The Social Consequences of Climate Change in the Central Mesa Verde Region

Abstract

The consequences of climate change vary over space and time. Effective studies of human responses to climatically induced environmental change must therefore sample the environmental diversity experienced by specific societies. We reconstruct population histories from A.D. 600 to 1280 in six environmentally distinct portions of the central Mesa Verde region in southwestern Colorado, relating these to climate-driven changes in agricultural potential. In all but one subregion, increases in maize-niche size led to increases in population size. Maize-niche size is also positively correlated with regional estimates of birth rates. High birth rates continued to accompany high population levels even as productive conditions declined in the A.D. 1200s. We reconstruct prominent imbalances between the maize-niche size and population densities in two subregions from A.D. 1140 to 1180 and from A.D. 1225 to 1260. We propose that human responses in those subregions, beginning by the mid-A.D. 1200s, contributed to violence and social collapse across the entire society. Our findings are relevant to discussions of how climate change will affect contemporary societies.

An Anthropological Perspective on the Climate Change and Violence Relationship

“…Proxy climate data indicates a history of rainfall variability punctuated by prolonged droughts, including the Great Drought of 1276-1299 CE which preceded the final abandonment of population dense settlements in the central Mesa Verde and northern Rio Grande areas [66][67][68]. Reconstruction of populations and agricultural potential in six distinct environmental areas of Mesa Verde show that increases in maize production and use of land amenable to rain-fed maize agriculture strongly correlated to population growth of pre-Pueblo communities [67]. Populations continued to grow even after maximizing the land under maize production, which advanced environmental degradation through deforestation and overhunting of deer.…”

“…Populations continued to grow even after maximizing the land under maize production, which advanced environmental degradation through deforestation and overhunting of deer. During cooler dry periods, agricultural conditions in parts of Mesa Verde remained stable enough to continue maize production, albeit at a reduced level, which drew people in from more marginal settlements [66][67][68]. Denser populations during rough periods strained available resources and evidence suggests that, at the societal level, social and political inequalities affected household access to arable land and thus production.…”

“…Denser populations during rough periods strained available resources and evidence suggests that, at the societal level, social and political inequalities affected household access to arable land and thus production. Human remains at some of the denser settlements show signs of violent trauma including warfare, massacres, and cannibalism, and in the central Mesa Verde violence tends to be greater during periods of high variance in maize production and low potential production per capita [21,67]. Violent events preceded outmigration and the final abandonment of dense settlements as residents left, likely seeking greater security and a more stable food supply.…”

Twenty-first century approaches to ancient problems: Climate and society

“…General improvement in these techniques has allowed modelbased archaeologists to move away from simple correlations between climatic variability and changes in human history and pay more attention to the causal pathways responsible for these correlations (41).…”

“…Food-sharing models strongly suggest that interhousehold exchanges of maize and meat permitted larger populations to be supported, encouraged people to aggregate in villages (especially in periods of high production), and stabilized reliance on domesticated turkey that became important in the northern Southwest in the 11th century AD following depression of deer populations. Tacking between results from maize-niche modeling, agent-based models, trophic network modeling, and empirical research allows us to suggest that long-term regional population growth, depression of important wild resources (especially deer), extreme dependence on just one cultigen, climateinduced migration into portions of the central Mesa Verde region that were highly susceptible to drought, religious, and probably political balkanization, conflict, and perhaps hostile encounters with mobile foragers just entering the Southwest from the north together created the context for its final abandonment (41). We should expect to find similar complexity in cases of climate-related culture change in other times and places where conditions cannot be viewed so clearly (97).…”