(This is the first in series of posts about the environmental context of human ecosystems and archaeological sites, ca. AD 800-1700).
Following the lead of geologists, paleontologists, and climatologists, in recent years archaeologists have been paying more attention to the Medieval Warm Period. Ancient histories and proxy climate records such as tree rings, ancient changes in lake levels, and data from lake, estuary, and ocean sediment cores indicate a long term warming trend in the northern hemisphere. For example, a warmer climate in the 10th through 13th centuries allowed the Norse to colonize Greenland, until the onset of the Little Ice Age after AD 1300 severely affected food for their livestock, and drastically interfered with North Atlantic navigation. The Medieval Warm Period in western Europe was a period of boom agricultural production, as sufficient rainfall combined with longer growing seasons led to population growth, new farming communities, and a powerful economic base for monarchs and the Church. In terms of these effects in the North Atlantic and Western Europe, the Medieval Warm Period is often seen as significantly beneficial to human populations and the flowering of European culture during the Middle Ages. It even seems associated with the rapid expansion of the ancestral Inuit (Eskimo) culture across the North American Arctic. These are some of the most commonly held images of the Medieval Warm Period.
However, the warming trend wasn’t as beneficial in some parts of the world, including the portions of North America that were affected by prolonged droughts. The periods of drought are perhaps most familiar to students of the Pueblo cultures of the American Southwest. Here, archaeologists have discussed for some time whether droughts of the 12th and 13th centuries AD led to the abandonment of Chaco Canyon and other important Pueblo settlements. As the archaeologist and writer Brian Fagan has chronicled in his 2008 book The Great Warming, severe, decades-long droughts also affected a much wider area of the American West, including the Great Basin and the California coast. And recently, Larry Benson and colleagues (2009) have demonstrated patterns of extreme variation in rainfall affecting the large, ancient community of Cahokia in the American Midwest. A significant wet period in the 11th century was followed by long periods of severe drought in the 12th-13th centuries. Drought appears to have caused the abandonment of important upland farming communities (which had been established during the preceding wet interval), and social unrest led to the fortification of the political and ceremonial center of the ancient city. After more than two centuries of prolonged or recurrent drought, Cahokia was essentially abandoned by the mid-14th century.
In the Hudson Valley, archaeological sites dating to the period AD 1000-1300 appear to be scarce, or at least relatively invisible to archaeologists. This trend had been noted, for example, by former New York State Archaeologist Robert E. Funk (1976), and has continued to hold through the era of more recent archaeological research and Cultural Resource Management studies. Could the Medieval Warm Period have affected Hudson Valley Native American populations in some significant way, such as causing population decline, out-migration, or a reorganization of settlement patterns? Because of scarce archaeological evidence, these questions are difficult to answer. However, maps of the distributions of 12th and 13th century droughts produced by Benson et al (2009) show the Hudson valley on the edge, or just within, the area affected by dry conditions (although not nearly as severe conditions as plagued Cahokia or the Southwest). Drier conditions could have adversely affected corn cultivation on sandy, Hudson River floodplain soils. According to Benson et al’s (2009) maps, decreased spring-summer rainfall would also have affected the flow of water from the west, whose tributaries feed the Hudson from the Mohawk River and the Catskill and Adirondack Mountains.
In addition to the implications of Benson et al’s (2009) maps-- which essentially are tree-ring based reconstructions of continental scale drought patterns-- three studies from the Hudson- Mohawk drainage suggest the possibility of significant climate change effects. First, stratigraphic and radiocarbon data found in soil cores taken from Collins Lake along the Mohawk River indicate a long period of increased storminess from about AD 1180-1600 near Schenectady (White and Rodbell n.d.). This period overlaps the last part of the Medieval Warm Period and the early part of the Little Ice Age (AD 1300-1860). Severe droughts continued into, or recurred over this period of time in several parts of eastern North America, as noted by archaeologist David Anderson and colleagues (1995), among others. What is intriguing is the notion that droughty periods may encompass changes in the seasonality and severity of rainstorms, a topic of great currency and concern during the late 20th-early 21st century period of global warming.
Second, although the Collins Lake data are not conclusive evidence of Medieval Warm Period effects, and reflect conditions also spanning much of the Little Ice Age, a Hudson River study cited by Brian Fagan (2008:229) shows direct evidence of the prolonged warming trend. Analysis of a core of lower Hudson estuary sediments by Pederson et al (2005) shows signatures of a prolonged warm period, including increases in charcoal and pine pollen, as well as evidence of increased erosion. These trends are tied into a radiocarbon chronology, and this study is seen by the authors as part of a pattern of evidence of drought along the eastern North American coast during the Medieval Warm Period.
The Collins Lake and lower Hudson estuary studies indicate an environment affected by drought, lower water levels, and greater storminess. Increased storminess leading to sudden influxes of water to typically low river levels may have increased the risk of losing floodplain crops due to untimely floods over the river banks. The third case to consider may bear on this issue and is from the upper Hudson region near Albany. Here, the Cultural Resource Management archaeological data recovery program that excavated the Goldkrest Site on Papscanee Island, Rensselaer County, provides some very interesting circumstantial evidence regarding the possible effects of flooding during the Medieval Warm Period. The initial period of human occupation of the site (long before the Medieval Warm Period) is indicated by a small hearth-site (ca. AD 360+/- 70) deeply buried in floodplain sand. This site contained a small hearth and very few artifacts, representing a briefly occupied camp. Geoarchaeological analysis indicates that ground surfaces were unstable and floodplain building rapid during this time and until about AD 1000, when a more stable ground surface (but one still affected by floods) began to form (Schuldenrein 1997). The site’s excavator, Lucianne Lavin (2004), interprets a cluster of radiocarbon dates associated with evidence of burning of this surface as indicating forest clearing by humans using fire. This clearing may have been done to create aboriginal gardens, although no evidence of habitation associated with gardens is documented until the period when another cluster of radiocarbon dates-- and associated house patterns, pottery, and corn fragments-- indicates settlement during the 15th-17th centuries. Is it possible that this lag between clearing and settlement is related to a Medieval Warm Period threat of severe floods? If so, human settlement on this particular floodplain would have been discouraged during the Medieval Warm Period, and crop loss due to flooding (in addition to drought) would have limited the effectiveness of corn agriculture with some palpable regularity.
Could the response to these conditions have encouraged a diverse subsistence pattern integrating a variety of riverine, floodplain and upland resources? Is there evidence of a decentralized and mobile settlement pattern awaiting discovery, hidden just below the typical limit of effective archaeological visibility, (which is so often conditioned by small site size and sparse artifacts)? Will new data on archaeology and ancient environments fill the apparent information gap associated with the Medieval Warm Period in the Hudson Valley?
With these questions posed, time spent in careful investigation will tell.
Anderson, David G., David W. Stahle, and Malcolm Cleaveland
1995 Paleoclimate and the Potential Food Reserves of Mississippian Societies: A Case Study from the Savannah River Valley. American Antiquity 60:258-286.
Benson, Larry V., Timothy R. Pauketat, and Edward R. Cook
2009 Cahokia’s Boom and Bust in the Context of Climate Change. American Antiquity 74:467-483.
2008 The Great Warming: Climate Change and the Rise and Fall of Civilizations. Bloomsbury Press, New York.
Funk, Robert E.
1976 Recent Contributions to Hudson Valley Prehistory. New York Sate Museum Memoir 22, Albany.
2004 Mohican/Algonquian Settlement Patterns: An Archaeological Perspective. In The Continuance - An Algonquian Peoples Seminar. New York State Museum Bulletin 501, Albany.
Pederson, Dee Cabaniss, Dorothy M. Peteet, Dorothy Kurdyla, and Tom Guilderson
2005 Medieval Warming, Little Ice Age, and European Impact on the Environment During the last Millennium in the Lower Hudson Valley, New York. Quaternary Research 63(2):238-249.
1997 Summary Geoarchaeological Observations at the Goldkrest Site, CNG TL-470, East Greenbush, New York. In Stage III Archaeological Investigations: The Goldkrest Site, CNG TL-470, East Greenbush, New York, Appendix 7. Archeological Research Specialists, Meriden, Connecticut.
White, Ian Robert and Donald T. Rodbell
n.d. A ~ 1000 Year Record of Sedimentation in Collins Lake as Evidence of Local Storminess and Flooding on the Mohawk River (New York). http://minerva.union.edu/garverj/mohawk. Consulted on April 14, 2010.