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Book Chapter

Rate and Magnitude of Past Global Climate Changes

By
John P. Bluemle
John P. Bluemle
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Joseph M. Sabel
Joseph M. Sabel
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Wibjörn Karlén
Wibjörn Karlén
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Published:
January 01, 2001

Abstract

Existing data indicate that the earth’s climate is probably warming. Politicians and the media typically assume this warming is the result of human activity. This article summarizes previous climate changes to test the validity of assigning causality to human activity.

Records of glacial advances and retreats indicate relative summer temperature. Lacustrine and subaerial sediments afford a record of glacier advances and retreats from the Pleistocene to the present time. Palynology offers a record of species succession in response to climate changes. Dendrochronology is another indicator of summer temperature. Isotopic paleontology offers a measurement of temperature at the time of marine sediment deposition, and isotopic evaluation of continental ice is an indicator of temperature at the time of precipitation. Anthropologic sources contain significant climate data, such as information about villages overrun by glaciers, open- ocean iceberg density, or harbors filled with ice. Today, scientists are capable of direct measurement of climatic conditions.

These sources record continual changes in climate. Broadly, the temperature changed 15° to 20°C from the Paleocene to the Neogene. Perhaps there was as much as another 10°C change in the Pleistocene. Correlative data from North America, Greenland, and Scandinavia indicate many climate changes were truly global in scope. Although it is difficult to develop precise paleothermometry, qualitative evaluations indicate sudden and dramatic changes in climate. Some are perhaps as great as a change from conditions warmer than today to a full glacial climate in as little as 100 years. The converse can be true. Current data indicate a trend of change that is substantially severe but no greater in rate or magnitude, and probably less in both, than many changes that have occurred in the past.

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Contents

AAPG Studies in Geology

Geological Perspectives of Global Climate Change

Lee C. Gerhard
Lee C. Gerhard
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William E. Harrison
William E. Harrison
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Bernold M. Hanson
Bernold M. Hanson
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American Association of Petroleum Geologists
Volume
47
ISBN electronic:
9781629810669
Publication date:
January 01, 2001

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