Division of Energy

Global Climate Change: Paleoclimatology

Paleoclimatology is the science of studying the geologic record of the Earth's climatic history before historic times. Records of temperature and rainfall patterns can be found in tree rings, ice caps, and glaciers, ocean and lake sediments, and in rocks as old as one billion years.

Paleoclimatology is important in understanding the origin and distribution of certain types of oil and mineral deposits, and more recently in attempting to predict future climatic trends by studying prehistoric climate changes.

Current computer climatic simulation models predict that the anticipated doubling of carbon dioxide concentration in the atmosphere in the next century will cause a significant rise in the earth's average surface temperature. It is also possible that this will disrupt air circulation patterns causing flooding in coastal areas and possible drought in some of the earth's great agricultural areas. The time period covered by historic climatological observations is too short to test the ability of the computer models to reliably predict future climatic trends.

Reconstructing Ancient Climates

The reconstruction of the earth's climatic history, particularly that of the past one million years, provides a data base upon which to test the reliability of computer models and also provides valuable information on the climatic changes that have occurred in the past, and therefore, changes that can be anticipated in the future.

• Tree rings provide the most accurate climatological data from 4,000 years ago to the present. They provide excellent data on drought cycles as well as general information on temperature changes.
• Ice cores from ice caps and glaciers show annual snow depths and the air temperature at which the snow fell for the past 160,000 years. The latter is made possible by the fact that 160/180 ratios in snow vary with changes in temperature. The composition of the atmosphere at the time of ice formation is determined by analysis of air bubbles trapped within the ice.
• Ancient soils provide clues as to the distribution of rainfall over the earth at the time they were formed. Windblown dust from arctic or desert plains indicate aridity while the formation of gumbo soils indicate deposition under humid conditions.
• The paleobotanical and mineralogical characteristics of sediment fill in recent lakes provide clues as to local rainfall and temperature trends for the past 10,000 years.
• Analysis of sediment cores from modern oceans provide insights into the climatic record as far back as 100 million years by the determination of 160/180 isotope ratios in sea shells.
• Stratigraphic relationships of Paleozoic and Mesozoic Era (from 600 million years ago to 50 million years ago) carbonate rocks indicate many sea level changes possibly related to continental glaciation.
• The presence of till is indicative of periods of glaciation.

Implications of Paleoclimatological Studies

• We are living in an abnormally cool period since the earth's average surface temperature for most of its history averaged 22 Celsius compared to the present 14 C.
• Ice ages occur at approximately 250-million-year intervals.
• Fossil evidence suggest that during the Mesozoic Era (230 to 50 million years ago) the earth was 10 C to 15 C warmer than today.
• One million years ago the current ice-age (Pleistocene) began.
• Glacial stages last more than 100,000 years and are interrupted by interglacial stages that last about 10,000 years.
• We are now living in an abnormally warm period compared to the earth's average temperature for the last one million years (during which glaciation has prevailed).
• The current interglacial period has been subject to climatic changes on a smaller scale than the change from glacial to interglacial but still large enough to disrupt civilizations.
• About 8,000 years ago (climatic optimum) average temperatures in the northern hemisphere averaged a degree or two Celsius higher than those of today. (Rise of Egyptian, Sumerian, and Oriental civilizations.)
• About 5,000 years ago regions in north Africa and Arabia which were once covered with lush vegetation turned to desert.
• Wet, stormy periods occurred about 4,000 and 3,000 years ago.
• Studies of large scale stabilized dunes in the High Plains of Colorado indicate that they have been activated four times in the past 10,000 years, but have been stabilized for the past 1,000 years. The results of the study indicate that anticipated climate changes due to greenhouse warming could reactivate dune fields in Colorado, Texas, Wyoming, and New Mexico.