Carbon Dioxide In Earth's Atmosphere
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In Earth's atmosphere,
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 ...
is a trace gas that plays an integral part in the
greenhouse effect The greenhouse effect occurs when greenhouse gases in a planet's atmosphere insulate the planet from losing heat to space, raising its surface temperature. Surface heating can happen from an internal heat source (as in the case of Jupiter) or ...
,
carbon cycle The carbon cycle is a part of the biogeochemical cycle where carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of Earth. Other major biogeochemical cycles include the nitrogen cycle and the water cycl ...
,
photosynthesis Photosynthesis ( ) is a system of biological processes by which photosynthetic organisms, such as most plants, algae, and cyanobacteria, convert light energy, typically from sunlight, into the chemical energy necessary to fuel their metabo ...
and oceanic carbon cycle. It is one of three main greenhouse gases in the atmosphere of
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 ...
. The concentration of carbon dioxide () in the atmosphere reached 427 ppm (0.0427%) on a molar basis in 2024, representing 3341 gigatonnes of . This is an increase of 50% since the start of the
Industrial Revolution The Industrial Revolution, sometimes divided into the First Industrial Revolution and Second Industrial Revolution, was a transitional period of the global economy toward more widespread, efficient and stable manufacturing processes, succee ...
, up from 280 ppm during the 10,000 years prior to the mid-18th century. The increase is due to human activity. The current increase in concentrations is primarily driven by the burning of fossil fuels.IPCC (2022
Summary for policy makers
i
Climate Change 2022: Mitigation of Climate Change. Contribution of Working Group III to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change
, Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA
Other significant human activities that emit include cement production,
deforestation Deforestation or forest clearance is the removal and destruction of a forest or stand of trees from land that is then converted to non-forest use. Deforestation can involve conversion of forest land to farms, ranches, or urban use. Ab ...
, and biomass burning. The increase in atmospheric concentrations of and other long-lived greenhouse gases such as
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 ...
increase the absorption and emission of infrared radiation by the atmosphere. This has led to a rise in average global temperature and ocean acidification. Another direct effect is the fertilization effect. The increase in atmospheric concentrations of causes a range of further
effects of climate change Effects of climate change are well documented and growing for Earth's natural environment and human societies. Changes to the climate system include an Instrumental temperature record, overall warming trend, Effects of climate change on the ...
on the environment and human living conditions. Carbon dioxide is a greenhouse gas. It absorbs and emits infrared radiation at its two infrared-active vibrational frequencies. The two
wavelength In physics and mathematics, wavelength or spatial period of a wave or periodic function is the distance over which the wave's shape repeats. In other words, it is the distance between consecutive corresponding points of the same ''phase (waves ...
s are 4.26  ÎŒm (2,347 cm−1) (asymmetric stretching vibrational mode) and 14.99 ÎŒm (667 cm−1) (bending vibrational mode). plays a significant role in influencing
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 surface temperature through the greenhouse effect. Light emission from the Earth's surface is most intense in the infrared region between 200 and 2500 cm−1, as opposed to light emission from the much hotter Sun which is most intense in the visible region. Absorption of infrared light at the vibrational frequencies of atmospheric traps energy near the surface, warming the surface of Earth and its lower atmosphere. Less energy reaches the upper atmosphere, which is therefore cooler because of this absorption. The present atmospheric concentration of is the highest for 14 million years. Concentrations of in the atmosphere were as high as 4,000 ppm during the Cambrian period about 500 million years ago, and as low as 180 ppm during the
Quaternary glaciation The Quaternary glaciation, also known as the Pleistocene glaciation, is an alternating series of glacial period, glacial and interglacial, interglacial periods during the Quaternary period that began 2.58 Year#SI prefix multipliers, Ma (million ...
of the last two million years. Reconstructed temperature records for the last 420 million years indicate that atmospheric concentrations peaked at approximately 2,000 ppm. This peak happened during the
Devonian The Devonian ( ) is a period (geology), geologic period and system (stratigraphy), system of the Paleozoic era (geology), era during the Phanerozoic eon (geology), eon, spanning 60.3 million years from the end of the preceding Silurian per ...
period (400 million years ago). Another peak occurred in the
Triassic The Triassic ( ; sometimes symbolized 🝈) is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.4 Mya. The Triassic is t ...
period (220–200 million years ago).


Current concentration and future trends


Current situation

Since the start of the
Industrial Revolution The Industrial Revolution, sometimes divided into the First Industrial Revolution and Second Industrial Revolution, was a transitional period of the global economy toward more widespread, efficient and stable manufacturing processes, succee ...
, atmospheric concentration have been increasing, causing
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 ...
and ocean acidification. In October 2023 the average level of in Earth's atmosphere, adjusted for seasonal variation, was 422.17 parts per million by volume (ppm). Figures are published monthly by the National Oceanic & Atmospheric Administration (NOAA). The value had been about 280 ppm during the 10,000 years up to the mid-18th century. Each part per million of in the atmosphere represents approximately 2.13 gigatonnes of carbon, or 7.82 gigatonnes of . It was pointed out in 2021 that "the current rates of increase of the concentration of the major greenhouse gases (carbon dioxide, methane and nitrous oxide) are unprecedented over at least the last 800,000 years". it is estimated that 2,650 gigatonnes of have been emitted by human activity since 1850, with annual emissions of 42 gigatonnes per year. About 1,050 gigatonnes remain in the atmosphere following absorption by oceans and land. Some fraction (a projected 20–35%) of the fossil carbon transferred thus far will persist in the atmosphere as elevated levels for many thousands of years after these carbon transfer activities begin to subside.


Annual and regional fluctuations

Atmospheric concentrations fluctuate slightly with the seasons, falling during the
Northern Hemisphere The Northern Hemisphere is the half of Earth that is north of the equator. For other planets in the Solar System, north is defined by humans as being in the same celestial sphere, celestial hemisphere relative to the invariable plane of the Solar ...
spring and summer as plants consume the gas and rising during northern autumn and winter as plants go dormant or die and decay. The level drops by about 6 or 7 ppm (about 50 Gt) from May to September during the Northern Hemisphere's growing season, and then goes up by about 8 or 9 ppm. The
Northern Hemisphere The Northern Hemisphere is the half of Earth that is north of the equator. For other planets in the Solar System, north is defined by humans as being in the same celestial sphere, celestial hemisphere relative to the invariable plane of the Solar ...
dominates the annual cycle of concentration because it has much greater land area and plant biomass in mid-latitudes (30-60 degrees) than the Southern Hemisphere. Concentrations reach a peak in May as the Northern Hemisphere spring greenup begins, and decline to a minimum in October, near the end of the growing season. Concentrations also vary on a regional basis, most strongly near the ground with much smaller variations aloft. In urban areas concentrations are generally higher and indoors they can reach 10 times background levels.


Measurements and predictions made in the recent past

* Data from 2009 found that the global mean concentration was rising at a rate of approximately 2 ppm/year and accelerating. * The daily average concentration of atmospheric at Mauna Loa Observatory first exceeded 400 ppm on 10 May 2013 although this concentration had already been reached in the Arctic in June 2012. Data from 2013 showed that the concentration of carbon dioxide in the atmosphere is this high "for the first time in 55 years of measurement—and probably more than 3 million years of Earth history." * As of 2018, concentrations were measured to be 410 ppm.


Measurement techniques

The concentrations of carbon dioxide in the atmosphere are expressed as parts per million by volume (abbreviated as ppmv, or ppm(v), or just ppm). To convert from the usual ppmv units to ppm mass (abbreviated as ppmm, or ppm(m)), multiply by the ratio of the
molar mass In chemistry, the molar mass () (sometimes called molecular weight or formula weight, but see related quantities for usage) of a chemical substance ( element or compound) is defined as the ratio between the mass () and the amount of substance ...
of CO2 to that of air, i.e. times 1.52 (44.01 divided by 28.96). The first reproducibly accurate measurements of atmospheric CO2 were from flask sample measurements made by Dave Keeling at
Caltech The California Institute of Technology (branded as Caltech) is a private university, private research university in Pasadena, California, United States. The university is responsible for many modern scientific advancements and is among a small g ...
in the 1950s. Measurements at Mauna Loa have been ongoing since 1958. Additionally, measurements are also made at many other sites around the world. Many measurement sites are part of larger global networks. Global network data are often made publicly available.


Data networks

There are several surface measurement (including flasks and continuous in situ) networks including NOAA/ ERSL, WDCGG, and RAMCES. The NOAA/ESRL Baseline Observatory Network, and the Scripps Institution of Oceanography Network data are hosted at the CDIAC at ORNL. The World Data Centre for Greenhouse Gases (WDCGG), part of GAW, data are hosted by the JMA. The Reseau Atmospherique de Mesure des Composes an Effet de Serre database (RAMCES) is part of IPSL. From these measurements, further products are made which integrate data from the various sources. These products also address issues such as data discontinuity and sparseness. GLOBALVIEW- is one of these products.


Analytical methods to investigate sources of CO2

* The burning of long-buried fossil fuels releases containing carbon of different isotopic ratios to those of living plants, enabling distinction between natural and human-caused contributions to concentration.e.g. * There are higher atmospheric concentrations in the Northern Hemisphere, where most of the world's population lives (and emissions originate from), compared to the southern hemisphere. This difference has increased as anthropogenic emissions have increased. * Atmospheric O levels are decreasing in Earth's atmosphere as it reacts with the carbon in fossil fuels to form .


Causes of the current increase


Anthropogenic CO2 emissions

While absorption and release is always happening as a result of natural processes, the recent rise in levels in the atmosphere is known to be mainly due to human (anthropogenic) activity.Eyring, V., N.P. Gillett, K.M. Achuta Rao, R. Barimalala, M. Barreiro Parrillo, N. Bellouin, C. Cassou, P.J. Durack, Y. Kosaka, S.  McGregor, S. Min, O. Morgenstern, and Y. Sun, 2021
Chapter 3: Human Influence on the Climate System
. I
Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change
[Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. PĂ©an, S. Berger, N. Caud, Y. Chen, L.  Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 423–552,
Anthropogenic carbon emissions exceed the amount that can be taken up or balanced out by natural sinks. Thus carbon dioxide has gradually accumulated in the atmosphere and, as of May 2022, its concentration is 50% above pre-industrial levels. The extraction and burning of fossil fuels, releasing carbon that has been underground for many millions of years, has increased the atmospheric concentration of . As of year 2019 the extraction and burning of geologic fossil carbon by humans releases over 30 gigatonnes of (9 billion tonnes carbon) each year.Friedlingstein, P., Jones, M., O'Sullivan, M., Andrew, R., Hauck, J., Peters, G., Peters, W., Pongratz, J., Sitch, S., Le QuĂ©rĂ©, C. and 66 others (2019) "Global carbon budget 2019". ''Earth System Science Data'', 11(4): 1783–1838. . Material was copied from this source, which is available under a Creative Commons Attribution 4.0 International License. This larger disruption to the natural balance is responsible for recent growth in the atmospheric concentration. Currently about half of the carbon dioxide released from the burning of fossil fuels is not absorbed by vegetation and the oceans and remains in the
atmosphere An atmosphere () is a layer of gases that envelop an astronomical object, held in place by the gravity of the object. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A stellar atmosph ...
. Burning fossil fuels such as
coal Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other Chemical element, elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal i ...
,
petroleum Petroleum, also known as crude oil or simply oil, is a naturally occurring, yellowish-black liquid chemical mixture found in geological formations, consisting mainly of hydrocarbons. The term ''petroleum'' refers both to naturally occurring un ...
, and
natural gas Natural gas (also fossil gas, methane gas, and gas) is a naturally occurring compound of gaseous hydrocarbons, primarily methane (95%), small amounts of higher alkanes, and traces of carbon dioxide and nitrogen, hydrogen sulfide and helium ...
is the leading cause of increased
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 ...
;
deforestation Deforestation or forest clearance is the removal and destruction of a forest or stand of trees from land that is then converted to non-forest use. Deforestation can involve conversion of forest land to farms, ranches, or urban use. Ab ...
is the second major cause. In 2010, 9.14 gigatonnes of carbon (GtC, equivalent to 33.5 gigatonnes of or about 4.3 ppm in Earth's atmosphere) were released from fossil fuels and cement production worldwide, compared to 6.15 GtC in 1990. In addition, land use change contributed 0.87 GtC in 2010, compared to 1.45 GtC in 1990. In the period 1751 to 1900, about 12 GtC were released as to the atmosphere from burning of fossil fuels, whereas from 1901 to 2013 the figure was about 380 GtC. The
International Energy Agency The International Energy Agency (IEA) is a Paris-based autonomous intergovernmental organization, established in 1974, that provides policy recommendations, analysis and data on the global energy sector. The 31 member countries and 13 associatio ...
estimates that the top 1% of emitters globally each had carbon footprints of over 50 tonnes of in 2021, more than 1,000 times greater than those of the bottom 1% of emitters. The global average energy-related carbon footprint is around 4.7 tonnes of per person.


Roles in natural processes on Earth


Greenhouse effect

On Earth, carbon dioxide is the most relevant, direct greenhouse gas that is influenced by human activities. Water is responsible for most (about 36–70%) of the total greenhouse effect, and the role of water vapor as a greenhouse gas depends on temperature. Carbon dioxide is often mentioned in the context of its increased influence as a greenhouse gas since the pre-industrial (1750) era. In 2013, the increase in CO2 was estimated to be responsible for 1.82 W m−2 of the 2.63 W m−2 change in radiative forcing on Earth (about 70%). Earth's natural
greenhouse effect The greenhouse effect occurs when greenhouse gases in a planet's atmosphere insulate the planet from losing heat to space, raising its surface temperature. Surface heating can happen from an internal heat source (as in the case of Jupiter) or ...
makes life as we know it possible, and carbon dioxide in the atmosphere plays a significant role in providing for the relatively high temperature on Earth. The greenhouse effect is a process by which thermal radiation from a planetary atmosphere warms the planet's surface beyond the temperature it would have in the absence of its atmosphere.A concise description of the greenhouse effect is given in the ''Intergovernmental Panel on Climate Change Fourth Assessment Report,'' "What is the Greenhouse Effect?
FAQ 1.3 – AR4 WGI Chapter 1: Historical Overview of Climate Change Science
, IPCC Fourth Assessment Report, Chapter 1, p. 115: "To balance the absorbed incoming olarenergy, the Earth must, on average, radiate the same amount of energy back to space. Because the Earth is much colder than the Sun, it radiates at much longer wavelengths, primarily in the infrared part of the spectrum (see Figure 1). Much of this thermal radiation emitted by the land and ocean is absorbed by the atmosphere, including clouds, and reradiated back to Earth. This is called the greenhouse effect."
Stephen H. Schneider, in ''Geosphere-biosphere Interactions and Climate,'' Lennart O. Bengtsson and Claus U. Hammer, eds., Cambridge University Press, 2001, , pp. 90–91.
E. Claussen, V.A. Cochran, and D.P. Davis, ''Climate Change: Science, Strategies, & Solutions,'' University of Michigan, 2001. p. 373.
A. Allaby and M. Allaby, ''A Dictionary of Earth Sciences,'' Oxford University Press, 1999, , p. 244.
The concept of more atmospheric CO2 increasing ground temperature was first published by
Svante Arrhenius Svante August Arrhenius ( , ; 19 February 1859 – 2 October 1927) was a Swedish scientist. Originally a physicist, but often referred to as a chemist, Arrhenius was one of the founders of the science of physical chemistry. In 1903, he received ...
in 1896. The increased radiative forcing due to increased CO2 in the Earth's atmosphere is based on the physical properties of CO2 and the non-saturated absorption windows where CO2 absorbs outgoing long-wave energy. The increased forcing drives further changes in Earth's energy balance and, over the longer term, in Earth's climate.


Carbon cycle

Atmospheric carbon dioxide plays an integral role in the Earth's
carbon cycle The carbon cycle is a part of the biogeochemical cycle where carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of Earth. Other major biogeochemical cycles include the nitrogen cycle and the water cycl ...
whereby is removed from the atmosphere by some natural processes such as
photosynthesis Photosynthesis ( ) is a system of biological processes by which photosynthetic organisms, such as most plants, algae, and cyanobacteria, convert light energy, typically from sunlight, into the chemical energy necessary to fuel their metabo ...
and deposition of carbonates, to form limestones for example, and added back to the atmosphere by other natural processes such as respiration and the acid dissolution of carbonate deposits. There are two broad carbon cycles on Earth: the fast carbon cycle and the slow carbon cycle. The fast carbon cycle refers to movements of carbon between the environment and living things in the
biosphere The biosphere (), also called the ecosphere (), is the worldwide sum of all ecosystems. It can also be termed the zone of life on the Earth. The biosphere (which is technically a spherical shell) is virtually a closed system with regard to mat ...
whereas the slow carbon cycle involves the movement of carbon between the atmosphere, oceans, soil, rocks, and volcanism. Both cycles are intrinsically interconnected and atmospheric facilitates the linkage. Natural sources of atmospheric include volcanic
outgassing Outgassing (sometimes called offgassing, particularly when in reference to indoor air quality) is the release of a gas that was dissolved, trapped, frozen, or absorbed in some material. Outgassing can include sublimation and evaporation (whic ...
, the
combustion Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combustion ...
of organic matter,
wildfires A wildfire, forest fire, or a bushfire is an unplanned and uncontrolled fire in an area of Combustibility and flammability, combustible vegetation. Depending on the type of vegetation present, a wildfire may be more specifically identified as a ...
and the respiration processes of living
aerobic organism An aerobic organism or aerobe is an organism that can survive and grow in an oxygenated environment. The ability to exhibit aerobic respiration may yield benefits to the aerobic organism, as aerobic respiration yields more energy than anaerobic ...
s. Man-made sources of include the burning of
fossil fuels A fossil fuel is a flammable carbon compound- or hydrocarbon-containing material formed naturally in the Earth's crust from the buried remains of prehistoric organisms (animals, plants or microplanktons), a process that occurs within geologica ...
, as well as some industrial processes such as cement making. Natural sources of are more or less balanced by natural
carbon sink A carbon sink is a natural or artificial carbon sequestration process that "removes a  greenhouse gas, an aerosol or a precursor of a greenhouse gas from the atmosphere". These sinks form an important part of the natural carbon cycle. An overar ...
s, in the form of chemical and biological processes which remove from the atmosphere. For example, the decay of organic material in forests, grasslands, and other land vegetation - including forest fires - results in the release of about 436  gigatonnes of (containing 119 gigatonnes carbon) every year, while uptake by new growth on land counteracts these releases, absorbing 451 Gt (123 Gt C). Although much in the early atmosphere of the young Earth was produced by volcanic activity, modern volcanic activity releases only 130 to 230  megatonnes of each year. From the human pre-industrial era to 1940, the terrestrial biosphere represented a net source of atmospheric (driven largely by land-use changes), but subsequently switched to a net sink with growing fossil carbon emissions. Carbon moves between the atmosphere, vegetation (dead and alive), the soil, the surface layer of the ocean, and the deep ocean. A detailed model has been developed by Fortunat Joos in
Bern Bern (), or Berne (), ; ; ; . is the ''de facto'' Capital city, capital of Switzerland, referred to as the "federal city".; ; ; . According to the Swiss constitution, the Swiss Confederation intentionally has no "capital", but Bern has gov ...
and colleagues, called the Bern model. A simpler model based on it gives the fraction of remaining in the atmosphere as a function of the number of years after it is emitted into the atmosphere: :f(t)=0.217+0.259\exp(-t/172.9)+0.338\exp(-t/18,51)+0.186\exp(-t/1.186) According to this model, 21.7% of the carbon dioxide released into the air stays there forever, but of course this is not true if carbon-containing material is removed from the cycle (and stored) in ways that are not operative at present ( artificial sequestration).


Oceanic carbon cycle

The Earth's oceans contain a large amount of in the form of bicarbonate and carbonate ions—much more than the amount in the atmosphere. The bicarbonate is produced in reactions between rock, water, and carbon dioxide. From 1850 until 2022, the ocean has absorbed 26% of total anthropogenic emissions. However, the rate at which the ocean will take it up in the future is less certain. Even if equilibrium is reached, including dissolution of carbonate minerals, the increased concentration of bicarbonate and decreased or unchanged concentration of carbonate ion will give rise to a higher concentration of un-ionized carbonic acid and dissolved . This higher concentration in the seas, along with higher temperatures, would mean a higher equilibrium concentration of in the air. A study published in ''
Science Advances ''Science Advances'' is a peer-reviewed multidisciplinary open-access scientific journal established in early 2015 and published by the American Association for the Advancement of Science. The journal's scope includes all areas of science. Hist ...
'' in 2025 concluded that faster flow of the Antarctic Circumpolar Current (ACC) at higher latitudes causes upwelling of isotopically light deep waters around Antarctica, likely increasing atmospheric carbon dioxide levels and thereby potentially constituting a critical positive feedback for future warming.


Effects of current increase


Direct effects

Direct effects of increasing CO2 concentrations in the atmosphere include increasing global temperatures, ocean acidification and a CO2 fertilization effect on plants and crops.


Temperature rise on land


Temperature rise in oceans


Ocean acidification


CO2 fertilization effect


Other direct effects

emissions have also led to the stratosphere contracting by 400 meters since 1980, which could affect satellite operations, GPS systems and radio communications.


Indirect effects and impacts


Approaches for reducing CO2 concentrations

Carbon dioxide has unique long-term effects on climate change that are nearly "irreversible" for a thousand years after emissions stop (zero further emissions). The greenhouse gases
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 ...
and nitrous oxide do not persist over time in the same way as carbon dioxide. Even if human carbon dioxide emissions were to completely cease, atmospheric temperatures are not expected to decrease significantly in the short term. This is because the air temperature is determined by a balance between heating, due to greenhouse gases, and cooling due to heat transfer to the ocean. If emissions were to stop, CO2 levels and the heating effect would slowly decrease, but simultaneously the cooling due to heat transfer would diminish (because sea temperatures would get closer to the air temperature), with the result that the air temperature would decrease only slowly. Sea temperatures would continue to rise, causing thermal expansion and some sea level rise. Lowering global temperatures more rapidly would require carbon sequestration or geoengineering. Various techniques have been proposed for removing excess carbon dioxide from the atmosphere.


Concentrations in the geologic past

Estimates in 2023 found that the current carbon dioxide concentration in the atmosphere may be the highest it has been in the last 14 million years. However the
IPCC Sixth Assessment Report The Sixth Assessment Report (AR6) of the United Nations (UN) Intergovernmental Panel on Climate Change (IPCC) is the sixth in a series of reports which assess the available scientific information on climate change. Three Working Groups (WGI, II, ...
estimated similar levels 3 to 3.3 million years ago in the mid-Pliocene warm period. This period can be a proxy for likely climate outcomes with current levels of . Carbon dioxide is believed to have played an important effect in regulating Earth's temperature throughout its 4.54 billion year history. Early in the Earth's life, scientists have found evidence of liquid water indicating a warm world even though the Sun's output is believed to have only been 70% of what it is today. Higher carbon dioxide concentrations in the early Earth's atmosphere might help explain this faint young sun paradox. When Earth first formed, Earth's atmosphere may have contained more greenhouse gases and concentrations may have been higher, with estimated partial pressure as large as , because there was no bacterial
photosynthesis Photosynthesis ( ) is a system of biological processes by which photosynthetic organisms, such as most plants, algae, and cyanobacteria, convert light energy, typically from sunlight, into the chemical energy necessary to fuel their metabo ...
to reduce the gas to carbon compounds and oxygen.
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 ...
, a very active greenhouse gas, may have been more prevalent as well. Carbon dioxide concentrations have shown several cycles of variation from about 180 parts per million during the deep glaciations of the
Holocene The Holocene () is the current geologic time scale, geological epoch, beginning approximately 11,700 years ago. It follows the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene to ...
and
Pleistocene The Pleistocene ( ; referred to colloquially as the ''ice age, Ice Age'') is the geological epoch (geology), epoch that lasted from to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fin ...
to 280 parts per million during the interglacial periods. Carbon dioxide concentrations have varied widely over the Earth's history. It is believed to have been present in Earth's first atmosphere, shortly after Earth's formation. The second atmosphere, consisting largely of
nitrogen Nitrogen is a chemical element; it has Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a Nonmetal (chemistry), nonmetal and the lightest member of pnictogen, group 15 of the periodic table, often called the Pnictogen, pnictogens. ...
and was produced by outgassing from volcanism, supplemented by gases produced during the late heavy bombardment of Earth by huge
asteroids An asteroid is a minor planet—an object larger than a meteoroid that is neither a planet nor an identified comet—that orbits within the Solar System#Inner Solar System, inner Solar System or is co-orbital with Jupiter (Trojan asteroids). As ...
. A major part of carbon dioxide emissions were soon dissolved in water and incorporated in carbonate sediments. The production of free oxygen by cyanobacterial photosynthesis eventually led to the Great Oxygenation Event, oxygen catastrophe that ended Earth's second atmosphere and brought about the Earth's third atmosphere (the modern atmosphere) 2.4 billion years ago. Carbon dioxide concentrations dropped from 4,000 parts per million during the Cambrian period about 500 million years ago to as low as 180 parts per million 20,000 years ago .


Drivers of ancient-Earth CO2 concentration

On long timescales, atmospheric concentration is determined by the balance among Geochemical cycle, geochemical processes including organic carbon burial in sediments, silicate rock weathering, and Volcanic gas, volcanic degassing. The net effect of slight imbalances in the
carbon cycle The carbon cycle is a part of the biogeochemical cycle where carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of Earth. Other major biogeochemical cycles include the nitrogen cycle and the water cycl ...
over tens to hundreds of millions of years has been to reduce atmospheric . On a timescale of billions of years, such downward trend appears bound to continue indefinitely as occasional massive historical releases of buried carbon due to volcanism will become less frequent (as earth mantle cooling and progressive exhaustion of Geothermal gradient, internal radioactive heat proceed further). The rates of these processes are extremely slow; hence they are of no relevance to the atmospheric concentration over the next hundreds or thousands of years.


Photosynthesis in the geologic past

Over the course of Earth's geologic history concentrations have played a role in biological evolution. The first photosynthetic organisms probably evolution, evolved early in the evolutionary history of life and most likely used reducing agents such as hydrogen or hydrogen sulfide as sources of electrons, rather than water. Cyanobacteria appeared later, and the excess oxygen they produced contributed to the oxygen catastrophe, which rendered the Evolution of multicellularity, evolution of complex life possible. In recent geologic times, low concentrations below 600 parts per million might have been the stimulus that favored the evolution of C4 carbon fixation, plants which increased greatly in abundance between 7 and 5 million years ago over plants that use the less efficient C3 carbon fixation, metabolic pathway. At current atmospheric pressures photosynthesis shuts down when atmospheric concentrations fall below 150 ppm and 200 ppm although some microbes can extract carbon from the air at much lower concentrations.


Measuring ancient-Earth CO2 concentration

The most direct method for measuring atmospheric carbon dioxide concentrations for periods before instrumental sampling is to measure bubbles of air (fluid inclusions, fluid or gas inclusions) trapped in the Antarctica, Antarctic or Greenland ice sheets. The most widely accepted of such studies come from a variety of Antarctic cores and indicate that atmospheric concentrations were about 260–280 ppm immediately before industrial emissions began and did not vary much from this level during the preceding 10,000 annum, years. The longest ice core record comes from East Antarctica, where ice has been sampled to an age of 800,000 years. During this time, the atmospheric carbon dioxide concentration has varied between 180 and 210 ppm during ice ages, increasing to 280–300 ppm during warmer interglacials. mole fractions in the atmosphere have gone up by around 35 percent since the 1900s, rising from 280 parts per million by volume to 387 parts per million in 2009. One study using evidence from stomata of fossilized leaves suggests greater variability, with mole fractions above 300 ppm during the period ten to seven thousand years ago, though others have argued that these findings more likely reflect calibration or contamination problems rather than actual CO2 variability. Because of the way air is trapped in ice (pores in the ice close off slowly to form bubbles deep within the firn) and the time period represented in each ice sample analyzed, these figures represent averages of atmospheric concentrations of up to a few centuries rather than annual or decadal levels. Ice cores provide evidence for greenhouse gas concentration variations over the past 800,000 years. Both CO2 and concentrations vary between glacial and interglacial phases, and these variations correlate strongly with temperature. Direct data does not exist for periods earlier than those represented in the ice core record, a record that indicates that CO2 mole fractions stayed within a range of 180 ppm to 280 ppm throughout the last 800,000 years, until the increase of the last 250 years. However, various Proxy (climate), proxy measurements and models suggest larger variations in past epochs: 500 million years ago CO2 levels were likely 10 times higher than now. Various proxy measurements have been used to try to determine atmospheric CO2 concentrations millions of years in the past. These include boron and carbon isotope ratios in certain types of marine sediments, and the numbers of stomata observed on fossil plant leaves. Phytane is a type of diterpenoid alkane. It is a breakdown product of chlorophyll, and is now used to estimate ancient levels. Phytane gives both a continuous record of concentrations but it also can overlap a break in the record of over 500 million years.


720 to 400 million years ago

There is evidence for high concentrations of over 6,000 ppm between 600 and 400 million years ago, and of over 3,000 ppm between 200 and 150 million years ago. Indeed, higher CO2 concentrations are thought to have prevailed throughout most of the Phanerozoic Eon (geology), Eon, with concentrations four to six times current concentrations during the Mesozoic era, and ten to fifteen times current concentrations during the early Palaeozoic era until the middle of the
Devonian The Devonian ( ) is a period (geology), geologic period and system (stratigraphy), system of the Paleozoic era (geology), era during the Phanerozoic eon (geology), eon, spanning 60.3 million years from the end of the preceding Silurian per ...
period, about 400 million years ago. The spread of land plants is thought to have reduced CO2 concentrations during the late Devonian, and plant activities as both sources and sinks of CO2 have since been important in providing stabilizing feedbacks. Earlier in Earth's history, in the Neoproterozoic Era, an 82-million year period of intermittent, widespread glaciation extending to the equator (Snowball Earth) ended suddenly at 635 Ma. after released during volcanic outgassing built up to ~12% (~120,000 ppm). This caused extreme greenhouse conditions, rapid deglaciation, and carbonate deposition as limestone at rates which may have been as fast as 40 cm per year. The end of the Snowball Earth glaciations marks the transition between the Cryogenian and Ediacaran Periods, and may have contributed to the radiation of metazoan life in the Phanerozoic.


60 to 5 million years ago

Atmospheric concentration continued to fall after about 60 million years ago. About 34 million years ago, the time of the Eocene–Oligocene extinction event and when the Antarctic ice sheet started to take its current form, was about 760 ppm, and there is geochemical evidence that concentrations were less than 300 ppm by about 20 million years ago. Decreasing concentration, with a tipping point of 600 ppm, was the primary agent forcing Antarctic glaciation. Low concentrations may have been the stimulus that favored the evolution of C4 carbon fixation, plants, which increased greatly in abundance between 7 and 5 million years ago.


See also

* Carbon budget * Global surface temperature


References


External links


Current global map of carbon dioxide concentrations.Global Carbon Dioxide Circulation
(NASA; 13 December 2016)
Video (03:10) – A Year in the Life of Earth's
(NASA; 17 November 2014) {{DEFAULTSORT:Carbon Dioxide In Earth's Atmosphere Atmosphere of Earth Carbon dioxide Greenhouse gases fr:Dioxyde de carbone#CO2 dans l'atmosphĂšre terrestre