Learning from the Past
by Lester R. Brown, Earth Policy Institute, Washington D.C., U.S.A.
Our twenty-first century global civilization is not the first to face the prospect of environmentally induced economic decline. The question is how we will respond. We do have one unique asset at our command–an archeological record that shows us what happened to earlier civilizations that got into environmental trouble and failed to respond.
As Jared Diamond points out in his book Collapse, some of the early societies that were in environmental trouble were able to change their ways in time to avoid decline and collapse. Six centuries ago, for example, Icelanders realized that overgrazing on their grass-covered highlands was leading to extensive soil loss from the inherently thin soils of the region. Rather than lose the grasslands and face economic decline, farmers joined together to determine how many sheep the highlands could sustain and then allocated quotas among themselves, thus preserving their grasslands and avoiding what Garrett Hardin later termed the “tragedy of the commons.”
The Icelanders understood the consequences of overgrazing and reduced their sheep numbers to a level that could be sustained. We understand the consequences of burning fossil fuels and the resulting CO2 buildup in the atmosphere. Unlike the Icelanders who were able to restrict their livestock numbers, we have not been able to restrict our CO2 emissions.
Not all societies have fared as well as the Icelanders, whose economy continues to produce wool and to thrive. The early Sumerian civilization of the fourth millennium BC was an extraordinary one, advancing far beyond any that had existed before. Its carefully engineered irrigation system gave rise to a highly productive agriculture, one that enabled farmers to produce a food surplus, supporting formation of the first cities. Managing the irrigation system required a sophisticated social organization. The Sumerians had the first cities and the first written language, the cuneiform script.
By any measure it was an extraordinary civilization, but there was an environmental flaw in the design of its irrigation system, one that would eventually undermine its food supply. The water that backed up behind dams built across the Euphrates was diverted onto the land through a network of gravity-fed canals. Some water was used by the crops, some evaporated, and some percolated downward. In this region, where underground drainage was weak, percolation slowly raised the water table. As the water climbed to within inches of the surface, it began to evaporate into the atmosphere, leaving behind salt. Over time, the accumulation of salt on the soil surface lowered its productivity.
As salt accumulated and wheat yields declined, the Sumerians shifted to barley, a more salt-tolerant plant. This postponed Sumer’s decline, but it was treating the symptoms, not the cause, of falling crop yields. As salt concentrations continued to build, the yields of barley eventually declined also. The resultant shrinkage of the food supply undermined the economic foundation of this once-great civilization. As land productivity declined, so did the civilization.
Archeologist Robert McC. Adams has studied the site of ancient Sumer on the central floodplain of the Euphrates River, an empty, desolate area now outside the frontiers of cultivation. He describes how the “tangled dunes, long disused canal levees, and the rubble-strewn mounds of former settlement contribute only low, featureless relief. Vegetation is sparse, and in many areas it is almost wholly absent….Yet at one time, here lay the core, the heartland, the oldest urban, literate civilization in the world.”
The New World counterpart to Sumer is the Mayan civilization that developed in the lowlands of what is now Guatemala. It flourished from AD 250 until its collapse around AD 900. Like the Sumerians, the Mayans had developed a sophisticated, highly productive agriculture, this one based on raised plots of earth surrounded by canals that supplied water.
As with Sumer, the Mayan demise was apparently linked to a failing food supply. For this New World civilization, it was deforestation and soil erosion that undermined agriculture. Changes in climate may also have played a role. Food shortages apparently triggered civil conflict among the various Mayan cities as they competed for food. Today this region is covered by jungle, reclaimed by nature.
During the later centuries of the Mayan civilization, a new society was evolving on faraway Easter Island, some 166 square kilometers of land in the South Pacific roughly 3,200 kilometers west of South America and 2,200 kilometers from Pitcairn Island, the nearest habitation. Settled around AD 400, this civilization flourished on a volcanic island with rich soils and lush vegetation, including trees that grew 25 meters tall with trunks 2 meters in diameter. Archeological records indicate that the islanders ate mainly seafood, principally dolphins–a mammal that could only be caught by harpoon from large sea-going canoes.
The Easter Island society flourished for several centuries, reaching an estimated population of 20,000. As its human numbers gradually increased, tree cutting exceeded the sustainable yield of forests. Eventually the large trees that were needed to build the sturdy canoes disappeared, depriving islanders of access to the dolphins and dramatically shrinking their food supply. The archeological record shows that at some point human bones became intermingled with the dolphin bones, suggesting a desperate society that had resorted to cannibalism. Today the island has fewer than 4,000 residents.
One unanswerable question about these earlier civilizations was whether they knew what was causing their decline. Did the Sumerians understand that the rising salt content in the soil from water evaporation was reducing their wheat yields? If they knew, were they simply unable to muster the political support needed to lower water tables, just as the world today is struggling unsuccessfully to lower carbon emissions?
These are just three of the many early civilizations that moved onto an economic path that nature could not sustain. We, too, are on such a path. Any one of several trends of environmental degradation could undermine civilization as we know it. Just as the irrigation system that defined the early Sumerian economy had a flaw, so too does the fossil fuel energy system that defines our modern economy. For them it was a rising water table that undermined the economy; for us it is rising CO2 levels that threaten to disrupt economic progress. In both cases, the trend is invisible.
Whether it resulted from the salting of Sumer’s cropland, the deforestation and soil erosion of the Mayans, or the depleted forests and loss of the distant-water fishing capacity of the Easter Islanders, collapse of these early civilizations appears to have been associated with a decline in food supply. Today the annual addition of more than 70 million people to a world population of over 6 billion at a time when water tables are falling, temperatures are rising, and oil supplies will soon be shrinking suggests that the food supply again may be the vulnerable link between the environment and the economy.