| Summary: | A presentation to the Seminar on Sustainable Development NBA 573, BEE 673 Sage Hall B-11 If the 4.6 billion years the earth has been in existence is one day of geologic time, all of recorded earth history corresponds to the last one tenth of one second of that day- hardly enough time to form an opinion of what is going on in the room in which you are sitting, and hardly a good basis for forming a perspective on climate change. Geology provides the needed perspective. From direct evidence (glacial striations, ice-rafted drop stones, changes in pollen, ice cover, and sea level) and indirect evidence (changes in the isotopic composition of sediments and ice, and in the dust content of polar ice) geologists infer that the earth may have been alternatively completely frozen (-50C) and very warm (+50C) in Late Proterozoic time (800-600 million years ago). Thereafter the earth was warmer than present except for "ice ages" in Pennsylvanian and Permian time (~320-250 million years ago) and in the Quaternary (last 4 million years). Before the last decline in global temperature, England had a climate similar to that of Indonesia. Fossils of crocodiles and broad leaf tropical plants are preserved in the Eocene (40 million year-old) clays there. Continental glaciers developed in Antarctica ~34 million years ago and in Greenland ~8 million years ago. Starting about 2 million years ago continental glaciers periodically covered North America and Europe. Each glacial cycle was ~120,000 years in duration: 100,000 years of ice growth (ice-house conditions) and 20,000 years of warmer, interglacial, green-house conditions. The end of each interglacial was abrupt. The last glacial cycle started about 130,000 years ago. Ice reached Ithaca, New York about 45,000 years ago. At its maximum extent the ice reached to Long Island, and there was ~ 1 mile of ice over Ithaca. The ice age ended abruptly ~12,000 years ago and the last ice melted in Canada ~5,500 years ago. Our interglacial has probably been more uniform in temperature than ...
|
|---|