The Magnitude and Rate of Past Global Climate Changes

Abstract

The earth's climate is constantly changing and currently warming. This paper is an evaluation of previous climate changes intended to test the validity of assigning causality to human activity. Records of glacial advances and retreats indicate changes in relative summer temperature. Lacustrine and subaerial sediments afford a record of glacier advances and retreats from the end of the Pleistocene. Palynology offers a record of species succession in response to climate changes. Dendrochronology indicates summer temperature. Isotope paleontology provides a measurement of temperature at the time of marine sediment deposition. Isotopic evaluation of continental ice is an indicator of temperature at the time of precipitation. Anthropologic sources provide significant climate data, such as information about villages overrun by glaciers, open-ocean iceberg density, or harbors filled with ice. Available sources record continual changes in climate. The temperature lowered 15 to 20°C from the Paleocene to the Neogene. Another 10°C change occurred in the Pleistocene. Correlative data from North America, Greenland, and Scandinavia indicate many climate changes were global in scope. It is difficult to develop precise paleothermometry, but qualitative evaluations indicate sudden and dramatic changes in climate. Some changes 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 severe but no greater in rate or magnitude, and probably less in both, than many changes that have occurred in the recent geologic past.