Paleoclimatology

Paleoclimatology

Overview
Paleoclimatology is the study of changes in climate
Climate
Climate encompasses the statistics of temperature, humidity, atmospheric pressure, wind, rainfall, atmospheric particle count and other meteorological elemental measurements in a given region over long periods...

 taken on the scale of the entire history of Earth
History of Earth
The history of the Earth describes the most important events and fundamental stages in the development of the planet Earth from its formation 4.578 billion years ago to the present day. Nearly all branches of natural science have contributed to the understanding of the main events of the Earth's...

. It uses a variety of proxy
Proxy (climate)
In the study of past climates is known as paleoclimatology, climate proxies are preserved physical characteristics of the past that stand in for direct measurements , to enable scientists to reconstruct the climatic conditions that prevailed during much of the Earth's history...

 methods from the Earth and life
Life sciences
The life sciences comprise the fields of science that involve the scientific study of living organisms, like plants, animals, and human beings. While biology remains the centerpiece of the life sciences, technological advances in molecular biology and biotechnology have led to a burgeoning of...

 sciences to obtain data previously preserved within (e.g.) rocks
Rock (geology)
In geology, rock or stone is a naturally occurring solid aggregate of minerals and/or mineraloids.The Earth's outer solid layer, the lithosphere, is made of rock. In general rocks are of three types, namely, igneous, sedimentary, and metamorphic...

, sediment
Sediment
Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....

s, ice sheet
Ice sheet
An ice sheet is a mass of glacier ice that covers surrounding terrain and is greater than 50,000 km² , thus also known as continental glacier...

s, tree rings, coral
Coral
Corals are marine animals in class Anthozoa of phylum Cnidaria typically living in compact colonies of many identical individual "polyps". The group includes the important reef builders that inhabit tropical oceans and secrete calcium carbonate to form a hard skeleton.A coral "head" is a colony of...

s, shell
Mollusc shell
The mollusc shell is typically a calcareous exoskeleton which encloses, supports and protects the soft parts of an animal in the phylum Mollusca, which includes snails, clams, tusk shells, and several other classes...

s and microfossils; it then uses these records to determine the past states of the Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

's various climate regions and its atmospheric
Atmosphere
An atmosphere is a layer of gases that may surround a material body of sufficient mass, and that is held in place by the gravity of the body. An atmosphere may be retained for a longer duration, if the gravity is high and the atmosphere's temperature is low...

 system. Paleoclimatology has wider implications for climate change
Climate change
Climate change is a significant and lasting change in the statistical distribution of weather patterns over periods ranging from decades to millions of years. It may be a change in average weather conditions or the distribution of events around that average...

 today.
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Encyclopedia
Paleoclimatology is the study of changes in climate
Climate
Climate encompasses the statistics of temperature, humidity, atmospheric pressure, wind, rainfall, atmospheric particle count and other meteorological elemental measurements in a given region over long periods...

 taken on the scale of the entire history of Earth
History of Earth
The history of the Earth describes the most important events and fundamental stages in the development of the planet Earth from its formation 4.578 billion years ago to the present day. Nearly all branches of natural science have contributed to the understanding of the main events of the Earth's...

. It uses a variety of proxy
Proxy (climate)
In the study of past climates is known as paleoclimatology, climate proxies are preserved physical characteristics of the past that stand in for direct measurements , to enable scientists to reconstruct the climatic conditions that prevailed during much of the Earth's history...

 methods from the Earth and life
Life sciences
The life sciences comprise the fields of science that involve the scientific study of living organisms, like plants, animals, and human beings. While biology remains the centerpiece of the life sciences, technological advances in molecular biology and biotechnology have led to a burgeoning of...

 sciences to obtain data previously preserved within (e.g.) rocks
Rock (geology)
In geology, rock or stone is a naturally occurring solid aggregate of minerals and/or mineraloids.The Earth's outer solid layer, the lithosphere, is made of rock. In general rocks are of three types, namely, igneous, sedimentary, and metamorphic...

, sediment
Sediment
Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....

s, ice sheet
Ice sheet
An ice sheet is a mass of glacier ice that covers surrounding terrain and is greater than 50,000 km² , thus also known as continental glacier...

s, tree rings, coral
Coral
Corals are marine animals in class Anthozoa of phylum Cnidaria typically living in compact colonies of many identical individual "polyps". The group includes the important reef builders that inhabit tropical oceans and secrete calcium carbonate to form a hard skeleton.A coral "head" is a colony of...

s, shell
Mollusc shell
The mollusc shell is typically a calcareous exoskeleton which encloses, supports and protects the soft parts of an animal in the phylum Mollusca, which includes snails, clams, tusk shells, and several other classes...

s and microfossils; it then uses these records to determine the past states of the Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

's various climate regions and its atmospheric
Atmosphere
An atmosphere is a layer of gases that may surround a material body of sufficient mass, and that is held in place by the gravity of the body. An atmosphere may be retained for a longer duration, if the gravity is high and the atmosphere's temperature is low...

 system. Paleoclimatology has wider implications for climate change
Climate change
Climate change is a significant and lasting change in the statistical distribution of weather patterns over periods ranging from decades to millions of years. It may be a change in average weather conditions or the distribution of events around that average...

 today. Scientists often consider past changes in environment and biodiversity to reflect on the current situation, and specifically the impact of climate on mass extinctions and biotic recovery.



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. Recent ice coring projects in the ice caps of Greenland
Greenland
Greenland is an autonomous country within the Kingdom of Denmark, located between the Arctic and Atlantic Oceans, east of the Canadian Arctic Archipelago. Though physiographically a part of the continent of North America, Greenland has been politically and culturally associated with Europe for...

 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
    Snow
    Snow is a form of precipitation within the Earth's atmosphere in the form of crystalline water ice, consisting of a multitude of snowflakes that fall from clouds. Since snow is composed of small ice particles, it is a granular material. It has an open and therefore soft structure, unless packed by...

     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.
  • Layering can be observed due to 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
    Oxygen-18
    Oxygen-18 is a natural, stable isotope of oxygen and one of the environmental isotopes.18O is an important precursor for the production of fluorodeoxyglucose used in positron emission tomography...

     quantity changes 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 and less as temperature decreases. 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
    Palynology
    Palynology is the science that studies contemporary and fossil palynomorphs, including pollen, spores, orbicules, dinoflagellate cysts, acritarchs, chitinozoans and scolecodonts, together with particulate organic matter and kerogen found in sedimentary rocks and sediments...

     includes the study of pollen for these purposes.
  • Volcanic ash
    Volcanic ash
    Volcanic ash consists of small tephra, which are bits of pulverized rock and glass created by volcanic eruptions, less than in diameter. There are three mechanisms of volcanic ash formation: gas release under decompression causing magmatic eruptions; thermal contraction from chilling on contact...

     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.


Dendroclimatology
Dendroclimatology
Dendroclimatology is the science of determining past climates from trees . Tree rings are wider when conditions favor growth, narrower when times are difficult. Other properties of the annual rings, such as maximum latewood density have been shown to be better proxies than simple ring width...

: Climatic information can be obtained through an understanding of changes in tree growth. Generally, trees respond to changes in climatic variables by speeding up or slowing down growth, which in turn is generally reflected a greater or lesser thickness in growth rings. Different species, however, respond to changes in climatic variables in different ways. A tree-ring record is established by compiling information from many living trees in a specific area. Older intact wood that has escaped decay can extend the time covered by the record by matching the ring depth changes to contemporary specimens. Using this method some areas have tree-ring records dating back a few thousand years. Older wood not connected to a contemporary record can be dated generally with radiocarbon techniques. A tree-ring record can be used to produce information regarding precipitation, temperature, hydrology, and fire corresponding to a particular area.

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
    Palynology
    Palynology is the science that studies contemporary and fossil palynomorphs, including pollen, spores, orbicules, dinoflagellate cysts, acritarchs, chitinozoans and scolecodonts, together with particulate organic matter and kerogen found in sedimentary rocks and sediments...

    , 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
    Calcite
    Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate . The other polymorphs are the minerals aragonite and vaterite. Aragonite will change to calcite at 380-470°C, and vaterite is even less stable.-Properties:...

     in Foraminifera
    Foraminifera
    The Foraminifera , or forams for short, are a large group of amoeboid protists which are among the commonest plankton species. They have reticulating pseudopods, fine strands of cytoplasm that branch and merge to form a dynamic net...

     tests, can be used to reconstruct past temperature.
  • Isotopic ratios can provide further information. Specifically, the record responds to changes in temperature and ice volume, and the 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; further, features such as "fossilised" sand dunes can be identified. Scientists can get a grasp of long term climate by studying sedimentary rock
Sedimentary rock
Sedimentary rock are types of rock that are formed by the deposition of material at the Earth's surface and within bodies of water. Sedimentation is the collective name for processes that cause mineral and/or organic particles to settle and accumulate or minerals to precipitate from a solution....

 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 (see also sclerochronology
Sclerochronology
The term sclerochronology dates from the early 1970s, and was coined in 1974 following pioneering work on nuclear test atolls by Knutson and Buddemeier. Sclerochronology is the study of physical and chemical variations in the accretionary hard tissues of invertebrates and coralline red algae, and...

): 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.

Limitations


A consortium called the European Project for Ice Coring in Antarctica (EPICA) has drilled at Dome C in the East Antarctic ice sheet, and retrieved an ice core which dates to roughly 740,000 years old. The project has been working in the same location to core a final section that could reach back to 900,000 years or even further. The international ice core community has, under the auspices of International Partnerships in Ice Core Sciences (IPICS), defined a priority project to obtain the oldest possible ice core record from Antarctica, an ice core record reaching back to or towards 1.5 million years ago. The deep marine record, the source of most isotopic data, only exists on oceanic plates, which are eventually subducted — the oldest remaining material is old. Older sediments are also more prone to corruption by diagenesis
Diagenesis
In geology and oceanography, diagenesis is any chemical, physical, or biological change undergone by a sediment after its initial deposition and during and after its lithification, exclusive of surface alteration and metamorphism. These changes happen at relatively low temperatures and pressures...

. Resolution and confidence in the data decrease over time.

Notable climate events in Earth history


Knowledge of precise climatic events decreases as the record goes further back in time. Some notable climate events:
  • Faint young Sun paradox
    Faint young Sun paradox
    The faint young Sun paradox or problem describes the apparent contradiction between observations of liquid water early in the Earth's history and the astrophysical expectation that the Sun's output would be only 70% as intense during that epoch as it is during the modern epoch. The issue was raised...

     (start)
  • Huronian glaciation (~2400Mya Earth completely covered in ice probably due to Great Oxygenation Event
    Great Oxygenation Event
    The Great Oxygenation Event , also called the Oxygen Catastrophe or Oxygen Crisis or Great Oxidation, was the biologically induced appearance of free oxygen in Earth's atmosphere. This major environmental change happened around 2.4 billion years ago.Photosynthesis was producing oxygen both before...

    )
  • Later Neoproterozoic Snowball Earth
    Snowball Earth
    The Snowball Earth hypothesis posits that the Earth's surface became entirely or nearly entirely frozen at least once, some time earlier than 650 Ma . Proponents of the hypothesis argue that it best explains sedimentary deposits generally regarded as of glacial origin at tropical...

     (~600Mya, Precursor to the Cambrian Explosion
    Cambrian explosion
    The Cambrian explosion or Cambrian radiation was the relatively rapid appearance, around , of most major phyla, as demonstrated in the fossil record, accompanied by major diversification of other organisms, including animals, phytoplankton, and calcimicrobes...

    )
  • Andean-Saharan glaciation (~450Mya)
  • Carboniferous Rainforest Collapse
    Carboniferous Rainforest Collapse
    The Carboniferous Rainforest Collapse was an extinction event that occurred around 305 million years ago in the Carboniferous period). Vast coal forests covered the equatorial region of Euramerica...

     (~300Mya)
  • Permian-Triassic extinction event
    Permian-Triassic extinction event
    The Permian–Triassic extinction event, informally known as the Great Dying, was an extinction event that occurred 252.28 Ma ago, forming the boundary between the Permian and Triassic geologic periods, as well as the Paleozoic and Mesozoic eras...

     (251.4Mya)
  • Paleocene-Eocene Thermal Maximum
    Paleocene-Eocene Thermal Maximum
    The most extreme change in Earth surface conditions during the Cenozoic Era began at the temporal boundary between the Paleocene and Eocene epochs . This event, the Paleocene–Eocene Thermal Maximum , was associated with rapid global...

     (Paleocene
    Paleocene
    The Paleocene or Palaeocene, the "early recent", is a geologic epoch that lasted from about . It is the first epoch of the Palaeogene Period in the modern Cenozoic Era...

    -Eocene
    Eocene
    The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...

    , 55Mya)
  • Younger Dryas
    Younger Dryas
    The Younger Dryas stadial, also referred to as the Big Freeze, was a geologically brief period of cold climatic conditions and drought between approximately 12.8 and 11.5 ka BP, or 12,800 and 11,500 years before present...

    /The Big Freeze (~11Kya)
  • Holocene climatic optimum
    Holocene climatic optimum
    The Holocene Climate Optimum was a warm period during roughly the interval 9,000 to 5,000 years B.P.. This event has also been known by many other names, including: Hypsithermal, Altithermal, Climatic Optimum, Holocene Optimum, Holocene Thermal Maximum, and Holocene Megathermal.This warm period...

     (~7-3Kya)
  • Climate changes of 535-536 (535-536 AD)
  • Medieval warm period
    Medieval Warm Period
    The Medieval Warm Period , Medieval Climate Optimum, or Medieval Climatic Anomaly was a time of warm climate in the North Atlantic region, that may also have been related to other climate events around the world during that time, including in China, New Zealand, and other countries lasting from...

     (900-1300)
  • Little ice age
    Little Ice Age
    The Little Ice Age was a period of cooling that occurred after the Medieval Warm Period . While not a true ice age, the term was introduced into the scientific literature by François E. Matthes in 1939...

     (1300-1800)
  • Year Without a Summer
    Year Without a Summer
    The Year Without a Summer was 1816, in which severe summer climate abnormalities caused average global temperatures to decrease by about 0.4–0.7 °C , resulting in major food shortages across the Northern Hemisphere...

     (1816)

History of the atmosphere



Earliest atmosphere


The outgassings of the Earth was stripped away by solar wind
Solar wind
The solar wind is a stream of charged particles ejected from the upper atmosphere of the Sun. It mostly consists of electrons and protons with energies usually between 1.5 and 10 keV. The stream of particles varies in temperature and speed over time...

s early in the history of the planet until a steady state was established, the first atmosphere. Based on today's volcanic evidence, this atmosphere would have contained 60% hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

, 20% oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 (mostly in the form of water vapor
Water vapor
Water vapor or water vapour , also aqueous vapor, is the gas phase of water. It is one state of water within the hydrosphere. Water vapor can be produced from the evaporation or boiling of liquid water or from the sublimation of ice. Under typical atmospheric conditions, water vapor is continuously...

), 10% carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

, 5 to 7% hydrogen sulfide
Hydrogen sulfide
Hydrogen sulfide is the chemical compound with the formula . It is a colorless, very poisonous, flammable gas with the characteristic foul odor of expired eggs perceptible at concentrations as low as 0.00047 parts per million...

, and smaller amounts of nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...

, carbon monoxide
Carbon monoxide
Carbon monoxide , also called carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal...

, free hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

, methane
Methane
Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...

 and inert gas
Inert gas
An inert gas is a non-reactive gas used during chemical synthesis, chemical analysis, or preservation of reactive materials. Inert gases are selected for specific settings for which they are functionally inert since the cost of the gas and the cost of purifying the gas are usually a consideration...

es.

A major rainfall led to the buildup of a vast ocean, enriching the other agents, first carbon dioxide and later nitrogen and inert gases. A major part of carbon dioxide exhalations were soon dissolved in water and built up carbonate sediments.

Second atmosphere


As early as 3.8 billion years ago, water related sediments have been found. About 3.4 billion years ago, nitrogen was the major part of the then stable second atmosphere. An influence of life has to be taken into account rather soon since hints on early life forms are to be found as early as 3.5 billion years ago. The fact that this is not in line with the — compared to today 30% lower — solar radiance of the early sun has been described as the faint young Sun paradox
Faint young Sun paradox
The faint young Sun paradox or problem describes the apparent contradiction between observations of liquid water early in the Earth's history and the astrophysical expectation that the Sun's output would be only 70% as intense during that epoch as it is during the modern epoch. The issue was raised...

.

The geological record, however, shows a continually relatively warm surface during the complete early temperature record
Temperature record
The temperature record shows the fluctuations of the temperature of the atmosphere and the oceans through various spans of time. The most detailed information exists since 1850, when methodical thermometer-based records began. There are numerous estimates of temperatures since the end of the...

 of the earth with the exception of one cold glacial phase about 2.4 billion years ago. In the late Archean Era an oxygen containing atmosphere began to develop from photosynthesizing algae. The early basic carbon isotopy is very much in line with what is found today As Jan Veizer
Jan Veizer
Ján Veizer is the Distinguished University Professor of Earth Sciences at the University of Ottawa and Institute for Geology, Mineralogy und Geophysis, of Bochum Ruhr University, he held the NSERC/Noranda/CIFAR Industrial Chair in Earth System Isotope and Environmental Geochemistry until 2004...

 assumed that not only did we have life as far back as we had rocks, but there was as much life then as today and the fundamental features of the carbon cycle
Carbon cycle
The carbon cycle is the biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of the Earth...

 were established as early as 4 billion years ago.

Third atmosphere


The accretion
Accretion (geology)
Accretion is a process by which material is added to a tectonic plate or a landmass. This material may be sediment, volcanic arcs, seamounts or other igneous features.-Description:...

 of continents about 3.5 billion years ago added plate tectonics
Plate tectonics
Plate tectonics is a scientific theory that describes the large scale motions of Earth's lithosphere...

, constantly rearranging the continents and also shaping long-term climate evolution by allowing the transfer of carbon dioxide to large land-based carbonate storages. Free oxygen did not exist until about 1.7 billion years ago and this can be seen with the development of the red beds
Red beds
Red beds are sedimentary rocks, which typically consist of sandstone, siltstone, and shale that are predominantly red in color due to the presence of ferric oxides. Frequently, these red-colored sedimentary strata locally contain thin beds of conglomerate, marl, limestone, or some combination of...

 and the end of the banded iron formation
Banded iron formation
Banded iron formations are distinctive units of sedimentary rock that are almost always of Precambrian age. A typical BIF consists of repeated, thin layers of iron oxides, either magnetite or hematite , alternating with bands of iron-poor shale and chert...

s. This signifies a shift from a reducing
Redox
Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....

 atmosphere to an oxidising atmosphere. O2 showed major ups and downs until reaching a steady state of more than 15%. The following time span was the Phanerozoic, during which oxygen-breathing metazoan life forms began to appear.

Precambrian climate


In the first three quarters of the Earth's history, only one major glaciation is to be found in the geological record. Since about 950 million years ago, the Earth's climate has varied regularly between large-scale or just polar cap wide glaciation and extensively tropical climates. 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
Milky Way
The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...

 and compared to the previous time, significantly reduced solar wind
Solar wind
The solar wind is a stream of charged particles ejected from the upper atmosphere of the Sun. It mostly consists of electrons and protons with energies usually between 1.5 and 10 keV. The stream of particles varies in temperature and speed over time...

.

The climate of the late Precambrian showed some major glaciation events spreading over much of the earth. At this time the continents were bunched up in the Rodinia
Rodinia
In geology, Rodinia is the name of a supercontinent, a continent which contained most or all of Earth's landmass. According to plate tectonic reconstructions, Rodinia existed between 1.1 billion and 750 million years ago, in the Neoproterozoic era...

 supercontinent. Massive deposits of tillites are found and anomalous isotopic signatures are found, which gave rise to the Snowball Earth
Snowball Earth
The Snowball Earth hypothesis posits that the Earth's surface became entirely or nearly entirely frozen at least once, some time earlier than 650 Ma . Proponents of the hypothesis argue that it best explains sedimentary deposits generally regarded as of glacial origin at tropical...

 hypothesis. As the Proterozoic Eon drew to a close, the Earth started to warm up. By the dawn of the Cambrian and the Phanerozoic, life forms were abundant in the Cambrian explosion
Cambrian explosion
The Cambrian explosion or Cambrian radiation was the relatively rapid appearance, around , of most major phyla, as demonstrated in the fossil record, accompanied by major diversification of other organisms, including animals, phytoplankton, and calcimicrobes...

 with average global temperatures of about 22 °C
Celsius
Celsius is a scale and unit of measurement for temperature. It is named after the Swedish astronomer Anders Celsius , who developed a similar temperature scale two years before his death...

.

Phanerozoic climate


Major drivers for the preindustrial ages have been variations of the sun, volcanic ashes and exhalations, relative movements of the earth towards the sun and tectonically induced effects as for major sea currents, watersheds and ocean oscillations. In the early Phanerozoic, increased atmospheric carbon dioxide concentrations have been linked to driving or amplifying increased global temperatures. Royer et al. 2004 found a climate sensitivity for the rest of the Phanerozoic which was calculated to be similar to today's modern range of values.

The difference in global mean temperatures between a fully glacial Earth and an 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 requirement for the development of large scale ice sheets seems to be the arrangement of continental land masses at or near the poles. The constant rearrangement of continents by plate tectonics
Plate tectonics
Plate tectonics is a scientific theory that describes the large scale motions of Earth's lithosphere...

 can also shape long-term climate evolution. However, the presence or absence of land masses at the poles is not sufficient to guarantee glaciations or exclude polar ice caps. Evidence exists of past warm periods in Earth's climate when polar land masses similar to Antarctica were home to deciduous
Deciduous
Deciduous means "falling off at maturity" or "tending to fall off", and is typically used in reference to trees or shrubs that lose their leaves seasonally, and to the shedding of other plant structures such as petals after flowering or fruit when ripe...

 forests rather than ice sheets.

The relatively warm local minimum between Jurassic
Jurassic
The Jurassic is a geologic period and system that extends from about Mya to  Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...

 and Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...

 goes along with widespread tectonic activity, e.g. the breakup of supercontinent
Supercontinent
In geology, a supercontinent is a landmass comprising more than one continental core, or craton. The assembly of cratons and accreted terranes that form Eurasia qualifies as a supercontinent today.-History:...

s.

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
Ice age
An ice age or, more precisely, glacial age, is a generic geological period of long-term reduction in the temperature of the Earth's surface and atmosphere, resulting in the presence or expansion of continental ice sheets, polar ice sheets and alpine glaciers...

. Some of the most severe fluctuations, such as the Paleocene-Eocene Thermal Maximum
Paleocene-Eocene Thermal Maximum
The most extreme change in Earth surface conditions during the Cenozoic Era began at the temporal boundary between the Paleocene and Eocene epochs . This event, the Paleocene–Eocene Thermal Maximum , was associated with rapid global...

, may be related to rapid climate changes due to sudden collapses of natural methane clathrate
Methane clathrate
Methane clathrate, also called methane hydrate, hydromethane, methane ice, "fire ice", natural gas hydrate or just gas hydrate, is a solid clathrate compound in which a large amount of methane is trapped within a crystal structure of water, forming a solid similar to ice...

 reservoirs in the oceans.

A similar, single event of induced severe climate change after a meteorite impact has been proposed as reason for the Cretaceous-Tertiary extinction event
Cretaceous-Tertiary extinction event
The Cretaceous–Paleogene extinction event, formerly named and still commonly referred to as the Cretaceous-Tertiary extinction event, occurred approximately 65.5 million years ago at the end of the Maastrichtian age of the Cretaceous period. It was a large-scale mass extinction of animal and plant...

. Other major thresholds are the Permian-Triassic
Permian-Triassic extinction event
The Permian–Triassic extinction event, informally known as the Great Dying, was an extinction event that occurred 252.28 Ma ago, forming the boundary between the Permian and Triassic geologic periods, as well as the Paleozoic and Mesozoic eras...

, and Ordovician-Silurian extinction events
Ordovician-Silurian extinction events
The Ordovician–Silurian extinction event, or quite commonly the Ordovician extinction, was the third-largest of the five major extinction events in Earth's history in terms of percentage of genera that went extinct and second largest overall in the overall loss of life. Between about 450 Ma to 440...

 with various reasons suggested.

Quaternary sub-era


The Quaternary
Quaternary
The Quaternary Period is the most recent of the three periods of the Cenozoic Era in the geologic time scale of the ICS. It follows the Neogene Period, spanning 2.588 ± 0.005 million years ago to the present...

 sub-era includes the current climate. There has been a cycle of ice age
Ice age
An ice age or, more precisely, glacial age, is a generic geological period of long-term reduction in the temperature of the Earth's surface and atmosphere, resulting in the presence or expansion of continental ice sheets, polar ice sheets and alpine glaciers...

s for the past 2.2–2.1 million years (starting before the Quaternary in the late Neogene
Neogene
The Neogene is a geologic period and system in the International Commission on Stratigraphy Geologic Timescale starting 23.03 ± 0.05 million years ago and ending 2.588 million years ago...

 Period).

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.

Short term (104 to 106 years)


Geologically short-term (<120,000 year) temperatures are believed to be driven by orbital factors (see Milankovitch cycles
Milankovitch cycles
Milankovitch theory describes the collective effects of changes in the Earth's movements upon its climate, named after Serbian civil engineer and mathematician Milutin Milanković, who worked on it during First World War internment...

) amplified by changes in greenhouse gases. The arrangements of land masses on the Earth's surface are believed to influence the effectiveness of these orbital forcing effects.

Medium term (106 to 108 years)


Continental drift affects the thermohaline circulation
Thermohaline circulation
The term thermohaline circulation refers to a part of the large-scale ocean circulation that is driven by global density gradients created by surface heat and freshwater fluxes....

, which transfers heat between the equatorial regions and the poles, as does the extent of polar ice coverage.

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
Solar variation
Solar variation is the change in the amount of radiation emitted by the Sun and in its spectral distribution over years to millennia. These variations have periodic components, the main one being the approximately 11-year solar cycle . The changes also have aperiodic fluctuations...

 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. See the web site Paleomap Project for images of the polar landmass distributions through time.

Comparisons of plate tectonic continent reconstructions
Plate reconstruction
Plate reconstruction is the process of reconstructing the positions of tectonic plates relative to each other or to other reference frames, such as the earth's magnetic field or groups of hotspots, in the geological past...

 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. Today, Greenland
Greenland
Greenland is an autonomous country within the Kingdom of Denmark, located between the Arctic and Atlantic Oceans, east of the Canadian Arctic Archipelago. Though physiographically a part of the continent of North America, Greenland has been politically and culturally associated with Europe for...

, Antarctica, and the northern portions of Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...

, Asia
Asia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...

, and North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...

 are situated such that a minor change in solar energy will tip the balance between year-round snow/ice preservation and complete summer melting. The presence of snow and ice is a well-understood positive feedback
Positive feedback
Positive feedback is a process in which the effects of a small disturbance on a system include an increase in the magnitude of the perturbation. That is, A produces more of B which in turn produces more of A. In contrast, a system that responds to a perturbation in a way that reduces its effect is...

 mechanism for climate. 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
PH
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...

 levels.

Long term (108 to 109 years)



It has been proposed that long term galactic motions of the sun have a major influence on the Earth's climate. There are two principal motions, the first and most significant is the orbit of the sun around the galactic centre with a period of the order of 240 million years. Since this period is different from the rotation period of the galactic spiral arms, the sun, and the earth with it, will periodically pass through the arms (estimates of the period are uncertain and vary from 143 million years to 176 million years). The second is an oscillatory bobbing motion, similar to a floating buoy, which will periodically take the sun through the galactic disc. The period of this bobbing motion is 67 million years, so a pass through the galactic plane will occur every 33 million years. The causal link between these galactic motions and climate is unclear but one (controversial) postulate is the effect that entering a denser region of the galaxy will have on increasing the cosmic ray flux (CRF). This theory has been criticised, both for overstating the correlation with CRF and for failing to propose a believable mechanism that would allow CRF to drive temperature. The claims by Henrik Svensmark
Henrik Svensmark
Henrik Svensmark is a physicist at the Danish National Space Center in Copenhagen who studies the effects of cosmic rays on cloud formation. His work presents hypotheses about solar activity as an indirect cause of global warming; his research has suggested a possible link through the interaction...

 that CRF also strongly affects short term climate changes is even more controversial and has been challenged by many.

It has also been suggested that there is some correlation between these galactic cycles and geological periods. The reason for this is postulated to be that the earth experiences many more impact events while passing through high density regions of the galaxy. Both the climate changes and sudden impacts may cause, or contribute to, extinction event
Extinction event
An extinction event is a sharp decrease in the diversity and abundance of macroscopic life. They occur when the rate of extinction increases with respect to the rate of speciation...

s.

Very long term (109 years or more)


Jan Veizer
Jan Veizer
Ján Veizer is the Distinguished University Professor of Earth Sciences at the University of Ottawa and Institute for Geology, Mineralogy und Geophysis, of Bochum Ruhr University, he held the NSERC/Noranda/CIFAR Industrial Chair in Earth System Isotope and Environmental Geochemistry until 2004...

 and Nir Shaviv
Nir Shaviv
Nir Joseph Shaviv is an Israeli/American physics professor, carrying out research in the fields of astrophysics and climate science. He is currently an associate professor at the Racah Institute of Physics of the Hebrew University of Jerusalem....

 have proposed the interaction of cosmic ray
Cosmic ray
Cosmic rays are energetic charged subatomic particles, originating from outer space. They may produce secondary particles that penetrate the Earth's atmosphere and surface. The term ray is historical as cosmic rays were thought to be electromagnetic radiation...

s, solar wind
Solar wind
The solar wind is a stream of charged particles ejected from the upper atmosphere of the Sun. It mostly consists of electrons and protons with energies usually between 1.5 and 10 keV. The stream of particles varies in temperature and speed over time...

 and the various magnetic fields to explain the long term evolution of earth's climate. According to Shaviv, the early sun had emitted a stronger solar wind with a protective effect against cosmic rays. In that early age, a moderate greenhouse effect comparable to today's would have been sufficient to explain an ice free earth and the faint young sun paradox
Faint young sun paradox
The faint young Sun paradox or problem describes the apparent contradiction between observations of liquid water early in the Earth's history and the astrophysical expectation that the Sun's output would be only 70% as intense during that epoch as it is during the modern epoch. The issue was raised...

. The solar minimum around 2.4 billion years ago is consistent with an established cosmic ray flux modulation by a variable star formation rate in the Milky Way and there is also a hint of an extinction event at this time. Within the last billion years the solar wind has significantly diminished. It is only within this more recent time that passages of the heliosphere through the spiral arms of the galaxy have been able to gain a strong and regularly modulating influence as described above.

Over the very long term the energy output of the sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

 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
Stellar evolution
Stellar evolution is the process by which a star undergoes a sequence of radical changes during its lifetime. Depending on the mass of the star, this lifetime ranges from only a few million years to trillions of years .Stellar evolution is not studied by observing the life of a single...

.

See also

  • Geologic temperature record
    Geologic temperature record
    The Geologic temperature record are changes in Earth's environment as determined from geologic evidence on multi-million to billion year time scales...

  • Paleothermometry, the study of ancient temperatures
  • Paleotempestology
    Paleotempestology
    Paleotempestology is the study of past tropical cyclone activity by means of geological proxies as well as historical documentary records. The term was coined by Kerry Emanuel.-Sedimentary proxy records:...

    , the study of past tropical cyclone activity
  • Dendroclimatology
    Dendroclimatology
    Dendroclimatology is the science of determining past climates from trees . Tree rings are wider when conditions favor growth, narrower when times are difficult. Other properties of the annual rings, such as maximum latewood density have been shown to be better proxies than simple ring width...

  • Historical climatology
    Historical climatology
    Historical climatology is the study of historical changes in climate and their effect on human history and development. This differs from paleoclimatology which encompasses climate change over the entire history of the earth. The study seeks to define periods in human history where temperature or...

    , the study of climate over human history (as opposed to earth
    Earth
    Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

    's)
  • CLIWOC
    Cliwoc
    The Climatological database for the world's oceans was a research project to convert ships' logbooks into a computerised database. It was funded by the European Union, and the bulk of the work was done between 2001 and 2003...

    , Climatological database for the world's oceans (1759–1854)
  • Shen Kuo
    Shen Kuo
    Shen Kuo or Shen Gua , style name Cunzhong and pseudonym Mengqi Weng , was a polymathic Chinese scientist and statesman of the Song Dynasty...

    , 11th-century Chinese scientist who realized the possibilities of paleoclimatology while observing ancient petrified bamboos buried underground in a northern, dry climate
  • Paleomap
    Paleomap
    Paleomaps are maps of continents and mountain ranges in the distant past or future. Until the 1960s, paleomaps were not very satisfactory as it was difficult to understand many quite distinctive features. For example huge river deltas seemed to be associated with what must have been quite small...

     Map of different ages and climates of the earth
  • Table of historic and prehistoric climate indicators
    Table of Historic and Prehistoric Climate Indicators
    This table is a reference tool for rapidly locating Wikipedia articles on Historic and Prehistoric climate indicators of all types.To Add:* Alkenone analysis* TEX-86 analysis* Nile river flood levels* Trace mineral ratios in deltaic sediment...


External links