Climate change is a change in the statistical distribution of
weatherWeather is a set of all the phenomena occurring in a given atmosphere at a given time. Weather phenomena lie in the troposphere. Weather refers, generally, to day-to-day temperature and precipitation activity, whereas climate is the term for the average atmospheric conditions over longer periods...
over
periods of timeDuration is an amount of time or a particular time interval. In sounds and music, aduration is a property of a tone that becomes one of the bases of rhythm.-Sound and music:A tone may be sustained for varying lengths of time...
that range from decades to millions of years. It can be a change in the average weather or a change in the distribution of weather events around an average (for example, greater or fewer extreme weather events). Climate change may be limited to a specific
regionRegion is most commonly a geographical term that is used in various ways among the different branches of geography. In general, a region is a medium-scale area of land or water, smaller than the whole areas of interest , and larger than a specific site...
, or may occur across the whole
EarthEarth is the third planet from the Sun. It is the fifth largest of the eight planets in the solar system, and the largest of the terrestrial planets in the Solar System in terms of diameter, mass and density...
.
In recent usage, especially in the context of
environmental policyEnvironmental policy is any [course of] action deliberately taken [or not taken] to manage human activities with a view to prevent, reduce, or mitigate harmful effects on nature and natural resources, and ensuring that man-made changes to the environment do not have harmful effects on...
, climate change usually refers to changes in modern
climateClimate encompasses the statistics of temperature, humidity, atmospheric pressure, wind, rainfall, atmospheric particle count and numerous other meteorological elements in a given region over long periods of time...
(see
global warmingGlobal warming is the increase in the average temperature of the Earth's near-surface air and oceans since the mid-20th century and its projected continuation. Global surface temperature increased 0.74 ± 0.18 °C during the last century...
). For information on temperature measurements over various periods, and the data sources available, see
temperature recordThe temperature record shows the fluctuations of the temperature of the atmosphere and the oceans through various spans of time. The most detailed information exists since 1850, when methodical thermometer-based records began. There are numerous estimates of temperatures since the end of the...
. For attribution of climate change over the past century, see
attribution of recent climate changeAttribution of recent climate change is the effort to scientifically ascertain mechanisms responsible for relatively recent changes observed in the Earth's climate...
.
Causes
Factors that can shape climate are often called climate forcings. These include such processes as variations in solar radiation, deviations in the Earth's
orbitIn physics, an orbit is the gravitationally curved path of one object around a point or another body, for example the gravitational orbit of a planet around a star....
, mountain-building and
continental driftContinental drift is the movement of the Earth's continents relative to each other. The hypothesis that continents 'drift' was first put forward by Abraham Ortelius in 1596 and was fully developed by Alfred Wegener in 1912...
, and changes in
greenhouse gasGreenhouse gases are gases in an atmosphere that absorb and emit radiation within the thermal infrared range. This process is the fundamental cause of the greenhouse effect. The main greenhouse gases in the Earth's atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, and ozone...
concentrations. There are a variety of climate change feedbacks that can either amplify or diminish the initial forcing. Some parts of the climate system, such as the oceans and ice caps, respond slowly in reaction to climate forcing because of their large mass. Therefore, the climate system can take centuries or longer to fully respond to new external forcings.
Plate tectonics
Over the course of millions of years, the motion of tectonic plates reconfigures global land and ocean areas and generates topography. This can affect both global and local patterns of climate and atmosphere-ocean circulation.
The position of the continents determines the geometry of the oceans and therefore influences patterns of ocean circulation. The locations of the seas are important in controlling the transfer of heat and moisture across the globe, and therefore, in determining global climate. A recent example of tectonic control on ocean circulation is the formation of the
Isthmus of PanamaThe Isthmus of Panama, 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 was formed some 3 million years ago during the Pliocene epoch. It contains the country of Panama and...
about 5 million years ago, which shut off direct mixing between the Atlantic and Pacific Oceans. This strongly affected the ocean dynamics of what is now the
Gulf StreamThe Gulf Stream, together with its northern extension towards Europe, the North Atlantic Drift, is a powerful, warm, and swift Atlantic ocean current that originates in the Gulf of Mexico, exits through the Strait of Florida, and follows the eastern coastlines of the United States and Newfoundland...
and may have led to Northern Hemisphere ice cover. Earlier, during the
CarboniferousThe Carboniferous is a geologic period and system that extends from the end of the Devonian period, about 359.2 ± 2.5 Ma , to the beginning of the Permian period, about 299.0 ± 0.8 Ma ....
period, plate tectonics may have triggered the large-scale storage of carbon and increased glaciation. Geologic evidence points to a "megamonsoonal" circulation pattern during the time of the
supercontinentIn geology, a supercontinent is a landmass comprising more than one continental core, or craton. The assembly of cratons and accreted terranes that form Eurasia qualifies as a supercontinent today.-History:...
PangaeaPangaea, Pangæa, or Pangea was the supercontinent that existed during the Paleozoic and Mesozoic eras about 250 million years ago, before the component continents were separated into their current configuration.The name was first used by the German originator of the continental...
, and climate modeling suggests that the existence of the supercontinent was conductive to the establishment of monsoons.
More locally, topography can influence climate. The existence of mountains (as a product of plate tectonics through mountain-building) can cause orographic precipitation. Humidity generally decreases and diurnal temperature swings generally increase with increasing elevation. Mean temperature and the length of the growing season also decrease with increasing elevation. This, along with orographic precipitation, is important for the existence of low-latitude alpine glaciers and the varied flora and fauna along at different elevations in montane
ecosystemAn ecosystem is a system of interdependent organisms which share the same habitat, in an area functioning together with all of the physical factors of the environment. Ecosystems can be permanent or temporary. Ecosystems usually form a number of food webs...
s.
The size of continents is also important. Because of the stabilizing effect of the oceans on temperature, yearly temperature variations are generally lower in coastal areas than they are inland. A larger supercontinent will therefore have more area in which climate is strongly seasonal than will several smaller continents and/or
island arcAn island arc is a type of archipelago formed by plate tectonics as one oceanic tectonic plate subducts under another and produces magma. Island arcs that develop along the edges of a continent may be known as a volcanic arc, though most people find the distinction of little benefit.In the...
s.
Solar output
The
sunThe Sun is the star at the center of the Solar System. The Earth and other matter orbit the Sun, which by itself accounts for about 99.86% of the Solar System's mass....
is the predominant source for
energyIn physics, energy is a scalar physical quantity that describes the amount of work that can be performed by a force, an attribute of objects and systems that is subject to a conservation law...
input to the Earth. Both long- and short-term variations in solar intensity are known to affect global climate.
Early in
Earth's historyThe history of the Earth describes the most important events and fundamental stages in the development of the planet Earth from its formation to the present day during the last 4.54 billion years. Nearly all branches of natural science have contributed to the understanding of the main events of the...
the sun emitted only 70% as much power as it does today. With the same atmospheric composition as exists today, liquid water should not have existed on Earth. However, there is evidence for the presence of water on the early Earth, in the
HadeanThe Hadean is the geologic eon before the Archean. It started at Earth's formation about 4.6 billion years ago , and ended roughly 3.8 billion years ago, though the latter date varies according to different sources. The name "Hadean" derives from Hades, Greek for "Underworld," referring to the...
and
ArcheanThe Archean is a geologic eon before the Proterozoic and Paleoproterozoic, before 2.5 Ga . Instead of being based on stratigraphy, this date is defined chronometrically...
eons, leading to what is known as the
faint young sun paradoxThe faint young Sun paradox or problem describes the apparent contradiction between observations of liquid water early in the Earth's history and the astrophysical expectation that the Sun's output would be only 70% as intense during that epoch as it is during the modern epoch...
. Hypothesized solutions to this paradox include a vastly different atmosphere, with much higher concentrations of
greenhouse gasGreenhouse gases are gases in an atmosphere that absorb and emit radiation within the thermal infrared range. This process is the fundamental cause of the greenhouse effect. The main greenhouse gases in the Earth's atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, and ozone...
es than currently exist Over the following approximately 4 billion years, the energy output of the sun increased and atmospheric composition changed, with the
oxygenation of the atmosphereThe Great Oxidation Event was a major environmental change around associated with the appearance of free oxygen in the atmosphere....
being the most notable alteration. The luminosity of the sun will continue to increase as it follows the
main sequenceThe main sequence is a continuous and distinctive band of stars that appear on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung-Russell diagrams after their co-developers, Ejnar Hertzsprung and Henry Norris Russell...
. These changes in luminosity, and the sun's ultimate death as it becomes a
red giantA red giant is a luminous giant star of low or intermediate mass that is in a late phase of stellar evolution. The outer atmosphere is inflated and tenuous, making the radius immense and the surface temperature low, somewhere from 5,000 K and lower...
and then a
white dwarfA white dwarf, also called a degenerate dwarf, is a small star composed mostly of electron-degenerate matter. They are very dense; a white dwarf's mass is comparable to that of the Sun and its volume is comparable to that of the Earth. Its faint luminosity comes from the emission of stored...
, will have large effects on climate, with the red giant phase possibly ending life on Earth.
Solar output also
variesSolar variations refer here to changes in the amount of total solar radiation and its spectral distribution. There are periodic components to these variations, the principal one being the 11-year solar cycle , as well as aperiodic fluctuations. Solar activity has been measured by satellites during...
on shorter time scales, including the 11-year
solar cycleThe solar cycle, or the solar magnetic activity cycle, is the main source of periodic solar variation driving variations in space weather. The cycle is observed by counting the frequency and placement of sunspots visible on the Sun...
and longer-term
modulationModulation is the process of varying one waveform in relation to another waveform. In telecommunications, modulation is used to convey a message, or a musician may modulate the tone from a musical instrument by varying its volume, timing and pitch. Often a high-frequency sinusoid waveform is used...
s. The 11-year
sunspotA sunspot is an area on the Sun's surface that is marked by intense magnetic activity, which inhibits convection, forming areas of reduced surface temperature. They can be visible from Earth without the aid of a telescope...
cycle produces low-latitude warming and high-latitude cooling over limited areas of statistical significance in the
stratosphereThe stratosphere is the second major layer of Earth's atmosphere, just above the troposphere, and below the mesosphere. It is stratified in temperature, with warmer layers higher up and cooler layers farther down. This is in contrast to the troposphere near the Earth's surface, which is cooler...
with an amplitude of approximately 1.5°C. But although "variability associated with the 11-yr solar cycle has a significant influence on stratospheric temperatures. ...there is still no consensus on the exact magnitude and spatial structure". These stratospheric variations are consistent with the idea that excess equatorial heating can drive
thermal windThe thermal wind is a vertical shear in the geostrophic wind caused by a horizontal temperature gradient. Its name is a misnomer, because the thermal wind is not actually a wind, but rather a wind gradient.- Physical Intuition :...
s. In the near-surface
troposphereThe troposphere is the lowest portion of Earth's atmosphere. It contains approximately 75 percent of the atmosphere's mass and 99 percent of its water vapor and aerosols....
, there is only a small change in temperature (on the order of a tenth of a degree, and only statistically significant in limited areas underneath the peaks in stratospheric zonal wind speed) due to the 11-year solar cycle. Solar intensity variations are considered to have been influential in triggering the
Little Ice AgeThe Little Ice Age was a period of cooling that occurred after a warmer era known as the Medieval Warm Period. While not a true ice age, the term was introduced into scientific literature by François E. Matthes in 1939...
, and for some of the warming observed from 1900 to 1950. The cyclical nature of the sun's energy output is not yet fully understood; it differs from the very slow change that is happening within the sun as it ages and evolves, with some studies pointing toward solar radiation increases from cyclical sunspot activity affecting
global warmingGlobal warming is the increase in the average temperature of the Earth's near-surface air and oceans since the mid-20th century and its projected continuation. Global surface temperature increased 0.74 ± 0.18 °C during the last century...
.
Orbital variations
Slight variations in Earth's
orbitIn physics, an orbit is the gravitationally curved path of one object around a point or another body, for example the gravitational orbit of a planet around a star....
lead to changes in the amount of sunlight reaching the Earth's surface and how it is distributed across the globe. The former is similar to solar variations in that there is a change to the power input from the sun to the Earth system. The latter is due to how the orbital variations affect when and where sunlight is received by the Earth. The three types of orbital variations are variations in Earth's
eccentricityIn astrodynamics, under standard assumptions, any orbit must be of conic section shape. The eccentricity of this conic section, the orbit's eccentricity, is an important parameter of the orbit that defines its absolute shape...
, changes in
the tilt angle of Earth's axis of rotationIn astronomy, axial tilt is the angle between an object's rotational axis and a line perpendicular to its orbital plane. The angle is measured between the line perpendicular to object's orbital plane and object's rotational axis passing through north pole at which the planet appears to rotate...
, and
precessionPrecession refers to a change in the orientation of the rotation axis of a rotating body. It can be defined as a change in direction of the rotation axis in which the second Euler angle is constant...
of Earth's axis. Combined together, these produce
Milankovitch cyclesMilankovitch Theory describes the collective effects of changes in the Earth's movements upon its climate, named after Serbian civil engineer and mathematician Milutin Milanković...
which have a large impact on climate and are notable for their correlation to
glacialA glacial period is an interval of time within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the other hand, are periods of warmer climate within an ice age...
and interglacial periods, their correlation with the advance and retreat of the
SaharaThe Sahara , , "The Greatest Desert") is the world's largest hot desert. At over 9,000,000 square kilometres , it covers most of Northern Africa, making it almost as large as the United States or the continent of Europe. The desert stretches from the Red Sea, including parts of the Mediterranean...
, and for their
appearanceCyclostratigraphy is the study of astronomically forced climate cycles within sedimentary successions. Astronomical cycles are variations of the Earth's orbit around the sun due to the gravitational interaction with other masses within the solar system. Due to this cyclicity solar irradiation...
in the
stratigraphic recordthumb|200px|The layer cakelike appearance of concordant strata laid down over hundreds of thousands of years.thumb|200px|The layer cakelike appearance of concordant strata laid down over hundreds of thousands of years....
.
Volcanism
Volcanism is a process of conveying material from the
crustIn geology, a crust is the outermost solid shell of a rocky planet or moon, which is chemically distinct from the underlying mantle. The crusts of Earth, our Moon, Mercury, Venus, Mars, Io, and other planetary bodies have been generated largely by igneous processes, and these crusts are richer in...
and
mantleThe mantle is a part of an astronomical object. The interior of the Earth, similar to the other terrestrial planets, is chemically divided into layers. The mantle is a highly viscous layer between the crust and the outer core. Earth's mantle is about 2,970 km thick rocky shell that...
of the Earth to its surface. Volcanic eruptions, geysers, and
hot springsHot Springs may refer to:* Hot Springs, Arkansas*Hot Springs, California**Hot Springs, Lassen County, California**Hot Springs, Modoc County, California**Hot Springs, Plumas County, California* Hot Springs, Montana* Hot Springs, North Carolina...
, are examples of volcanic processes which release gases and/or particulates into the atmosphere.
Eruption3. Conduit
4. Base
5. Sill
6. Dike
7. Layers of ash emitted by the volcano
8. Flank| 9. Layers of lava emitted by the volcano
10. Throat
11. Parasitic cone
12. Lava flow
13. Vent
14. Crater
15...
s large enough to affect climate occur on average several times per century, and cause cooling (by partially blocking the transmission of solar radiation to the Earth's surface) for a period of a few years. The eruption of
Mount PinatuboMount Pinatubo is an active stratovolcano located on the island of Luzon, at the intersection of the borders of the Philippine provinces of Zambales, Tarlac, and Pampanga...
in 1991, the second largest terrestrial eruption of the 20th century (after the 1912 eruption of
NovaruptaNovarupta, meaning "new eruption", is a volcano located on the Alaska Peninsula in Katmai National Park and Preserve, about southwest of Anchorage. Formed in 1912 during the largest volcanic eruption of the 20th century, Novarupta released 30 times the volume of magma as the 1980 eruption of...
) affected the climate substantially. Global temperatures decreased by about 0.5 °C (0.9 °F). The eruption of
Mount TamboraMount Tambora is an active stratovolcano, also known as a composite volcano, on Sumbawa island, Indonesia. Sumbawa is flanked both to the north and south by oceanic crust, and Tambora was formed by the active subduction zones beneath it...
in 1815 caused the
Year Without a SummerThe Year Without a Summer was 1816, in which severe summer climate abnormalities destroyed crops in Northern Europe, the Northeastern United States and eastern Canada.Historian John D...
. Much larger eruptions, known as
large igneous provinceLarge Igneous provinces are extremely large accumulations of igneous rocks, either or both intrusive and extrusive, found in the earths crust...
s, occur only a few times every hundred million years, but may cause global warming and mass extinctions.
Volcanoes are also part of the extended
carbon cycleThe carbon cycle is the biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of the Earth...
. Over very long (geological) time periods, they release carbon dioxide from the Earth's crust and mantle, counteracting the uptake by sedimentary rocks and other geological
carbon dioxide sinkA carbon sink is a natural or manmade reservoir that accumulates and stores some carbon-containing chemical compound for an indefinite period.The main natural sinks are:*Absorption of carbon dioxide by the oceans*Photosynthesis by plants and algae...
s. According to the US Geological Survey, however, estimates are that human activities generate more than 130 times the amount of carbon dioxide emitted by volcanoes.
Ocean variability
The ocean is a fundamental part of the climate system. Short-term fluctuations (years to a few decades) such as the
El Niño–Southern OscillationEnsō is a Japanese word meaning "circle" and a concept strongly associated with Zen. Ensō is one of the most common subjects of Japanese calligraphy even though it is a symbol and not a character. It symbolizes enlightenment, strength, elegance, the Universe, and the void; it can also symbolize...
, the
Pacific decadal oscillationThe Pacific decadal oscillation is a pattern of Pacific climate variability that shifts phases on at least inter-decadal time scale, usually about 20 to 30 years. The PDO is detected as warm or cool surface waters in the Pacific Ocean, north of 20° N...
, the
North Atlantic oscillationThe North Atlantic oscillation is a climatic phenomenon in the North Atlantic Ocean of fluctuations in the difference of atmospheric pressure at sea-level between the Icelandic Low and the Azores high. Through east-west oscillation motions of the Icelandic Low and the Azores high, it controls the...
, and the
Arctic oscillationThe Arctic oscillation is the dominant pattern of non-seasonal sea-level pressure variations north of 20N latitude, and it is characterized by pressure anomalies of one sign in the Arctic with the opposite anomalies centered about 37-45N...
, represent climate variability rather than climate change. On longer time scales, alterations to ocean processes such as
thermohaline circulationThe term thermohaline circulation refers to the part of the large-scale ocean circulation that is driven by global density gradients created by surface heat and freshwater fluxes....
play a key role in redistributing heat by carrying out a very slow and extremely deep movement of
waterWater is an ubiquitous chemical substance that is composed of hydrogen and oxygen and is essential for all known forms of life.In typical usage, water refers only to its liquid form or state, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam. Water covers 71%...
, and the long-term redistribution of
heatIn physics and thermodynamics, heat is the process of energy transfer from one body or system due to thermal contact, which in turn is defined as an energy transfer to a body in any other way than due to work performed on the body....
in the world's oceans.
Human influences
Anthropogenic factors are human activities that change the environment. In some cases the chain of causality of human influence on the climate is direct and unambiguous (for example, the effects of irrigation on local humidity), whilst in other instances it is less clear. Various hypotheses for human-induced climate change have been argued for many years. Presently the
scientific consensus on climate changeNational and international science academies and scientific societies have assessed the current scientific opinion, in particular on recent global warming...
is that human activity is very likely the cause for the rapid increase in global average temperatures over the past several decades. Consequently, the debate has largely shifted onto ways to reduce further human impact and to find ways to adapt to change that has already occurred.
Of most concern in these anthropogenic factors is the increase in CO
2 levels due to emissions from
fossil fuelFossil fuels or mineral fuels are fuels formed by natural resources such as anaerobic decomposition of buried dead organisms. The age of the organisms and their resulting fossil fuels is typically millions of years, and sometimes exceeds 650 million years...
combustion, followed by
aerosolsParticulates, alternatively referred to as particulate matter or fine particles, are tiny particles of solid or liquid suspended in a gas or liquid. In contrast, aerosol refers to particles and the gas together. Sources of particulate matter can be man made or natural...
(particulate matter in the atmosphere) and
cementIn the most general sense of the word, a cement is a binder, a substance which sets and hardens independently, and can bind other materials together. The word "cement" traces to the Romans, who used the term "opus caementicium" to describe masonry which resembled concrete and was made from crushed...
manufacture. Other factors, including land use,
ozone depletionOzone depletion describes two distinct, but related observations: a slow, steady decline of about 4% per decade in the total volume of ozone in Earth's stratosphere since the late 1970s, and a much larger, but seasonal, decrease in stratospheric ozone over Earth's polar regions during the same...
, animal agriculture and deforestation, are also of concern in the roles they play - both separately and in conjunction with other factors - in affecting climate.
Physical evidence for climatic change
Evidence for climatic change is taken from a variety of sources that can be used to reconstruct past climates. Reasonably complete global records of surface temperature are available beginning from the mid-late 1800s. For earlier periods, most of the evidence is indirect—climatic changes are inferred from changes in indicators that reflect climate, such as
vegetationVegetation is a general term for the plant life of a region; it refers to the ground cover provided by plants. It is a general term, without specific reference to particular taxa, life forms, structure, spatial extent, or any other specific botanical or geographic characteristics. It is broader...
,
ice coreAn ice core is a core sample from the accumulation of snow and ice over many years that have re-crystallized and have trapped air bubbles from previous time periods...
s,
dendrochronologyDendrochronology or tree-ring dating is the scientific method of dating based on the analysis of patterns of tree-rings. Dendrochronology can date the time at which tree rings were formed, in many types of wood, to the exact calendar year...
, sea level change, and glacial geology.
Historical & Archaeological evidence
Climate change in the recent past may be detected by corresponding changes in settlement and agricultural patterns. Archaeological evidence,
oral historyOral history can be defined as the recording, preservation and interpretation of historical information, based on the personal experiences and opinions of the speaker....
and historical documents can offer insights into past changes in the climate. Climate change effects have been linked to the collapse of various civilisations.
Glaciers
GlacierA glacier is a perennial mass of ice which moves over land. A glacier forms in locations where the mass accumulation of snow and ice exceeds ablation over many years...
s are among the most sensitive indicators of climate change, advancing when climate cools (for example, during the period known as the
Little Ice AgeThe Little Ice Age was a period of cooling that occurred after a warmer era known as the Medieval Warm Period. While not a true ice age, the term was introduced into scientific literature by François E. Matthes in 1939...
) and retreating when climate warms. Glaciers grow and shrink, both contributing to natural variability and amplifying externally forced changes. A world glacier inventory has been compiled since the 1970s. Initially based mainly on aerial photographs and maps, this compilation has resulted in a detailed inventory of more than 100,000 glaciers covering a total area of approximately 240,000 km
2 and, in preliminary estimates, for the recording of the remaining ice cover estimated to be around 445,000 km
2. The World Glacier Monitoring Service collects data annually on
glacier retreatGlacier retreat or glacial retreat is discussed in several articles, depending on the time frame of interest, and whether the climatological process or individual glaciers are being considered. Articles on these topics include:...
and
glacier mass balanceCrucial to the survival of a glacier is its mass balance, the difference between accumulation and ablation . Climate change may cause variations in both temperature and snowfall, causing changes in mass balance. Changes in mass balance control a glacier's long term behavior and is the most...
From this data, glaciers worldwide have been found to be shrinking significantly, with strong glacier retreats in the 1940s, stable or growing conditions during the
1920sThe 1920s was the decade that ran from January 1, 1920, to December 31, 1929. It is sometimes referred to as the Roaring Twenties or the Jazz Age, when speaking about the United States, Canada or the United Kingdom...
and
1970sThe 1970s was the decade that ran from January 1, 1970, to December 31, 1979.In the Western world, social progressive values that began in the 1960s, such as increasing political awareness and political and economic liberty of women, continued to grow...
, and again retreating from the mid
1980sThe 1980s was the decade that ran from January 1, 1980, to December 31, 1989.The time period saw social, economic and general change as wealth and production migrated to newly industrializing economies...
to present. Mass balance data indicate 17 consecutive years of negative glacier mass balance.
The most significant climate processes since the middle to late
PlioceneThe Pliocene epoch is the period in the geologic timescale that extends from 5.332 million to 2.588 million years before present....
(approximately 3 million years ago) are the glacial and
interglacialAn interglacial is a geological interval of warmer global average temperature that separates glacial periods within an ice age. The current Holocene interglacial has persisted since the end of the Pleistocene, about 11,400 years ago....
cycles. The present interglacial period (the
HoloceneThe Holocene is a geological epoch which began approximately 11 700 years ago . According to traditional geological thinking, the Holocene continues to the present. The Holocene is part of the Neogene and Quaternary periods. Its name comes from the Greek words and , meaning "entirely...
) has lasted about 11,700 years. Shaped by
orbital variationsMilankovitch Theory describes the collective effects of changes in the Earth's movements upon its climate, named after Serbian civil engineer and mathematician Milutin Milanković...
, responses such as the rise and fall of
continentalContinental is the adjective form of continent. Continental may refer to:* Continental , an album by UK band Saint Etienne* Continental , a brand of dried and pre-packaged foods used by Unilever in Australia...
ice sheets and significant sea-level changes helped create the climate. Other changes, including
Heinrich eventHeinrich events, first described by marine geologist Hartmut Heinrich, occurred during the last glacial period, or "ice age". During such events, armadas of icebergs broke off from glaciers and traversed the North Atlantic. The icebergs contained rock mass eroded by the glaciers, and as they...
s, Dansgaard–Oeschger events and the
Younger DryasThe Younger Dryas stadial, named after the alpine/tundra wildflower Dryas octopetala, and also referred to as the Big Freeze, was a geologically brief cold climate period following the Bølling/Allerød interstadial at the end of the Pleistocene between approximately 12,800 to 11,500 years ago, and...
, however, illustrate how glacial variations may also influence climate without the
forcing effectOrbital forcing is the effect on climate of slow changes in the tilt of the Earth's axis and shape of the orbit . These orbital changes change the total amount of sunlight reaching the Earth by up to 25% at mid-latitudes...
of orbital changes.
Glaciers leave behind
moraineA moraine is any glacially formed accumulation of unconsolidated glacial debris which can occur in currently glaciated and formerly glaciated regions, such as those areas acted upon by a past ice age. This debris may have been plucked off the valley floor as a glacier advanced or it may have...
s that contain a wealth of material - including organic matter that may be accurately dated - recording the periods in which a glacier advanced and retreated. Similarly, by
tephrochronological250px|thumb|right|Tephra horizons in south-central [[Iceland]]. The thick and light coloured layer at the height of the [[volcanologists]] hands is [[rhyolitic]] [[tephra]] from [[Hekla]]....
techniques, the lack of glacier cover can be identified by the presence of soil or volcanic
tephra250px|thumb|right|Tephra horizons in south-central [[Iceland]]. The thick and light coloured layer at the height of the [[volcanologists]] hands is [[rhyolitic]] tephra from [[Hekla]]....
horizons whose date of deposit may also be precisely ascertained.
Vegetation
A change in the type, distribution and coverage of vegetation may occur given a change in the climate; this much is obvious. In any given scenario, a mild change in climate may result in increased precipitation and warmth, resulting in improved plant growth and the subsequent sequestration of airborne CO
2. Larger, faster or more radical changes, however, may well result in vegetation stress, rapid plant loss and desertification in certain circumstances.
Ice cores
Analysis of ice in a core drilled from a
ice sheetAn ice sheet is a mass of glacier ice that covers surrounding terrain and is greater than 50,000 km² . The only current ice sheets are in Antarctica and Greenland; during the last glacial period at Last Glacial Maximum the Laurentide ice sheet covered much of Canada and North America, the...
such as the
Antarctic ice sheetThe Antarctic ice sheet is one of the two polar ice caps of the Earth. It covers about 98% of the Antarctic continent and is the largest single mass of ice on Earth. It covers an area of almost 14 million square km and contains 30 million cubic km of ice...
, can be used to show a link between temperature and global sea level variations. The air trapped in bubbles in the ice can also reveal the CO
2 variations of the atmosphere from the distant past, well before modern environmental influences. The study of these ice cores has been a significant indicator of the changes in CO
2 over many millennia, and continue to provide valuable information about the differences between ancient and modern atmospheric conditions.
Dendrochronology
Dendochronology is the analysis of tree ring growth patterns to determine the age of a tree. From a climate change viewpoint, however, Dendochronology can also indicate the climatic conditions for a given number of years. Wide and thick rings indicate a fertile, well-watered growing period, whilst thin, narrow rings indicate a time of lower rainfall and less-than-ideal growing conditions.
Pollen analysis
PalynologyPalynology is the science that studies contemporary and fossil palynomorphs, including pollen, spores, orbicules, dinoflagellate cysts, acritarchs, chitinozoans and scolecodonts, together with particulate organic matter and kerogen found in sedimentary rocks and sediments...
is the study of contemporary and fossil
palynomorphPalynomorph is the geological term used to describe a particle of a size between five and 500 micrometres, found in rock deposits and composed of organic material such as chitin, pseudochitin and sporopollenin...
s, including
pollenPollen is a fine to coarse powder containing the microgametophytes of seed plants, which produce the male gametes . Pollen grains have a hard coat that protects the sperm cells during the process of their movement between the stamens to the pistil of flowering plants or from the male cone to the...
. Palynology is used to infer the geographical distribution of plant species, which vary under different climate conditions. Different groups of plants have
pollenPollen is a fine to coarse powder containing the microgametophytes of seed plants, which produce the male gametes . Pollen grains have a hard coat that protects the sperm cells during the process of their movement between the stamens to the pistil of flowering plants or from the male cone to the...
with distinctive shapes and surface textures, and since the outer surface of pollen is composed of a very resilient material, they resist decay. Changes in the type of pollen found in different sedimentation levels in lakes, bogs or river deltas indicate changes in plant communities; which are dependent on climate conditions.
Insects
Remains of
beetleBeetles are the group of insects with the largest number of known species. They are classified in the order Coleoptera , which contains more described species than in any other order in the animal kingdom, constituting about 25% of all known life-forms...
s are common in freshwater and land sediments. Different species of beetles tend to be found under different climatic conditions. Given the extensive lineage of beetles whose genetic makeup has not altered significantly over the millennia, knowledge of the present climatic range of the different species, and the age of the sediments in which remains are found, past climatic conditions may be inferred.
Sea level change
Global sea level change for much of the last century has generally been estimated using
tide gaugeA tide gauge is a device for measuring sea level and detecting tsunamis.Sensors continuously record the height of the water level with respect to a height reference surface close to the geoid...
measurements collated over long periods of time to give a long-term average. More recently,
altimeterAn altimeter is an instrument used to measure the altitude of an object above a fixed level. The measurement of altitude is called altimetry, which is related to the term bathymetry, the measurement of depth underwater.-Pressure altimeter:...
measurements — in combination with accurately determined
satelliteIn the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavor. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon....
orbits — have provided an improved measurement of global sea level change.
See also
General
- Paleoclimatology
Paleoclimatology is the study of climate change taken on the scale of the entire history of Earth. It uses records from ice sheets, tree rings, sediment, and rocks to determine the past state of the climate system on Earth....
and links therein
- Atmospheric physics
Atmospheric physics is the application of physics to the study of the atmosphere. Atmospheric physicists attempt to model Earth's atmosphere and the atmospheres of the other planets using fluid flow equations, chemical models, radiation balancing, and energy transfer processes in the atmosphere...
- Glossary of climate change
This article serves as a glossary of climate change terms. It lists terms that are related to global warming.-0-9:* 100,000-year problem - a discrepancy between the climate response and the forcing from the amount of incoming solar radiation.-A:...
- List of climate change topics
Climate of the deep past
- Faint young sun paradox
The faint young Sun paradox or problem describes the apparent contradiction between observations of liquid water early in the Earth's history and the astrophysical expectation that the Sun's output would be only 70% as intense during that epoch as it is during the modern epoch...
- Oxygen catastrophe
The Great Oxidation Event was a major environmental change around associated with the appearance of free oxygen in the atmosphere....
- Snowball earth
Snowball Earth refers to hypotheses regarding paleoclimatic global-scale glaciation, claiming that the Earth's surface was nearly or entirely frozen at some points in its past. The occurrence of Snowball Earths remains controversial...
Climate of the last 500 million years
- Cretaceous Thermal Maximum
- Ice age
The general term "ice age" or, more precisely, "glacial age" denotes a geological period of long-term reduction in the temperature of the Earth's surface and atmosphere, resulting in an expansion of continental ice sheets, polar ice sheets and alpine glaciers. Within a long-term ice age, individual...
s
- Paleocene–Eocene Thermal Maximum
- Permo–Carboniferous Glaciation
Climate of recent glaciations
- Bond event
Bond events are North Atlantic climate fluctuations occurring every ≈1,470 years throughout the Holocene. Eight such events have been identified. Bond events may be the interglacial relatives of the glacial Dansgaard-Oeschger events....
- Dansgaard-Oeschger event
Dansgaard-Oeschger events are rapid climate fluctuations that occurred 25 times during the last glacial period. Some scientists claim that the events occur quasi-periodically with a recurrence time being a multiple of 1,470 years, but this is debated...
- Younger Dryas
The Younger Dryas stadial, named after the alpine/tundra wildflower Dryas octopetala, and also referred to as the Big Freeze, was a geologically brief cold climate period following the Bølling/Allerød interstadial at the end of the Pleistocene between approximately 12,800 to 11,500 years ago, and...
Recent climate
- Anthropocene
The term Anthropocene is used by some scientists to describe the most recent period in the Earth's history. It has no precise start date, but may be considered to start in the late 18th century when the activities of humans first began to have a significant global impact on the Earth's climate and...
- Global warming
Global warming is the increase in the average temperature of the Earth's near-surface air and oceans since the mid-20th century and its projected continuation. Global surface temperature increased 0.74 ± 0.18 °C during the last century...
- Hardiness Zone Migration
Hardiness Zone Migration refers to the geographical shifts observed in agricultural hardiness zones as a result of climate change....
- Holocene Climatic Optimum
The Holocene Climate Optimum was a warm period during roughly the interval 9,000 to 5,000 years B.P.. This event has also been known by many other names, including: Hypsithermal, Altithermal, Climatic Optimum, Holocene Optimum, Holocene Thermal Maximum, and Holocene Megathermal.This warm period...
- Little Ice Age
The Little Ice Age was a period of cooling that occurred after a warmer era known as the Medieval Warm Period. While not a true ice age, the term was introduced into scientific literature by François E. Matthes in 1939...
- Medieval Warm Period
The Medieval Warm Period or Medieval Climate Optimum was a time of warm climate in the North Atlantic region, lasting from about AD 800–1300. It was followed by a cooler period in the North Atlantic termed the Little Ice Age. The MWP is often invoked in discussions of global warming...
- Temperature record of the past 1000 years
The temperature record of the past 1,000 years describes the reconstruction of temperature for the last 1000 years on the Northern Hemisphere, later extended back to 2000 years and also to cover the southern hemisphere. A reconstruction is needed because a reliable surface temperature record...
- Year Without a Summer
The Year Without a Summer was 1816, in which severe summer climate abnormalities destroyed crops in Northern Europe, the Northeastern United States and eastern Canada.Historian John D...
Further reading
- Emanuel, K. A. (2005)
- IPCC. (2007) Climate change 2007: the physical science basis (summary for policy makers), IPCC.
- Miller, C. and Edwards, P. N. (ed.)(2001) Changing the Atmosphere: Expert Knowledge and Environmental Governance, MIT Press
- Ruddiman, W. F. (2003) The anthropogenic greenhouse era began thousands of years ago, Climate Change 61 (3): 261-293
- Ruddiman, W. F. (2005) Plows, Plagues and Petroleum: How Humans Took Control of Climate, Princeton University Press
- Ruddiman, W. F., Vavrus, S. J. and Kutzbach, J. E. (2005) A test of the overdue-glaciation hypothesis, Quaternary Science Review, 24:11
- Schmidt, G. A., Shindel, D. T. and Harder, S. (2004) A note of the relationship between ice core methane concentrations and insolation GRL v31 L23206
External links