that these theories often are proposed by persons with excellent credentials in other fields of study but who are not specialists in antiquity. As a consequence, they tend to underrate the degree to which ancient societies were able to deal with problems confronting them or to determine their own destinies. For example, nonspecialists make the mistake of assuming that climate variations caused civilization to appear quite suddenly around 3000 B.C.E., when in reality all of the important components under discussion-that is, irrigation and food production methods-had been in place for over a thousand years. It was the development of other factors not so clearly related to climate, such as writing, metallurgy, and the potter's wheel, that resulted in these cultures being defined in the modern day as civilizations. In addition, the peoples of antiquity were quite capable of recovering from disasters and of responding to changes in very imaginative ways. Thus it will be seen, for example, that the movement of the centers of culture and civilization increasingly toward the west was part of a long process of human economic and social development, not simply the result of a hot and dry period around 500 B.c.E., as climate determinists contend.

Which is not to say, of course, that nature had no effect on human societies. Long-term droughts certainly could cause people to migrate, seeking new food sources. Some kinds of short-term variations in the natural environment, such as failures of the Nile River to flood, had clear consequences for agricultural productivity. And it may well be that increasing pressure on resources in Mesopotamia did lead to a consolidation of urban areas into larger centers and an increase in warfare, in a manner analogous to what would happen in the early Archaic Age of ancient Greece. But it is dangerous to be too narrowly focused in assigning a particular historical event to climatic or ecological changes: climate change did not alone lead to the creation of intensive irrigation systems, much less to civilization. And, in general, it also is always dangerous to argue that just because something happened after something else, it must have happened because of that something else.