J.R. McNeill
Georgetown University

I. Introduction

It is prudent to accept that the atmosphere and oceans are indeed warming, as the evidence tells us, and that this trend will accelerate in the decades ahead. While we do not and cannot know just how much warming will occur how fast, we can safely say that the rapidity of warming currently, and in all likelihood what the next decades hold, has few precedents in the history of the earth and none in the history of civilisation.

No instrumental records exist for prior episodes of climate change. The proxy evidence used for the reconstruction of climate history – palynology, foraminifera, oxygen isotopes and much more besides – can give a good but not a precise idea of past temperature and precipitation patterns.

The earth’s climate has never been static. For the past 2.7 million years, it has shown a pattern of alternating long ice ages and shorter interglacials, governed by cycles in the earth’s orbit around the sun. The last ice age was its height around 20,000 years ago. Its end (c. 11,000-6,000 years ago) was probably crucial for human history as it coincided with the emergence of agriculture in multiple locations. After that bout of warming – generally much slower than what we have witnessed in the last 100 years but not without sudden lurches now and again – global climate changed only modestly and slowly until the industrial age.1
While our Paleolithic ancestors did have to cope with rapid climate change from time to time, when they did so the earth had fewer people (or hominids) than Chicago has today, and they were accustomed to migrating with their scant possessions as a matter of course. Their response to adverse climate change (as to much else) was to walk elsewhere.

Since the emergence of agriculture, sedentarism, civilisation, and the settlement of all habitable parts of the globe, the Paleolithic response has become more and more impractical. Thus, while in earth history there are no doubt analogues for the climate change now underway, there are none in human history. We have entered uncharted terrain.

continue to:

II. Buffers, Resilience and Nature’s Shocks

III. Societal and Political Reverberations

IV. A Glance at the History of Technological and Social Change

V. Conclusion

1 Recent accounts of Holocene climate that are easily accessible to non-specialists include Eugene Linden, The Winds of Change: Climate, Weather and the Destruction of Civilization (New York: Simon & Schuster, 2006); Brian Fagan, The Long Summer: How Climate Changed Civilization (New York: Basic Books, 2004). Somewhat more technical are William James Burroughs, Climate Change in Prehistory: The End of the Reign of Chaos (Cambridge: Cambridge University Press, 2005); and Douglas MacDougall, Frozen Earth: The Once and Future Story of Ice Ages (Berkeley: University of California Press, 2004).