Climate Change and the Colorado High Country

In this paper by James Benedict, one of the foremost experts in Rocky Mountain archaeology, the author explores how climate change influenced human population density near the Continental Divide over the last 3000 years. Benedict explains that the Continental Divide area is a good place study how climate change affected humans because it is considered a marginal environment. Thus, early human (and non-human) inhabitants of this area lived a kind of feast or famine existence and so were extremely vulnerable to even slight shifts in climate.

These early residents of the mountains exhibited a mobile lifestyle since the large animals they hunted were migratory (bison, elk, deer and sheep) and vegetation that they ate was scarce and only available at certain times of year. In addition, weather and landscape conditions at the higher altitudes were unforgiving and harsh and necessitated that winter base camps be located at lower elevations. During summer and early fall, people were highly mobile and travelled into high altitudes to hunt, forage, trade, etc.

Benedict analyzed carbon dates from numerous archaeological sites to determine that, during the last 3000 years, the number of sites found has increased dramatically. Although extreme taphonomic processes skew the record in the Rocky Mountain region, it is inferred from this data that population density rose significantly since 1000 B.C. This population increase was likely due to both growth within extant groups and migration of non-mountain peoples into the area.

Lichenometry, the study of lichen growth to determine the length of time period that rock has been exposed, was used to graph climatic shifts within the 3000-year time period. Lichen can only survive for a few years if covered by snow for too many weeks of the year. So, Benedict used this snow-kill information to discover when there was a period of time when snow melt was at a minimum. He then compared these trends to population density data.

The results show that during times when snow cover lasted the longest, the animals that were hunted by people did not visit their usual grazing grounds due to lack of exposed vegetation. Benedict hypothesizes that because the game animals were not in abundance during these time periods, human population density decreased because the people would have had far less successful hunting seasons. Since these human residents got most of their food in the form of big-game meat (80%-90%), there would have been no incentive for them to stay when these animals were not available. Thus, during times of increased snow cover, the area surrounding the Continental Divide of Colorado would not have been able to support a large population of humans, hence the large fluctuations in population density during the past 3000 years.

Benedict concludes by explaining that population density in marginal environments like the Rocky Mountains is valuable data for archaeology, ecology, climatology and general knowledge as a whole. He suggests that studies such as this one can be used to explain the fragility of regions like this even today. With climate changing at an exponential rate, it is vital that we understand how these shifts can dramatically influence our way of life.

Benedict, James B. 1999 Effects of Changing Climate on Game-Animal and Human Use of the Colorado High Country (U.S.A.) Since 1000 BC. Arctic, Antarctic, and Alpine Research, Vol. 31, No. 1, pp. 1-15. INSTAAR, University of Colorado.