Paleoclimatology (also Palaeoclimatology) is the study of climate change taken on the scale of the entire history of Earth. Climate encompasses the temperatures humidity rainfall atmospheric particle count and numerous other meteorogical factors in a given region over long periods of The history of Earth covers approximately 46 billion years (4567000000 years from Earth ’s formation out of the Solar nebula to the present It uses records from ice sheets, tree rings, sediment, and rocks to determine the past state of the climate system on Earth. An ice sheet is a mass of Glacier Ice that covers surrounding terrain and is greater than 50000 km² (20000 mile²) Dendrochronology (from Greek grc δένδρον dendron, "tree" grc χρόνος khronos, "time" and grc -λογία Sediment is any particulate matter that can be transported by fluid flow and which eventually is deposited as a layer of solid particles on the bed or bottom of a body of In Geology, rock is a naturally occurring aggregate of Minerals and/or Mineraloids The Earth's outer solid layer the ‘ Lithosphere EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001

Reconstructing ancient climates

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

Ice

Mountain Glaciers and the polar ice caps/ice sheets are a widely employed source of data in paleoclimatology. "Glacial" and "Glaciation" redirect here For the geological periods see Glacial period. An ice cap is an Ice mass that covers less than 50 000 km² of land area (usually covering a highland area An ice sheet is a mass of Glacier Ice that covers surrounding terrain and is greater than 50000 km² (20000 mile²) Recent 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.

• Inside of these layers scientists have found pollen, allowing them to estimate the total amount of plant growth of that year by the pollen count. Pollen is a fine to coarse powder consisting of microgametophytes ( pollen grains) which produce the male Gametes (sperm cells of The thickness of the layer can help to determine the amount of precipitation that year. Certain layers contain ash from volcanic eruptions.
• 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. This trapped air has proven a tremendously valuable source for direct measurement of the composition of air from the time the ice was formed.
• Because evaporation rates of water molecules with slightly heavier isotopes of hydrogen and oxygen are slightly different during warmer and colder periods, changes in the average temperature of the ocean surface are reflected in slightly different ratios between those isotopes. Isotopes (Greek isos = "equal" tópos = "site place" are any of the different types of atoms ( Nuclides Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the Various cycles in those isotope ratios have been detected.

Dendroclimatology

This science retrieves climate information from tree rings. Dendroclimatology is the science of determining past Climates from Trees (primarily Tree rings) Rings from living trees of great age give data about recent centuries back to a few millennia. Older intact wood that has escaped decay can extend the time covered by identifying patterns that match rings of known age from live trees. Petrified tree rings give paleoclimatology data over a much larger stretch of time. Petrified wood (from the Greek root "petro" meaning "rock" or "stone" literally "wood turned into stone" is a type of Fossil: it The fossil itself is dated with radioactive dating within a wide margin of error. FOSSIL is a standard protocol for allowing serial communication for Telecommunications programs under the DOS Operating system. Radiometric dating (often called radioactive dating) is a technique used to date materials usually based on a comparison between the observed abundance of a naturally occurring The rings themselves can give some information about rainfall and temperature during that epoch. The geologic time scale is a chronologic schema (or idealized Model) relating Stratigraphy to time that is used by Geologists and other

On a longer time scale, geologists must refer to the sedimentary record for data.

Sedimentary content

• Sediments, sometimes lithified to form rock, may contain remnants of preserved vegetation, animals, plankton or pollen, which may be characteristic of certain climatic zones. Palynology is the science that studies contemporary and fossil Palynomorphs including Pollen, Spores, Dinoflagellate Cysts Acritarchs
• Biomarker molecules such as the alkenones may yield information about their temperature of formation. Alkenones are highly resistant organic compounds ( Ketones) produced by Phytoplankton of the class Prymnesiophyceae.
• Chemical signatures, particularly Mg/Ca ratio of calcite in foramanifera tests, can be used to reconstruct past temperature. A paleothermometer is a methodology for determining past temperatures using a proxy found in a natural record such as a Sediment, Ice core, Tree rings The Foraminifera, ("Hole Bearers" or forams for short are a large group of Amoeboid Protists with reticulating Pseudopods fine
• 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 entangle.

Sedimentary facies

On a longer time scale, the rock record may show signs of sea level rise and fall; further, 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 these include major shifts in climate.

Corals

Coral "rings" are similar to tree rings, except they respond to different things, such as the water temperature and wave action. From this source, certain equipment can be used to derive the sea surface temperature and water salinity from the past few centuries. The δ¹⁸O of coraline red algae provides a useful proxy of sea surface temperature at high latitudes, where many traditional techniques are limited. ^[1]

Limitations

All records decrease in utility back in time. No ice exists that is over 1 million years old, and collecting and interpreting data over 800,000 years old is difficult. The deep marine record, our source of most isotopic data, only exists on oceanic plates, which are eventually subducted - the oldest remaining material is 140 million years old. Older sediments are also more prone to corruption by diagenesis. Consequently, our resolution and confidence in data decrease sharply over time.

Planet's timeline

See also: Geologic time scale and History of Earth

Our knowledge of precise climatic events decreases as we go further back in time. The geologic time scale is a chronologic schema (or idealized Model) relating Stratigraphy to time that is used by Geologists and other The history of Earth covers approximately 46 billion years (4567000000 years from Earth ’s formation out of the Solar nebula to the present Some notable events are noted below, with a timescale for context.

• Snowball Earth (~800Ma)
• Andean-Saharan glaciation (~450Ma)
• Permian-Triassic extinction event (251. The Snowball Earth Hypothesis as it was originally proposed]] Evidence The Snowball Earth hypothesis was originally devised to explain the apparent presence of The Andean-Saharan Glaciation was from 460 mya to 430 mya during the late Ordovician and the Silurian period The Permian–Triassic (P–Tr extinction event, informally known as the Great Dying, was an Extinction event that occurred, and 70 percent of terrestrial 4Ma)
• Paleocene-Eocene Thermal Maximum (Paleocene-Eocene, 55Ma)
• Younger Dryas/The Big Freeze (~11ka)
• Holocene climatic optimum (~7-3ka)
• Climate changes of 535-536 (535-536 AD)
• Medieval warm period (900-1300)
• Little ice age (1300-1800)
• Year Without a Summer (1816)

History of the atmosphere

Earliest atmosphere

The earliest atmosphere of the Earth was probably stripped away by solar winds early in the history of the planet. The Paleocene /Eocene boundary, was marked by the most rapid and significant climatic disturbance of the Cenozoic Era. The Paleocene or Palaeocene, "early dawn of the recent" is a geologic epoch that lasted from 65 The Eocene epoch (558 ± 02 - 339 ± 01 Ma) is a major division of the Geologic timescale and the second epoch of the Palaeogene period in The Younger Dryas Stadial, named after the alpine / tundra wildflower Dryas octopetala, and also referred to as the Big Freeze, was a brief (approximately The Holocene Climate Optimum was a warm period during roughly the interval 9000 to 5000 years B The Medieval Warm Period (MWP or Medieval Climate Optimum was a time of unusually Warm Climate in the North Atlantic region lasting from about The Little Ice Age (LIA was a period of cooling occurring after a warmer era known as the Medieval Warm Period or Medieval Climate Optimum The Year Without a Summer, also known as the Poverty Year, The Year There Was No Summer or Eighteen hundred and froze to death The solar wind is a Stream of charged particles&mdasha plasma &mdashthat are ejected from the upper atmosphere of the Sun. These gases were later replaced by an atmosphere derived from outgassing from the Earth. Sometime during the late Archean Era an oxygen atmosphere began to develop from photosynthesizing algae.

Carbon dioxide and free oxygen

,

Free oxygen did not exist until about 1,700 Ma (megaannum, a million years)and this can be seen with the development of the red beds and the end of the banded iron formations. This signifies a shift from a reducing atmosphere to an oxidising atmosphere. The early atmosphere and hydrosphere (up until about 2,000 Ma) were devoid of free oxygen. After photosynthesis developed, photoautotrophs began releasing O₂. Photoautotrophs or Phototroph ( Gk: photo = light auto = self troph = nourishment are Organisms (commonly plants that carry out Photosynthesis

The very early atmosphere of the earth contained mostly carbon dioxide (CO₂) : about 80%. Carbon dioxide ( Chemical formula:) is a Chemical compound composed of two Oxygen Atoms covalently bonded to a single This gradually dropped to about 20% by 3,500 Ma. This coincides with the development of the first bacteria about 3,500 Ma. By the time of the development of photosynthesis (2,700 Ma), CO₂ levels in the atmosphere were in the range of 15%. During the period from about 2,700 Ma to about 2,000 Ma, photosynthesis dropped the CO₂ concentrations from about 15% to about 8%. By about 2,000 Ma free O₂ was beginning to accumulate. This gradual reduction in CO₂ levels continued to about 600 Ma at which point CO₂ levels were below 1% and O₂ levels had risen to more than 15%. 600Ma corresponds to the end of the Precambrian and the beginning of the Cambrian, the end of the cryptozoic and the beginning of the Phanerozic, and the beginning of oxygen-breathing life.

Precambrian climate

The climate of the late Precambrian was typically cold with glaciation spreading over much of the earth. "Glacial" and "Glaciation" redirect here For the geological periods see Glacial period. At this time the continents were bunched up in a supercontinent called Rodinia. For the Genus of Metalmark butterflies, see Rodinia (butterfly. Massive deposits of tillites are found and anomalous isotopic signatures are found which are consistent with the idea that the earth at this time was a massive snowball. The Snowball Earth Hypothesis as it was originally proposed]] Evidence The Snowball Earth hypothesis was originally devised to explain the apparent presence of Map of Rodinia at the end of the Precambrian after Australia and Antarctica rotated away from the southern hemisphere.

As the Proterozoic Eon drew to a close, the Earth started to warm up. By the dawn of the Cambrian and the Phanerozoic Eon, Earth was experiencing average global temperatures of about +22 °C. The Celsius Temperature scale was previously known as the centigrade scale. Hundreds of millions of years of ice were replaced with the balmy tropical seas of the Cambrian Period within which life exploded at a rate never seen before or after.

Phanerozoic Climate

500 million years of climate change

500 million years of changes in carbon dioxide concentrations

Qualitatively, the Earth's climate was varied between conditions that support large-scale continental glaciation and those which are extensively tropical and lack permanent ice caps even at the poles. The time scale for this variation is roughly 140 million years and may be related to Earth's motion into and out of galactic spiral arms (Veizer and Shaviv 2003). The Milky Way (a translation of the Latin Via Lactea, in turn derived from the Greek Γαλαξίας (Galaxias sometimes referred to simply The difference in global mean temperatures between a fully glacial earth and ice free Earth is estimated at approximately 10 °C, though far larger changes would be observed at high latitudes and smaller ones at low latitudes. One key requirement for the development of large scale ice sheets is the arrangement of continental land masses at or near the poles. With plate tectonics constantly rearranging the continents, it can also shape long-term climate evolution. Plate tectonics (from Greek τέκτων tektōn "builder" or "mason" describes the large scale motions of Earth 's Lithosphere However, the presence of land masses at the poles is not sufficient to guarantee glaciations. Evidence exists of past warm periods in Earth's climate when polar land masses similar to Antarctica were home to deciduous forests rather than ice sheets. Botany Autumn leaf color. See --> In Botany and Horticulture, deciduous Plants, including

Changes in the atmosphere may also exert an important influence over climate change. The establishment of CO₂-consuming (and oxygen-producing) photosythesizing organisms in the Precambrian led to the production of an atmosphere much like today's, though for most of this period it was much higher in CO₂ than today. Similarly, the Earth's average temperature was also frequently higher than at present, though it has been argued that over very long time scales climate is largely decoupled from carbon dioxide variations (Veizer et al. 2000). Or more specifically that changing continental configurations and mountain building probably have a larger impact on climate than carbon dioxide. Others dispute this, and suggest that the variations of temperature in response to carbon dioxide changes have been underestimated (Royer et al. 2004). However, it is clear that the preindustrial atmosphere with only 280 ppm CO₂ is not far from the lowest ever occurring since the rise of macroscopic life.

Superimposed on the long-term evolution between hot and cold climates have been many short-term fluctuations in climate similar to, and sometimes more severe than, the varying glacial and interglacial states of the present ice age. An ice age is a period of long-term reduction in the Temperature of the Earth 's surface and atmosphere resulting in an expansion of continental Ice sheets Some of the most severe fluctuations, such as the Paleocene-Eocene Thermal Maximum, may be related to rapid increases in atmospheric carbon dioxide due to the collapse of natural methane reservoirs in the oceans (see methane clathrates). The Paleocene /Eocene boundary, was marked by the most rapid and significant climatic disturbance of the Cenozoic Era. Methane is a Chemical compound with the molecular formula. It is the simplest Alkane, and the principal component of Natural gas. Methane clathrate, also called methane hydrate or methane ice, is a solid form of water that contains a large amount of Methane within its Crystal Severe climate changes also seem to have occurred during the course of the Cretaceous-Tertiary, Permian-Triassic, and Ordovician-Silurian extinction events; however, it is unclear to what degree these changes caused the extinctions rather than merely responding to other processes that may have been more directly responsible for the extinctions. The Cretaceous–Tertiary extinction event, which occurred approximately ( Ma) was a large-scale mass extinction of animal and plant species in a geologically The Permian–Triassic (P–Tr extinction event, informally known as the Great Dying, was an Extinction event that occurred, and 70 percent of terrestrial

Quaternary sub-era

The Quaternary sub-era includes the current climate. Overview The term Quaternary ("fourth" was proposed by Giovanni Arduino in 1759 for alluvial deposits in the Po river valley in northern There has been a cycle of ice ages for the past 2. An ice age is a period of long-term reduction in the Temperature of the Earth 's surface and atmosphere resulting in an expansion of continental Ice sheets 2-2. 1 million years (starting before the Quaternary in the late Neogene Period). The Neogene is a geologic period and system starting 2303 ± 0

Ice core data for the past 400,000 years. Note length of glacial cycles averages ~100,000 years. Blue curve is temperature, green curve is CO₂, and red curve is windblown glacial dust (loess). Today's date is on the left side of the graph.

Note in the graphic on the right the strong 120,000 year periodicity of the cycles, and the striking asymmetry of the curves. This asymmetry is believed to result from complex interactions of feedback mechanisms. It has been observed that ice ages deepen by progressive steps, but the recovery to interglacial conditions occurs in one big step.

Controlling Factors

Geologically short-term (<120,000 year) temperatures are believed to be driven by orbital factors (see Milankovitch cycles). Milankovitch cycles are the collective effect of changes in the Earth 's movements upon its climate named after Serbian civil engineer and Mathematician The arrangements of land masses on the Earth's surface are believed to reinforce these orbital forcing effects.

Continental drift obviously affects the thermohaline circulation, which transfers heat between the equatorial regions and the poles, as does the extent of polar ice coverage. The term thermohaline circulation (THC refers to the part of the large-scale ocean circulation that is thought to be driven by global density gradients created by surface heat and

The timing of ice ages throughout geologic history is in part controlled by the position of the continental plates on the surface of the Earth. When landmasses are concentrated near the polar regions, there is an increased chance for snow and ice to accumulate. Small changes in solar energy can tip the balance between summers in which the winter snow mass completely melts and summers in which the winter snow persists until the following winter. Solar variations are changes in the amount of Solar radiation emitted by the Sun. See the web site Paleomap Project for images of the polar landmass distributions through time.

Comparisons of plate tectonic continent reconstructions and paleoclimatic studies show that the Milankovitch cycles have the greatest effect during geologic eras when landmasses have been concentrated in polar regions, as is the case today. Plate tectonics (from Greek τέκτων tektōn "builder" or "mason" describes the large scale motions of Earth 's Lithosphere Today, Greenland, Antarctica, and the northern portions of Europe, Asia, and North America are situated such that a minor change in solar energy will tip the balance between year-round snow/ice preservation and complete summer melting. Greenland (Kalaallit Nunaat meaning "Land of the Greenlanders" Grønland is a self-governing Danish Province located between the The presence of snow and ice is a well-understood positive feedback mechanism for climate. Positive feedback, sometimes referred to as "cumulative causation" is a Feedback loop system in which the system responds to perturbation in the same direction The Earth today is considered to be prone to ice age glaciations.

Another proposed factor in long term temperature change is the Uplift-Weathering Hypothesis, first put forward by T. C. Chamberlin in 1899 and later independently proposed in 1988 by Maureen Raymo and colleagues, where upthrusting mountain ranges expose minerals to weathering resulting in their chemical conversion to carbonates thereby removing CO₂ from the atmosphere and cooling the earth. Others have proposed similar effects due to changes in average water table levels and consequent changes in sub-surface biological activity and PH levels. pH is the measure of the acidity or alkalinity of a Solution.

Over the very long term the energy output of the sun has gradually increased, on the order of 5% per billion (10⁹) years, and will continue to do so until it reaches the end of its current phase of stellar evolution. The Sun (Sol is the Star at the center of the Solar System. Stellar evolution is the process by which a Star undergoes a sequence of radical changes during its lifetime

See also

• Geologic temperature record
• Paleothermometry, the study of ancient temperatures
• Dendroclimatology
• Historical climatology, the study of climate over human history (as opposed to earth's)
• Cliwoc, Climatological database for the world's oceans (1759-1854)
• Shen Kuo, 11th century Chinese scientist who realized the possibilities of paleoclimatology while observing ancient petrified bamboos buried underground in a northern, dry climate

References

• Bradley, Raymond S. (1985. ) Quaternary paleoclimatology : methods of paleoclimatic reconstruction (Boston: Allen & Unwin) ISBN 0-04-551067-9, ISBN 0-04-551068-7.
• Imbrie, John. (1986) Ice ages : solving the mystery (Cambridge, Massachusetts: Harvard University Press, 1986, c1979).
• Margulis, Lynn, and Dorion Sagan. (c1986) Origins of sex: three billion years of genetic recombination (New Haven : Yale University Press) Series : The Bio-origins series; ISBN 0-300-03340-0.
• Gould, Stephen Jay. (c1989) Wonderful life, the story of the Burgess Shale (New York: W. W. Norton) ISBN 0-393-02705-8.
• Crowley, Thomas J. , and North, Gerald R. (1996) Paleoclimatology (Oxford, UK: Clarendon Press) Series : Oxford monographs on geology and geophysics no. 18; ISBN 0-19-510533-8.
• Veizer, J. , Godderis, Y. and François, L. M. (2000) "Evidence for decoupling of atmospheric CO2 and global climate during the Phanerozoic eon", in Nature, volume 408, pages 698-701.
• Shaviv, N. and Veizer, J. (2003) "Celestial driver of Phanerozoic climate?", in GSA Today July 2003, volume 13, number 7, pages 4-10. <http://www.gsajournals.org/gsaonline/?request=get-document&issn=1052-5173&volume=013&issue=07&page=0004>
• Royer, Dana L. and Robert A. Berner, Isabel P. Montañez, Neil J. Tabor, David J. Beerling (2004) "CO2 as a primary driver of Phanerozoic climate", in GSA Today July 2004, volume 14, number 3, pages 4-10. <http://www.gsajournals.org/gsaonline/?request=get-document&issn=1052-5173&volume=014&issue=03&page=0004>
• Shaviv, N. and Veizer, J. (2004) "CO2 as a primary driver of Phanerozoic climate:COMMENT", in GSA Today 14/17, 18. <http://www.gsajournals.org/pdf/online_forum/i1052-5173-14-3-e4.pdf>
• Drummond, Carl N. and Wilkinson, Bruce H. , (2006) Interannual Variability in Climate Data, Journal of Geology, v. 114, p. 325-339.

External links

• A Brief Introduction to History of Climate, an excellent overview by Prof. Richard A Muller of UC Berkley.
• NOAA Paleoclimatology
• AGU Paleoclimatology and climate system dynamics
• Paleoclimatology in the 21st century
• Environmental Literacy Council
• Climate change and Palaeoclimatology News Archive
• The Uplift-Weathering Hypothesis
• NASA's GISS paleoclimate site
• CalPal - Cologne Radiocarbon Calibration & Paleoclimate Research Package
• [1]Ice-driven CO2 feedback on ice volume by W. F. Ruddiman
• [2]Rapid Climate Change