Correlating climate change and archaeological data, an award-winning historian offers the first comprehensive overview of how the Medieval Warm Period and the Little Ice Age significantly impacted the Native cultures of the American Southwest, Southern Plains, and Southeast.
Series: Clifton and Shirley Caldwell Texas Heritage Endowment, Number Eighteen
Climate change is today’s news, but it isn’t a new phenomenon. Centuries-long cycles of heating and cooling are well documented for Europe and the North Atlantic. These variations in climate, including the Medieval Warm Period (MWP), AD 900 to 1300, and the early centuries of the Little Ice Age (LIA), AD 1300 to 1600, had a substantial impact on the cultural history of Europe. In this pathfinding volume, William C. Foster marshals extensive evidence that the heating and cooling of the MWP and LIA also occurred in North America and significantly affected the cultural history of Native peoples of the American Southwest, Southern Plains, and Southeast.
Correlating climate change data with studies of archaeological sites across the Southwest, Southern Plains, and Southeast, Foster presents the first comprehensive overview of how Native American societies responded to climate variations over seven centuries. He describes how, as in Europe, the MWP ushered in a cultural renaissance, during which population levels surged and Native peoples substantially intensified agriculture, constructed monumental architecture, and produced sophisticated works of art. Foster follows the rise of three dominant cultural centers—Chaco Canyon in New Mexico, Cahokia on the middle Mississippi River, and Casas Grandes in northwestern Chihuahua, Mexico—that reached population levels comparable to those of London and Paris. Then he shows how the LIA reversed the gains of the MWP as population levels and agricultural production sharply declined; Chaco Canyon, Cahokia, and Casas Grandes collapsed; and dozens of smaller villages also collapsed or became fortresses.
- Chapter 1. The Tenth Century
- Chapter 2. The Eleventh Century
- Chapter 3. The Twelfth Century
- Chapter 4. The Thirteenth Century
- Chapter 5. The Fourteenth Century
- Chapter 6. The Fifteenth Century
- Chapter 7. The Sixteenth Century
- Summary and Conclusion
European historians and climate scientists have long recognized that the Medieval Warm Period (ca. AD 900 to 1300 AD) and the early centuries of the Little Ice Age (ca. AD 1300 to 1600) strongly influenced the climate and the economic and cultural history of Europe. The European historian and climatologist H. H. Lamb characterizes the impact of the Medieval Warm Period on Europe as significantly contributing to the unprecedented expansion of the agrarian economy, the rapid increase in population density, and “the first great awakening of European civilization.”
In characterizing the effect of the Little Ice Age on Europe, Lamb and other European historians write that during the cold and mesic period the agricultural economy faltered, agrarian societies were in stress, and warfare and the bubonic plague substantially decreased population levels. However, Lamb’s study covered only Europe and the North Atlantic and did not include an assessment of climate and culture change in North America.
Writing in 2007, the anthropologist Arlene Rosen concurs with Lamb’s assessment regarding climate and culture change in Europe and writes as follows: “The Late Holocene, although more stable than previous periods, does have enough variability to greatly impact human societies as seen in the influence of the Medieval Warm Period and the Little Ice Age on European civilization in the last 1,500 years.”
In her 2010 study of the history of global climate change, Claire Parkinson, a senior NASA climatologist and member of the National Academy of Engineering, also concludes that the impact of the Medieval Warm Period has been fully documented for Europe but that its impact on the cultural history of North America is still unknown.
It is significant that Rosen and Parkinson, like Lamb, describe the impact of the Medieval Warm Period and the Little Ice Age on European cultural history but offer no review and assessment of the impact of climate change during the last one thousand years on the cultural history of the Native peoples of North America.
Perhaps the studies of climate and culture change by Lamb and more recently by Rosen and Parkinson are limited to Europe, the Near East, and the North Atlantic because the story of how North American Native peoples and societies responded to climate change during the Medieval Warm Period and the Little Ice Age has not been told.
That is the purpose of this study. More specifically, the primary purpose of this work is to review archaeological site reports and other scientific studies and documentary information currently available to access the effects of the Medieval Warm Period and the early centuries of the Little Ice Age on the Native cultures and peoples living in the southern latitudes of the temperate zone of North America.
For information on climate change in the Northern Hemisphere, specifically including North America, during the seven-hundred-year study period, this work relies primarily on a recent report on surface temperature reconstructions prepared by the National Academy of Sciences at the request of Congress. The National Research Council (NRC), the research and operating arm of the National Academy of Sciences, published the report in 2006: Surface Temperature Reconstructions for the Last 2,000 Years. Climate change in the study area, namely the southern latitudes of the Temperate Zone of North America, during the study period AD 900–1600 is fully documented in the report.
I reemphasize that this study does not cover climate and culture change in Mesoamerica or in the tropics; neither does it include areas in the northern latitudes of the temperate zone of North America above 40° north latitude or the Arctic. For the purpose of this study, the southern temperate zone of North America includes generally the area between the Tropic of Cancer and 40° north latitude.
The NRC also describes the methodology employed in preparing its 2006 report and the types of evidence relied upon. The reconstructions of surface temperature are based primarily on dendrochronology (tree ring records), on marine and other sediment reports, and on studies of ice isotopes, glacier records, and boreholes in permafrost and glacial ice.
The report offers several relevant conclusions with respect to the seven-hundred-year time period included in the present study. The report concludes that “[l]arge-scale surface temperature reconstructions yield a generally consistent picture of temperature trends during the preceding millennium, including relatively warm conditions centered around A.D. 1000 (identified by some as the ‘Medieval Warm Period’) and a relative cold period (or ‘Little Ice Age’) centered around 1700.” In summary, the report provides the scientific basis for the statements made in this study that—like Europe and the North Atlantic region— the southern temperate zone of North America was substantially influenced by the climatic periods referred to herein and elsewhere as the Medieval Warm Period and the Little Ice Age.
The NRC report also includes a section entitled “Consequences of Climate Change for Past Societies,” in which it notes that agrarian societies such as those found throughout Europe and in parts of North America during the study period were exceptionally vulnerable to rapid climate change. The report states: “The implications of changing climatic conditions have often been most immediate for agrarian economies, particularly in environmentally marginal lands.” In both Europe and North America, environmentally marginal lands for agrarian economies included the marginal uplands in the higher latitudes and elevations.
In support of this conclusion, the NRC report cites the widespread contraction of rural settlements in upland regions of Europe to lower-lying terrain associated with the overall climate deterioration that began in the sixteenth century. Other examples cited include the Norse expansion in the North Atlantic in the early decades of the Medieval Warm Period and the Anasazi abandonment of the Four Corners area in the American Southwest during the twelfth and thirteenth centuries
As Europe and parts of the American Southwest and Southeast had agrarian economies or were substantially intensifying agriculture during the Medieval Warm Period, the dramatic climate change that occurred during the seven-hundred-year study period is reflected in surprisingly similar forms of cultural change in the agrarian societies in Europe, the North Atlantic, the American Southwest, and the Southeast. This study also notes that by AD 900, Europe had long been a continent of mature agrarian societies, but that many Native societies in the American Southwest and Southeast then were only beginning to substantially intensify agricultural production.
For information on how climate change impacted societies in western Europe, Iceland, and Greenland, Lamb and other European historians have relied in large part on documentary and historical records. However, the 2006 NRC report suggests, “In areas where writing was not widespread or preserved [i.e., North America during the tenth through the fifteenth centuries], archeological evidence such as excavated ruins can also sometimes offer clues as to how climate may have been changing at certain times in history and how human societies may have responded to those changes.”
As suggested in the NRC report, I cite in this study archaeological evidence from specific excavated sites and regional archaeological overviews that include information on climate and culture change in the southern latitudes of the temperate zone of North America during the last two thousand years and earlier. As archaeologists usually specialize in specific geographic regions, I attempt to compare and integrate information from archaeological reports prepared by numerous specialists on the American Southwest and Southeast.
I also cite specific marine sediment reports that indicate changes in sea level and climate patterns. The NRC report concludes that both the Medieval Warm Period and the Little Ice Age are accurately reflected in worldwide marine sediment reports prepared by marine scientists. Marine sediment reports contain information about sea-level change dating back over two thousand years and include their own named periods of climate and sea-level change that temporally correspond very closely with the named periods of climate change used in the 2006 NRC report.
Citing H. H. Lamb, the NRC report adds that, in addition to scientific studies, “historical observations, preserved mainly in documentary form, can provide valuable records about past climate states.” Again following the NRC report, I review in this study documentary accounts of sixteenth-century European explorations across the southern temperate zone of North America including the American Southwest, the Southern Plains, and the Southeast for information on climate change and changes in Native cultural patterns during the sixteenth century.
Organization of Work
This work divides the study period from AD 900 to 1600 into seven chapters, each covering one century. In each chapter, a summary of the climate and cultural history of the hundred-year period is presented, beginning with western Europe and followed by the Norse settlement of Iceland, Greenland, and Newfoundland in the North Atlantic. Next, for each century, the climate and Native cultural history of the southern latitudes of the temperate zone of North America are reviewed in more detail. Information from recent studies of over fifty specific archaeological sites plus regional archaeological overviews provide the basis for assessing climate and culture change in the American Southwest, the Southern Plains, the Trans-Mississippi South, and the Southeast during the period of the tenth through fifteenth centuries. In the final chapter (“The Sixteenth Century”), information on climate and cultural change in North America is based primarily on sixteenth-century Spanish expedition documentary sources.
In numerous site-specific excavation studies and regional overviews, American archaeologists detail how Native North American culture changed during the prehistoric period and interpret the impact of the Medieval Warm Period and the Little Ice Age on Native American cultural history. Regional archaeological overviews often include archaeological sites in only one region or state. However, the present study includes archaeological sites from across the continent, from Arizona and northwest Chihuahua, Mexico, to Florida and Georgia on the Atlantic. The study specifically notes parallels in the chronology of climate and culture change as they appear, often synchronically, in many areas across the North American continent, the North Atlantic, and Europe.
For purposes of the present work, the study area includes the lower latitudes of the North American temperate zone, which is divided into four major regions—the American Southwest, the Southern Plains, the Trans-Mississippi South, and the Southeast. For our purposes, the term “American Southwest” includes all or parts of the states of Arizona, Utah, northern Chihuahua, New Mexico, and Far West Texas. “Southern Plains” refers to parts of Oklahoma; the Texas Panhandle region; central, coastal, and southern Texas; and, at times, parts of northern Mexico. The term “Trans-Mississippi South” includes parts of southern Missouri, Arkansas, eastern Oklahoma, northern Louisiana, and East Texas; and the term “Southeast” includes parts of eastern Missouri, western Illinois, western Tennessee, Mississippi, Alabama, Georgia, and northern Florida.
For the American Southwest, the study focuses first on the Four Corners region, particularly on Chaco Canyon. We are fortunate to have three recent comprehensive reviews of Chaco Canyon and the San Juan Valley, one by Joan Mathien (2005), a second by Bryan Fagan (2005), and a third by Steven Lekson (2006). Suzanne K. Fish and Paul R. Fish recently (2007) edited a detailed study of the Hohokam people in southern and central Arizona. In the review of Mimbres people, I rely principally on the works of J. J. Brody, Harry J. Shafer, Anne I. Woosley, and Allen J. McIntyre.
For the Casas Grandes River Valley and Paquimé, the massive eight-volume study by Charles C. Di Peso and his associates provides the basic source of information. But Di Peso’s original 1974 study of the site and area is supplemented by the work of several contemporary archaeologists, including Michael E. Whalen, Paul E. Minnis, Emiliano Gallaga, Gillian E. Newell, Steven Swanson, and other highly competent Mexican and American scholars.
For West Texas, the study cites archaeological studies by Myles R. Miller and Harry J. Shafer in the Jornada Mogollon region and a number of site-specific studies of the eastern Trans-Pecos by Robert J. Mallouf, William (Andy) Cloud, Andrea J. Ohl, John D. Seebach, and their associates with the Center for Big Bend Studies at Sul Ross State University. For the lower Pecos we look to studies of rock art of the region—studies by Solvig Turpin, W. W. Newcomb, and Carolyn Boyd.
For the Texas Panhandle region, the sources used include principally Robert L. Brooks, Douglas K. Boyd, Vance T. Holliday, and Eileen Johnson. Archaeological studies and overviews by Michael B. Collins, Thomas R. Hester, Robert Ricklis, and Richard Weinstein provide the principal sources of information on Central Texas, the Texas coastal region, South Texas, and the Southern Plains.
In the Trans-Mississippi South, Timothy K. Perttula is my principal source for information on the East Texas Caddo, but the works of Dee Ann Story and Robert Rogers are also frequently cited. James A. Brown’s study of the northern Caddoan site of Spiro in eastern Oklahoma provides the basic information on the chronology and history of Spiro. I rely principally on Martha Ann Rolingson’s several published works for information on the Plum Bayou culture and the Toltec site.
There is a massive amount of published material on the cultural emergence, florescence, and collapse of Cahokia located near the junction of the Missouri and Mississippi Rivers. In this study, the recent works of Timothy R. Pauketat are primarily relied upon although several other writers, including Thomas E. Emerson, are also cited. For information on the chronology and culture of Moundville, the study cites principally Vernon J. Knight and Vincas P. Steponaitis but also refers to the more recent studies of Moundville by John H. Blitz and Gregory D. Wilson. Adam King’s work provides the essential source of information on the western Georgia site of Etowah.
David G. Anderson’s study of the Savannah River chiefdoms provides the basic information on the Mississippian site of Irene located near the mouth of the Savannah River. Anderson recently also prepared a comprehensive and frequently cited overview of Late Prehistoric climate and culture change in the Southeast.
In the last chapter, covering the sixteenth century, a review is given of documentary accounts from three major sixteenth-century Spanish expeditions that first explored the study area including the American Southwest, the Southern Plains, the Trans-Mississippi South, and the Southeast. As Spain claimed the entire study area during the period, the sixteenth-century expeditions reviewed were all initiated by Spanish authorities.
In 1528, the Pánfilo de Narváez expedition landed in Florida, and eight years later, after spending most of their time near the Texas coast, Cabeza de Vaca and three survivors arrived in Mexico City. Two documentary accounts of the long journey provide valuable information on the climate during the eight-year period and the cultural ways of the Native peoples whom he encountered across the continent.
About three years after Cabeza de Vaca’s small party reached Mexico City, Hernando de Soto was authorized to commence an expedition from Florida across the Southeast. After spending about three years in the field, marching from Florida to western Arkansas and later to Central Texas, Spanish troops returned to the Mississippi River and sailed to Mexico. There are four accounts of the expedition that describe in detail the strength and vitality of the numerous local chiefdoms encountered and the winter climate that halted the De Soto–Moscoso expedition for several months each winter.
While De Soto was conducting an expedition across the Southeast, Francisco Vázquez de Coronado and his troops in western Mexico began an expedition that took them across the Southwest and parts of the Southern and Central Plains to the western edge of the Eastern Woodlands culture in central Kansas. During the three-year expedition, Spanish chroniclers recorded the vitality of the Pueblo people in New Mexico, the Plains Indians culture, the vast herds of bison on the Southern Plains, and the deep snow and ice conditions that annually suspended Coronado’s movement throughout the winter months.
The numerous accounts of the three large sixteenth-century Spanish expeditions clearly record the cold and wet climatic conditions across the Southwest and Southeast during the century and document cultural changes made by the Native peoples in response to the Little Ice Age.
3800 BC to AD 900
The reconstruction of periods of climate change in North America during the third and fourth millennium BC is based in part on recent marine sediment studies in the Gulf of Mexico. As mentioned earlier, the 2006 NRC report specifically identifies marine sediment studies conducted in estuaries and coastal settings as a significant source for insights in reconstructing climate change. In 2004 the Florida Geological Survey published an investigation by James Balsillie and Joseph Donoghue of the high resolution sea-level history for the Gulf of Mexico since the last glacial maximum. The investigation concluded that the sea level in the Gulf rose steadily and sharply during the early Holocene Epoch and the Altithermal to a high sea-level stand (with a moderate to warm climatic episode) that continued throughout the fourth millennium BC.
The 2004 study indicates that the sea level in the Gulf dropped suddenly and severely during the early centuries of the third millennium BC. The sea level then stabilized at the lower sea-level range (with a cooler and more mesic climatic period) prevailing throughout the balance of the third millennium and the first several centuries of the second millennium BC.
Within the last decade independent climate scientists and archaeologists have prepared and published in scientific journals climate-reconstruction studies that collectively conclude that oscillating climate swings every 500 to 800 years are evident in the history of climate change in the southern temperate zone of North America for at least the last four thousand years or so. Apparently, the Medieval Warm Period, the Little Ice Age, and the Current Warm Period may represent in parts of the temperate zone of North America only the last millennium of oscillating climatic change that occurred and reoccurred during the last four millennia or more.
The reconstruction of oscillating periods of climate change during the last four thousand years is documented in reports and peer-reviewed articles in scientific journals published during the first decade of the twenty-first century by the National Academy of Sciences, the American Association for the Advancement of Science, and the Society for American Archaeology. The following is a condensation of the conclusions reached in the recent studies.
The Southeastern archaeologist Tristram R. Kidder, writing in 2006 in the quarterly journal of the Society for American Archaeology, emphasizes that “the prevailing views of the role of climate change as an agent in the Holocene cultural history are influenced by the perception that the past 10,500 years were characterized by relatively stable climates.” However, Kidder corrects the misconception by adding: “There is now evidence of significant climate variation in the Holocene.” He then suggests that the major climate-forcing processes include variations in galactic cosmic ray intensity, solar insulation, and the Southern (El Nino) and North Atlantic Oscillations.
Kidder characterizes the period after 1800 BC as a moderate to warm climatic episode in the Lower Mississippi River Valley during which the Poverty Point culture arose and flourished in Louisiana and Mississippi. Kidder writes that the warm period of about eight hundred years in the Mississippi River Valley was a time of relatively high population densities, a wide diversity of settlement patterns, and expanded long-distance trade.
The American archaeologist David G. Anderson concurs with Kidder’s assessment. Writing in 2001 about the same warm period, from ca. 1800 BC to 1000 BC, in the Southeast, Anderson says: “During this interval, essentially modern climate, sea level, and vegetation emerged. Mound construction, long-distance prestige-good exchange, and warfare expanded, culminating in dramatic cultural expressions like Poverty Point.”
Neither Kidder nor Anderson insist that the moderate to warm climatic period from about 1800 BC to 1000 BC in the Lower Mississippi River Valley necessarily represented a local manifestation of a broader global climatic period. However, there is evidence that the climate in Eurasia was also moderate to warm during the same period, dating from immediately after ca. 2000 BC. In his 2008 study of climate and culture change in Eurasia in the late Bronze Age (ca. 2000–1000 BC), Michael D. Franchetti writes: “Recent paleo-climate studies in the Dzhungar region suggest that the climate of the second millennium BCE was broadly comparable with that documented today.”
At the close or collapse of the Poverty Point culture, ca. 1000 BC, the climate in the southern temperate zone of North America, and perhaps globally, drastically changed to a much colder and more mesic period, according to Kidder and other American and European archaeologists and climate scientists. Kidder argues in his 2006 study that beginning around 1000 BC in eastern North America, lower population densities are recorded along with a more limited range of settlements, reduced long-distance trade, and limited architecture and artifact diversity.
Recent studies of climate change in the Southwest during the same five-hundred-year period (ca. 1000 to 500 BC) agree with Kidder’s assessment that the cool and wet episode extended well beyond the Lower Mississippi River Valley. For example, in commenting on climate and environmental change on the lower Pecos River in Texas, Solveig A. Turpin writes that around 1000 BC there was “a short but influential mesic interlude that permitted the expansion of the Great Plains grasslands and their characteristic fauna as far south as the Rio Grande.”
In Europe, climate scientists studying the history of natural climate variability have also identified a significant cooling period that occurred on the continent immediately after 1000 BC. In 2008, Jüng Beer and Bas van Geel reported that in Europe during the period ca. 950–700 BC or later, “solar activity abruptly declined, precipitation in north-west Europe suddenly increased, while temperature declined.”
Around 300 BC, the climate pattern in eastern North America and Europe switched again, according to Anderson. He characterizes the archaeological and paleoclimatic record on the middle Mississippi River during the period from ca. 300 BC to AD 400 as an interval in which long-distance networks of trade and other forms of interaction reemerged, spectacular mounds and earthwork complexes were again constructed, and some individuals were buried in elaborately provisioned tombs within massive mounds.50 Anderson refers to this time as the Hopewellian interaction or the Middle Woodland Period in eastern North America. According to Anderson, this same seven-hundred-year warm period in Europe is referred to as the Roman Optimum or Roman Warm Period, during which the classic Greek and Roman cultures emerged and Western civilization first flourished.
Apparently the Roman Warm Period impacted not only the eastern Mediterranean but Iberia as well. In her recent study of climate and culture change in Iberia during the first millennium BC, Joan Sanmarti writes that between ca. 400 and 200 BC, population in Iberia increased to unprecedented levels, the agrarian economy expanded, and agriculture intensified as indicated by an increase in the number and size of silos.
Climate scientists employ different names for the cold and wet climatic period of about five hundred years that followed the Roman Warm Period. A figure included in the 2006 NRC report identifies the cool episode as the “Early Medieval Cool Period.” Regardless of how the period is dubbed by climate scientists, historians characterize it as the Dark Ages, during which agrarian economies in Europe were under severe stress. Anderson writes that during the cool and mesic period, many parts of North America and Europe exhibited evidence of depopulation, changes in land use, large-scale population relocations, and a reduction in organizational complexity.
The cold stretch came to a close around AD 900 with the start of the Medieval Warm Period: the commencement date of the present study. With this background I proceed with the story of climate and culture change in the present study area of North America during the tenth century.
“Climate and Culture Change in North America AD 900-1600 is an ambitious synthesis of archaeological and historical evidence concerning the effects of climate on human societies...The book is suitable for a range of audiences and I think it could make a good text for a course on climate and culture change or one on North American archaeology...The book deserves to be read as a beginning point for a long, thoughtful discussion about climate and culture change in North America and is a welcome addition to the literature on the subject.”
The Midcontinental Journal of Archaeology