In the Andes, climate affects the position and size of glaciers; the location, frequency, seasonality, and quantity of precipitation; sea level; the position of the snow line and of vegetation belts; the frequency and intensity of El Nino/Southern Oscillation (ENSO) events; and plant and animal distributions. Furthermore, the Andes are located on a subducting plate margin (the oceanic Nazca Plate is sliding under the continental South American Plate), so the region is subject to frequent seismic activity and volcanism. Earthquakes, volcanic eruptions, and the tsunamis sometimes associated with seismic activity not only have a devastating impact on the people, but on the towns, cities, and economic infrastructure such as irrigation works (de Silva and Francis 1991; Giesecke and Silgado 1981; Oliver-Smith 1986). However, because of the unusual shallow-angle subduction under northern and central Peru, active volcanism does not occur here as it does in Ecuador and in southern Peru, Bolivia, northern Chile, and Argentina (Barazangi and Isacks 1976). Consequently, this sector of the Central Andes lacks catastrophic volcanic eruptions and obsidian (a volcanic glass highly prized as a lithic raw material). However in southern Peru there have been major volcanic eruptions, such as that of Huaynaputina in AD 1600, which blanketed the region with ash (de Silva and Zielinski 1998).
Paleoclimatic paleoenvironmental studies in the Central Andes are ongoing, with new discoveries yearly. Here, we summarize the major sources of information on past conditions and changes; later, we will point to some important instances of climatic or environmental alterations that correlate with cultural change. To keep up with the cutting edge, readers are encouraged to follow the contents of journals such as Science, Nature, Geology, Quaternary Research, Quaternary International, Quaternary Science Reviews, Palaeegeegraphy, Palaeeclimatelegy, Palaeoecology, and Geoarchaeology in addition to the standard archaeological literature.
The high Andes offer a multitude of paleoclimatic archives. These include ice cores from ice caps and glaciers (sometimes with annual resolution) (e. g., Thompson et al. 1985, 1995, 1998), glacial deposits (e. g., Rodbell and Seltzer 2000), wetland and lake cores (e. g., Abbott et al. 1997), salar (salt flat) cores (Geyh et al. 1999), packrat middens
(Betancourt et al. 2000), archaeological sites (e. g., Aldenderfer 1998), and others. In contrast to the highlands, the extreme aridity and cool oceanic waters along the Central Andean coast mean that this region lacks pollen catchments and corals, two important sources of paleoclimatic data in other coastal regions. Glaciers never extended to the tropical Andean coast. Cores from the ocean floor have critical hiatuses through the middle of the Holocene and/or their recent segments have not been published in detail. Consequently, archaeological sites and their contents play an important role in reconstructing coastal climate over the 13,000 years of human presence (Sandweiss 2003).
Every paleoclimatic archive requires interpretation; many are not directly suited to the scale or locale of archaeological sites (Dincauze 2000), and extending inferences beyond the immediate region of the record requires recognizing teleconnections (longdistance climatic interactions) and positing that the same teleconnections operated at the time of interest. Paleoclimate modeling is another approach to reconstructing past environments and climates in the Andes. However, thus far few models operate at the human scale that would be of most use to archaeologists, and there is little agreement among different models at any spatial scale.
Humans had arrived in the Andes by about 13,000 years ago, at the end of the Pleistocene epoch as the last ice age was drawing to a close (Dillehay 2000; Lavallee 2000). Through most of the world, this was a period of radical and often abrupt climatic change (Taylor et al. 1997, inter alia). Nor was the succeeding Holocene epoch (the last 11,400 years) the time of stability once envisaged (e. g., Stager and Mayewski 1997; see articles in Palaeogeography, Palaeoclimatology, Palaeoecology vol. 194[1-3], 2003, for recent, regional Andean data). Though swings were less radical than in the Pleistocene, Holocene climatic variability occurred during a time of increasing human population size and density, increasing sedentism, and developing dependence on agropastoral subsistence systems—in other words, a time of ever greater vulnerability to change.
From the end of the Pleistocene Epoch to the present, global climate has cycled through many phases and events with local, Andean expressions, at millennial, centennial, decadal, and interannual time scales. The earliest well-dated archaeological sites in the Central Andes date to the Younger Dryas, a 1,600-year cold reversal in much of the world, the last gasp of the waning ice age from 13,000-11,400 cal yr BP. In much of the world, the mid-Holocene (9000-3000 cal yr BP) was a time of greater than present warmth; in the Atacama Desert of northern Chile and parts of southern Peru, this appears to have a period of great aridity and low human populations labeled by Nunez as the “archaeological silence” (Grosjean et al. 1997; Sandweiss et al. 1998; however, as usual there is controversy, see for example Betancourt et al. 2000; Grosjean et al. 2001). At the same time, the first part of this period (9000-5800 cal yr BP) saw mildly increased precipitation on the north coast of Peru. The second part of the mid-Holocene (5800-3000 cal yr BP) witnessed the rise of monument building, fishing, irrigation farming, complex societies on the central and north coasts of Peru and in the adjacent highlands in a climatic context of coastal desiccation and increased interannual variability. To the south, these developments tended to lag, appearing as much as a millennium later, toward the close of the dry period (Sandweiss 2003; Calgero Santoro, personal communication)
In the Central Andes as elsewhere, people have played major roles in changing their environment, not always for the better (Dincauze 2000; Redman 1999). Humans are active geomorphic agents (Denevan 1992; Erickson 1992; Hooke 2000) as well as frequent meddlers with the biota (Gade 1999; Johannessen and Hastorf 1990). As in much of the world, the adoption of agriculture had the most visible impact in the Andes, both by generating new
Species and by changing the landscape and available habitats (Denevan 2001; Zaro and Umire 2005). In quebradas of the western slopes, small-scale irrigation began by 6100 cal yr BP and led to “artificially created wet agroecosystems” (Dillehay et al. 2005). On the desert coast, the advent of irrigation systems (beginning perhaps as early as 4400 cal yr BP) expanded the vegetated portion of valleys from narrow gallery forests to the entire floodplain and even in places onto the desert margin. Much later, during the Middle Horizon, terracing began to transform the high Andes by radically increasing the amount of flat surface available for planting (Moseley 2001: 232-233), while the construction of raised fields in the Lake Titicaca region during the first millennium AD (1950-950cal yr BP) vastly enhanced the agricultural potential of that harsh region (e. g., Erickson 1988, 1992). One study has found that Andean terraces were particularly effective in preserving soil quality even after centuries of agricultural use (Sandor and Eash 1991, 1995). In the Llanos de Mojos of Bolivia raised fields were also constructed over a vast area (Denevan 1966; Erickson 1995; Walker 2004). In addition to farming, other deliberate or inadvertent human actions altered environments and the resources that they offered to people, and even deliberate actions often had unintended consequences (Redman 1999).
World History
