Climate Change and Human Civilization
Christina Hulbe, Portland State University

A defining characteristic of human civilization is change. Over the millennia, civilizations have risen, fallen, and risen again. Many theories have been put forward to explain the fall of civilizations, most involving cultural factors such as imperial aspiration and excessive complexity. Recently, climate variability has been recognized as an important external forcing that must be added to our understanding of human history. Understanding the role of climate in that history requires collaboration between researchers in the social and natural sciences. In this presentation, the sudden collapse of the Akkadian Empire (2350 to 2150 BC, Earth's first empire) will be discussed in the context of climate variability.

Earth's modern climate is characterized by a small set of modes of variability: northern and southern annular modes (the NAM and SAM, respectively) of variability encircling the poles; the Pacific North American pattern, observed in the pressure gradient between Hawaii and the Aleutian Islands; and the well-known tropical El-Nino Southern Oscillation (ENSO) pattern. Variability in these patterns affects atmospheric pressure patterns and in turn yields variations in wind pattern and strength, temperature, and precipitation on time scales ranging from weeks to decades. Together, they play an important role in modulating the statistics of weather and climate experienced at any given time and place on the globe. On longer time scales, they may prescribe a significant part of Earth's climate variability. Trends in climate, driven by or reflected in the systematic changes in the atmospheric modes, may have played a role in the fates of past civilizations.

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