Carbon dioxide (chemical formula CO2) is a colorless gas with a
density about 60% higher than that of dry air.
Carbon dioxide consists
of a carbon atom covalently double bonded to two oxygen atoms. It
occurs naturally in
Earth's atmosphere as a trace gas. The current
concentration is about 0.04% (405 ppm) by volume, having risen
from pre-industrial levels of 280 ppm. Natural sources include
volcanoes, hot springs and geysers, and it is freed from carbonate
rocks by dissolution in water and acids. Because carbon dioxide is
soluble in water, it occurs naturally in groundwater, rivers and
lakes, ice caps, glaciers and seawater. It is present in deposits of
petroleum and natural gas.
Carbon dioxide is odorless at normally
encountered concentrations, however, at high concentrations, it has a
sharp and acidic odor.
As the source of available carbon in the carbon cycle, atmospheric
carbon dioxide is the primary carbon source for life on
Earth and its
concentration in Earth's pre-industrial atmosphere since late in the
Precambrian has been regulated by photosynthetic organisms and
geological phenomena. Plants, algae and cyanobacteria use light energy
to photosynthesize carbohydrate from carbon dioxide and water, with
oxygen produced as a waste product.
CO2 is produced by all aerobic organisms when they metabolize
carbohydrates and lipids to produce energy by respiration. It is
returned to water via the gills of fish and to the air via the lungs
of air-breathing land animals, including humans.
Carbon dioxide is
produced during the processes of decay of organic materials and the
fermentation of sugars in bread, beer and wine making. It is produced
by combustion of wood and other organic materials and fossil fuels
such as coal, peat, petroleum and natural gas. It is an unwanted
byproduct in many large scale oxidation processes, for example, in the
production of acrylic acid (over 5 million tons/year).
It is a versatile industrial material, used, for example, as an inert
gas in welding and fire extinguishers, as a pressurizing gas in air
guns and oil recovery, as a chemical feedstock and as a supercritical
fluid solvent in decaffeination of coffee and supercritical
drying. It is added to drinking water and carbonated beverages
including beer and sparkling wine to add effervescence. The frozen
solid form of CO2, known as dry ice is used as a refrigerant and as an
abrasive in dry-ice blasting.
Carbon dioxide is the most significant long-lived greenhouse gas in
Earth's atmosphere. Since the
Industrial Revolution anthropogenic
emissions – primarily from use of fossil fuels and deforestation –
have rapidly increased its concentration in the atmosphere, leading to
global warming. The CO2 released into the atmosphere as a result of
the use of fossil fuels "represents 99.4% of CO2 emissions in
Carbon dioxide also causes ocean acidification because it
dissolves in water to form carbonic acid.
2 Chemical and physical properties
2.1 Structure and bonding
2.2 In aqueous solution
2.3 Chemical reactions of CO2
2.4 Physical properties
3 Isolation and production
4.1 Precursor to chemicals
4.3 Inert gas
4.4 Fire extinguisher
4.5 Supercritical CO2 as solvent
4.6 Agricultural and biological applications
4.7 Medical and pharmacological uses
4.8 Oil recovery
4.9 Bio transformation into fuel
Coal bed methane recovery
4.12 Minor uses
5 In Earth's atmosphere
6 In the oceans
7 Biological role
Photosynthesis and carbon fixation
7.2.1 Below 1%
7.3 Human physiology
7.3.2 Transport in the blood
7.3.3 Regulation of respiration
8 Additional media
9 See also
11 Further reading
12 External links
Crystal structure of dry ice
Carbon dioxide was the first gas to be described as a discrete
substance. In about 1640, the Flemish chemist Jan Baptist van
Helmont observed that when he burned charcoal in a closed vessel, the
mass of the resulting ash was much less than that of the original
charcoal. His interpretation was that the rest of the charcoal had
been transmuted into an invisible substance he termed a "gas" or "wild
spirit" (spiritus sylvestris).
The properties of carbon dioxide were further studied in the 1750s by
the Scottish physician Joseph Black. He found that limestone (calcium
carbonate) could be heated or treated with acids to yield a gas he
called "fixed air." He observed that the fixed air was denser than air
and supported neither flame nor animal life. Black also found that
when bubbled through limewater (a saturated aqueous solution of
calcium hydroxide), it would precipitate calcium carbonate. He used
this phenomenon to illustrate that carbon dioxide is produced by
animal respiration and microbial fermentation. In 1772, English
Joseph Priestley published a paper entitled Impregnating Water
with Fixed Air in which he described a process of dripping sulfuric
acid (or oil of vitriol as Priestley knew it) on chalk in order to
produce carbon dioxide, and forcing the gas to dissolve by agitating a
bowl of water in contact with the gas.
Carbon dioxide was first liquefied (at elevated pressures) in 1823 by
Humphry Davy and Michael Faraday. The earliest description of
solid carbon dioxide was given by Adrien-Jean-Pierre Thilorier, who in
1835 opened a pressurized container of liquid carbon dioxide, only to
find that the cooling produced by the rapid evaporation of the liquid
yielded a "snow" of solid CO2.
Chemical and physical properties
Stretching and bending oscillations of the CO2 carbon dioxide
molecule. Upper left: symmetric stretching. Upper right: antisymmetric
stretching. Lower line: degenerate pair of bending modes.
Structure and bonding
See also: Molecular orbital diagram §
The carbon dioxide molecule is linear and centrosymmetric. The
carbon–oxygen bond length is 116.3 pm, noticeably shorter than
the bond length of a C–O single bond and even shorter than most
other C–O multiply-bonded functional groups. Since it is
centrosymmetric, the molecule has no electrical dipole. Consequently,
only two vibrational bands are observed in the
IR spectrum – an
antisymmetric stretching mode at 2349 cm−1 and a degenerate
pair of bending modes at 667 cm−1. There is also a symmetric
stretching mode at 1388 cm−1 which is only observed in the
In aqueous solution
See also: Carbonic acid
Carbon dioxide is soluble in water, in which it reversibly forms H
3 (carbonic acid), which is a weak acid since its ionization in water
2 + H
2O ⇌ H
The hydration equilibrium constant of carbonic acid is
displaystyle K_ mathrm h = frac rm [H_ 2 CO_ 3 ] rm [CO_
2 (aq)] =1.70times 10^ -3
(at 25 °C). Hence, the majority of the carbon dioxide is not
converted into carbonic acid, but remains as CO2 molecules, not
affecting the pH.
The relative concentrations of CO
3, and the deprotonated forms HCO−
3 (bicarbonate) and CO2−
3(carbonate) depend on the pH. As shown in a Bjerrum plot, in neutral
or slightly alkaline water (pH > 6.5), the bicarbonate form
predominates (>50%) becoming the most prevalent (>95%) at the pH
of seawater. In very alkaline water (pH > 10.4), the predominant
(>50%) form is carbonate. The oceans, being mildly alkaline with
typical pH = 8.2–8.5, contain about 120 mg of bicarbonate per
Being diprotic, carbonic acid has two acid dissociation constants, the
first one for the dissociation into the bicarbonate (also called
hydrogen carbonate) ion (HCO3−):
H2CO3 ⇌ HCO3− + H+
Ka1 = 6999250000000000000♠2.5×10−4 mol/L; pKa1 = 3.6 at 25
This is the true first acid dissociation constant, defined as
displaystyle K_ a1 = frac rm [HCO_ 3 ^ - ][H^ + ] rm [H_ 2
CO_ 3 ]
, where the denominator includes only covalently bound H2CO3 and does
not include hydrated CO2(aq). The much smaller and often-quoted value
near 6993416000000000000♠4.16×10−7 is an apparent value
calculated on the (incorrect) assumption that all dissolved CO2 is
present as carbonic acid, so that
displaystyle K_ mathrm a1 rm (apparent) = frac rm [HCO_ 3
^ - ][H^ + ] rm [H_ 2 CO_ 3 ]+[CO_ 2 (aq)]
. Since most of the dissolved CO2 remains as CO2 molecules,
Ka1(apparent) has a much larger denominator and a much smaller value
than the true Ka1.
The bicarbonate ion is an amphoteric species that can act as an acid
or as a base, depending on pH of the solution. At high pH, it
dissociates significantly into the carbonate ion (CO32−):
HCO3− ⇌ CO32− + H+
Ka2 = 6992469000000000000♠4.69×10−11 mol/L; pKa2 = 10.329
In organisms carbonic acid production is catalysed by the enzyme,
Chemical reactions of CO2
This section needs expansion. You can help by adding to it. (June
CO2 is a weak electrophile. Its reaction with basic water illustrates
this property, in which case hydroxide is the nucleophile. Other
nucleophiles react as well. For example, carbanions as provided by
Grignard reagents and organolithium compounds react with CO2 to give
MR + CO2 → RCO2M
where M = Li or MgBr and R = alkyl or aryl.
In metal carbon dioxide complexes, CO2 serves as a ligand, which can
facilitate the conversion of CO2 to other chemicals.
The reduction of CO2 to CO is ordinarily a difficult and slow
CO2 + 2 e− + 2H+ → CO + H2O
Photoautotrophs (i.e. plants and cyanobacteria) use the energy
contained in sunlight to photosynthesize simple sugars from CO2
absorbed from the air and water:
n CO2 + n H
2O → (CH
n + n O
The redox potential for this reaction near pH 7 is about −0.53 V
versus the standard hydrogen electrode. The nickel-containing enzyme
carbon monoxide dehydrogenase catalyses this process.
Carbon dioxide data
Pellets of "dry ice", a common form of solid carbon dioxide
Carbon dioxide is colorless. At low concentrations the gas is odorless
however, at sufficiently-high concentrations, it has a sharp, acidic
odor. At standard temperature and pressure, the density of carbon
dioxide is around 1.98 kg/m3, about 1.67 times that of air.
Carbon dioxide has no liquid state at pressures below 5.1 standard
atmospheres (520 kPa). At 1 atmosphere (near mean sea level
pressure), the gas deposits directly to a solid at temperatures below
−78.5 °C (−109.3 °F; 194.7 K) and the solid
sublimes directly to a gas above −78.5 °C. In its solid state,
carbon dioxide is commonly called dry ice.
Pressure–temperature phase diagram of carbon dioxide
Liquid carbon dioxide forms only at pressures above 5.1 atm; the
triple point of carbon dioxide is about 5.1 bar (517 kPa) at
217 K (see phase diagram). The critical point is 7.38 MPa at
31.1 °C. Another form of solid carbon dioxide observed
at high pressure is an amorphous glass-like solid. This form of
glass, called carbonia, is produced by supercooling heated CO2 at
extreme pressure (40–48
GPa or about 400,000 atmospheres) in a
diamond anvil. This discovery confirmed the theory that carbon dioxide
could exist in a glass state similar to other members of its elemental
family, like silicon (silica glass) and germanium dioxide. Unlike
silica and germania glasses, however, carbonia glass is not stable at
normal pressures and reverts to gas when pressure is released.
At temperatures and pressures above the critical point, carbon dioxide
behaves as a supercritical fluid known as supercritical carbon
Isolation and production
Carbon dioxide can be obtained by distillation from air, but the
method is inefficient. Industrially, carbon dioxide is predominantly
an unrecovered waste product, produced by several methods which may be
practiced at various scales.
The combustion of all carbon-based fuels, such as methane (natural
gas), petroleum distillates (gasoline, diesel, kerosene, propane),
coal, wood and generic organic matter produces carbon dioxide and,
except in the case of pure carbon, water. As an example, the chemical
reaction between methane and oxygen:
4+ 2 O
2+ 2 H
It is produced by thermal decomposition of limestone, CaCO
3 by heating (calcining) at about 850 °C (1,560 °F), in
the manufacture of quicklime (calcium oxide, CaO), a compound that has
many industrial uses:
3→ CaO + CO
Iron is reduced from its oxides with coke in a blast furnace,
producing pig iron and carbon dioxide:
Carbon dioxide is a byproduct of the industrial production of hydrogen
by steam reforming and ammonia synthesis. These processes begin with
the reaction of water and natural gas (mainly methane).
Acids liberate CO2 from most metal carbonates. Consequently, it may be
obtained directly from natural carbon dioxide springs, where it is
produced by the action of acidified water on limestone or dolomite.
The reaction between hydrochloric acid and calcium carbonate
(limestone or chalk) is shown below:
3+ 2 HCl → CaCl
The carbonic acid (H
3) then decomposes to water and CO2:
Such reactions are accompanied by foaming or bubbling, or both, as the
gas is released. They have widespread uses in industry because they
can be used to neutralize waste acid streams.
Carbon dioxide is a by-product of the fermentation of sugar in the
brewing of beer, whisky and other alcoholic beverages and in the
production of bioethanol.
Yeast metabolizes sugar to produce CO2 and
ethanol, also known as alcohol, as follows:
6 → 2 CO
2+ 2 C
All aerobic organisms produce CO2 when they oxidize carbohydrates,
fatty acids, and proteins. The large number of reactions involved are
exceedingly complex and not described easily. Refer to (cellular
respiration, anaerobic respiration and photosynthesis). The equation
for the respiration of glucose and other monosaccharides is:
6 + 6 O
2 → 6 CO
2 + 6 H
Anaerobic organisms decompose organic material producing methane and
carbon dioxide together with traces of other compounds. Regardless
of the type of organic material, the production of gases follows well
defined kinetic pattern.
Carbon dioxide comprises about 40-45% of the
gas that emanates from decomposition in landfills (termed "landfill
gas"). Most of the remaining 50-55% is methane.
Carbon dioxide is used by the food industry, the oil industry, and the
chemical industry. The compound has varied commercial uses but one
of its greatest use as a chemical is in the production of carbonated
beverages; it provides the sparkle in carbonated beverages such as
soda water, beer and sparkling wine.
Precursor to chemicals
This section needs expansion. You can help by adding to it. (July
In the chemical industry, carbon dioxide is mainly consumed as an
ingredient in the production of urea, with a smaller fraction being
used to produce methanol and a range of other products, such as
metal carbonates and bicarbonates. Some carboxylic
acid derivatives such as sodium salicylate are prepared using CO2 by
the Kolbe-Schmitt reaction.
In addition to conventional processes using CO2 for chemical
production, electrochemical methods are also being explored at a
research level. In particular, the use of renewable energy for
production of fuels from CO2 (such as methanol) is attractive as this
could result in fuels that could be easily transported and used within
conventional combustion technologies but have no net CO2
Carbon dioxide bubbles in a soft drink.
Carbon dioxide is a food additive used as a propellant and acidity
regulator in the food industry. It is approved for usage in the EU
E number E290), US and Australia and New Zealand
(listed by its INS number 290).
A candy called
Pop Rocks is pressurized with carbon dioxide gas at
about 4 x 106 Pa (40 bar, 580 psi). When placed in the mouth, it
dissolves (just like other hard candy) and releases the gas bubbles
with an audible pop.
Leavening agents cause dough to rise by producing carbon dioxide.
Baker's yeast produces carbon dioxide by fermentation of sugars within
the dough, while chemical leaveners such as baking powder and baking
soda release carbon dioxide when heated or if exposed to acids.
Carbon dioxide is used to produce carbonated soft drinks and soda
water. Traditionally, the carbonation of beer and sparkling wine came
about through natural fermentation, but many manufacturers carbonate
these drinks with carbon dioxide recovered from the fermentation
process. In the case of bottled and kegged beer, the most common
method used is carbonation with recycled carbon dioxide. With the
exception of British Real Ale, draught beer is usually transferred
from kegs in a cold room or cellar to dispensing taps on the bar using
pressurized carbon dioxide, sometimes mixed with nitrogen.
Dry ice used to preserve grapes after harvest.
Carbon dioxide in the form of dry ice is often used during the cold
soak phase in wine making to cool clusters of grapes quickly after
picking to help prevent spontaneous fermentation by wild yeast. The
main advantage of using dry ice over water ice is that it cools the
grapes without adding any additional water that might decrease the
sugar concentration in the grape must, and thus the alcohol
concentration in the finished wine.
Carbon dioxide is also used to
create a hypoxic environment for carbonic maceration, the process used
Carbon dioxide is sometimes used to top up wine bottles or other
storage vessels such as barrels to prevent oxidation, though it has
the problem that it can dissolve into the wine, making a previously
still wine slightly fizzy. For this reason, other gases such as
nitrogen or argon are preferred for this process by professional wine
It is one of the most commonly used compressed gases for pneumatic
(pressurized gas) systems in portable pressure tools.
is also used as an atmosphere for welding, although in the welding
arc, it reacts to oxidize most metals. Use in the automotive industry
is common despite significant evidence that welds made in carbon
dioxide are more brittle than those made in more inert atmospheres. It
is used as a welding gas primarily because it is much less expensive
than more inert gases such as argon or helium. When
used for MIG welding, CO2 use is sometimes referred to as MAG welding,
for Metal Active Gas, as CO2 can react at these high temperatures. It
tends to produce a hotter puddle than truly inert atmospheres,
improving the flow characteristics. Although, this may be due to
atmospheric reactions occurring at the puddle site. This is usually
the opposite of the desired effect when welding, as it tends to
embrittle the site, but may not be a problem for general mild steel
welding, where ultimate ductility is not a major concern.
It is used in many consumer products that require pressurized gas
because it is inexpensive and nonflammable, and because it undergoes a
phase transition from gas to liquid at room temperature at an
attainable pressure of approximately 60 bar (870 psi, 59 atm),
allowing far more carbon dioxide to fit in a given container than
Life jackets often contain canisters of pressured
carbon dioxide for quick inflation.
Aluminium capsules of CO2 are also
sold as supplies of compressed gas for air guns, paintball
markers/guns, inflating bicycle tires, and for making carbonated
water. Rapid vaporization of liquid carbon dioxide is used for
blasting in coal mines. High concentrations of carbon dioxide can also
be used to kill pests. Liquid carbon dioxide is used in supercritical
drying of some food products and technological materials, in the
preparation of specimens for scanning electron microscopy[citation
needed] and in the decaffeination of coffee beans.
Use of a CO2 fire extinguisher.
Carbon dioxide can be used to extinguish flames by flooding the
environment around the flame with the gas. It does not itself react to
extinguish the flame, but starves the flame of oxygen by displacing
it. Some fire extinguishers, especially those designed for electrical
fires, contain liquid carbon dioxide under pressure.
extinguishers work well on small flammable liquid and electrical
fires, but not on ordinary combustible fires, because although it
excludes oxygen, it does not cool the burning substances significantly
and when the carbon dioxide disperses they are free to catch fire upon
exposure to atmospheric oxygen. Their desirability in electrical fire
stems from the fact that, unlike water or other chemical based
Carbon dioxide will not cause short circuits, leading to even
more damage to equipment. Because it is a gas, it is also easy to
dispense large amounts of the gas automatically in IT infrastructure
rooms, where the fire itself might be hard to reach with more
immediate methods because it is behind rack doors and inside of cases.
Carbon dioxide has also been widely used as an extinguishing agent in
fixed fire protection systems for local application of specific
hazards and total flooding of a protected space. International
Maritime Organization standards also recognize carbon dioxide systems
for fire protection of ship holds and engine rooms.
based fire protection systems have been linked to several deaths,
because it can cause suffocation in sufficiently high concentrations.
A review of CO2 systems identified 51 incidents between 1975 and the
date of the report (2000), causing 72 deaths and 145 injuries.
Supercritical CO2 as solvent
See also: Supercritical carbon dioxide
Liquid carbon dioxide is a good solvent for many lipophilic organic
compounds and is used to remove caffeine from coffee.
has attracted attention in the pharmaceutical and other chemical
processing industries as a less toxic alternative to more traditional
solvents such as organochlorides. It is used by some dry cleaners for
this reason (see green chemistry). It is used in the preparation of
some aerogels because of the properties of supercritical carbon
Agricultural and biological applications
Plants require carbon dioxide to conduct photosynthesis. The
atmospheres of greenhouses may (if of large size, must) be enriched
with additional CO2 to sustain and increase the rate of plant
growth. At very high concentrations (100 times atmospheric
concentration, or greater), carbon dioxide can be toxic to animal
life, so raising the concentration to 10,000 ppm (1%) or higher for
several hours will eliminate pests such as whiteflies and spider mites
in a greenhouse.
It has been proposed that CO2 from power generation be bubbled into
ponds to stimulate growth of algae that could then be converted into
Medical and pharmacological uses
In medicine, up to 5% carbon dioxide (130 times atmospheric
concentration) is added to oxygen for stimulation of breathing after
apnea and to stabilize the O
2 balance in blood.
Carbon dioxide can be mixed with up to 50% oxygen, forming an
inhalable gas; this is known as
Carbogen and has a variety of medical
and research uses.
Carbon dioxide is used in enhanced oil recovery where it is injected
into or adjacent to producing oil wells, usually under supercritical
conditions, when it becomes miscible with the oil. This approach can
increase original oil recovery by reducing residual oil saturation by
between 7% to 23% additional to primary extraction. It acts as
both a pressurizing agent and, when dissolved into the underground
crude oil, significantly reduces its viscosity, and changing surface
chemistry enabling the oil to flow more rapidly through the reservoir
to the removal well. In mature oil fields, extensive pipe networks
are used to carry the carbon dioxide to the injection points.
Bio transformation into fuel
Carbon capture and utilization
A strain of the cyanobacterium
Synechococcus elongatus has been
genetically engineered to produce the fuels isobutyraldehyde and
isobutanol from CO2 using photosynthesis.
Comparison of phase diagrams of carbon dioxide (red) and water (blue)
as a log-lin chart with phase transitions points at 1 atmosphere
Liquid and solid carbon dioxide are important refrigerants, especially
in the food industry, where they are employed during the
transportation and storage of ice cream and other frozen foods. Solid
carbon dioxide is called "dry ice" and is used for small shipments
where refrigeration equipment is not practical. Solid carbon dioxide
is always below −78.5 °C at regular atmospheric pressure,
regardless of the air temperature.
Liquid carbon dioxide (industry nomenclature R744 or R-744) was used
as a refrigerant prior to the discovery of R-12 and may enjoy a
renaissance due to the fact that
R134a contributes to climate change
more than CO2 does. Its physical properties are highly favorable for
cooling, refrigeration, and heating purposes, having a high volumetric
cooling capacity. Due to the need to operate at pressures of up to 130
bar (1880 psi), CO2 systems require highly resistant components that
have already been developed for mass production in many sectors. In
automobile air conditioning, in more than 90% of all driving
conditions for latitudes higher than 50°, R744 operates more
efficiently than systems using R134a. Its environmental advantages
(GWP of 1, non-ozone depleting, non-toxic, non-flammable) could make
it the future working fluid to replace current HFCs in cars,
supermarkets, and heat pump water heaters, among others.
fielded CO2-based beverage coolers and the U.S. Army is interested in
CO2 refrigeration and heating technology.
The global automobile industry is expected to decide on the
next-generation refrigerant in car air conditioning. CO2 is one
discussed option.(see Sustainable automotive air conditioning)
Coal bed methane recovery
In enhanced coal bed methane recovery, carbon dioxide would be pumped
into the coal seam to displace methane, as opposed to current methods
which primarily rely on the removal of water (to reduce pressure) to
make the coal seam release its trapped methane.
A carbon dioxide laser.
Carbon dioxide is the lasing medium in a carbon dioxide laser, which
is one of the earliest type of lasers.
Carbon dioxide can be used as a means of controlling the pH of
swimming pools, by continuously adding gas to the water, thus
keeping the pH from rising. Among the advantages of this is the
avoidance of handling (more hazardous) acids. Similarly, it is also
used in the maintaining reef aquaria, where it is commonly used in
calcium reactors to temporarily lower the pH of water being passed
over calcium carbonate in order to allow the calcium carbonate to
dissolve into the water more freely where it is used by some corals to
build their skeleton.
Used as the primary coolant in the British advanced gas-cooled reactor
for nuclear power generation.
Carbon dioxide induction is commonly used for the euthanasia of
laboratory research animals. Methods to administer CO2 include placing
animals directly into a closed, prefilled chamber containing CO2, or
exposure to a gradually increasing concentration of CO2. In 2013, the
American Veterinary Medical Association issued new guidelines for
carbon dioxide induction, stating that a displacement rate of 10% to
30% of the gas chamber volume per minute is optimal for the humane
euthanization of small rodents.
Carbon dioxide is also used in several related cleaning and surface
In Earth's atmosphere
Carbon dioxide in
Earth's atmosphere and
Keeling Curve of atmospheric CO2 concentrations measured at Mauna
Carbon dioxide in
Earth's atmosphere is a trace gas, currently (early
2017) having a global average concentration of 404 parts per million
by volume (or 614 parts per million by mass). Atmospheric
concentrations of carbon dioxide fluctuate slightly with the seasons,
falling during the
Northern Hemisphere spring and summer as plants
consume the gas and rising during northern autumn and winter as plants
go dormant or die and decay. 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.
Yearly increase of atmospheric CO2: In the 1960s, the average annual
increase was 37% of the 2000–2007 average.
The concentration of carbon dioxide has risen due to human
Combustion of fossil fuels and deforestation have
caused the atmospheric concentration of carbon dioxide to increase by
about 43% since the beginning of the age of industrialization.
Most carbon dioxide from human activities is released from burning
coal and other fossil fuels. Other human activities, including
deforestation, biomass burning, and cement production also produce
carbon dioxide. Human activities emit about 29 billion tons of carbon
dioxide per year, while volcanoes emit between 0.2 and 0.3 billion
tons. Human activities have caused CO2 to increase above
levels not seen in hundreds of thousands of years. Currently, about
half of the carbon dioxide released from the burning of fossil fuels
remains in the atmosphere and is not absorbed by vegetation and the
Carbon dioxide is a greenhouse gas, absorbing and emitting infrared
radiation at its two infrared-active vibrational frequencies (see the
section "Structure and bonding" above). This causes carbon dioxide to
warm the surface and lower atmosphere while cooling the upper
atmosphere. Increases in atmospheric concentrations of CO2 and
other long-lived greenhouse gases such as methane, nitrous oxide and
ozone have correspondingly strengthened their absorption and emission
of infrared radiation, causing the rise in average global temperature
since the mid-20th century.
Carbon dioxide is of greatest concern
because it exerts a larger overall warming influence than all of these
other gases combined and because it has a long atmospheric lifetime
(hundreds to thousands of years).
Earth's atmosphere if half of global-warming emissions are not
NASA computer simulation).
Not only do increasing carbon dioxide concentrations lead to increases
in global surface temperature, but increasing global temperatures also
cause increasing concentrations of carbon dioxide. This produces a
positive feedback for changes induced by other processes such as
orbital cycles. Five hundred million years ago the carbon dioxide
concentration was 20 times greater than today, decreasing to 4–5
times during the
Jurassic period and then slowly declining with a
particularly swift reduction occurring 49 million years ago.
Local concentrations of carbon dioxide can reach high values near
strong sources, especially those that are isolated by surrounding
terrain. At the Bossoleto hot spring near
Rapolano Terme in Tuscany,
Italy, situated in a bowl-shaped depression about 100 m
(330 ft) in diameter, concentrations of CO2 rise to above 75%
overnight, sufficient to kill insects and small animals. After sunrise
the gas is dispersed by convection. High concentrations of CO2
produced by disturbance of deep lake water saturated with CO2 are
thought to have caused 37 fatalities at
Cameroon in 1984
and 1700 casualties at
Cameroon in 1986.
In the oceans
Pterapod shell dissolved in seawater adjusted to an ocean chemistry
projected for the year 2100.
Carbon dioxide dissolves in the ocean to form carbonic acid (H2CO3),
bicarbonate (HCO3−) and carbonate (CO32−). There is about fifty
times as much carbon dissolved in the oceans as exists in the
atmosphere. The oceans act as an enormous carbon sink, and have taken
up about a third of CO2 emitted by human activity.
As the concentration of carbon dioxide increases in the atmosphere,
the increased uptake of carbon dioxide into the oceans is causing a
measurable decrease in the pH of the oceans, which is referred to as
ocean acidification. This reduction in pH affects biological systems
in the oceans, primarily oceanic calcifying organisms. These effects
span the food chain from autotrophs to heterotrophs and include
organisms such as coccolithophores, corals, foraminifera, echinoderms,
crustaceans and mollusks. Under normal conditions, calcium carbonate
is stable in surface waters since the carbonate ion is at
supersaturating concentrations. However, as ocean pH falls, so does
the concentration of this ion, and when carbonate becomes
undersaturated, structures made of calcium carbonate are vulnerable to
dissolution. Corals, coccolithophore
algae, coralline algae, foraminifera,
shellfish and pteropods experience reduced calcification or
enhanced dissolution when exposed to elevated CO
Gas solubility decreases as the temperature of water increases (except
when both pressure exceeds 300 bar and temperature exceeds 393 K, only
found near deep geothermal vents) and therefore the rate of uptake
from the atmosphere decreases as ocean temperatures rise.
Most of the CO2 taken up by the ocean, which is about 30% of the total
released into the atmosphere, forms carbonic acid in equilibrium
with bicarbonate. Some of these chemical species are consumed by
photosynthetic organisms that remove carbon from the cycle. Increased
CO2 in the atmosphere has led to decreasing alkalinity of seawater,
and there is concern that this may adversely affect organisms living
in the water. In particular, with decreasing alkalinity, the
availability of carbonates for forming shells decreases, although
there's evidence of increased shell production by certain species
under increased CO2 content.
NOAA states in their May 2008 "State of the science fact sheet for
ocean acidification" that:
"The oceans have absorbed about 50% of the carbon dioxide (CO2)
released from the burning of fossil fuels, resulting in chemical
reactions that lower ocean pH. This has caused an increase in hydrogen
ion (acidity) of about 30% since the start of the industrial age
through a process known as "ocean acidification." A growing number of
studies have demonstrated adverse impacts on marine organisms,
The rate at which reef-building corals produce their skeletons
decreases, while production of numerous varieties of jellyfish
The ability of marine algae and free-swimming zooplankton to maintain
protective shells is reduced.
The survival of larval marine species, including commercial fish and
shellfish, is reduced."
Intergovernmental Panel on Climate Change
Intergovernmental Panel on Climate Change (IPCC) writes in
their Climate Change 2007: Synthesis Report:
"The uptake of anthropogenic carbon since 1750 has led to the ocean
becoming more acidic with an average decrease in pH of 0.1 units.
Increasing atmospheric CO2 concentrations lead to further
acidification ... While the effects of observed ocean
acidification on the marine biosphere are as yet undocumented, the
progressive acidification of oceans is expected to have negative
impacts on marine shell-forming organisms (e.g. corals) and their
Some marine calcifying organisms (including coral reefs) have been
singled out by major research agencies, including NOAA, OSPAR
commission, NANOOS and the IPCC, because their most current research
shows that ocean acidification should be expected to impact them
Carbon dioxide is also introduced into the oceans through hydrothermal
vents. The Champagne hydrothermal vent, found at the Northwest Eifuku
volcano in the Marianas Trench, produces almost pure liquid carbon
dioxide, one of only two known sites in the world as of 2004, the
other being in the Okinawa Trough. The finding of a submarine lake
of liquid carbon dioxide in the
Okinawa Trough was reported in
Carbon dioxide is an end product of cellular respiration in organisms
that obtain energy by breaking down sugars, fats and amino acids with
oxygen as part of their metabolism. This includes all plants, algae
and animals and aerobic fungi and bacteria. In vertebrates, the carbon
dioxide travels in the blood from the body's tissues to the skin
(e.g., amphibians) or the gills (e.g., fish), from where it dissolves
in the water, or to the lungs from where it is exhaled. During active
photosynthesis, plants can absorb more carbon dioxide from the
atmosphere than they release in respiration.
Photosynthesis and carbon fixation
Overview of photosynthesis and respiration.
Carbon dioxide (at right),
together with water, form oxygen and organic compounds (at left) by
photosynthesis, which can be respired to water and (CO2).
Overview of the
Calvin cycle and carbon fixation
Carbon fixation is a biochemical process by which atmospheric carbon
dioxide is incorporated by plants, algae and (cyanobacteria) into
energy-rich organic molecules such as glucose, thus creating their own
food by photosynthesis.
Photosynthesis uses carbon dioxide and water
to produce sugars from which other organic compounds can be
constructed, and oxygen is produced as a by-product.
Ribulose-1,5-bisphosphate carboxylase oxygenase, commonly abbreviated
to RuBisCO, is the enzyme involved in the first major step of carbon
fixation, the production of two molecules of
CO2 and ribulose bisphosphate, as shown in the diagram at left.
RuBisCO is thought to be the single most abundant protein on
Phototrophs use the products of their photosynthesis as internal food
sources and as raw material for the biosynthesis of more complex
organic molecules, such as polysaccharides, nucleic acids and
proteins. These are used for their own growth, and also as the basis
of the food chains and webs that feed other organisms, including
animals such as ourselves. Some important phototrophs, the
coccolithophores synthesise hard calcium carbonate scales. A
globally significant species of coccolithophore is Emiliania huxleyi
whose calcite scales have formed the basis of many sedimentary rocks
such as limestone, where what was previously atmospheric carbon can
remain fixed for geological timescales.
Plants can grow as much as 50 percent faster in concentrations of
1,000 ppm CO2 when compared with ambient conditions, though this
assumes no change in climate and no limitation on other nutrients.
Elevated CO2 levels cause increased growth reflected in the
harvestable yield of crops, with wheat, rice and soybean all showing
increases in yield of 12–14% under elevated CO2 in FACE
Increased atmospheric CO2 concentrations result in fewer stomata
developing on plants which leads to reduced water usage and
increased water-use efficiency. Studies using FACE have shown
that CO2 enrichment leads to decreased concentrations of
micronutrients in crop plants. This may have knock-on effects on
other parts of ecosystems as herbivores will need to eat more food to
gain the same amount of protein.
The concentration of secondary metabolites such as phenylpropanoids
and flavonoids can also be altered in plants exposed to high
concentrations of CO2.
Plants also emit CO2 during respiration, and so the majority of plants
and algae, which use C3 photosynthesis, are only net absorbers during
the day. Though a growing forest will absorb many tons of CO2 each
year, a mature forest will produce as much CO2 from respiration and
decomposition of dead specimens (e.g., fallen branches) as is used in
photosynthesis in growing plants. Contrary to the long-standing
view that they are carbon neutral, mature forests can continue to
accumulate carbon and remain valuable carbon sinks, helping to
maintain the carbon balance of Earth's atmosphere. Additionally, and
crucially to life on earth, photosynthesis by phytoplankton consumes
dissolved CO2 in the upper ocean and thereby promotes the absorption
of CO2 from the atmosphere.
Carbon dioxide poisoning
Main symptoms of carbon dioxide toxicity, by increasing volume percent
Carbon dioxide content in fresh air (averaged between sea-level and 10
kPa level, i.e., about 30 km (19 mi) altitude) varies
between 0.036% (360 ppm) and 0.041% (410 ppm), depending on the
CO2 is an asphyxiant gas and not classified as toxic or harmful in
accordance with Globally Harmonized System of Classification and
Labelling of Chemicals standards of United Nations Economic Commission
for Europe by using the OECD Guidelines for the Testing of Chemicals.
In concentrations up to 1% (10,000 ppm), it will make some people feel
drowsy and give the lungs a stuffy feeling. Concentrations of 7%
to 10% (70,000 to 100,000 ppm) may cause suffocation, even in the
presence of sufficient oxygen, manifesting as dizziness, headache,
visual and hearing dysfunction, and unconsciousness within a few
minutes to an hour. The physiological effects of acute carbon
dioxide exposure are grouped together under the term hypercapnia, a
subset of asphyxiation.
Because it is heavier than air, in locations where the gas seeps from
the ground (due to sub-surface volcanic or geothermal activity) in
relatively high concentrations, without the dispersing effects of
wind, it can collect in sheltered/pocketed locations below average
ground level, causing animals located therein to be suffocated.
Carrion feeders attracted to the carcasses are then also killed.
Children have been killed in the same way near the city of
Goma by CO2
emissions from the nearby volcano Mt. Nyiragongo. The Swahili
term for this phenomenon is 'mazuku'.
Rising levels of CO2 threatened the
Apollo 13 astronauts who had to
adapt cartridges from the command module to supply the carbon dioxide
scrubber in the lunar module, which they used as a lifeboat.
Adaptation to increased concentrations of CO2 occurs in humans,
including modified breathing and kidney bicarbonate production, in
order to balance the effects of blood acidification (acidosis).
Several studies suggested that 2.0 percent inspired concentrations
could be used for closed air spaces (e.g. a submarine) since the
adaptation is physiological and reversible, as decrement in
performance or in normal physical activity does not happen at this
level of exposure for five days. Yet, other studies show a
decrease in cognitive function even at much lower levels.
Also, with ongoing respiratory acidosis, adaptation or compensatory
mechanisms will be unable to reverse such condition.
There are few studies of the health effects of long-term continuous
CO2 exposure on humans and animals at levels below 1%. Occupational
CO2 exposure limits have been set in the United States at 0.5% (5000
ppm) for an eight-hour period. At this CO2 concentration,
International Space Station
International Space Station crew experienced headaches, lethargy,
mental slowness, emotional irritation, and sleep disruption.
Studies in animals at 0.5% CO2 have demonstrated kidney calcification
and bone loss after eight weeks of exposure. A study of humans
exposed in 2.5 hour sessions demonstrated significant effects on
cognitive abilities at concentrations as low as 0.1% (1000ppm) CO2
likely due to CO2 induced increases in cerebral blood flow.
Another study observed a decline in basic activity level and
information usage at 1000 ppm, when compared to 500 ppm.
Poor ventilation is one of the main causes of excessive CO2
concentrations in closed spaces.
Carbon dioxide differential above
outdoor concentrations at steady state conditions (when the occupancy
and ventilation system operation are sufficiently long that CO2
concentration has stabilized) are sometimes used to estimate
ventilation rates per person. Higher CO2
concentrations are associated with occupant health, comfort and
performance degradation.
ASHRAE Standard 62.1–2007
ventilation rates may result in indoor concentrations up to 2,100 ppm
above ambient outdoor conditions. Thus if the outdoor concentration is
400 ppm, indoor concentrations may reach 2,500 ppm with ventilation
rates that meet this industry consensus standard. Concentrations in
poorly ventilated spaces can be found even higher than this (range of
3,000 or 4,000).
Miners, who are particularly vulnerable to gas exposure due to an
insufficient ventilation, referred to mixtures of carbon dioxide and
nitrogen as "blackdamp," "choke damp" or "stythe." Before more
effective technologies were developed, miners would frequently monitor
for dangerous levels of blackdamp and other gases in mine shafts by
bringing a caged canary with them as they worked. The canary is more
sensitive to asphyxiant gases than humans, and as it became
unconscious would stop singing and fall off its perch. The Davy lamp
could also detect high levels of blackdamp (which sinks, and collects
near the floor) by burning less brightly, while methane, another
suffocating gas and explosion risk, would make the lamp burn more
Reference ranges or averages for partial pressures of carbon dioxide
Venous blood carbon dioxide
Arterial blood carbon dioxide
The body produces approximately 2.3 pounds (1.0 kg) of carbon
dioxide per day per person, containing 0.63 pounds (290 g)
of carbon. In humans, this carbon dioxide is carried through the
venous system and is breathed out through the lungs, resulting in
lower concentrations in the arteries. The carbon dioxide content of
the blood is often given as the partial pressure, which is the
pressure which carbon dioxide would have had if it alone occupied the
volume. In humans, the blood carbon dioxide contents is shown in
the table to the right:
Transport in the blood
CO2 is carried in blood in three different ways. (The exact
percentages vary depending whether it is arterial or venous blood).
Most of it (about 70% to 80%) is converted to bicarbonate ions HCO−
3 by the enzyme carbonic anhydrase in the red blood cells, by the
reaction CO2 + H
2O → H
3 → H+ + HCO−
5% – 10% is dissolved in the plasma
5% – 10% is bound to hemoglobin as carbamino compounds
Hemoglobin, the main oxygen-carrying molecule in red blood cells,
carries both oxygen and carbon dioxide. However, the CO2 bound to
hemoglobin does not bind to the same site as oxygen. Instead, it
combines with the N-terminal groups on the four globin chains.
However, because of allosteric effects on the hemoglobin molecule, the
binding of CO2 decreases the amount of oxygen that is bound for a
given partial pressure of oxygen. This is known as the Haldane Effect,
and is important in the transport of carbon dioxide from the tissues
to the lungs. Conversely, a rise in the partial pressure of CO2 or a
lower pH will cause offloading of oxygen from hemoglobin, which is
known as the Bohr effect.
Regulation of respiration
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Carbon dioxide is one of the mediators of local autoregulation of
blood supply. If its concentration is high, the capillaries expand to
allow a greater blood flow to that tissue.
Bicarbonate ions are crucial for regulating blood pH. A person's
breathing rate influences the level of CO2 in their blood. Breathing
that is too slow or shallow causes respiratory acidosis, while
breathing that is too rapid leads to hyperventilation, which can cause
Although the body requires oxygen for metabolism, low oxygen levels
normally do not stimulate breathing. Rather, breathing is stimulated
by higher carbon dioxide levels. As a result, breathing low-pressure
air or a gas mixture with no oxygen at all (such as pure nitrogen) can
lead to loss of consciousness without ever experiencing air hunger.
This is especially perilous for high-altitude fighter pilots. It is
also why flight attendants instruct passengers, in case of loss of
cabin pressure, to apply the oxygen mask to themselves first before
helping others; otherwise, one risks losing consciousness.
The respiratory centers try to maintain an arterial CO2 pressure of
40 mm Hg. With intentional hyperventilation, the CO2 content of
arterial blood may be lowered to 10–20 mm Hg (the oxygen
content of the blood is little affected), and the respiratory drive is
diminished. This is why one can hold one's breath longer after
hyperventilating than without hyperventilating. This carries the risk
that unconsciousness may result before the need to breathe becomes
overwhelming, which is why hyperventilation is particularly dangerous
before free diving.
3D model of CO2's HOMO.
3D model of CO2's LUMO.
Arterial blood gas
Carbon dioxide sensor
EcoCute – as refrigerants
List of least carbon efficient power stations
List of countries by carbon dioxide emissions
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Library resources about
Resources in your library
Resources in other libraries
International Chemical Safety Card 0021
CID 1 from PubChem
Carbon dioxide MSDS by Amerigas in the SDSdata.org database.
CDC – NIOSH Pocket Guide to Chemical Hazards –
Carbon Dioxide Properties, Uses, Applications
Dry Ice information
Trends in Atmospheric
Carbon Dioxide (NOAA)
Gas That Saves Lives". Popular Science, June 1942,
The on-line catalogue of CO2 natural emissions in Italy
Reactions, Thermochemistry, Uses, and Function of
Carbon Dioxide – Part One and
Carbon Dioxide – Part Two at The
Periodic Table of Videos (University of Nottingham)
Mixed oxidation states
Antimony tetroxide (Sb2O4)
Cobalt(II,III) oxide (Co3O4)
Europium(II,III) oxide (Eu3O4)
Iron(II,III) oxide (Fe3O4)
Lead(II,IV) oxide (Pb3O4)
Manganese(II,III) oxide (Mn3O4)
Silver(I,III) oxide (Ag2O2)
Triuranium octoxide (U3O8)
Carbon suboxide (C3O2)
Mellitic anhydride (C12O9)
Praseodymium(III,IV) oxide (Pr6O11)
Terbium(III,IV) oxide (Tb4O7)
+1 oxidation state
Copper(I) oxide (Cu2O)
Dicarbon monoxide (C2O)
Dichlorine monoxide (Cl2O)
Gallium(I) oxide (Ga2O)
Lithium oxide (Li2O)
Potassium oxide (K2O)
Rubidium oxide (Rb2O)
Silver oxide (Ag2O)
Thallium(I) oxide (Tl2O)
Sodium oxide (Na2O)
Water (hydrogen oxide) (H2O)
+2 oxidation state
Aluminium(II) oxide (AlO)
Barium oxide (BaO)
Beryllium oxide (BeO)
Cadmium oxide (CdO)
Calcium oxide (CaO)
Carbon monoxide (CO)
Chromium(II) oxide (CrO)
Cobalt(II) oxide (CoO)
Copper(II) oxide (CuO)
Europium(II) oxide (EuO)
Germanium monoxide (GeO))
Iron(II) oxide (FeO)
Lead(II) oxide (PbO)
Magnesium oxide (MgO)
Manganese(II) oxide (MnO)
Mercury(II) oxide (HgO)
Nickel(II) oxide (NiO)
Nitric oxide (NO)
Palladium(II) oxide (PdO)
Silicon monoxide (SiO)
Strontium oxide (SrO)
Sulfur monoxide (SO)
Disulfur dioxide (S2O2)
Tin(II) oxide (SnO)
Titanium(II) oxide (TiO)
Vanadium(II) oxide (VO)
Zinc oxide (ZnO)
+3 oxidation state
Aluminium oxide (Al2O3)
Antimony trioxide (Sb2O3)
Arsenic trioxide (As2O3)
Bismuth(III) oxide (Bi2O3)
Boron trioxide (B2O3)
Cerium(III) oxide (Ce2O3)
Dibromine trioxide (Br2O3)
Chromium(III) oxide (Cr2O3)
Dinitrogen trioxide (N2O3)
Dysprosium(III) oxide (Dy2O3)
Erbium(III) oxide (Er2O3)
Europium(III) oxide (Eu2O3)
Gadolinium(III) oxide (Gd2O3)
Gallium(III) oxide (Ga2O3)
Holmium(III) oxide (Ho2O3)
Indium(III) oxide (In2O3)
Iron(III) oxide (Fe2O3)
Lanthanum oxide (La2O3)
Lutetium(III) oxide (Lu2O3)
Manganese(III) oxide (Mn2O3)
Neodymium(III) oxide (Nd2O3)
Nickel(III) oxide (Ni2O3)
Phosphorus trioxide (P4O6)
Praseodymium(III) oxide (Pr2O3)
Promethium(III) oxide (Pm2O3)
Rhodium(III) oxide (Rh2O3)
Samarium(III) oxide (Sm2O3)
Scandium oxide (Sc2O3)
Terbium(III) oxide (Tb2O3)
Thallium(III) oxide (Tl2O3)
Thulium(III) oxide (Tm2O3)
Titanium(III) oxide (Ti2O3)
Tungsten(III) oxide (W2O3)
Vanadium(III) oxide (V2O3)
Ytterbium(III) oxide (Yb2O3)
Yttrium(III) oxide (Y2O3)
+4 oxidation state
Americium dioxide (AmO2)
Carbon dioxide (CO2)
Carbon trioxide (CO3)
Cerium(IV) oxide (CeO2)
Chlorine dioxide (ClO2)
Chromium(IV) oxide (CrO2)
Dinitrogen tetroxide (N2O4)
Germanium dioxide (GeO2)
Hafnium(IV) oxide (HfO2)
Lead dioxide (PbO2)
Manganese dioxide (MnO2)
Neptunium(IV) oxide (NpO2)
Nitrogen dioxide (NO2)
Osmium dioxide (OsO2)
Plutonium(IV) oxide (PuO2)
Praseodymium(IV) oxide (PrO2)
Protactinium(IV) oxide (PaO2)
Rhodium(IV) oxide (RhO2)
Ruthenium(IV) oxide (RuO2)
Selenium dioxide (SeO2)
Silicon dioxide (SiO2)
Sulfur dioxide (SO2)
Tellurium dioxide (TeO2)
Terbium(IV) oxide (TbO2)
Thorium dioxide (ThO2)
Tin dioxide (SnO2)
Titanium dioxide (TiO2)
Tungsten(IV) oxide (WO2)
Uranium dioxide (UO2)
Vanadium(IV) oxide (VO2)
Zirconium dioxide (ZrO2)
+5 oxidation state
Antimony pentoxide (Sb2O5)
Arsenic pentoxide (As2O5)
Dinitrogen pentoxide (N2O5)
Niobium pentoxide (Nb2O5)
Phosphorus pentoxide (P2O5)
Protactinium(V) oxide (Pa2O5)
Tantalum pentoxide (Ta2O5)
Vanadium(V) oxide (V2O5)
+6 oxidation state
Chromium trioxide (CrO3)
Molybdenum trioxide (MoO3)
Rhenium trioxide (ReO3)
Selenium trioxide (SeO3)
Sulfur trioxide (SO3)
Tellurium trioxide (TeO3)
Tungsten trioxide (WO3)
Uranium trioxide (UO3)
Xenon trioxide (XeO3)
Iridium trioxide (IrO3)
+7 oxidation state
Dichlorine heptoxide (Cl2O7)
Manganese heptoxide (Mn2O7)
Rhenium(VII) oxide (Re2O7)
Technetium(VII) oxide (Tc2O7)
+8 oxidation state
Osmium tetroxide (OsO4)
Ruthenium tetroxide (RuO4)
Xenon tetroxide (XeO4)
Iridium tetroxide (IrO4)
Hassium tetroxide (HsO4)
Oxides are sorted by oxidation state. Category:Oxides
Compounds derived from oxides
Inorganic compounds of carbon and related ions
Carbides [:C≡C:]2–, [::C::]4–, [:C=C=C:]4–
Oxides and related
Global warming and climate change
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Attribution of recent climate change
Earth's energy budget
Earth's radiation balance
Global warming potential
Land use, land-use change and forestry
Urban heat island
Global climate model
History of climate change science
Charles David Keeling
Opinion and climate change
Media coverage of climate change
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March for Science
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Climate change and agriculture
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Climate change and gender
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Glossary of climate change
Index of climate change articles
Molecules detected in outer space
Magnesium monohydride cation
Hydrogen cyanide (HCN)
Hydrogen isocyanide (HNC)
Protonated molecular hydrogen
Protonated carbon dioxide
Protonated hydrogen cyanide
Buckminsterfullerene (C60 fullerene, buckyball)
Ethyl methyl ether
Atomic and molecular astrophysics
Diffuse interstellar band
Earliest known life forms
Extraterrestrial liquid water
Helium hydride ion
Iron–sulfur world theory
Molecules in stars
Nexus for Exoplanet System Science
PAH world hypothesis
Polycyclic aromatic hydrocarbon
Polycyclic aromatic hydrocarbon (PAH)
RNA world hypothesis
Inorganic compounds of carbon and related ions
Carbides [:C≡C:]2–, [::C::]4–, [:C=C=C:]4–
Oxides and related