P200 Introduction to Prehistoric Archaeology

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Reconstructing Ice Age climate

Global climate has fluctuated through time, driven in part by the changing energy budget of the earth. As originally hypothesized by Milankovitch, earth's orbital parameters influence the distribution of energy falling on the earth's surface through time. Some of this energy is reflected back into space off of clouds, and highly reflective surfaces, like ice or snow (land surfaces with high "albedo"). The rest is absorbed by the oceans and landsurfaces or trapped in the atmosphere (e.g. by "greenhouse gases"). The differential distribution of energy (heat) across the globe drives ocean currents and atmospheric winds, and determines short-term (weather) and long-term climatic cycles. (Note that over the very long-term, the distribution of continental landmasses, mountain chains, etc, also influences global climate.)

During the last million years, earth's climate has experienced wide swings in climate, from relatively cold ("glacial) conditions to warm ("interglacial") ones. Each cycle has lasted approximately 100,000 years, and these cycles are called Ice Ages. Within each major glacial cycle a number of short-term, small-scale fluctuations have also occurred.

The effect of these climatic changes has been relatively minor in the tropics, but has had a major impact on terrestrial environments in the middle latitude, temperate regions, like Europe and North America.

Evidence of Climate Change:

There are many types of evidence that can be used to reconstruct the changing record of earth's past climate. Most of these are called "proxy indicators" of climate, because they follow the effects of ancient temperature changes, rather than documenting the temperature directly.

For example, in terrestrial environments, archaeologists can often relate their sites to:

For evidence of world-wide sequences of climate change, climatologists can sample sediments drilled from the deep ocean or from cores of ice drilled from ice caps (e.g. in Greenland and Antarctica). These cores have tiny strata (layers) that preserve chemical and biological indicators of environmental conditions at the time they were deposited. The strata can be dated directly using radio-metric techniques.

Links to good Paleo-climate sites and Ice Age sites on the web:

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