Throughout
Earth
Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...
's climate history (
Paleoclimate
Paleoclimatology ( British spelling, palaeoclimatology) is the scientific study of climates predating the invention of meteorological instruments, when no direct measurement data were available. As instrumental records only span a tiny part of ...
) its climate has fluctuated between two primary states: greenhouse and icehouse Earth.
Both climate states last for millions of years and should not be confused with the much smaller
glacial
A glacier (; or ) is a persistent body of dense ice, a form of rock, that is constantly moving downhill under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires ...
and
interglacial
An interglacial period (or alternatively interglacial, interglaciation) is a geological interval of warmer global average temperature lasting thousands of years that separates consecutive glacial periods within an ice age. The current Holocene i ...
periods, which occur as alternating phases within an icehouse period (known as an
ice age
An ice age is a long period of reduction in the temperature of Earth's surface and atmosphere, resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers. Earth's climate alternates between ice ages, and g ...
) and tend to last less than one million years. There are
five known icehouse periods in Earth's climate history, namely the
Huronian,
Cryogenian
The Cryogenian (from , meaning "cold" and , romanized: , meaning "birth") is a geologic period that lasted from . It is the second of the three periods of the Neoproterozoic era, preceded by the Tonian and followed by the Ediacaran.
The Cryoge ...
,
Andean-Saharan (also known as Early Paleozoic),
Late Paleozoic and
Late Cenozoic glaciations.
The main factors involved in changes of the paleoclimate are believed to be the concentration of atmospheric
greenhouse gas
Greenhouse gases (GHGs) are the gases in the atmosphere that raise the surface temperature of planets such as the Earth. Unlike other gases, greenhouse gases absorb the radiations that a planet emits, resulting in the greenhouse effect. T ...
es such as
carbon dioxide
Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...
() and less importantly
methane
Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The abundance of methane on Earth makes ...
(), changes in
Earth's orbit
Earth orbits the Sun at an astronomical unit, average distance of , or 8.317 light-second, light-minutes, in a retrograde and prograde motion, counterclockwise direction as viewed from above the Northern Hemisphere. One complete orbit takes & ...
, long-term changes in the
solar constant, and oceanic and
orogenic changes from
tectonic plate dynamics. Greenhouse and icehouse periods have played key roles in the
evolution of life on Earth by directly and indirectly forcing biotic
adaptation
In biology, adaptation has three related meanings. Firstly, it is the dynamic evolutionary process of natural selection that fits organisms to their environment, enhancing their evolutionary fitness. Secondly, it is a state reached by the p ...
and turnover at various spatial scales across time.
Greenhouse Earth
A "greenhouse Earth" is a period during which no continental
glaciers
A glacier (; or ) is a persistent body of dense ice, a form of rock, that is constantly moving downhill under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires ...
exist anywhere on the planet.
Additionally, the levels of carbon dioxide and other
greenhouse gases (such as water vapor and
methane
Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The abundance of methane on Earth makes ...
) are high, and
sea surface temperatures
Sea surface temperature (or ocean surface temperature) is the ocean temperature, temperature of ocean water close to the surface. The exact meaning of ''surface'' varies in the literature and in practice. It is usually between and below the sea ...
(SSTs) range from 28 °C (82.4 °F) in the tropics to 0 °C (32 °F) in the
polar regions
The polar regions, also called the frigid geographical zone, zones or polar zones, of Earth are Earth's polar ice caps, the regions of the planet that surround its geographical poles (the North Pole, North and South Poles), lying within the pol ...
.
Earth has been in a greenhouse state for about 85% of its history.
The state should not be confused with a hypothetical ''
runaway greenhouse effect'', which is an irreversible
tipping point that corresponds to the ongoing
runaway greenhouse effect on
Venus
Venus is the second planet from the Sun. It is often called Earth's "twin" or "sister" planet for having almost the same size and mass, and the closest orbit to Earth's. While both are rocky planets, Venus has an atmosphere much thicker ...
. The
IPCC
The Intergovernmental Panel on Climate Change (IPCC) is an intergovernmental body of the United Nations. Its job is to "provide governments at all levels with scientific information that they can use to develop climate policies". The World M ...
states that "a 'runaway greenhouse effect'—analogous to
hat ofVenus—appears to have virtually no chance of being induced by
anthropogenic
Anthropogenic ("human" + "generating") is an adjective that may refer to:
* Anthropogeny, the study of the origins of humanity
Anthropogenic may also refer to things that have been generated by humans, as follows:
* Human impact on the enviro ...
activities."
Causes
There are several theories as to how a greenhouse Earth can come about. Geologic climate proxies indicate that there is a strong correlation between a greenhouse state and high CO
2 levels.
However, it is important to recognize that high CO
2 levels have traditionally been interpreted as feedback to Earth's climate rather than as an independent driver, but geologic drivers of CO
2 and climate change have been identified. Other phenomena have instead likely played a key role in influencing global climate by altering oceanic and atmospheric currents
and increasing the net amount of solar radiation absorbed by Earth's atmosphere.
Such phenomena may include but are not limited to tectonic shifts that result in the release of greenhouse gases (such as CO
2 and CH
4) via
volcanic activity.
Volcanoes emit massive amounts of CO
2 and methane into the atmosphere when they are active, which can trap enough heat to cause a greenhouse effect. On Earth, atmospheric concentrations of greenhouse gases like carbon dioxide (CO
2) and methane (CH
4) are higher, trapping solar energy in the atmosphere via the greenhouse effect. Methane, the main component of natural gas, is responsible for more than a quarter of the current global warming. It is a formidable pollutant with an 80-fold higher
global warming potential
Global warming potential (GWP) is a measure of how much heat a greenhouse gas traps in the atmosphere over a specific time period, relative to carbon dioxide (). It is expressed as a multiple of warming caused by the same mass of carbon dioxide ( ...
than CO
2 in the 20 years after it has been introduced into the atmosphere. An increase in the solar constant increases the net amount of solar energy absorbed into Earth's atmosphere,
and changes in Earth's
obliquity and
eccentricity
Eccentricity or eccentric may refer to:
* Eccentricity (behavior), odd behavior on the part of a person, as opposed to being "normal"
Mathematics, science and technology Mathematics
* Off-Centre (geometry), center, in geometry
* Eccentricity (g ...
increase the net amount of solar radiation absorbed into Earth's atmosphere.
Icehouse Earth

Earth is now in an icehouse state, and ice sheets are present in both poles simultaneously.
Climatic proxies indicate that greenhouse gas concentrations tend to lower during an icehouse Earth. Similarly, global temperatures are also lower under Icehouse conditions.
Earth then fluctuates between glacial and interglacial periods, and the size and the distribution of continental ice sheets fluctuate dramatically.
The fluctuation of the ice sheets results in changes in regional climatic conditions that affect the range and the distribution of many terrestrial and oceanic species.
On scales ranging from thousands to hundreds of millions of years, the Earth's climate has transitioned from warm to chilly intervals within life-sustaining ranges. There have been three periods of glaciation in the Phanerozoic Eon (Ordovician, Carboniferous, and Cenozoic), each lasting tens of millions of years and bringing ice down to sea level at mid-latitudes. During these frigid "icehouse" intervals, sea levels were generally lower, CO
2 levels in the atmosphere were lower, net photosynthesis and carbon burial were lower, and oceanic volcanism was lower than during the alternate "greenhouse" intervals. Transitions from Phanerozoic icehouse to greenhouse intervals coincided with biotic crises or catastrophic extinction events, indicating complicated biosphere-hydrosphere feedbacks.
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The glacial and interglacial periods tend to alternate in accordance with solar and climatic oscillation until Earth eventually returns to a greenhouse state.
Earth's current icehouse state is known as the Quaternary Ice Age and began approximately 2.58 million years ago. However, an ice sheet has existed in Antarctica for approximately 34 million years. Earth is now in a clement interglacial period that started approximately 11,800 years ago. Earth will likely phase into another interglacial period such as the Eemian, which occurred between 130,000 and 115,000 years ago, during which evidence of forest in North Cape, Norway, and hippopotamus in the Rhine and Thames Rivers can be observed. Earth is expected to continue to transition between glacial and interglacial periods until the cessation of the Quaternary Ice Age and will then enter another greenhouse state.
Causes
It is well established that there is strong correlation between low levels and an icehouse state, with evidence that the balance between geologic sources, weathering and carbon burial is responsible for secular transitions from Greenhouse and Icehouse climates and a clear role of ocean carbon storage changes in driving most of Quaternary and climate change. However, other factors such as solar, orbital and plate-tectonic forcing also influence climate[Woodard, S. C., & Thomas, D. J. (2012). ''Oceanic and atmospheric response to climate change over varying geologic timescales.'' by Stella C. Woodard. exas A&M University] and the global carbon cycle.
Potential drivers of previous icehouse states include the movement of the tectonic plates and the opening and the closing of oceanic gateways. They seem to play a crucial part in driving Earth into an icehouse state, as tectonic shifts result in the transportation of cool, deep water, which circulates to the ocean surface and assists in ice sheet development at the poles. Examples of oceanic current shifts as a result of tectonic plate dynamics include the opening of the Tasmanian Gateway 36.5 million years ago, which separated Australia and Antarctica, and the opening of the Drake Passage 32.8 million years ago by the separation of South America
South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...
and Antarctica
Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean (also known as the Antarctic Ocean), it contains the geographic South Pole. ...
, both of which are believed to have allowed for the development of the Antarctic ice sheet. The closing of the Isthmus of Panama
The Isthmus of Panama, historically known as the Isthmus of Darien, is the narrow strip of land that lies between the Caribbean Sea and the Pacific Ocean, linking North America, North and South America. The country of Panama is located on the i ...
and of the Indonesian seaway approximately 3 to 4 million years ago may also be a contributor to Earth's current icehouse state. One proposed driver of the Ordovician Ice Age was the evolution of land plants. Under that paradigm, the rapid increase in photosynthetic biomass gradually removed from the atmosphere and replaced it with increasing levels of , which induced global cooling. One proposed driver of the Quaternary Ice age is the collision of the Indian Subcontinent
The Indian subcontinent is a physiographic region of Asia below the Himalayas which projects into the Indian Ocean between the Bay of Bengal to the east and the Arabian Sea to the west. It is now divided between Bangladesh, India, and Pakista ...
with Eurasia
Eurasia ( , ) is a continental area on Earth, comprising all of Europe and Asia. According to some geographers, Physical geography, physiographically, Eurasia is a single supercontinent. The concept of Europe and Asia as distinct continents d ...
to form the Himalayas
The Himalayas, or Himalaya ( ), is a mountain range in Asia, separating the plains of the Indian subcontinent from the Tibetan Plateau. The range has some of the Earth's highest peaks, including the highest, Mount Everest. More than list of h ...
and the Tibetan Plateau
The Tibetan Plateau, also known as the Qinghai–Tibet Plateau or Qingzang Plateau, is a vast elevated plateau located at the intersection of Central Asia, Central, South Asia, South, and East Asia. Geographically, it is located to the north of H ...
. Under that paradigm, the resulting continental uplift revealed massive quantities of unweathered silicate rock , which reacted with to produce (lime) and (silica). The was eventually transported to the ocean and taken up by plankton, which then died and sank to the bottom of the ocean, which effectively removed from the atmosphere.
Glacials and interglacials
Within icehouse states are "glacial
A glacier (; or ) is a persistent body of dense ice, a form of rock, that is constantly moving downhill under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires ...
" and "interglacial
An interglacial period (or alternatively interglacial, interglaciation) is a geological interval of warmer global average temperature lasting thousands of years that separates consecutive glacial periods within an ice age. The current Holocene i ...
" periods that cause ice sheets to build up or to retreat. The main causes for glacial and interglacial periods are variations in the movement of Earth around the Sun. The astronomical components, discovered by the Serbian geophysicist Milutin Milanković
Milutin Milanković (sometimes Anglicisation of names, anglicised as Milutin Milankovitch; sr-Cyrl, Милутин Миланковић, ; 28 May 1879 – 12 December 1958) was a Serbian mathematician, astronomer, climatologist, geophysics, geo ...
and now known as Milankovitch cycles, include the axial tilt
In astronomy, axial tilt, also known as obliquity, is the angle between an object's rotational axis and its orbital axis, which is the line perpendicular to its orbital plane; equivalently, it is the angle between its equatorial plane and orbita ...
of Earth, the orbital eccentricity
In astrodynamics, the orbital eccentricity of an astronomical object is a dimensionless parameter that determines the amount by which its orbit around another body deviates from a perfect circle. A value of 0 is a circular orbit, values be ...
(or shape of the orbit
In celestial mechanics, an orbit (also known as orbital revolution) is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an ...
), and the precession
Precession is a change in the orientation of the rotational axis of a rotating body. In an appropriate reference frame it can be defined as a change in the first Euler angle, whereas the third Euler angle defines the rotation itself. In o ...
(or wobble) of Earth's rotation
Earth's rotation or Earth's spin is the rotation of planet Earth around its own Rotation around a fixed axis, axis, as well as changes in the orientation (geometry), orientation of the rotation axis in space. Earth rotates eastward, in progra ...
. The tilt of the axis tends to fluctuate from 21.5° to 24.5° and back every 41,000 years on the vertical axis. The change actually affects the seasonality
In time series data, seasonality refers to the trends that occur at specific regular intervals less than a year, such as weekly, monthly, or quarterly. Seasonality may be caused by various factors, such as weather, vacation, and holidays and consi ...
on Earth since a change in solar radiation
Sunlight is the portion of the electromagnetic radiation which is emitted by the Sun (i.e. solar radiation) and received by the Earth, in particular the visible light perceptible to the human eye as well as invisible infrared (typically p ...
hits certain areas of the planet more often on a higher tilt, and a lower tilt creates a more even set of seasons worldwide. The changes can be seen in ice cores, which also contain evidence that during glacial times (at the maximum extension of the ice sheets), the atmosphere had lower levels of carbon dioxide (). That may be caused by change in physical ocean circulation, biological productivity and acid
An acid is a molecule or ion capable of either donating a proton (i.e. Hydron, hydrogen cation, H+), known as a Brønsted–Lowry acid–base theory, Brønsted–Lowry acid, or forming a covalent bond with an electron pair, known as a Lewis ...
- base chemistry. During an icehouse period, only 20% of the time is spent in interglacial, or warmer times. Model simulations suggest that the current interglacial climate state will continue for at least another 100,000 years because of emissions, including the complete deglaciation of the Northern Hemisphere.
Snowball Earth
A "snowball Earth" is the complete opposite of greenhouse Earth in which Earth's surface is completely frozen over. However, a snowball Earth technically does not have continental ice sheets like during the icehouse state. "The Great Infra-Cambrian
The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordov ...
Ice Age" has been claimed to be the host of such a world, and in 1964, the scientist W. Brian Harland brought forth his discovery of indications of glaciers in the low latitudes (Harland and Rudwick). That became a problem for Harland because of the thought of the "Runaway Snowball Paradox" (a kind of Snowball effect) that once Earth enters the route of becoming a snowball Earth, it would never be able to leave that state. However, brought up a solution to the paradox in 1992. Since the continents were then huddled at the low and the middle latitudes, there was less ocean water available to absorb the higher amount solar energy hitting the tropics, and there was also an increase in rainfall because more land exposed to higher solar energy might have caused chemical weathering, which would contribute to removal of CO from the atmosphere. Both conditions might have caused a substantial drop in CO atmospheric levels which resulted in cooling temperatures and increasing ice albedo (ice reflectivity of incoming solar radiation), which would further increase global cooling (a positive feedback). That might have been the mechanism of entering Snowball Earth state. Kirschvink explained that the way to get out of Snowball Earth state could be connected again to carbon dioxide. A possible explanation is that during Snowball Earth, volcanic activity would not halt but accumulate atmospheric CO. At the same time, global ice cover would prevent chemical weathering (particularly hydrolysis
Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution reaction, substitution, elimination reaction, elimination, and solvation reactions in which water ...
), responsible for removal of CO from the atmosphere. CO therefore accumulated in the atmosphere. Once the atmosphere accumulation of CO reached a threshold, temperature would rise enough for ice sheets to start melting. That would in turn reduce the ice albedo effect, which would in turn further reduce the ice cover and allow an exit from Snowball Earth. At the end of Snowball Earth, before the equilibrium "thermostat" between volcanic activity and the by then slowly resuming chemical weathering was reinstated, CO in the atmosphere had accumulated enough to cause temperatures to peak to as much as 60 °C, thrusting the Earth into a brief moist greenhouse state. Around the same geologic period of Snowball Earth (it is debated if it was the cause or the result of Snowball Earth), the Great Oxygenation Event (GOE) was occurring. The event known as the Cambrian Explosion followed and produced the beginnings of populous bilateral organisms, as well as a greater diversity and mobility in multicellular life. However, some biologists claim that a complete snowball Earth could not have happened since photosynthetic
Photosynthesis ( ) is a Biological system, system of biological processes by which Photoautotrophism, photosynthetic organisms, such as most plants, algae, and cyanobacteria, convert light energy, typically from sunlight, into the chemical ener ...
life would not have survived under many meters of ice without sunlight
Sunlight is the portion of the electromagnetic radiation which is emitted by the Sun (i.e. solar radiation) and received by the Earth, in particular the visible spectrum, visible light perceptible to the human eye as well as invisible infrare ...
. However, sunlight has been observed to penetrate meters of ice in Antarctica. Most scientists now believe that a "hard" Snowball Earth, one completely covered by ice, is probably impossible. However, a "slushball Earth," with points of opening near the equator
The equator is the circle of latitude that divides Earth into the Northern Hemisphere, Northern and Southern Hemisphere, Southern Hemispheres of Earth, hemispheres. It is an imaginary line located at 0 degrees latitude, about in circumferen ...
, is considered to be possible.
Recent studies may have again complicated the idea of a snowball Earth. In October 2011, a team of French researchers announced that the carbon dioxide during the last speculated "snowball Earth" may have been lower than originally stated, which provides a challenge in finding out how Earth got out of its state and whether a snowball or a slushball Earth occurred.
Transitions
Causes
The Eocene
The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...
, which occurred between 56.0 and 33.9 million years ago, was Earth's warmest temperature period for 100 million years. However, the "super-greenhouse" period had eventually become an icehouse period by the late Eocene. It is believed that the decline of CO2 caused the change, but mechanisms of positive feedback
Positive feedback (exacerbating feedback, self-reinforcing feedback) is a process that occurs in a feedback loop where the outcome of a process reinforces the inciting process to build momentum. As such, these forces can exacerbate the effects ...
may have contributed to the cooling.
The best available record for a transition from an icehouse to greenhouse period in which plant life existed is for the Permian
The Permian ( ) is a geologic period and System (stratigraphy), stratigraphic system which spans 47 million years, from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.902 Mya. It is the s ...
period, which occurred around 300 million years ago. A major transition took place over the subsequent 40 million years and caused Earth to change from a moist, icy planet in which rainforest
Rainforests are forests characterized by a closed and continuous tree Canopy (biology), canopy, moisture-dependent vegetation, the presence of epiphytes and lianas and the absence of wildfire. Rainforests can be generally classified as tropi ...
s covered the tropics to a hot, dry, and windy location in which little could survive. Professor Isabel P. Montañez of University of California, Davis
The University of California, Davis (UC Davis, UCD, or Davis) is a Public university, public Land-grant university, land-grant research university in Davis, California, United States. It is the northernmost of the ten campuses of the University ...
, who has researched the time period, found the climate to be "highly unstable" and to be "marked by dips and rises in carbon dioxide."
Impacts
The Eocene-Oligocene transition was the latest and occurred approximately 34 million years ago. It resulted in a rapid global cooling, the glaciation of Antarctica, and a series of biotic extinction events. The most dramatic species turnover event associated with the time period is the Grande Coupure
Grande means "large" or "great" in many of the Romance languages. It may also refer to:
Places
* Grande, Germany, a municipality in Germany
* Grande Communications, a telecommunications firm based in Texas
* Grande-Rivière (disambiguation)
* Ar ...
, a period that saw the replacement of European tree-dwelling and leaf-eating mammal species by migratory species from Asia.
Research
Paleoclimatology
Paleoclimatology ( British spelling, palaeoclimatology) is the scientific study of climates predating the invention of meteorological instruments, when no direct measurement data were available. As instrumental records only span a tiny part of ...
is a branch of science that attempts to understand the history of greenhouse and icehouse conditions over geological time. The study of ice cores, dendrochronology
Dendrochronology (or tree-ring dating) is the scientific method of chronological dating, dating tree rings (also called growth rings) to the exact year they were formed in a tree. As well as dating them, this can give data for dendroclimatology, ...
, ocean
The ocean is the body of salt water that covers approximately 70.8% of Earth. The ocean is conventionally divided into large bodies of water, which are also referred to as ''oceans'' (the Pacific, Atlantic, Indian Ocean, Indian, Southern Ocean ...
and lake
A lake is often a naturally occurring, relatively large and fixed body of water on or near the Earth's surface. It is localized in a basin or interconnected basins surrounded by dry land. Lakes lie completely on land and are separate from ...
sediment
Sediment is a solid material that is transported to a new location where it is deposited. It occurs naturally and, through the processes of weathering and erosion, is broken down and subsequently sediment transport, transported by the action of ...
s ( varve), palynology
Palynology is the study of microorganisms and microscopic fragments of mega-organisms that are composed of acid-resistant organic material and occur in sediments, sedimentary rocks, and even some metasedimentary rocks. Palynomorphs are the mic ...
, (paleobotany
Paleobotany or palaeobotany, also known as paleophytology, is the branch of botany dealing with the recovery and identification of plant fossils from geological contexts, and their use for the biological reconstruction of past environments ( pal ...
), isotope
Isotopes are distinct nuclear species (or ''nuclides'') of the same chemical element. They have the same atomic number (number of protons in their Atomic nucleus, nuclei) and position in the periodic table (and hence belong to the same chemica ...
analysis (such as radiometric dating
Radiometric dating, radioactive dating or radioisotope dating is a technique which is used to Chronological dating, date materials such as Rock (geology), rocks or carbon, in which trace radioactive impurity, impurities were selectively incorporat ...
and stable isotope analysis), and other climate proxies allows scientists to create models of Earth's past energy budgets and the resulting climate. One study has shown that atmospheric carbon dioxide levels during the Permian
The Permian ( ) is a geologic period and System (stratigraphy), stratigraphic system which spans 47 million years, from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.902 Mya. It is the s ...
age rocked back and forth between 250 parts per million
In science and engineering, the parts-per notation is a set of pseudo-units to describe the small values of miscellaneous dimensionless quantity, dimensionless quantities, e.g. mole fraction or mass fraction (chemistry), mass fraction.
Since t ...
, which is close to today's levels, up to 2,000 parts per million. Studies on lake sediments suggest that the "hothouse" or "super-greenhouse" Eocene
The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...
was in a "permanent El Niño
EL, El or el may refer to:
Arts and entertainment Fictional entities
* El, a character from the manga series ''Shugo Chara!'' by Peach-Pit
* Eleven (''Stranger Things'') (El), a fictional character in the TV series ''Stranger Things''
* El, fami ...
state" after the 10 °C warming of the deep ocean and high latitude surface temperatures shut down the Pacific Ocean
The Pacific Ocean is the largest and deepest of Earth's five Borders of the oceans, oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean, or, depending on the definition, to Antarctica in the south, and is ...
's El Niño- Southern Oscillation. A theory was suggested for the Paleocene–Eocene Thermal Maximum
The Paleocene–Eocene thermal maximum (PETM), alternatively ”Eocene thermal maximum 1 (ETM1)“ and formerly known as the "Initial Eocene" or “Late Paleocene thermal maximum", was a geologically brief time interval characterized by a ...
on the sudden decrease of the carbon isotopic composition of the global inorganic carbon pool by 2.5 parts per million. A hypothesis posed for this drop of isotopes was the increase of methane hydrates, the trigger for which remains a mystery. The increase of atmospheric methane, which happens to be a potent but short-lived greenhouse gas, increased the global temperatures by 6 °C with the assistance of the less potent carbon dioxide.
List of icehouse and greenhouse periods
* A greenhouse period ran from 4.6 to 2.4 billion years ago.
* Huronian glaciation – an icehouse period that ran from 2.4 billion to 2.1 billion years ago
* A greenhouse period ran from 2.1 billion to 720 million years ago.
* Cryogenian
The Cryogenian (from , meaning "cold" and , romanized: , meaning "birth") is a geologic period that lasted from . It is the second of the three periods of the Neoproterozoic era, preceded by the Tonian and followed by the Ediacaran.
The Cryoge ...
– an icehouse period that ran from 720 to 635 million years ago during which the entire Earth was at times frozen over
* A greenhouse period ran from 635 million years ago to 450 million years ago.
* Andean-Saharan glaciation – an icehouse period that ran from 450 million to 420 million years ago
* A greenhouse period ran from 420 million years ago to 360 million years ago.
* Late Paleozoic Ice Age – an icehouse period that ran from 360 million to 260 million years ago
* A greenhouse period ran from 260 million years ago to 33.9 million years ago.
* Late Cenozoic Ice Age – the current icehouse period, which began 33.9 million years ago
Modern conditions
Currently, Earth is in an icehouse climate state. About 34 million years ago, ice sheets began to form in Antarctica
Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean (also known as the Antarctic Ocean), it contains the geographic South Pole. ...
; the ice sheets in the Arctic
The Arctic (; . ) is the polar regions of Earth, polar region of Earth that surrounds the North Pole, lying within the Arctic Circle. The Arctic region, from the IERS Reference Meridian travelling east, consists of parts of northern Norway ( ...
did not start forming until 2 million years ago. Some processes that may have led to the current icehouse may be connected to the development of the Himalayan Mountains and the opening of the Drake Passage between South America
South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...
and Antarctica, but climate model simulations suggest that the early opening of the Drake Passage played only a minor role, and the later constriction of the Tethys and Central American Seaways is more important in explaining the observed Cenozoic cooling. Scientists have tried to compare the past transitions between icehouse and greenhouse, and vice versa, to understand what type of climate state Earth will have next.
Without the human influence on the greenhouse gas concentration, a glacial
A glacier (; or ) is a persistent body of dense ice, a form of rock, that is constantly moving downhill under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires ...
period would be the next climate state. Predicted changes in orbital forcing suggest that in absence of human-made global warming
Present-day climate change includes both global warming—the ongoing increase in global average temperature—and its wider effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes ...
, the next glacial period would begin at least 50,000 years from now (see Milankovitch cycles), but the ongoing anthropogenic greenhouse gas emissions mean the next climate state will be a greenhouse Earth period. Permanent ice is actually a rare phenomenon in the history of Earth and occurs only in coincidence with the icehouse effect, which has affected about 20% of Earth's history.
See also
* List of periods and events in climate history
References
{{portal bar, Earth sciences, Geology, Paleontology
Glaciology
History of climate variability and change
Earth