Throughout
Earth
Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...
's climate history (
Paleoclimate
Paleoclimatology (British spelling, palaeoclimatology) is the study of climates for which direct measurements were not taken. As instrumental records only span a tiny part of Earth's history, the reconstruction of ancient climate is important to ...
) 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
glacial
A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the other hand, are periods of warmer climate betw ...
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 in ...
periods, which occur as alternate phases within an icehouse period and tend to last less than 1 million years. There are
five known Icehouse periods in Earth's climate history, which are known as the
Huronian
The Huronian glaciation (or Makganyene glaciation) was a period where several Ice age, ice ages occurred during the deposition of the Huronian Supergroup, rather than a single continuous event as it is commonly misrepresented to be. The depositi ...
,
Cryogenian
The Cryogenian (from grc, κρύος, krýos, meaning "cold" and , romanized: , meaning "birth") is a geologic period that lasted from . It forms the second geologic period of the Neoproterozoic Era, preceded by the Tonian Period and followed by ...
,
Andean-Saharan
The Andean-Saharan glaciation, also known as the Early Palaeozoic Icehouse, the Early Palaeozoic Ice Age, the Late Ordovician glaciation, the end-Ordovician glaciation, or the Hirnantian glaciation, occurred during the Paleozoic from approximately ...
,
Late Paleozoic
Late may refer to:
* LATE, an acronym which could stand for:
** Limbic-predominant age-related TDP-43 encephalopathy, a proposed form of dementia
** Local-authority trading enterprise, a New Zealand business law
** Local average treatment effect, ...
, and
Late Cenozoic glaciations.
The main factors involved in changes of the paleoclimate are believed to be the concentration of atmospheric
carbon dioxide
Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...
(), changes in
Earth's orbit
Earth orbits the Sun at an average distance of 149.60 million km (92.96 million mi) in a counterclockwise direction as viewed from above the Northern Hemisphere. One complete orbit takes days (1 sidereal year), during which time Earth ...
, long-term changes in the
solar constant
The solar constant (''GSC'') is a flux density measuring mean solar electromagnetic radiation (total solar irradiance) per unit area. It is measured on a surface perpendicular to the rays, one astronomical unit (au) from the Sun (roughly the ...
, and oceanic and
orogenic
Orogeny is a mountain building process. An orogeny is an event that takes place at a convergent boundary, convergent plate margin when plate motion compresses the margin. An ''orogenic belt'' or ''orogen'' develops as the compressed plate crumpl ...
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 and turnover at various spatial scales across time.
Greenhouse Earth
![IceAgeEarth](https://upload.wikimedia.org/wikipedia/commons/b/b4/IceAgeEarth.jpg)
A "greenhouse Earth" is a period during which no continental
glaciers
A glacier (; ) is a persistent body of dense ice that is constantly moving under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires distinguishing features, such as ...
exist anywhere on the planet.
Additionally, the levels of carbon dioxide and other
greenhouse gases
A greenhouse gas (GHG or GhG) is a gas that absorbs and emits radiant energy within the thermal infrared range, causing the greenhouse effect. The primary greenhouse gases in Earth's atmosphere are water vapor (), carbon dioxide (), methane ...
(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 relative abundance of methane on Eart ...
) are high, and
sea surface temperatures
Sea surface temperature (SST), or ocean surface temperature, is the ocean temperature close to the surface. The exact meaning of ''surface'' varies according to the measurement method used, but it is between and below the sea surface. Air masse ...
(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 zones or polar zones, of Earth are the regions of the planet that surround its geographical poles (the North and South Poles), lying within the polar circles. These high latitudes are dominated by float ...
.
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
A runaway greenhouse effect occurs when a planet's atmosphere contains greenhouse gas in an amount sufficient to block thermal radiation from leaving the planet, preventing the planet from cooling and from having liquid water on its surface. A ...
'', which is an irreversible
tipping point that corresponds to the ongoing
runaway greenhouse effect
A runaway greenhouse effect occurs when a planet's atmosphere contains greenhouse gas in an amount sufficient to block thermal radiation from leaving the planet, preventing the planet from cooling and from having liquid water on its surface. A ...
on
Venus
Venus is the second planet from the Sun. It is sometimes called Earth's "sister" or "twin" planet as it is almost as large and has a similar composition. As an interior planet to Earth, Venus (like Mercury) appears in Earth's sky never fa ...
. The
IPCC
The Intergovernmental Panel on Climate Change (IPCC) is an intergovernmental body of the United Nations. Its job is to advance scientific knowledge about climate change caused by human activities. The World Meteorological Organization (WMO) a ...
states that "a 'runaway greenhouse effect'—analogous to
hat of
A hat is a head covering which is worn for various reasons, including protection against weather conditions, ceremonial reasons such as university graduation, religious reasons, safety, or as a fashion accessory. Hats which incorporate mecha ...
Venus—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
Counterintuitively, anthropogenic may also refer to things that have been generated by humans, as follows:
* Human im ...
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 are interpreted as an indicator of Earth's climate, rather than as an independent driver. 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
Volcanism, vulcanism or volcanicity is the phenomenon of eruption of molten rock (magma) onto the surface of the Earth or a solid-surface planet or moon, where lava, pyroclastics, and volcanic gases erupt through a break in the surface called a ...
,
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's a formidable pollutant with an 80-fold higher global warming potential than CO
2 in the 20 years after it's 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
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 orbit ...
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-center, in geometry
* Eccentricity (graph theory) of a v ...
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.
">9/sup>
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
The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS). It follows the Neogene Period and spans from 2.58 million years ...
and began approximately 2.58 million years ago. However, an ice sheet has existed in Antarctic 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
The Eemian (also called the last interglacial, Sangamonian, Sangamonian Stage, Ipswichian, Mikulin, Kaydaky, penultimate,NOAA - Penultimate Interglacial Period http://www.ncdc.noaa.gov/global-warming/penultimate-interglacial-period Valdivia or Ri ...
, 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.[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] However, that does not mean that decreasing atmospheric levels is a primary driver of a transition to the icehouse state. Rather, it may be an indicator of other solar, geologic, and atmospheric processes at work.
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
The Drake Passage (referred to as Mar de Hoces Hoces Sea"in Spanish-speaking countries) is the body of water between South America's Cape Horn, Chile and the South Shetland Islands of Antarctica. It connects the southwestern part of the Atla ...
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 relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the southe ...
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, it contains the geographic South Pole. Antarctica is the fifth-largest contine ...
, both of which are believed to have allowed for the development of the Antarctic ice sheet
The Antarctic ice sheet is one of the two polar ice caps of Earth. It covers about 98% of the Antarctic continent and is the largest single mass of ice on Earth, with an average thickness of over 2 kilometers. It covers an area of almost and ...
. The closing of the Isthmus of Panama
The Isthmus of Panama ( es, Istmo de Panamá), also 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 and South America. It contains the country ...
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 list of the physiographic regions of the world, physiographical region in United Nations geoscheme for Asia#Southern Asia, Southern Asia. It is situated on the Indian Plate, projecting southwards into the Indian O ...
with Eurasia
Eurasia (, ) is the largest continental area on Earth, comprising all of Europe and Asia. Primarily in the Northern and Eastern Hemispheres, it spans from the British Isles and the Iberian Peninsula in the west to the Japanese archipelago a ...
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 planet's highest peaks, including the very highest, Mount Everest. Over 100 ...
and the Tibetan Plateau
The Tibetan Plateau (, also known as the Qinghai–Tibet Plateau or the Qing–Zang Plateau () or as the Himalayan Plateau in India, is a vast elevated plateau located at the intersection of Central, South and East Asia covering most of the Ti ...
. 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 glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the other hand, are periods of warmer climate betw ...
" 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 in ...
" 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 Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...
. The astronomical components, discovered by the Serbian geophysicist Milutin Milanković
Milutin Milanković (sometimes anglicised as Milankovitch; sr-Cyrl, Милутин Миланковић ; 28 May 1879 – 12 December 1958) was a Serbian mathematician, astronomer, climatologist, geophysicist, civil engineer and popularizer of ...
and now known as Milankovitch cycles
Milankovitch cycles describe the collective effects of changes in the Earth's movements on its climate over thousands of years. The term was coined and named after Serbian geophysicist and astronomer Milutin Milanković. In the 1920s, he hypot ...
, 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 orbi ...
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 betwee ...
(or shape of the orbit
In celestial mechanics, an orbit 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 object or position in space such as a p ...
), 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 othe ...
(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 retrograd ...
. 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 is the presence of variations 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 a ...
on Earth since a change in solar radiation
Solar irradiance is the power per unit area (surface power density) received from the Sun in the form of electromagnetic radiation in the wavelength range of the measuring instrument.
Solar irradiance is measured in watts per square metre (W/m ...
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 the increase or the redistribution of the acid
In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a sequ ...
- base balance with bicarbonate
In inorganic chemistry, bicarbonate (IUPAC-recommended nomenclature: hydrogencarbonate) is an intermediate form in the deprotonation of carbonic acid. It is a polyatomic anion with the chemical formula .
Bicarbonate serves a crucial biochemic ...
and carbonate
A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonate g ...
ion
An ion () is an atom or molecule with a net electrical charge.
The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conven ...
s that deals with alkalinity
Alkalinity (from ar, القلوي, al-qaly, lit=ashes of the saltwort) is the capacity of water to resist acidification. It should not be confused with basicity, which is an absolute measurement on the pH scale.
Alkalinity is the strength of ...
. 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 Deglaciation is the transition from full glacial conditions during ice ages, to warm interglacials, characterized by global warming and sea level rise due to change in continental ice volume. Thus, it refers to the retreat of a glacier, an ice shee ...
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 Period ( ; sometimes symbolized C with bar, Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million ...
Ice Age" has been claimed to be the host of such a world, and in 1964, the scientist W. Brian Harland
Walter Brian Harland (22 March 1917 – 1 November 2003) was a British geologist at the Department of Geology, later University of Cambridge Department of Earth Sciences, England, from 1948 to 2003. He was a leading figure in geological exp ...
brought forth his discovery of indications of glaciers in the low latitudes
The tropics are the regions of Earth surrounding the Equator. They are defined in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in
the Southern Hemisphere at S. The tropics are also referred to ...
(Harland and Rudwick). That became a problem for Harland because of the thought of the "Runaway Snowball Paradox" (a kind of Snowball effect
A snowball effect is a process that starts from an initial state of small significance and builds upon itself, becoming larger (graver, more serious), and also perhaps potentially dangerous or disastrous (a vicious circle), though it might be b ...
) 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 before they eventually settled down. 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
The Cambrian explosion, Cambrian radiation, Cambrian diversification, or the Biological Big Bang refers to an interval of time approximately in the Cambrian Period when practically all major animal phyla started appearing in the fossil recor ...
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 process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored in c ...
life would not have survived under many meters of ice without sunlight
Sunlight is a portion of the electromagnetic radiation given off by the Sun, in particular infrared, visible, and ultraviolet light. On Earth, sunlight is scattered and filtered through Earth's atmosphere, and is obvious as daylight when t ...
. 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 a circle of latitude, about in circumference, that divides Earth into the Northern and Southern hemispheres. It is an imaginary line located at 0 degrees latitude, halfway between the North and South poles. The term can als ...
, 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 ( ) Epoch is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene' ...
, which occurred between 53 and 49 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 which exacerbates the effects of a small disturbance. That is, the effects of a perturbation on a system include an increase in the ...
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 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 251.9 Mya. It is the last period of the Paleoz ...
period
Period may refer to:
Common uses
* Era, a length or span of time
* Full stop (or period), a punctuation mark
Arts, entertainment, and media
* Period (music), a concept in musical composition
* Periodic sentence (or rhetorical period), a concept ...
, which occurred around 300 million years ago. A major transition took place 40 million years ago and caused Earth to change from a moist, icy planet in which rainforest
Rainforests are characterized by a closed and continuous tree canopy, moisture-dependent vegetation, the presence of epiphytes and lianas and the absence of wildfire. Rainforest can be classified as tropical rainforest or temperate rainfores ...
s covered the tropics to a hot, dry, and windy location in which little could survive. Professor Isabel P. Montañez
Isabel Patricia Montañez is a paleoclimatologist specializing in geochemical records of ancient climate change. She is a Distinguished Professor and a Chancellor's Leadership Professor in the Department of Earth and Planetary Sciences at Univers ...
of University of California, Davis
The University of California, Davis (UC Davis, UCD, or Davis) is a public land-grant research university near Davis, California. Named a Public Ivy, it is the northernmost of the ten campuses of the University of California system. The institut ...
, 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)
*Arroi ...
, 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 study of climates for which direct measurements were not taken. As instrumental records only span a tiny part of Earth's history, the reconstruction of ancient climate is important to ...
is a branch of science that attempts to understand the history of greenhouse and icehouse conditions over geological time. The study of ice core
An ice core is a core sample that is typically removed from an ice sheet or a high mountain glacier. Since the ice forms from the incremental buildup of annual layers of snow, lower layers are older than upper ones, and an ice core contains ic ...
s, dendrochronology
Dendrochronology (or tree-ring dating) is the scientific method of dating tree rings (also called growth rings) to the exact year they were formed. As well as dating them, this can give data for dendroclimatology, the study of climate and atmos ...
, ocean
The ocean (also the sea or the world ocean) is the body of salt water that covers approximately 70.8% of the surface of Earth and contains 97% of Earth's water. An ocean can also refer to any of the large bodies of water into which the wo ...
and lake
A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much large ...
sediment
Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand an ...
s (varve
A varve is an annual layer of sediment or sedimentary rock.
The word 'varve' derives from the Swedish word ''varv'' whose meanings and connotations include 'revolution', 'in layers', and 'circle'. The term first appeared as ''Hvarfig lera'' (var ...
), palynology
Palynology is the "study of dust" (from grc-gre, παλύνω, palynō, "strew, sprinkle" and '' -logy'') or of "particles that are strewn". A classic palynologist analyses particulate samples collected from the air, from water, or from deposit ...
, (paleobotany
Paleobotany, which is also spelled as palaeobotany, is the branch of botany dealing with the recovery and identification of plant remains from geological contexts, and their use for the biological reconstruction of past environments (paleogeogr ...
), isotope
Isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers (mass numbers) ...
analysis (such as radiometric dating
Radiometric dating, radioactive dating or radioisotope dating is a technique which is used to date materials such as rocks or carbon, in which trace radioactive impurities were selectively incorporated when they were formed. The method compares t ...
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 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 251.9 Mya. It is the last period of the Paleoz ...
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 small values of miscellaneous dimensionless quantities, e.g. mole fraction or mass fraction. Since these fractions are quantity-per-quantity measures, they ...
, 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 ( ) Epoch is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene' ...
was in a "permanent El Nino
EL, El or el may refer to:
Religion
* El (deity), a Semitic word for "God"
People
* EL (rapper) (born 1983), stage name of Elorm Adablah, a Ghanaian rapper and sound engineer
* El DeBarge, music artist
* El Franco Lee (1949–2016), American po ...
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 oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the continen ...
's El Nino-Southern Oscillation
Southern may refer to:
Businesses
* China Southern Airlines, airline based in Guangzhou, China
* Southern Airways, defunct US airline
* Southern Air, air cargo transportation company based in Norwalk, Connecticut, US
* Southern Airways Express, M ...
. A theory was suggested for the Paleocene–Eocene Thermal Maximum
The Paleocene–Eocene thermal maximum (PETM), alternatively (ETM1), and formerly known as the "Initial Eocene" or "", was a time period with a more than 5–8 °C global average temperature rise across the event. This climate event o ...
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 hydrate
Methane clathrate (CH4·5.75H2O) or (8CH4·46H2O), also called methane hydrate, hydromethane, methane ice, fire ice, natural gas hydrate, or gas hydrate, is a solid clathrate compound (more specifically, a clathrate hydrate) in which a large amo ...
s, the trigger for which remains a mystery. The increase of atmospheric methane
Atmospheric methane is the methane present in Earth's atmosphere. Atmospheric methane concentrations are of interest because it is one of the most potent greenhouse gases in Earth's atmosphere. Atmospheric methane is rising.
The 20-year glob ...
, 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
The Huronian glaciation (or Makganyene glaciation) was a period where several ice ages occurred during the deposition of the Huronian Supergroup, rather than a single continuous event as it is commonly misrepresented to be. The deposition of thi ...
– 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 grc, κρύος, krýos, meaning "cold" and , romanized: , meaning "birth") is a geologic period that lasted from . It forms the second geologic period of the Neoproterozoic Era, preceded by the Tonian Period and followed by ...
– 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
The Andean-Saharan glaciation, also known as the Early Palaeozoic Icehouse, the Early Palaeozoic Ice Age, the Late Ordovician glaciation, the end-Ordovician glaciation, or the Hirnantian glaciation, occurred during the Paleozoic from approximately ...
– 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 Late Cenozoic Ice Age,National Academy of Sciences - The National Academies Press - Continental Glaciation through Geologic Times https://www.nap.edu/read/11798/chapter/8#80 or Antarctic Glaciation began 33.9 million years ago at the Eocen ...
– 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, it contains the geographic South Pole. Antarctica is the fifth-largest contine ...
; the ice sheets in the Arctic
The Arctic ( or ) is a polar regions of Earth, polar region located at the northernmost part of Earth. The Arctic consists of the Arctic Ocean, adjacent seas, and parts of Canada (Yukon, Northwest Territories, Nunavut), Danish Realm (Greenla ...
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
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 planet's highest peaks, including the very highest, Mount Everest. Over 100 ...
and the opening of the Drake Passage
The Drake Passage (referred to as Mar de Hoces Hoces Sea"in Spanish-speaking countries) is the body of water between South America's Cape Horn, Chile and the South Shetland Islands of Antarctica. It connects the southwestern part of the Atla ...
between South America
South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the southe ...
and Antarctica, but climate model simulations suggest that the early opening of the Drake Passage played only a limited 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 glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the other hand, are periods of warmer climate betw ...
period would be the next climate state. Predicted changes in orbital forcing
Orbital forcing is the effect on climate of slow changes in the tilt of the Earth's axis and shape of the Earth's orbit around the sun (see Milankovitch cycles). These orbital changes modify the total amount of sunlight reaching the Earth by up to ...
suggest that in absence of human-made global warming
In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to E ...
, the next glacial period would begin at least 50,000 years from now (see Milankovitch cycles
Milankovitch cycles describe the collective effects of changes in the Earth's movements on its climate over thousands of years. The term was coined and named after Serbian geophysicist and astronomer Milutin Milanković. In the 1920s, he hypot ...
), but the ongoing anthropogenic greenhouse gas emissions
Greenhouse gas emissions from human activities strengthen the greenhouse effect, contributing to climate change. Most is carbon dioxide from burning fossil fuels: coal, oil, and natural gas. The largest emitters include coal in China and larg ...
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
The list of periods and events in climate history includes some notable climate events known to paleoclimatology. Knowledge of precise climatic events decreases as the record goes further back in time. The timeline of glaciation covers ice ages s ...
References
{{portal bar, Earth sciences, Geology, Paleontology
Glaciology
History of climate variability and change
Earth