The geologic record of climatic change

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Abstract
This paper reviews the principal results from paleoclimate studies and includes background material slanted toward climate modelers. The inferred temperature history of the last 4.6 billion years indicates major changes in the components of the earth's climate system. A secular change in global insolation receipt is due to a 20–30% increase in solar luminosity since the formation of the earth. A CO2‐H2O greenhouse effect may have offset the lower luminosity during early earth history. Inferred fluctuations of global temperature have occurred over a broad range of time scales. On time scales of 106–108years, paleogeographic factors (e.g., continental drift and sea level changes) have contributed significantly to temperature changes associated with transitions between nonglacial and glacial states. Preliminary modeling efforts indicate that additional factors (e.g., CO2, changes in atmospheric circulation) must also be considered in order to explain the origin of nonglacial climates. The origin of polar ice caps may result from ocean circulation changes that were caused by plate tectonic processes. Fluctuations of ice volume on a time scale of 10³–105years correlate with insolation variations caused by orbital perturbations. Feedback interactions within the land‐sea‐air‐ice system (e.g., ocean circulation changes and bedrock dynamics) have been responsible for a significant modulation of the orbital signal. Ice ages may be due to orbitally induced temperature changes superimposed on a global cooling of terrestrial origin.