Category: Nations and peoples

In a world where the map of global climate change is always shifting, the conditions that once made a civilization flourish can never be taken for granted. There is a constant ebb and flow of migration and return-migration, as changes in weather patterns modify a people's environment and sources of sustenance. These changes have often proven so drastic as to contribute to the demise of previously stable civilizations throughout history, from ancient times to the present.

Deforestation: The process by which areas are stripped of forests and tree cover, exposing the underlying soil to erosive forces

Desertification: The process by which once semi-arable lands are converted into desert

El Niño-Southern Oscillation: A climatic phenomenon wherein the normally cold ocean currents off the Pacific Coast of South America reverse, affecting global weather patterns

Little Ice Age: Time period from around 1250 to 1850 characterized by cooling global temperatures Medieval Warm Period: Time period from around 800 to 1250 when European and possibly global temperatures were generally warming

The extent to which climatic change has affected the genesis, development, location, nature, rise, and fall of civilizations throughout history has been a matter of long-standing debate. The issue has gained a sharper edge and assumed a greater urgency, however, in an era of increasing environmental awareness. Any agreement among scholars seems to be primarily on a broad scale, rather than on specifics. The wider view is that the globe has been in a predominantly warming trend for the last seventeen thousand years. This thaw in the wake of the last major ice age has been proposed as the main factor that started, propelled, and then sustained the spectacular advance of human civilization, notably from around 3000 BCE to the present. However, when historians attempt to determine causal factors contributing to the success and failure of particular cultures and civilizations, factors other than climate, such as political and societal factors have to be taken into account.

A long-standing debate has raged over what might have caused the demise of the Indus River Valley culture. Sprawled along the alluvial plain of the Indus River in what later became Pakistan, it was the largest in terms of land area of the four earliest cradles of civilization. Dependent on the agricultural productivity of the fertile soil along the riverbanks, it was highly urbanized and had strong trade links with Mesopotamia. The cities were painstakingly planned; buildings were constructed of oven-baked brick; spacious streets were almost perfectly laid out in modern grid fashion; and the cities employed advanced drainage and sewage disposal mechanisms.

The Indus River Valley culture (IVC) flourished beginning around 2500 BCE. (also known as the Page 219  |  Top of Article“mature period”), though the civilization began around 3300 BC. After the mature period of the Indus River Valley culture (2600–1900 BCE) during which the population has been estimated to be roughly five million during the peak of the mature period, the civilization then declined after 1900 BCE and became depopulated by no later than 1200 to 1100 BCE. Different theories have been advanced to explain its downfall, none of which has proven conclusive. Increasing evidence indicates, however, that climatic and environmental factors may have been leading causes of the downturn in the culture's fortunes, rather than theorized attacks by Aryan invaders. According to one scenario, a climatic change seems to have triggered increased rainfall, leading to massive flooding. The demand for wood to fire the kilns used to produce bricks had denuded the forests, and this deforestation had eroded the soil, rendering it vulnerable to the flooding. Another climate change theory claims that drought, warmer temperatures, and anthropogenic deforestation resulted in desertification, which caused the large-scale abandonment of the Indus cities.

Civilization has modified the environment over much of the planet. Scotland, shown here, was once densely forested and probably even had temperate rain forests. It was deforested for fuel and timber for shipbuilding. A few remnants of the original forests are now protected and other areas have been reforested. (© Steven I. Dutch) (© Steven I. Dutch)

The Old Kingdom civilization of Egypt, 2686–2150 BCE, was renowned as the era of pyramid construction and exemplary of strength and prosperity. However, there is some evidence that global climate change possibly caused the disruption of the annual flooding of the Nile River—perhaps augmented by El Niño-Southern Oscillation (ENSO) effects—and thus, might have brought about a devastating drought cycle that led to the termination of the Old Kingdom. The kingdom's demise was followed by a chaotic 150 years known as the First Intermediate Period.

The climatic vulnerability of Mesopotamia has been amply attested to in the cuneiform texts of its various civilizations, as well as being evidenced by the archaeological record. The Akkadian Empire (about 2350–2150 BCE), which encompassed Mesopotamia and the Fertile Crescent up to the Levantine Coast, was apparently brought low by a series of very severe winters combined with drought conditions that were perhaps occasioned by volcanic eruptions. Another such massive drought cycle around 1200 BCE is also believed to have contributed to the ending of the Hittite Empire and Mycenaean Greece.

Lack of documentation makes it difficult to gauge the scale of the impact that climate may have had on pre-Columbian Native American cultures. The Anasazi, who dwelled in present-day portions of the southwestern United States from around 700 to 1300 CE, had no such documentation to begin with, so their abrupt collapse has proven even more puzzling. The Maya of Mexico and Central America, whose civilization was the most advanced and probably the best documented, suffered the nearly wholesale destruction of their books by Spanish missionaries.

The Navajo term “Anasazi,” or “Ancient Ones,” has been used to denote the Pueblo cultures known variously in different regions as the Hohokam, Mogollon, and Patayan. These peoples inhabited the area around the modern Four Corners—where Utah, Colorado, Arizona, and New Mexico converge—and southward into the greater part of the modern state of Chihuahua, Mexico. They constructed the spectacular cliff dwellings that still dot the regions they once inhabited, including Mesa Verde, Chaco Canyon, and Canyon de Chelly. Around 1150 CE, a particularly severe and prolonged period of drought drove the Anasazi to nearby areas where water was slightly more accessible, and the descendents of the Anasazi can be found among the present-day Pueblo.

Deriving, most likely, from the more ancient cultures of the Olmec and Teotihuacan in southern Mexico, the people known as the Maya flourished in the region of the Mexican Yucatán Peninsula and the modern countries of Guatemala, Belize, El Salvador, and Honduras around 200 to 900 CE. Massive and sophisticated in their architectural designs and elaborate pyramids, Mayan city-states burgeoned into mini-empires under autocratic kings who claimed to serve as conduits to the gods to ensure their people's prosperity. The once-baffling collapse of these city-states has recently thought to have been caused by a series of droughts and deforestation; the resulting crop failures drove the Maya to abandon both their faith in these kings and the city-states themselves, which became isolated ruins.

The enigmatic Moche culture of the Andes lasted from about 100 to 750 CE along the northern coastline of Peru and coincided with the Nazca culture to the south. Both ended abruptly, leaving little more than major artifacts, such as Moche pottery and the Nazca lines in the Nazca Desert. There is some disputed evidence that extensive ENSO episodes set off alternating patterns of flooding and drought, causing both civilizations to crumble. The more extensive Tiahuanaco culture, centered around an urban site in Bolivia, flourished from about 700 to 1150 CE, left giant stonework ruins, and seems to have perished from the effects of the same massive drought period that destroyed the Anasazi.

The more isolated islands of Pacific Oceania could be expected to offer more examples of vulnerability: Because of their remoteness, the scarcity of land and resources, and the potential capriciousness of nature, they have been home to some of the Page 221  |  Top of Articlefrailest of human societies. These societies, however, met with different outcomes. For example, the native culture of Easter Island seems to have come to an end in part through a murderous civil war brought on by deforestation and social unrest. It is possible that an ENSO episode exacerbated conditions of drought and scarcity, thus bringing about the culture's final destruction.

The fate of the Norse settlements in Greenland offers the most readily documented example of the negative impact of climate change. In roughly 980 CE, the Viking warlord Eric the Red sailed from Iceland to establish a Scandinavian colony in what is now known as Greenland. During the Medieval Warm Period, the colony thrived and expanded, concentrating into two major settlements. An eastern settlement was located on the island's extreme southern coast, and a less significant settlement was founded 320 kilometers up the western coast. In its heyday, each settlement may have had a population of approximately five thousand. Their economic mainstays were cattle and sheep grazing, as well as trade, mainly with the Icelandic and Norwegian peoples.

Around 1250 CE, as the Medieval Warm Period gave way to the Little Ice Age, glaciers advanced dramatically across Greenland. (The term “Little Ice Age” is used differently by different writers. Many use it to refer to the climate cooling from about 1300 to 1850, while others use it for the latter half of that interval, when cooling was greatest, beginning around 1550 or 1600.) Growing seasons shortened; temperatures plummeted; and hunting, grazing, and agricultural land became scarce. The Greenlanders, always in an isolated position, became even more cut off as ice packs began blocking the passage routes to and from Iceland and Norway. Increasingly harsh conditions also drove the Inuit (Eskimos) south and west, and almost immediately, armed clashes broke out between them and the Norse, as both groups competed for dwindling sources of sustenance. The Inuit proved to be the more readily adaptable to change, while the Norse were reluctant to alter their ways. Thus, by around 1400 CE, the western and eastern settlements lay abandoned as the Vikings either starved, died at the hands of the Inuit, or fled.

Though there exists little doubt that climate change and environmental factors have affected the course of civilization, there remains an element of debate over their relationship to other causal factors such as outside encroachment and internal dissension. It may well be different in each case. The ability of climate to influence history may affect contemporary politics and public policy decision making. If the correlation between climatic or environmental events and the decline of civilizations could be conclusively established, then it would logically follow that governments should work to prevent or to alleviate the effects of such events in the interests of self-preservation.

Raymond Pierre Hylton

Updated by: Ben Riley

See also: Arctic peoples ; Deforestation ; Desertification ; Easter Island ; El Niño-Southern Oscillation and global warming ; Greenland ice cap ; Little Ice Age ; Medieval Warm Period ; Paleoclimates and paleoclimate change .