Historical documents, along with archeological and paleobiological evidence, can also reveal how societies and ecosystems have responded to climate variability in the past. This section provides a short illustrative summary of past human responses to climate change. However, it is important to note the danger of circular reasoning in this sphere, in the sense that the same evidence for cultural response cannot also be used to infer climatic causality. It is also clear that past societal responses have in general not been predictable or predetermined in advance. Although societies may have been required to adapt to new conditions, the outcome has depended on the success of the choices that were made (Diamond 2005, Rosen in press).

The implications of changing climatic conditions have often been most immediate for agrarian economies, particularly in environmentally marginal lands, and for long-distance communications. In the former case, there was a widespread contraction of rural settlement in upland regions of Europe to lower-lying terrain, associated with the overall climatic deterioration between the late 16th and mid-18th centuries (Parry 1978). In Iceland, an increase in storminess and in winter sea ice cover during the Little Ice Age hampered seaborne communications across the North Atlantic, on which the island’s population was critically dependent. The 1780s brought not only the most severe pack ice of any decade since the 16th century (Ogilvie 1992) but also poisoning of livestock and humans by hydrogen fluoride gases released by the Laki fissure eruption. In combination, this killed more than 75 percent of Iceland’s livestock and 25 percent of its human population and brought society close to collapse. Other examples where climate change may have played a part in societal collapse include the Classic Maya during the 9th century A.D. and the Anasazi of the American Southwest during the 12th and 13th centuries. Both of these cases were linked to periods of extended drought conditions (Hodell et al. 1995, Dean 1998). Climate-induced stress can also act as a stimulus to innovate; for example, declines in rainfall or shifts in temperature have sometimes been followed by technological developments, such as irrigation (Rosen in press).

It is also possible to find examples of climatic changes that were not accompanied by any obvious direct social consequences, and to find cases where the same climatic change had sharply contrasting consequences for different social groups in the same area. A clear example of contrasting adaptations and success/failure in the same environment is provided by the Inuit and the Vikings in western Greenland and the Arctic during the onset of the Little Ice Age. The Norse settlements of Greenland were always marginal, not only because climatic conditions were poorly suited for agriculture but also because of isolation from their parent cultures in northern Europe. In the face of increasingly harsh climatic conditions, populations declined, the western Viking settlement was abandoned around 1350, and the eastern settlement followed suit about a century later. The Norse perceived the adverse changes in climate as a function of cosmological disorder and built ever more impressive churches, rather than adopting new technologies or searching for new sources of food (Barlow et al. 1997, Buckland et al. 1996, McIntosh et al. 2000, Diamond 2005, Rosen in press).

During the same period of medieval warmth that had encouraged Norse expansion, retreating sea ice appears to have allowed an eastward migration of native Inuits along the Arctic shore from Alaska, and thence southward into the same areas of west Greenland being colonized by the Vikings. And like the Norse, these Thule Inuit

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