Editing Paleoclimatology

{{Paleontology}}
{{Short description|Study of changes in ancient climate}}
{{Use dmy dates|date=June 2018}}

'''Paleoclimatology''' ([[American and British English spelling differences|British spelling]], '''palaeoclimatology''') is the scientific study of [[climate]]s predating the invention of [[meteorological instrument]]s, when no direct measurement data were available.<ref>{{Cite book|title=Paleoclimatology: Reconstructing Climates of the Quaternary|last=Bradley|first=Raymond|publisher=Elsevier|year=2015|isbn=978-0-12-386913-5|location=Oxford|pages=1}}</ref> As instrumental records only span a tiny part of [[Earth's history]], the reconstruction of ancient climate is important to understand natural variation and the evolution of the current climate.

Paleoclimatology uses a variety of [[proxy (climate)|proxy]] methods from [[Earth science|Earth]] and [[list of life sciences|life sciences]] to obtain data previously preserved within [[Rock (geology)|rocks]], [[sediment]]s, [[borehole]]s, [[ice sheet]]s, [[tree ring]]s, [[coral]]s, [[mollusc shell|shells]], and [[Micropaleontology#Microfossils|microfossils]]. Combined with techniques to date the proxies, the paleoclimate records are used to determine the past states of [[Earth's atmosphere]].

The scientific field of paleoclimatology came to maturity in the 20th century. Notable periods studied by paleoclimatologists include the frequent [[glacial period|glaciations]] that Earth has undergone, rapid cooling events like the [[Younger Dryas]], and the rapid warming during the [[Paleocene–Eocene Thermal Maximum]]. Studies of past changes in the environment and biodiversity often reflect on the current situation, specifically the impact of climate on [[extinction event|mass extinctions]] and biotic recovery and current [[climate change|global warming]].<ref name="SahneyBenton2008RecoveryFromProfoundExtinction">{{cite journal|url= |last1=Sahney|first1=S.|last2=Benton|first2=M.J.|name-list-style=amp|year=2008|title=Recovery from the most profound mass extinction of all time|journal=Proceedings of the Royal Society B: Biological Sciences|doi=10.1098/rspb.2007.1370|volume=275|pages=759–65|pmid=18198148|issue=1636|pmc=2596898}}</ref><ref>{{harvnb|Cronin|2010|p=1}}</ref>

Studying paleoclimatology is important when looking towards the Earth's future regarding climate specifically. 

==History==
{{Main|History of climate change science|Historical climatology}}
Notions of a changing climate most likely evolved in [[ancient Egypt]], [[Mesopotamia]], the [[Indus Valley civilisation|Indus Valley]] and [[History of China|China]], where prolonged periods of droughts and floods were experienced.<ref name=Fairbridge>{{cite book|title=Encyclopedia of Paleoclimatology and Ancient Environments|chapter=history of paleoclimatology|last=Fairbridge|first=Rhodes|editor-last=Gornitz|editor-first=Vivien|pages=414–426|isbn=978-1-4020-4551-6|publisher=Springer Nature|date=31 October 2008}}</ref> In the seventeenth century, [[Robert Hooke]] postulated that fossils of giant turtles found in [[Dorset]] could only be explained by a once warmer climate, which he thought could be explained by a shift in Earth's axis.<ref name=Fairbridge /> Fossils were, at that time, often explained as a consequence of a biblical flood.<ref name='Cronin' /> Systematic observations of sunspots started by amateur astronomer [[Heinrich Schwabe]] in the early 19th century, starting a discussion of the Sun's influence on Earth's climate.<ref name="Fairbridge" />

The scientific study of paleoclimatology began to take shape in the early 19th century, when discoveries about glaciations and natural changes in Earth's past climate helped to understand the [[greenhouse effect]]. It was only in the 20th century that paleoclimatology became a unified scientific field. Before, different aspects of Earth's climate history were studied by a variety of disciplines.<ref name='Cronin'>{{Cite book|url=https://cup.columbia.edu/book/principles-of-paleoclimatology/9780231109550|title=Principles of Paleoclimatology|last=Cronin|first=Thomas M.|date=1999|publisher=Columbia University Press|isbn=9780231503044|pages=8–10}}</ref> At the end of the 20th century, the empirical research into Earth's ancient climates started to be combined with computer models of increasing complexity. A new objective also developed in this period: finding ancient analog climates that could provide information about current [[global warming|climate change]].<ref name='Cronin' />

==Reconstructing ancient climates==
[[File:Earth's average surface temperature over the past 500 million years.png|thumb|upright=2|Preliminary results from a [[National Museum of Natural History|Smithsonian Institution]] project, showing Earth's average surface temperature over the past 500 million years<ref>{{Cite web |date=2023-11-22 |title=What's the hottest Earth's ever been? |publisher=[[NOAA]] |url=http://www.climate.gov/news-features/climate-qa/whats-hottest-earths-ever-been |access-date=2024-06-03 |website=www.climate.gov |language=en}}</ref><ref>{{Cite web |last=Soul | first=Laura |work=Smithsonian Magazine |title=Leading Scientists Convene to Chart 500M Years of Global Climate Change |url=http://www.smithsonianmag.com/blogs/national-museum-of-natural-history/2018/04/24/leading-scientists-convene-to-chart-500m-years-of-global-climate-change/ |date=2018-04-24 |access-date=2024-06-03 |language=en}}</ref>]]
[[File:All palaeotemps.svg|thumb|right|upright=3|Palaeotemperature graphs placed together]]
[[File:Sauerstoffgehalt-1000mj2.png|thumb|upright=2|The oxygen content in the atmosphere over the last billion years]]
{{Main|Proxy (climate)}}
Paleoclimatologists employ a wide variety of techniques to deduce ancient climates. The techniques used depend on which variable has to be reconstructed (this could be [[temperature]], [[precipitation]], or something else) and how long ago the climate of interest occurred. For instance, the deep marine record, the source of most isotopic data, exists only on oceanic plates, which are eventually [[Subduction|subducted]]; the oldest remaining material is {{ma|200|million years}} old. Older sediments are also more prone to corruption by [[diagenesis]]. This is due to the millions of years of disruption experienced by the rock formations, such as pressure, tectonic activity, and fluid flowing. These factors often result in a lack in quality or quantity of data, which causes resolution and confidence in the data decrease over time.

Specific techniques used to make inferences on ancient climate conditions are the use of lake sediment cores and speleothems. These utilize an analysis of sediment layers and rock growth formations respectively, amongst element-dating methods utilizing oxygen, carbon and uranium.

===Proxies for climate===

====Direct Quantitative Measurements====
The Direct Quantitative Measurements method is the most direct approach to understand the change in a climate. Comparisons between recent data to older data allows a researcher to gain a basic understanding of weather and climate changes within an area. There is a disadvantage to this method. Data of the climate only started being recorded in the mid-1800s. This means that researchers can only utilize 150 years of data. That is not helpful when trying to map the climate of an area 10,000 years ago. This is where more complex methods can be used. <ref>{{cite book |last1=Saltzman |first1=Barry |title=Dynamical Paleoclimatology: Generalized Theory of Global Climate Change |date=2002 |publisher=Academic Press |location=Google Scholar |isbn=978-0-12-617331-4 |url=https://books.google.com/books?id=kJkE52UtpXcC&dq=paleoclimatology&pg=PP1 |access-date=1 April 2024}}</ref>

====Ice====
Mountain [[glacier]]s 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 [[European Project for Ice Coring in Antarctica|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 ({{delta|18|O|link}}) 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 but it also depends on factors such as water salinity and the volume of water locked up in ice sheets. Various cycles in isotope ratios have been detected.
* [[Pollen#In the fossil record|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. Volcanic events distribute ash with a unique set of properties (shape and color of particles, chemical signature). Establishing the ash's source will give a time period to associate with the layer of ice.

A multinational consortium, the [[European Project for Ice Coring in Antarctica]] (EPICA), has drilled an ice core in Dome C on the East Antarctic ice sheet and retrieved ice from roughly 800,000 years ago.<ref>{{cite journal|last1=Jouzel|first1=Jean|title=Orbital and Millennial Antarctic Climate Variability over the Past 800,000 Years|journal=Science|date=10 August 2007|volume=317|pages=793–796|doi=10.1126/science.1141038|last2=Masson-Delmotte|first2=V.|last3=Cattani|first3=O.|last4=Dreyfus|first4=G.|last5=Falourd|first5=S.|last6=Hoffmann|first6=G.|last7=Minster|first7=B.|last8=Nouet|first8=J.|last9=Barnola|first9=J. M.|last10=Chappellaz|first10=J.|last11=Fischer|first11=H.|last12=Gallet|first12=J. C.|last13=Johnsen|first13=S.|last14=Leuenberger|first14=M.|last15=Loulergue|first15=L.|last16=Luethi|first16=D.|last17=Oerter|first17=H.|last18=Parrenin|first18=F.|last19=Raisbeck|first19=G.|last20=Raynaud|first20=D.|last21=Schilt|first21=A.|last22=Schwander|first22=J.|last23=Selmo|first23=E.|last24=Souchez|first24=R.|last25=Spahni|first25=R.|last26=Stauffer|first26=B.|last27=Steffensen|first27=J. P.|last28=Stenni|first28=B.|last29=Stocker|first29=T. F.|last30=Tison|first30=J. L.|issue=5839|pmid=17615306|bibcode=2007Sci...317..793J|s2cid=30125808|display-authors=8|url=https://epic.awi.de/id/eprint/16356/1/Fis2007b.pdf}}</ref> 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.<ref name="Page 1 1 International Partnerships in Ice Core Sciences (IPICS)">{{cite web|title=Page 1 1 International Partnerships in Ice Core Sciences (IPICS) The oldest ice core: A 1.5 million year record of climate and greenhouse gases from Antarctica|url=https://docs.google.com/viewer?a=v&q=cache:q-s3FmzPx2IJ:www.pages-igbp.org/ipics/data/ipics_oldest_sip_final.pdf+oldest+ice+core+taken+was+from+the+Antarctic&hl=en&gl=us&pid=bl&srcid=ADGEEShU7yNImhQRe0OT1sDyHElyttKBXnyOnXCGkoaJmbd5ocjrRfY5_2e2LYTOf-SPPzfuZ6KM82kfyeSkoKQzCH3OSKAXsfeim00_D5l6gwdDCa0VtDqqLKqXzI0dlH1vcGdpF6_I&sig=AHIEtbSRsko6dyE5t8K9yXxvk6GYPekLCg&pli=1|access-date=22 September 2011}}</ref>

====Dendroclimatology====
{{Main|Dendroclimatology}}
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 by 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. This is done by comparing the number, thickness, ring boundaries, and pattern matching of tree growth rings.

The differences in thickness displayed in the growth rings in trees can often indicate the quality of conditions in the environment, and the fitness of the tree species evaluated. Different species of trees will display different growth responses to the changes in the climate. An evaluation of multiple trees within the same species, along with one of trees in different species, will allow for a more accurate analysis of the changing variables within the climate and how they affected the surrounding species.<ref>{{Cite journal |last1=Frank |first1=David |last2=Esper |first2=Jan |last3=Zorita |first3=Eduardo |last4=Wilson |first4=Rob |date=14 May 2010 |title=A noodle, hockey stick, and spaghetti plate: a perspective on high-resolution paleoclimatology |url=https://wires.onlinelibrary.wiley.com/doi/10.1002/wcc.53 |journal=WIREs Climate Change |language=en |volume=1 |issue=4 |pages=507–516 |doi=10.1002/wcc.53 |bibcode=2010WIRCC...1..507F |issn=1757-7780}}</ref>

Older intact wood that has escaped decay can extend the time covered by the record by matching the ring depth changes to contemporary specimens. By using that 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.

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

* Sediments, sometimes lithified to form rock, may contain remnants of preserved vegetation, animals, plankton, or [[Palynology|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 {{delta|18|O|link}} record responds to changes in temperature and ice volume, and the {{delta|13|C|link}} record reflects a range of factors, which are often difficult to disentangle.

[[File:Core+Repository+core samples2.jpg|right|thumb|Sea floor core sample labelled to identify the exact spot on the sea floor where the sample was taken. Sediments from nearby locations can show significant differences in chemical and biological composition.]]
;[[Sedimentary facies]]
On a longer time scale, the rock record may show signs of [[sea level]] rise and fall, and features such as [[Dune#Lithified dunes|"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.

====Sclerochronology====

;Corals (see also [[sclerochronology]])
Coral "rings<nowiki>''</nowiki> share similar evidence of growth to that of trees, and thus can be dated in similar ways. A primary difference is their environments and the conditions within those that they respond to. Examples of these conditions for coral include water temperature, freshwater influx, changes in pH, and wave disturbances. From there, specialized equipment, such as the Advanced Very High Resolution Radiometer (AVHRR) instrument, can be used to derive the [[sea surface temperature]] and water salinity from the past few centuries. The [[Δ18O|δ<sup>18</sup>O]] of [[Coralline algae|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.<ref name=Geology2008>{{cite journal|last1=Halfar|first1=J.|year=2008|doi=10.1130/G24635A.1|title=Coralline red algae as high-resolution climate recorders|journal=Geology|volume=36|pages=463|last2=Steneck|first2=R.S.|last3=Joachimski|first3=M.|last4=Kronz|first4=A.|last5=Wanamaker|first5=A.D.|issue=6|bibcode=2008Geo....36..463H|s2cid=129376515 }}</ref><ref name=Cobb>{{cite journal|last1=Cobb|first1=K.|last2=Charles|first2=C. D.|last3=Cheng|first3=H|last4=Edwards|first4=R. L.|year=2003|title=El Nino/Southern Oscillation and tropical Pacific climate during the past millennium|journal=Nature|volume=424|issue=6946|pages=271–6|pmid=12867972|doi=10.1038/nature01779|bibcode=2003Natur.424..271C|s2cid=6088699}}</ref>

====Landscapes and landforms====
Within [[climatic geomorphology]], one approach is to study [[Relict (geology)|relict landforms]] to infer ancient climates.<ref name=Gutix2>{{cite book|chapter-url=https://www.researchgate.net/publication/285964375|chapter=Climatic Geomorphology|title=Treatise on Geomorphology|volume=13|author-last=Gutiérrez|first1=Mateo|author-link=Mateo Gutiérrez|last2=Gutiérrez|first2=Francisco|year=2013|pages=115–131}}</ref> Being often concerned about past climates climatic geomorphology is considered sometimes to be a theme of [[historical geology]].<ref>{{cite book|date=2005|chapter=Chapter 1 Climatic geomorphology|title=Developments in Earth Surface Processes|editor-last=Gutiérrez|editor-first=Mateo|editor-link=Mateo Gutiérrez|volume=8|pages=3–32|doi=10.1016/S0928-2025(05)80051-3|isbn=978-0-444-51794-4}}</ref> Evidence of these past climates to be studied can be found in the landforms they leave behind. Examples of these landforms are those such as glacial landforms (moraines, striations), desert features (dunes, desert pavements), and coastal landforms (marine terraces, beach ridges).<ref>{{Cite web |last1=Douglas |first1=Peter |last2=Brenner |first2=Mark |last3=Curtis |first3=Jason |date=27 February 2016 |title=Methods and future directions for paleoclimatology in the Maya Lowlands. Global and Planetary Change. |doi=10.1016/j.gloplacha.2015.07.008 |url=https://doi.org/10.1016/j.gloplacha.2015.07.008 }}</ref> Climatic geomorphology is of limited use to study recent ([[Quaternary]], [[Holocene]]) large climate changes since there are seldom discernible in the geomorphological record.<ref name=Goudie2004>{{cite encyclopedia|last=Goudie|first=A.S.|editor-last=Goudie|editor-first=A.S.|author-link=Andrew Goudie (geographer)|encyclopedia=Encyclopedia of Geomorphology|title=Climatic geomorphology|year=2004|pages=162–164}}</ref>

===Timing of proxies===
The field of [[geochronology]] has scientists working on determining how old certain proxies are. For recent proxy archives of tree rings and corals the individual year rings can be counted, and an exact year can be determined. [[Radiometric dating]] uses the properties of radioactive elements in proxies. In older material, more of the radioactive material will have decayed and the proportion of different elements will be different from newer proxies. One example of radiometric dating is [[radiocarbon dating]]. In the air, [[cosmic ray]]s constantly convert nitrogen into a specific radioactive carbon isotope, [[Carbon-14|<sup>14</sup>C]]. When plants then use this carbon to grow, this isotope is not replenished anymore and starts decaying. The proportion of 'normal' carbon and Carbon-14 gives information of how long the plant material has not been in contact with the atmosphere.<ref>{{harvnb|Cronin|2010|pp=32–34}}.</ref>

==Notable climate events in Earth history==
{{See also|List of periods and events in climate history|Timeline of glaciation|History of Earth}}

Knowledge of precise climatic events decreases as the record goes back in time, but some notable climate events are known:
* [[Faint young Sun paradox]] (start)
* [[Huronian glaciation]] (~2400 Mya Earth completely covered in ice probably due to [[Great Oxygenation Event]])
* Later Neoproterozoic [[Snowball Earth]] (~600 Mya, precursor to the [[Cambrian Explosion]])
* [[Andean-Saharan glaciation]] (~450 Mya)
* [[Carboniferous Rainforest Collapse]] (~300 Mya)
* [[Permian–Triassic extinction event]] (251.9 Mya)
* [[Anoxic event|Oceanic anoxic events]] (~120 Mya, 93 Mya, and others)
* [[Cretaceous–Paleogene extinction event]] ({{period start|Paleogene}} Mya)
* [[Paleocene–Eocene Thermal Maximum]] ([[Paleocene]]–[[Eocene]], 55Mya)
* [[Last Glacial Maximum]] (~23,000 BCE)
* [[Younger Dryas]]/Big Freeze (~11,000 BCE)
* [[Holocene climatic optimum]] (~7000–3000 BCE)
* [[Extreme weather events of 535–536]] (535–536 CE)
* [[Medieval Warm Period]] (900–1300)
* [[Little Ice Age]] (1300–1800)
* [[Year Without a Summer]] (1816)

==History of the atmosphere==
{{Life timeline}}
{{See also|Atmosphere of Earth|History of Earth}}

===Earliest atmosphere===
The [[Paleoatmosphere|first atmosphere]] would have consisted of gases in the [[Solar nebula#Formation of planets|solar nebula]], primarily [[hydrogen]]. In addition, there would probably have been simple [[hydride]]s such as those now found in gas giants like [[Jupiter]] and [[Saturn]], notably [[water]] vapor, [[methane]], and [[ammonia]]. As the solar nebula dissipated, the gases would have escaped, partly driven off by the [[solar wind]].<ref name=Zahnle>{{cite journal|last1=Zahnle|first1=K.|last2=Schaefer|first2=L.|author2-link=Laura K. Schaefer|last3=Fegley|first3=B.|doi=10.1101/cshperspect.a004895|title=Earth's Earliest Atmospheres|journal=Cold Spring Harbor Perspectives in Biology|volume=2|issue=10|pages=a004895|year=2010|pmid=20573713|pmc=2944365}}</ref>

===Second atmosphere===
The next atmosphere, consisting largely of [[nitrogen]], [[carbon dioxide]], and inert gases, was produced by outgassing from [[volcanism]], supplemented by gases produced during the [[late heavy bombardment]] of Earth by huge [[asteroids]].<ref name=Zahnle/> A major part of carbon dioxide emissions were soon dissolved in water and built up carbonate sediments.

Water-related sediments have been found dating from as early as 3.8 billion years ago.<ref>B. Windley: ''The Evolving Continents.'' Wiley Press, New York 1984</ref> 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 in the history of the atmosphere because hints of early life forms have been dated to as early as 3.5 to 4.3 billion years ago.<ref>J. Schopf: ''Earth's Earliest Biosphere: Its Origin and Evolution.'' Princeton University Press, Princeton, N.J., 1983</ref> The fact that it is not perfectly in line with the 30% lower solar radiance (compared to today) of the early Sun has been described as the "[[faint young Sun paradox]]".

The geological record, however, shows a continually relatively warm surface during the complete early [[temperature record]] of Earth with the exception of one cold glacial phase about 2.4 billion years ago. In the late [[Archean|Archaean]] eon, an oxygen-containing atmosphere began to develop, apparently from photosynthesizing [[cyanobacteria]] (see [[Great Oxygenation Event]]) which have been found as [[stromatolite]] fossils from 2.7 billion years ago. The early basic carbon isotopy ([[isotope ratio]] proportions) was very much in line with what is found today, suggesting that the fundamental features of the [[carbon cycle]] were established as early as 4 billion years ago.

===Third atmosphere===
The constant rearrangement of continents by [[plate tectonics]] influences the long-term evolution of the atmosphere by transferring carbon dioxide to and from large continental carbonate stores. Free oxygen did not exist in the atmosphere until about 2.4 billion years ago, during the [[Great Oxygenation Event]], and its appearance is indicated by the end of the [[banded iron formations]]. Until then, any oxygen produced by photosynthesis was consumed by oxidation of reduced materials, notably iron. Molecules of free oxygen did not start to accumulate in the atmosphere until the rate of production of oxygen began to exceed the availability of reducing materials. That point was a shift from a [[redox|reducing]] atmosphere to an [[oxidizing]] atmosphere. O<sub>2</sub> showed major variations until reaching a steady state of more than 15% by the end of the Precambrian.<ref>Christopher R. Scotese, [http://www.scotese.com/precamb_chart.htm Back to Earth History: Summary Chart for the Precambrian], Paleomar Project</ref> The following time span was the [[Phanerozoic]] eon, during which oxygen-breathing [[metazoan life]] forms began to appear.

The amount of oxygen in the atmosphere has fluctuated over the last 600 million years, reaching a peak of 35%<ref name=Beerling2007>{{cite book|last=Beerling|first=David|author-link=David Beerling|year=2007|title=The emerald planet: how plants changed Earth's history|url=https://archive.org/details/emeraldplanethow00beer|url-access=registration|publisher=Oxford University press|isbn=9780192806024|page=[https://archive.org/details/emeraldplanethow00beer/page/n64 47]}}</ref> during the [[Carboniferous]] period, significantly higher than today's 21%. Two main processes govern changes in the atmosphere: plants [[photosynthesis|use carbon dioxide from the atmosphere]], releasing oxygen and the breakdown of [[pyrite]] and [[volcanic eruption]]s release [[sulfur]] into the atmosphere, which oxidizes and hence reduces the amount of oxygen in the atmosphere. However, volcanic eruptions also release carbon dioxide, which plants can convert to oxygen. The exact cause of the variation of the amount of oxygen in the atmosphere is not known. Periods with much oxygen in the atmosphere are associated with rapid development of animals. Today's atmosphere contains 21% oxygen, which is high enough for rapid development of animals.<ref>Peter Ward:[http://www.nap.edu/catalog.php?record_id=11630] Out of Thin Air: Dinosaurs, Birds, and Earth's Ancient Atmosphere</ref>

==Climate during geological ages==
[[File:GlaciationsinEarthExistancelicenced annotated.jpg|thumb|600px|right|Timeline of glaciations, shown in blue]]
{{See also|Timeline of glaciation}}
* The [[Huronian glaciation]], is the first known glaciation in Earth's history, and lasted from 2400 to 2100 million years ago.
* The [[Cryogenian glaciation]] lasted from 720 to 635 million years ago.
* The [[Andean-Saharan glaciation]] lasted from 450 to 420 million years ago.
* The [[Karoo glaciation]] lasted from 360 to 260 million years ago.
* The [[Quaternary glaciation]] is the current glaciation period and began 2.58 million years ago.

In 2020 scientists published a continuous, high-fidelity [[Global temperature record|record of variations in Earth's climate during the past 66 million years]] and identified four [[Greenhouse and icehouse Earth|climate states]], separated by transitions that include changing greenhouse gas levels and polar ice sheets volumes. They integrated data of various sources. The warmest climate state since the time of the dinosaur extinction, "Hothouse", endured from 56 Mya to 47 Mya and was ~14&nbsp;°C warmer than average modern temperatures.<ref>{{cite news |title=High-fidelity record of Earth's climate history puts current changes in context |url=https://phys.org/news/2020-09-high-fidelity-earth-climate-history-current.html |access-date=8 October 2020 |work=phys.org |language=en}}</ref><ref>{{cite journal |last1=Westerhold |first1=Thomas |last2=Marwan |first2=Norbert |last3=Drury |first3=Anna Joy |last4=Liebrand |first4=Diederik |last5=Agnini |first5=Claudia |last6=Anagnostou |first6=Eleni |last7=Barnet |first7=James S. K. |last8=Bohaty |first8=Steven M. |last9=Vleeschouwer |first9=David De |last10=Florindo |first10=Fabio |last11=Frederichs |first11=Thomas |last12=Hodell |first12=David A. |last13=Holbourn |first13=Ann E. |last14=Kroon |first14=Dick |last15=Lauretano |first15=Vittoria |last16=Littler |first16=Kate |last17=Lourens |first17=Lucas J. |last18=Lyle |first18=Mitchell |last19=Pälike |first19=Heiko |last20=Röhl |first20=Ursula |last21=Tian |first21=Jun |last22=Wilkens |first22=Roy H. |last23=Wilson |first23=Paul A. |last24=Zachos |first24=James C. |title=An astronomically dated record of Earth's climate and its predictability over the last 66 million years |journal=Science |date=11 September 2020 |volume=369 |issue=6509 |pages=1383–1387 |doi=10.1126/science.aba6853 |pmid=32913105 |bibcode=2020Sci...369.1383W |hdl=11577/3351324 |s2cid=221593388 |url=https://eprints.soton.ac.uk/444010/1/aba6853_v2Acc.pdf |access-date=8 October 2020 |language=en |issn=0036-8075}}</ref>

===Precambrian climate===
{{Main|Precambrian}}
The Precambrian took place between the time when Earth first formed 4.6 billion years ([[Giga-annum|Ga]]) ago, and 542 million years ago. The Precambrian can be split into two eons, the Archean and the Proterozoic, which can be further subdivided into eras.<ref>{{Citation |last1=Goddéris |first1=Yves |title=The Precambrian Climate |date=2021 |work=Paleoclimatology |pages=343–358 |editor-last=Ramstein |editor-first=Gilles |url=https://doi.org/10.1007/978-3-030-24982-3_26 |access-date=2024-02-09 |series=Frontiers in Earth Sciences |place=Cham |publisher=Springer International Publishing |language=en |doi=10.1007/978-3-030-24982-3_26 |isbn=978-3-030-24982-3 |last2=Ramstein |first2=Gilles |last3=Le Hir |first3=Guillaume |editor2-last=Landais |editor2-first=Amaëlle |editor3-last=Bouttes |editor3-first=Nathaelle |editor4-last=Sepulchre |editor4-first=Pierre}}</ref> The reconstruction of the Precambrian climate is difficult for various reasons including the low number of reliable indicators and a, generally, not well-preserved or extensive fossil record (especially when compared to the Phanerozoic eon). <ref>{{Citation |last1=Goddéris |first1=Yves |title=The Precambrian Climate |date=2021 |work=Paleoclimatology |pages=343–358 |editor-last=Ramstein |editor-first=Gilles |url=https://doi.org/10.1007/978-3-030-24982-3_26 |access-date=2024-02-09 |series=Frontiers in Earth Sciences |place=Cham |publisher=Springer International Publishing |language=en |doi=10.1007/978-3-030-24982-3_26 |isbn=978-3-030-24982-3 |last2=Ramstein |first2=Gilles |last3=Le Hir |first3=Guillaume |editor2-last=Landais |editor2-first=Amaëlle |editor3-last=Bouttes |editor3-first=Nathaelle |editor4-last=Sepulchre |editor4-first=Pierre}}</ref><ref>{{Cite journal |last1=Cosgrove |first1=Grace I. E. |last2=Colombera |first2=Luca |last3=Mountney |first3=Nigel P. |date=2024-03-01 |title=The Precambrian continental record: A window into early Earth environments |journal=Precambrian Research |volume=402 |pages=107286 |doi=10.1016/j.precamres.2023.107286 |issn=0301-9268|doi-access=free |bibcode=2024PreR..40207286C }}</ref> Despite these issues, there is evidence for a number of major climate events throughout the history of the Precambrian: [[Great Oxidation Event|The Great Oxygenation Event]], which started around 2.3 Ga ago (the beginning of the Proterozoic) is indicated by [[Biomarker|biomarkers]] which demonstrate the appearance of photosynthetic organisms. Due to the high levels of oxygen in the atmosphere from the GOE, [[Methane|CH<big><sub>4</sub></big>]] levels fell rapidly cooling the atmosphere causing the Huronian glaciation. For about 1 Ga after the glaciation (2–0.8 Ga ago), the Earth likely experienced warmer temperatures indicated by microfossils of photosynthetic eukaryotes, and oxygen levels between 5 and 18% of the Earth's current oxygen level. At the end of the Proterozoic, there is evidence of global glaciation events of varying severity causing a '[[Snowball Earth]]'.<ref>{{Citation |last1=Goddéris |first1=Yves |title=The Precambrian Climate |date=2021 |work=Paleoclimatology |pages=343–358 |editor-last=Ramstein |editor-first=Gilles |url=https://doi.org/10.1007/978-3-030-24982-3_26 |access-date=2024-02-09 |series=Frontiers in Earth Sciences |place=Cham |publisher=Springer International Publishing |language=en |doi=10.1007/978-3-030-24982-3_26 |isbn=978-3-030-24982-3 |last2=Ramstein |first2=Gilles |last3=Le Hir |first3=Guillaume |editor2-last=Landais |editor2-first=Amaëlle |editor3-last=Bouttes |editor3-first=Nathaelle |editor4-last=Sepulchre |editor4-first=Pierre}}</ref> Snowball Earth is supported by different indicators such as, glacial deposits, significant continental erosion called [[Great Unconformity|the Great Unconformity]], and sedimentary rocks called cap carbonates that form after a deglaciation episode. <ref>{{Citation |last1=Stern |first1=Robert J. |title=Neoproterozoic Glaciation—Snowball Earth Hypothesis |date=2021-01-01 |encyclopedia=Encyclopedia of Geology (Second Edition) |pages=546–556 |editor-last=Alderton |editor-first=David |url=https://www.sciencedirect.com/science/article/pii/B9780124095489121074 |access-date=2024-02-09 |place=Oxford |publisher=Academic Press |isbn=978-0-08-102909-1 |last2=Miller |first2=Nathan R. |editor2-last=Elias |editor2-first=Scott A.}}</ref>

===Phanerozoic climate===
[[File:Phanerozoic Climate Change.png|thumb|450px|Changes in [[oxygen-18]] ratios over the last 500 million years, indicating environmental change]]
{{Main|Phanerozoic}}
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.<ref>{{cite journal|last1=Came|first1=Rosemarie E.|last2=Eiler|first2=John M.|last3=Veizer|first3=Jan|last4=Azmy|first4=Karem|last5=Brand|first5=Uwe|last6=Weidman|first6=Christopher R|title=Coupling of surface temperatures and atmospheric CO<sub>2</sub> concentrations during the Palaeozoic era|journal=Nature|volume=449|pages=198–201|date=September 2007|doi=10.1038/nature06085|pmid=17851520|issue=7159|bibcode=2007Natur.449..198C|s2cid=4388925|url=https://authors.library.caltech.edu/35545/2/nature06085-s1.pdf}}</ref> Royer et al. 2004<ref name="Dana">{{cite journal|last1=Royer|first1=Dana L.|last2=Berner|first2=Robert A.|last3=Montañez|first3=Isabel P.|last4=Tabor|first4=Neil J.|last5=Beerling|first5=David J.|author5-link=David J. Beerling|title=CO<sub>2</sub> as a primary driver of Phanerozoic climate|journal=GSA Today|volume=14|issue=3|pages=4–10|date=July 2004|url=http://www.gsajournals.org/gsaonline/?request=get-document&issn=1052-5173&volume=014&issue=03&page=0004|doi=10.1130/1052-5173(2004)014<4:CAAPDO>2.0.CO;2|doi-access=free|bibcode=2004GSAT...14c...4R }}</ref> 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 10&nbsp;°C, though far larger changes would be observed at high latitudes and smaller ones at low latitudes.{{Citation needed|date=May 2013}} 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]] 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]] forests rather than ice sheets.

The relatively warm local minimum between [[Jurassic]] and [[Cretaceous]] goes along with an increase of subduction and mid-ocean ridge volcanism<ref>{{cite journal|author1=Douwe G. Van Der Meer|author2=Richard E. Zeebe|author3=Douwe J. J. van Hinsbergen|author4=Appy Sluijs|author5=Wim Spakman|author6=Trond H. Torsvik|title=Plate tectonic controls on atmospheric CO2 levels since the Triassic|journal=PNAS|volume=111|issue=12|pages=4380–4385|date=February 2014|doi=10.1073/pnas.1315657111|pmid=24616495|pmc=3970481|bibcode=2014PNAS..111.4380V|doi-access=free}}</ref> due to the breakup of the [[Pangea]] [[supercontinent]].

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]]. Some of the most severe fluctuations, such as the [[Paleocene-Eocene Thermal Maximum]], may be related to [[Abrupt climate change|rapid climate changes]] due to sudden collapses of natural [[methane clathrate]] reservoirs in the oceans.<ref>{{Cite journal|last1=Frieling|first1=Joost|last2=Svensen|first2=Henrik H.|last3=Planke|first3=Sverre|last4=Cramwinckel|first4=Margot J.|last5=Selnes|first5=Haavard|last6=Sluijs|first6=Appy|date=25 October 2016|title=Thermogenic methane release as a cause for the long duration of the PETM|journal=Proceedings of the National Academy of Sciences|language=en|volume=113|issue=43|pages=12059–12064|doi=10.1073/pnas.1603348113|issn=0027-8424|pmid=27790990|pmc=5087067|bibcode=2016PNAS..11312059F|doi-access=free}}</ref>

A similar, single event of induced severe climate change after a [[meteorite impact]] has been proposed as reason for the [[Cretaceous–Paleogene extinction event]]. Other major thresholds are the [[Permian-Triassic extinction event|Permian-Triassic]], and [[Ordovician-Silurian extinction events]] with various reasons suggested.

===Quaternary climate===
[[File:"EDC TempCO2Dust".svg|thumb|Ice core data for the past 800,000 years (x-axis values represent "age before 1950", so today's date is on the left side of the graph and older time on the right). Blue curve is temperature,<ref>{{cite journal|last1=Jouzel|first1=J.|last2=Masson-Delmotte|first2=V.|last3=Cattani|first3=O.|last4=Dreyfus|first4=G.|last5=Falourd|first5=S.|last6=Hoffmann|first6=G.|last7=Minster|first7=B.|last8=Nouet|first8=J.|last9=Barnola|first9=J. M.|date=10 August 2007|title=Orbital and Millennial Antarctic Climate Variability over the Past 800,000 Years|journal=Science|language=en|volume=317|issue=5839|pages=793–796|doi=10.1126/science.1141038|issn=0036-8075|pmid=17615306|bibcode=2007Sci...317..793J|s2cid=30125808|url=https://epic.awi.de/id/eprint/16356/1/Fis2007b.pdf}}</ref> red curve is atmospheric {{CO2}} concentrations,<ref>{{cite journal|last1=Lüthi|first1=Dieter|last2=Le Floch|first2=Martine|last3=Bereiter|first3=Bernhard|last4=Blunier|first4=Thomas|last5=Barnola|first5=Jean-Marc|last6=Siegenthaler|first6=Urs|last7=Raynaud|first7=Dominique|last8=Jouzel|first8=Jean|last9=Fischer|first9=Hubertus|date=15 May 2008|title=High-resolution carbon dioxide concentration record 650,000–800,000 years before present|journal=Nature|language=en|volume=453|issue=7193|pages=379–382|doi=10.1038/nature06949|issn=0028-0836|pmid=18480821|bibcode=2008Natur.453..379L|s2cid=1382081|url=https://epic.awi.de/id/eprint/18281/1/Lth2008a.pdf|doi-access=free}}</ref> and brown curve is dust fluxes.<ref>{{cite journal|last1=Lambert|first1=F.|last2=Delmonte|first2=B.|last3=Petit|first3=J. R.|last4=Bigler|first4=M.|last5=Kaufmann|first5=P. R.|last6=Hutterli|first6=M. A.|last7=Stocker|first7=T. F.|last8=Ruth|first8=U.|last9=Steffensen|first9=J. P.|date=3 April 2008|title=Dust-climate couplings over the past 800,000 years from the EPICA Dome C ice core|journal=Nature|language=en|volume=452|issue=7187|pages=616–619|doi=10.1038/nature06763|pmid=18385736|issn=0028-0836|bibcode=2008Natur.452..616L|doi-access=free}}</ref><ref>{{cite journal|last1=Lambert|first1=F.|last2=Bigler|first2=M.|last3=Steffensen|first3=J. P.|last4=Hutterli|first4=M.|last5=Fischer|first5=H.|title=Centennial mineral dust variability in high-resolution ice core data from Dome C, Antarctica|journal=Climate of the Past|volume=8|issue=2|pages=609–623|doi=10.5194/cp-8-609-2012|year=2012|bibcode=2012CliPa...8..609L|doi-access=free}}</ref> Note length of glacial-interglacial cycles averages ~100,000 years.]]
[[File:Holocene Temperature Variations.png|thumb|left|Holocene temperature variations]]
{{Main|Quaternary}}
{{See also|List of large-scale temperature reconstructions of the last 2,000 years}}
The Quaternary [[geological period]] includes the current climate. There has been a cycle of [[ice age]]s for the past 2.2–2.1 million years (starting before the Quaternary in the late [[Neogene]] 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.

The graph on the left shows the temperature change over the past 12,000 years, from various sources; the thick black curve is an average.

==Climate forcings==
{{Main|Climate forcing}}
Climate forcing is the difference between [[radiant energy]] ([[sunlight]]) received by the Earth and the [[outgoing longwave radiation]] back to space. Such [[radiative forcing]] is quantified based on the {{CO2}} amount in the [[tropopause]], in units of watts per square meter to the Earth's surface.<ref>{{cite web|year=2007|author=IPCC|title=Concept of Radiative Forcing|url=https://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch2s2-2.html|publisher=[[Intergovernmental Panel on Climate Change|IPCC]]|author-link=Intergovernmental Panel on Climate Change|access-date=14 April 2014|archive-date=4 January 2014|archive-url=https://web.archive.org/web/20140104053438/http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch2s2-2.html|url-status=dead}}</ref> Dependent on the [[radiative balance]] of incoming and outgoing energy, the Earth either warms up or cools down. Earth radiative balance originates from changes in solar [[insolation]] and the concentrations of [[greenhouse gases]] and [[aerosols]]. Climate change may be due to internal processes in Earth sphere's and/or following external forcings.<ref>{{cite web|year=2007|author=IPCC|title=What are Climate Change and Climate Variability?|url=https://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch9s9-1.html|publisher=[[Intergovernmental Panel on Climate Change|IPCC]]|author-link=Intergovernmental Panel on Climate Change}}</ref>

One example of a way this can be applied to study climatology is analyzing how the varying concentrations of CO2 affect the overall climate. This is done by using various proxies to estimate past greenhouse gas concentrations and compare those to that of the present day. Researchers are then able to assess their role in progression of climate change throughout Earth’s history.<ref>{{Cite book |last=Summerhayes |first=Colin P. |url=https://books.google.com/books?id=FQzoDwAAQBAJ&q=climate+forcing+CO2 |title=Paleoclimatology: From Snowball Earth to the Anthropocene |date=2020-09-08 |publisher=John Wiley & Sons |isbn=978-1-119-59138-2 |language=en}}</ref>

===Internal processes and forcings===
The Earth's [[climate system]] involves the [[atmosphere]], [[biosphere]], [[cryosphere]], [[hydrosphere]], and [[lithosphere]],<ref>{{cite web|publisher=NASA|title=Glossary, Climate system|url=http://earthobservatory.nasa.gov/Glossary/index.php?mode=alpha&seg=b&segend=d|date=March 2020}}</ref> and the sum of these processes from Earth's spheres is what affects the climate. Greenhouse gasses act as the internal forcing of the climate system. Particular interests in climate science and paleoclimatology focus on the study of Earth [[climate sensitivity]], in response to the sum of forcings. Analyzing the sum of these forcings contributes to the ability of scientists to make broad conclusive estimates on the Earth’s climate system. These estimates include the evidence for systems such as long term climate variability (eccentricity, obliquity precession), feedback mechanisms (Ice-Albedo Effect), and anthropogenic influence.<ref>{{Cite book |last=Saltzman |first=Barry |url=https://books.google.com/books?id=kJkE52UtpXcC&q=albedo&pg=PP1 |title=Dynamical Paleoclimatology: Generalized Theory of Global Climate Change |date=2002 |publisher=Academic Press |isbn=978-0-12-617331-4 |language=en}}</ref>

Examples:
* [[Thermohaline circulation]] (Hydrosphere)
* [[Life]] (Biosphere)

===External forcings===
* 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 internal forcing.<ref name="IPCC AR5">{{cite web|publisher=IPCC AR5|url=http://www.climatechange2013.org/images/report/WG1AR5_AnnexIII_FINAL.pdf|title=Annex III: Glossary|quote=Climate change may be due to natural internal processes or external forcings, such as modulations of the solar cycles, volcanic eruptions, and persistent anthropogenic changes in the composition of the atmosphere or in land use.}}</ref>
* Human changes of the composition of the atmosphere or land use.<ref name="IPCC AR5"/>
* Human activities causing anthropogenic greenhouse gas emissions leading to global warming and associated climate changes.
* Large asteroids that have cataclysmic impacts on Earth’s climate are considered external forcings.<ref>{{Cite book |last=Gornitz |first=Vivien |url=https://books.google.com/books?id=yRMgYc-8mTIC&q=asteroid&pg=PR14 |title=Encyclopedia of Paleoclimatology and Ancient Environments |date=2008-10-31 |publisher=Springer Science & Business Media |isbn=978-1-4020-4551-6 |language=en}}</ref>

===Mechanisms===
On timescales of millions of years, the uplift of mountain ranges and subsequent [[weathering]] processes of rocks and soils and the [[subduction]] of [[tectonic plates]], are an important part of the [[carbon cycle]].<ref>{{cite journal|last=Caldeira|first=Ken|title=Enhanced Cenozoic chemical weathering and the subduction of pelagic carbonate|journal=Nature|date=18 June 1992|volume=357|pages=578–581|doi=10.1038/357578a0|issue=6379|bibcode=1992Natur.357..578C|s2cid=45143101}}</ref><ref>{{cite journal|author1=Cin-Ty Aeolus Lee|author2=Douglas M. Morton|author3=Mark G. Little|author4=Ronald Kistler|author5=Ulyana N. Horodyskyj|author6=William P. Leeman|author7=Arnaud Agranier|title=Regulating continent growth and composition by chemical weathering|journal=PNAS|date=28 January 2008|volume=105|pages=4981–4986|doi=10.1073/pnas.0711143105|issue=13|pmid=18362343|pmc=2278177|bibcode=2008PNAS..105.4981L|doi-access=free}}</ref><ref>{{cite journal|last=van der Meer|first=Douwe|title=Plate tectonic controls on Atmospheric CO2 since the Triassic|journal=PNAS|date=25 March 2014|volume=111|pages=4380–4385|doi=10.1073/pnas.1315657111|issue=12|pmid=24616495|pmc=3970481|bibcode=2014PNAS..111.4380V|doi-access=free}}</ref> The weathering [[Co2 sequestration|sequesters {{CO2}}]], by the reaction of minerals with chemicals (especially [[silicate]] weathering with {{CO2}}) and thereby removing {{CO2}} from the atmosphere and reducing the radiative forcing. The opposite effect is [[volcanism]], responsible for the natural [[greenhouse effect]], by emitting {{CO2}} into the atmosphere, thus affecting [[glaciation]] (Ice Age) cycles. [[James Hansen|Jim Hansen]] suggested that humans emit {{CO2}} 10,000 times faster than natural processes have done in the past.<ref>{{cite web|year=2009|author=James Hansen|title=The 8 Minute Epoch 65 million Years with James Hansen|url=https://www.youtube.com/watch?v=pgC8yZT--0A| archive-url=https://ghostarchive.org/varchive/youtube/20211211/pgC8yZT--0A| archive-date=2021-12-11 | url-status=live|publisher=University of Oregon|author-link=James Hansen}}{{cbignore}}</ref>

[[Ice sheet]] dynamics and continental positions (and linked vegetation changes) have been important factors in the long term evolution of the Earth's climate.<ref>{{cite journal|last1=Royer|first1=D. L.|last2=Pagani|first2=M.|last3=Beerling|first3=David J.|author-link3=David Beerling|title=Geobiological constraints on Earth system sensitivity to CO2 during the Cretaceous and Cenozoic|journal=Geobiology|date=1 July 2012|volume=10|issue=4|pages=298–310|doi=10.1111/j.1472-4669.2012.00320.x|pmid=22353368|bibcode=2012Gbio...10..298R |s2cid=32023645|citeseerx=10.1.1.933.8880}}</ref> There is also a close correlation between {{CO2}} and temperature, where {{CO2}} has a strong control over global temperatures in Earth's history.<ref>{{cite journal|last=Royer|first=Dana L.|title=CO2-forced climate thresholds during the Phanerozoic|journal=Geochimica et Cosmochimica Acta|date=1 December 2006|volume=70|issue=23|pages=5665–5675|doi=10.1016/j.gca.2005.11.031|bibcode=2006GeCoA..70.5665R}}</ref>

==See also==

* {{annotated link|Cyclostratigraphy}}
* {{annotated link|Paleoatmosphere}}
* {{annotated link|Paleoceanography}}
* {{annotated link|Paleoecology}}
* {{annotated link|Paleothermometer}}
* {{annotated link|Paleohydrology}}
* {{annotated link|Paleotempestology}}
* {{annotated link|Paleomap}}
* {{annotated link|Reducing atmosphere}}
* {{annotated link|Table of historic and prehistoric climate indicators}}

==References==

===Notes===
{{reflist}}

===Bibliography===
{{Library resources box}}{{Refbegin}}
* {{cite book|last=Bradley|first=Raymond S.|title=Quaternary paleoclimatology: methods of paleoclimatic reconstruction|publisher=Allen & Unwin|location=Boston|year=1985|isbn=978-0-04-551067-2}}
* {{cite book|last=Cronin|first=Thomas N.|title=Paleoclimates: understanding climate change past and present|location=New York|publisher=Columbia University Press|year=2010|isbn=978-0-231-14494-0}}
* {{cite book|last=Imbrie|first=John|title=Ice ages: solving the mystery|publisher=Harvard University Press|location=Cambridge MA|year=1979|isbn=978-0-674-44075-3|url-access=registration|url=https://archive.org/details/iceagessolvingmy0000imbr_w0f3}}
* {{cite book|last1=Margulis|first1=Lynn|author-link=Lynn Margulis|first2=Dorion|last2=Sagan|author2-link=Dorion Sagan|title=Origins of sex: three billion years of genetic recombination|publisher=Yale University Press|location=New Haven|year=1986|isbn=978-0-300-03340-3|series=The Bio-origins series|url=https://archive.org/details/originsofsexthre00marg}}
* {{cite book|last=Gould|first=Stephen Jay|title=Wonderful life, the story of the Burgess Shale|publisher=W.W. Norton|location=New York|year=1989|isbn=978-0-393-02705-1|url=https://archive.org/details/wonderfullifebur00goul}}
* {{cite book|last1=Crowley|first1=Thomas J.|last2=North|first2=Gerald R.|title=Paleoclimatology|publisher=Clarendon Press|location=Oxford|year=1996|isbn=978-0-19-510533-9|series=Oxford monographs on geology and geophysics|volume=18}}
* ''The Climates of the Geological Past.'' (Die Klimate der geologischen Vorzeit). 1924, Wladimir Köppen, Alfred Wegener
** Facsimile of German original and English translation: [http://www.borntraeger-cramer.de/9783443010881 ''The climates of the geological past – Klimate der geologischen Vorzeit'']. Borntraeger, Berlin / Stuttgart 2015, {{ISBN|978-3-443-01088-1}}.
* 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, {{ISBN|3-406-54746-X}}
* {{cite book|author=William F. Ruddimann|title=Earth's Climate — Past and Future|publisher=Palgrave Macmillan|year=2001|isbn=978-0-7167-3741-4}}
* {{cite book|author=B. Windley|title=The Evolving Continents|publisher=Wiley Press|location=New York|year=1984}}
* {{cite journal|last1=Drummond|first1=Carl N.|last2=Wilkinson|first2=Bruce H.|name-list-style=amp|title=Interannual Variability in Climate Data|journal=Journal of Geology|volume=114|pages=325–339|year=2006|doi=10.1086/500992|bibcode=2006JG....114..325D|issue=3|s2cid=128885809}}
{{Refend}}

==External links==
{{Wikibooks|Historical Geology|Paleoclimatology: introduction}}
{{Commons category}}
{{Refbegin}}
*[http://www.ncdc.noaa.gov/paleo/paleo.html NOAA Paleoclimatology]
*[https://web.archive.org/web/20081216220433/http://stratus.astr.ucl.ac.be/textbook//pdf/Chapter_5.pdf Short history of climate]
{{Refend}}

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