The Effects of Climatic Change on the Fall of Civilization

For decades, the dominant view has been that cultural factors- war, religion, trade, palace intrigue- explain civilizations' ups and downs (Grossman 2002). As we are brought up through the educational system, tons of papers are written and chapters in textbooks are devoted to the clashes of armies and philosophies throughout history. What doesn't get nearly as much attention are climate and geographical factors during the life span of empires and civilization. Looking at two societies, the Sumerians and the Mayans, may demonstrate a need to change this trend in classrooms.

The Sumerians found themselves in such a weakened state by the 23rd century BC that they could scarcely defend themselves from invasion. They were a people not primarily disposed to war making and had only a citizen militia that could be called into service in times of need and imminent danger. The Semitic ruler Sargon I, also known later as The Great, was successful in taking the country through military domination. He went on to make a new capital in the northern region of Sumer in his own vision. It would grow to become the richest and most powerful city in the world in short order. As time went on the people of this northern region of Sumer, as well as the later conquerors of the region became known as Akkadians. This led to the land of Sumer acquiring and adopting both names, Sumer and Akkad (Guisepi 2006).

The Akkadian dynasty lasted about a century. Naram-Sin, the grandson of Sargon the Great, was on the throne when Agade was attacked and razed by a war like people from the Zagros mountains called Gutians. The assult didn't stop at the capital and soon all of Sumer was destroyed and its people under Gutian rule. Later generations would slowly shrug off the Gutian control however. Approxiamtely 80 years after Sumer's destruction, a governor by the name of Gudea returned his city of Lagash to prominence. We know of him in particular because of the numerous statues of him recovered in the region, making him the most well know Sumerian of all time. Complete independence was procured half a decade later when Utuhegal, king of Erech, beat back the Guptians, an event well documented by Sumerian historians (Guisepi 2003).

Ur-Nammu, one of Utuhegal's generals, founded the 3rd Dynasty of Ur a few years later. Around 2000 BC barbarian invaders attacked both Sumer and Akkad. Shortly before the start of the second millennium

B.C. the Amorite people of the western desert of Sumer attacked the kingdom, seized control in Akkad, and built a powerful new state around the city of Babylon . Over time critical cites such as Larsa and Isin fell to the Amorite. This destabilized the political structure

of Ur enough to entice the Elamites from Iran to assault Ur and end the Dynasty with the capture of Ibbi-Sin (Guisepi 2003).

It would seem that once again this was a case of rival civilizations sweeping in and taking over. However, further study indicates other, much more subtle, factors in the fall of the Sumerians. Ecological and climatic changes played a key role in weakening the once proud society. Paleoclimatic data from numerous sites document changes in the Mediterranean westerlies and monsoon rainfall during the time period with precipitation reductions of up to 30% that diminished agricultural production from the Aegean to the Indus (Weiss and Bradley 2001).

Two scientists by the name of Cullen and deMenocal conducted a study of the dust in the Gulf of Oman. In samples taken every 2 centimeters along the core, they measured the amounts of minerals, such as calcite, dolomite and quartz, that today make up a large proportion of the dust blown from Mesopotamia by the Shamal. They found that wind-blown dust levels in the Gulf of Oman were high during the last ice age until about 11,000 years ago, then settled down to levels more typical of today. But in the sample from 2000 B.C. plus or minus 100 years, as dated by carbon-14, the abundance of dust minerals jumped to two to six times above background, reaching levels not found at any other time in the past 10,000 years. The extreme dustiness, suggesting a wide-ranging area of dryness, persisted through the next sample 140 years later but faded away by the third sample, indicating a time period of drought of a few hundred years (Kerr 1998).

In addition, the soil may have become unusable due to salt deposit buildup over the years. Over the centuries, silt carried by the Tigris and Euphrates built up the streambeds. Eventually, the surrounding farmlands were below the level of the rivers. The Sumerians constructed levees to contain the rivers, which worked except during major floods.

The irrigated water went to the fields, where it often collected on the surface. The hot Mesopotamian sun evaporated the standing water and left behind layers of salt. The soil also became waterlogged in places. This caused the water table to rise, bringing more salt to the surface. One clay tablet with Sumerian writing recorded that "the earth turned white." The only solution to this salt problem, called salinization, was for the Sumerians to leave the land unwatered and fallow for several seasons to allow the water table to fall. The scarce rains would then slowly draw the salt down below the soil cultivation zone (CRF 2002). In general, high salt concentrations obstruct germination and impede the absorption of water and nutrients by plants (Jacobson and Adams 1958).

The Sumerian farmers knew that leaving the land alone for a while was the right thing to do. But the rulers of Sumer had based their wealth and power on the skills and labor of an ever-growing population. Therefore, they ordered the farmers to continue irrigating and planting the damaged land to produce more food.

Wheat is less tolerant of salt than barley. Based on clay tablet records, barley gradually replaced wheat in the Sumerian diet. Soon, the yields of barley and the other crops decreased steadily. The Sumerian people began to suffer from hunger, which led to malnutrition and disease (CRF 2002).

The shortsighted demands of the Sumerian rulers led to the collapse of their civilization. The rulers could no longer feed and pay for large armies. Peasant revolts and warfare among the Sumerian city-states erupted over control of remaining fertile farmlands. Finally, in 2370 B.C., the Akkadian Empire from the north conquered a weakened Sumer (CRF 2002).

It's true that the empire fell to foreign invaders but not without some internal assistance. In a sense, the rulers invited conquerors in by unintentionally weakening the entire population. Adequate steps were not taken to counteract the drought and salt build up and ultimately led to the downfall of one of the greatest civilizations in history. But this isn't the only time it has happened.