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Paleoclimatology


Paleoclimatology (in British spelling, palaeoclimatology) is the study of changes in climate taken on the scale of the entire history of Earth. It uses a variety of proxy methods from the Earth and life sciences to obtain data previously preserved within things such as rocks, sediments, ice sheets, tree rings, corals, shells and microfossils. It then uses the records to determine the past states of the Earth's various climate regions and its atmospheric system. Studies of past changes in the environment and biodiversity often reflect on the current situation, specifically the impact of climate on mass extinctions and biotic recovery.

The scientific study field of paleoclimate began to form in the early 19th century, when discoveries about glaciations and natural changes in Earth's past climate helped to understand the greenhouse effect.

Paleoclimatologists employ a wide variety of techniques to deduce ancient climates.

Mountain glaciers and the polar ice caps/ice sheets provide much data in paleoclimatology. Ice-coring projects in the ice caps of Greenland and Antarctica have yielded data going back several hundred thousand years, over 800,000 years in the case of the EPICA project.



  • Air trapped within fallen snow becomes encased in tiny bubbles as the snow is compressed into ice in the glacier under the weight of later years' snow. The trapped air has proven a tremendously valuable source for direct measurement of the composition of air from the time the ice was formed.
  • Layering can be observed because of seasonal pauses in ice accumulation and can be used to establish chronology, associating specific depths of the core with ranges of time.
  • Changes in the layering thickness can be used to determine changes in precipitation or temperature.
  • Oxygen-18 quantity changes (δ18O) in ice layers represent changes in average ocean surface temperature. Water molecules containing the heavier O-18 evaporate at a higher temperature than water molecules containing the normal Oxygen-16 isotope. The ratio of O-18 to O-16 will be higher as temperature increases. It also depends on other factors such as the water's salinity and the volume of water locked up in ice sheets. Various cycles in those isotope ratios have been detected.
  • Pollen has been observed in the ice cores and can be used to understand which plants were present as the layer formed. Pollen is produced in abundance and its distribution is typically well understood. A pollen count for a specific layer can be produced by observing the total amount of pollen categorized by type (shape) in a controlled sample of that layer. Changes in plant frequency over time can be plotted through statistical analysis of pollen counts in the core. Knowing which plants were present leads to an understanding of precipitation and temperature, and types of fauna present. Palynology includes the study of pollen for these purposes.
  • Volcanic ash is contained in some layers, and can be used to establish the time of the layer's formation. Each volcanic event distributed ash with a unique set of properties (shape and color of particles, chemical signature). Establishing the ash's source will establish a range of time to associate with layer of ice.
  • Sediments, sometimes lithified to form rock, may contain remnants of preserved vegetation, animals, plankton or pollen, which may be characteristic of certain climatic zones.
  • Biomarker molecules such as the alkenones may yield information about their temperature of formation.
  • Chemical signatures, particularly Mg/Ca ratio of calcite in Foraminifera tests, can be used to reconstruct past temperature.
  • Isotopic ratios can provide further information. Specifically, the δ18O record responds to changes in temperature and ice volume, and the δ13C record reflects a range of factors, which are often difficult to disentangle.
Sedimentary facies
On a longer time scale, the rock record may show signs of sea level rise and fall, and features such as "fossilised" sand dunes can be identified. Scientists can get a grasp of long term climate by studying sedimentary rock going back billions of years. The division of earth history into separate periods is largely based on visible changes in sedimentary rock layers that demarcate major changes in conditions. Often, they include major shifts in climate.
Corals (see also sclerochronology)
Coral "rings" are similar to tree rings except that they respond to different things, such as the water temperature, freshwater influx, pH changes, and wave action. From there, certain equipment can be used to derive the sea surface temperature and water salinity from the past few centuries. The δ18O of coralline red algae provides a useful proxy of the combined sea surface temperature and sea surface salinity at high latitudes and the tropics, where many traditional techniques are limited.
  • Air trapped within fallen snow becomes encased in tiny bubbles as the snow is compressed into ice in the glacier under the weight of later years' snow. The trapped air has proven a tremendously valuable source for direct measurement of the composition of air from the time the ice was formed.
  • Layering can be observed because of seasonal pauses in ice accumulation and can be used to establish chronology, associating specific depths of the core with ranges of time.
  • Changes in the layering thickness can be used to determine changes in precipitation or temperature.
  • Oxygen-18 quantity changes (δ18O) in ice layers represent changes in average ocean surface temperature. Water molecules containing the heavier O-18 evaporate at a higher temperature than water molecules containing the normal Oxygen-16 isotope. The ratio of O-18 to O-16 will be higher as temperature increases. It also depends on other factors such as the water's salinity and the volume of water locked up in ice sheets. Various cycles in those isotope ratios have been detected.
  • Pollen has been observed in the ice cores and can be used to understand which plants were present as the layer formed. Pollen is produced in abundance and its distribution is typically well understood. A pollen count for a specific layer can be produced by observing the total amount of pollen categorized by type (shape) in a controlled sample of that layer. Changes in plant frequency over time can be plotted through statistical analysis of pollen counts in the core. Knowing which plants were present leads to an understanding of precipitation and temperature, and types of fauna present. Palynology includes the study of pollen for these purposes.
  • Volcanic ash is contained in some layers, and can be used to establish the time of the layer's formation. Each volcanic event distributed ash with a unique set of properties (shape and color of particles, chemical signature). Establishing the ash's source will establish a range of time to associate with layer of ice.
  • Sediments, sometimes lithified to form rock, may contain remnants of preserved vegetation, animals, plankton or pollen, which may be characteristic of certain climatic zones.
  • Biomarker molecules such as the alkenones may yield information about their temperature of formation.
  • Chemical signatures, particularly Mg/Ca ratio of calcite in Foraminifera tests, can be used to reconstruct past temperature.
  • Isotopic ratios can provide further information. Specifically, the δ18O record responds to changes in temperature and ice volume, and the δ13C record reflects a range of factors, which are often difficult to disentangle.
  • The Milankovitch cycles determine Earth distance and position to the Sun. The solar insolation, is the total amount of solar radiation received by Earth.
  • Volcanic eruptions, are considered an external forcing.
  • Human changes of the composition of the atmosphere or land use.
  • Bradley, Raymond S. (1985). Quaternary paleoclimatology: methods of paleoclimatic reconstruction. Boston: Allen & Unwin. ISBN . 
  • Cronin, Thomas N. (2010). Paleoclimates: understanding climate change past and present. New York: Columbia University Press. ISBN . 
  • Imbrie, John (1979). Ice ages: solving the mystery. Cambridge MA: Harvard University Press. ISBN . 
  • Margulis, Lynn; Sagan, Dorion (1986). Origins of sex: three billion years of genetic recombination. The Bio-origins series. New Haven: Yale University Press. ISBN . 
  • Gould, Stephen Jay (1989). Wonderful life, the story of the Burgess Shale. New York: W.W. Norton. ISBN . 
  • Crowley, Thomas J.; North, Gerald R. (1996). Paleoclimatology. Oxford monographs on geology and geophysics. 18. Oxford: Clarendon Press. ISBN . 
  • The Climates of the Geological Past. (Die Klimate der geologischen Vorzeit). 1924, Wladimir Köppen, Alfred Wegener
  • Karl-Heinz Ludwig (2006). Eine kurze Geschichte des Klimas. Von der Entstehung der Erde bis heute, (A short history of climate, From the evolution of earth till today) Herbst,
  • William F. Ruddimann (2001). Earth's Climate — Past and Future. Palgrave Macmillan. ISBN . 
  • B. Windley (1984). The Evolving Continents. New York: Wiley Press. 
  • Drummond, Carl N. & Wilkinson, Bruce H. (2006). "Interannual Variability in Climate Data". Journal of Geology. 114 (3): 325–339. Bibcode:2006JG....114..325D. doi:10.1086/500992. 
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