Earth's atmosphere

Earth's atmosphere

Overview


The atmosphere of Earth is a layer of gases surrounding the planet Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

 that is retained by Earth's gravity. The atmosphere
Atmosphere
An atmosphere is a layer of gases that may surround a material body of sufficient mass, and that is held in place by the gravity of the body. An atmosphere may be retained for a longer duration, if the gravity is high and the atmosphere's temperature is low...

 protects life on Earth
Organism
In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...

 by absorbing ultraviolet
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...

 solar radiation, warming the surface through heat retention (greenhouse effect
Greenhouse effect
The greenhouse effect is a process by which thermal radiation from a planetary surface is absorbed by atmospheric greenhouse gases, and is re-radiated in all directions. Since part of this re-radiation is back towards the surface, energy is transferred to the surface and the lower atmosphere...

), and reducing temperature
Temperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...

 extremes between day
Daytime (astronomy)
On Earth, daytime is roughly the period on any given point of the planet's surface during which it experiences natural illumination from indirect or direct sunlight....

 and night
Night
Night or nighttime is the period of time when the sun is below the horizon. This occurs after dusk. The opposite of night is day...

 (the diurnal temperature variation
Diurnal temperature variation
Diurnal temperature variation is a meteorological term that relates to the variation in temperature that occurs from the highs of the day to the cool of nights.-Temperature lag:Temperature lag is an important factor in diurnal temperature variation...

).

Atmospheric stratification describes the structure of the atmosphere, dividing it into distinct layers, each with specific characteristics such as temperature or composition.
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Encyclopedia


The atmosphere of Earth is a layer of gases surrounding the planet Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

 that is retained by Earth's gravity. The atmosphere
Atmosphere
An atmosphere is a layer of gases that may surround a material body of sufficient mass, and that is held in place by the gravity of the body. An atmosphere may be retained for a longer duration, if the gravity is high and the atmosphere's temperature is low...

 protects life on Earth
Organism
In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...

 by absorbing ultraviolet
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...

 solar radiation, warming the surface through heat retention (greenhouse effect
Greenhouse effect
The greenhouse effect is a process by which thermal radiation from a planetary surface is absorbed by atmospheric greenhouse gases, and is re-radiated in all directions. Since part of this re-radiation is back towards the surface, energy is transferred to the surface and the lower atmosphere...

), and reducing temperature
Temperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...

 extremes between day
Daytime (astronomy)
On Earth, daytime is roughly the period on any given point of the planet's surface during which it experiences natural illumination from indirect or direct sunlight....

 and night
Night
Night or nighttime is the period of time when the sun is below the horizon. This occurs after dusk. The opposite of night is day...

 (the diurnal temperature variation
Diurnal temperature variation
Diurnal temperature variation is a meteorological term that relates to the variation in temperature that occurs from the highs of the day to the cool of nights.-Temperature lag:Temperature lag is an important factor in diurnal temperature variation...

).

Atmospheric stratification describes the structure of the atmosphere, dividing it into distinct layers, each with specific characteristics such as temperature or composition. The atmosphere has a mass of about 5 kg, three quarters of which is within about 11 km (6.8 mi; 36,089.2 ft) of the surface. The atmosphere becomes thinner and thinner with increasing altitude
Altitude
Altitude or height is defined based on the context in which it is used . As a general definition, altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The reference datum also often varies according to the context...

, with no definite boundary between the atmosphere and outer space
Outer space
Outer space is the void that exists between celestial bodies, including the Earth. It is not completely empty, but consists of a hard vacuum containing a low density of particles: predominantly a plasma of hydrogen and helium, as well as electromagnetic radiation, magnetic fields, and neutrinos....

. An altitude of 120 km (74.6 mi) is where atmospheric effects become noticeable during atmospheric reentry
Atmospheric reentry
Atmospheric entry is the movement of human-made or natural objects as they enter the atmosphere of a celestial body from outer space—in the case of Earth from an altitude above the Kármán Line,...

 of spacecraft. The Kármán line
Karman line
The Kármán line lies at an altitude of above the Earth's sea level, and is commonly used to define the boundary between the Earth's atmosphere and outer space...

, at 100 km (62.1 mi), also is often regarded as the boundary between atmosphere and outer space.

Air is the name given to atmosphere
Atmosphere
An atmosphere is a layer of gases that may surround a material body of sufficient mass, and that is held in place by the gravity of the body. An atmosphere may be retained for a longer duration, if the gravity is high and the atmosphere's temperature is low...

 used in breathing
Breathing
Breathing is the process that moves air in and out of the lungs. Aerobic organisms require oxygen to release energy via respiration, in the form of the metabolism of energy-rich molecules such as glucose. Breathing is only one process that delivers oxygen to where it is needed in the body and...

 and photosynthesis
Photosynthesis
Photosynthesis is a chemical process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea. Photosynthetic organisms are called photoautotrophs, since they can...

. Dry air contains roughly (by volume) 78.09% nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...

, 20.95% oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

, 0.93% argon
Argon
Argon is a chemical element represented by the symbol Ar. Argon has atomic number 18 and is the third element in group 18 of the periodic table . Argon is the third most common gas in the Earth's atmosphere, at 0.93%, making it more common than carbon dioxide...

, 0.039% carbon dioxide
Carbon dioxide in the Earth's atmosphere
The concentration of carbon dioxide in Earth's atmosphere is approximately 392 ppm by volume and rose by 2.0 ppm/yr during 2000–2009. 40 years earlier, the rise was only 0.9 ppm/yr, showing not only increasing concentrations, but also a rapid acceleration of concentrations...

, and small amounts of other gases. Air also contains a variable amount of water vapor
Water vapor
Water vapor or water vapour , also aqueous vapor, is the gas phase of water. It is one state of water within the hydrosphere. Water vapor can be produced from the evaporation or boiling of liquid water or from the sublimation of ice. Under typical atmospheric conditions, water vapor is continuously...

, on average around 1%. While air content and atmospheric pressure
Atmospheric pressure
Atmospheric pressure is the force per unit area exerted into a surface by the weight of air above that surface in the atmosphere of Earth . In most circumstances atmospheric pressure is closely approximated by the hydrostatic pressure caused by the weight of air above the measurement point...

 varies at different layers, air suitable for the survival of terrestrial plant
Terrestrial plant
A terrestrial plant is one that grows on land. Other types of plants are aquatic , epiphytic , lithophytes and aerial ....

s and terrestrial animal
Terrestrial animal
Terrestrial animals are animals that live predominantly or entirely on land , as compared with aquatic animals, which live predominantly or entirely in the water , or amphibians, which rely on a combination of aquatic and terrestrial habitats...

s is currently only known to be found in Earth's troposphere
Troposphere
The troposphere is the lowest portion of Earth's atmosphere. It contains approximately 80% of the atmosphere's mass and 99% of its water vapor and aerosols....

 and artificial atmospheres.

Composition


Air is mainly composed of nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...

, oxygen, and argon, which together constitute the major gases of the atmosphere. The remaining gases are often referred to as trace gases, among which are the greenhouse gas
Greenhouse gas
A greenhouse gas is a gas in an atmosphere that absorbs and emits radiation within the thermal infrared range. This process is the fundamental cause of the greenhouse effect. The primary greenhouse gases in the Earth's atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, and ozone...

es such as water vapor, carbon dioxide, methane, nitrous oxide, and ozone. Filtered air includes trace amounts of many other chemical compound
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...

s. Many natural substances may be present in tiny amounts in an unfiltered air sample, including dust
Dust
Dust consists of particles in the atmosphere that arise from various sources such as soil dust lifted up by wind , volcanic eruptions, and pollution...

, pollen
Pollen
Pollen is a fine to coarse powder containing the microgametophytes of seed plants, which produce the male gametes . Pollen grains have a hard coat that protects the sperm cells during the process of their movement from the stamens to the pistil of flowering plants or from the male cone to the...

 and spores, sea spray
Sea spray
Sea spray is a spray of water that forms when ocean waves crash.-Make up:As a result, salt spray contains a high concentration of mineral salts, particularly chloride anions.-Effects:...

, and volcanic ash
Volcanic ash
Volcanic ash consists of small tephra, which are bits of pulverized rock and glass created by volcanic eruptions, less than in diameter. There are three mechanisms of volcanic ash formation: gas release under decompression causing magmatic eruptions; thermal contraction from chilling on contact...

. Various industrial pollutant
Pollutant
A pollutant is a waste material that pollutes air, water or soil, and is the cause of pollution.Three factors determine the severity of a pollutant: its chemical nature, its concentration and its persistence. Some pollutants are biodegradable and therefore will not persist in the environment in the...

s also may be present, such as chlorine
Chlorine
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...

 (elementary or in compounds), fluorine
Fluorine
Fluorine is the chemical element with atomic number 9, represented by the symbol F. It is the lightest element of the halogen column of the periodic table and has a single stable isotope, fluorine-19. At standard pressure and temperature, fluorine is a pale yellow gas composed of diatomic...

 compounds, elemental mercury
Mercury (element)
Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...

, and sulfur
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...

 compounds such as sulfur dioxide
Sulfur dioxide
Sulfur dioxide is the chemical compound with the formula . It is released by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide unless the sulfur compounds are removed before burning the fuel...

 [SO2].
Composition of dry atmosphere, by volume
ppmv: parts per million by volume (note: volume fraction is equal to mole fraction for ideal gas only, see volume (thermodynamics))
Gas Volume
Nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...

 (N2)
780,840 ppmv (78.084%)
Oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 (O2)
209,460 ppmv (20.946%)
Argon
Argon
Argon is a chemical element represented by the symbol Ar. Argon has atomic number 18 and is the third element in group 18 of the periodic table . Argon is the third most common gas in the Earth's atmosphere, at 0.93%, making it more common than carbon dioxide...

 (Ar)
9,340 ppmv (0.9340%)
Carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

 (CO2)
390 ppmv (0.039%)
Neon
Neon
Neon is the chemical element that has the symbol Ne and an atomic number of 10. Although a very common element in the universe, it is rare on Earth. A colorless, inert noble gas under standard conditions, neon gives a distinct reddish-orange glow when used in either low-voltage neon glow lamps or...

 (Ne)
18.18 ppmv (0.001818%)
Helium
Helium
Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...

 (He)
5.24 ppmv (0.000524%)
Methane
Methane
Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...

 (CH4)
1.79 ppmv (0.000179%)
Krypton
Krypton
Krypton is a chemical element with the symbol Kr and atomic number 36. It is a member of Group 18 and Period 4 elements. A colorless, odorless, tasteless noble gas, krypton occurs in trace amounts in the atmosphere, is isolated by fractionally distilling liquified air, and is often used with other...

 (Kr)
1.14 ppmv (0.000114%)
Hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

 (H2)
0.55 ppmv (0.000055%)
Nitrous oxide
Nitrous oxide
Nitrous oxide, commonly known as laughing gas or sweet air, is a chemical compound with the formula . It is an oxide of nitrogen. At room temperature, it is a colorless non-flammable gas, with a slightly sweet odor and taste. It is used in surgery and dentistry for its anesthetic and analgesic...

 (N2O)
0.3 ppmv (0.00003%)
Carbon monoxide
Carbon monoxide
Carbon monoxide , also called carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal...

 (CO)
0.1 ppmv (0.00001%)
Xenon
Xenon
Xenon is a chemical element with the symbol Xe and atomic number 54. The element name is pronounced or . A colorless, heavy, odorless noble gas, xenon occurs in the Earth's atmosphere in trace amounts...

 (Xe)
0.09 ppmv (9%) (0.000009%)
Ozone
Ozone
Ozone , or trioxygen, is a triatomic molecule, consisting of three oxygen atoms. It is an allotrope of oxygen that is much less stable than the diatomic allotrope...

 (O3)
0.0 to 0.07 ppmv (0 to 7%)
Nitrogen dioxide
Nitrogen dioxide
Nitrogen dioxide is the chemical compound with the formula it is one of several nitrogen oxides. is an intermediate in the industrial synthesis of nitric acid, millions of tons of which are produced each year. This reddish-brown toxic gas has a characteristic sharp, biting odor and is a prominent...

 (NO2)
0.02 ppmv (2%) (0.000002%)
Iodine
Iodine
Iodine is a chemical element with the symbol I and atomic number 53. The name is pronounced , , or . The name is from the , meaning violet or purple, due to the color of elemental iodine vapor....

 (I2)
0.01 ppmv (1%) (0.000001%)
Ammonia
Ammonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...

 (NH3)
trace
Not included in above dry atmosphere:
Water vapor
Water vapor
Water vapor or water vapour , also aqueous vapor, is the gas phase of water. It is one state of water within the hydrosphere. Water vapor can be produced from the evaporation or boiling of liquid water or from the sublimation of ice. Under typical atmospheric conditions, water vapor is continuously...

 (H2O)
~0.40% over full atmosphere, typically 1%-4% at surface

Principal layers



In general, air pressure and density decrease in the atmosphere as height increases. However, temperature has a more complicated profile with altitude. Because the general pattern of this profile is constant and recognizable through means such as balloon soundings
Weather balloon
A weather or sounding balloon is a balloon which carries instruments aloft to send back information on atmospheric pressure, temperature, humidity and wind speed by means of a small, expendable measuring device called a radiosonde...

, temperature provides a useful metric to distinguish between atmospheric layers. In this way, Earth's atmosphere can be divided into five main layers. From highest to lowest, these layers are:

Exosphere



The outermost layer of Earth's atmosphere extends from the exobase upward. It is mainly composed of hydrogen and helium. The particles are so far apart that they can travel hundreds of kilometers without colliding with one another. Since the particles rarely collide, the atmosphere no longer behaves like a fluid. These free-moving particles follow ballistic trajectories and may migrate into and out of the magnetosphere
Magnetosphere
A magnetosphere is formed when a stream of charged particles, such as the solar wind, interacts with and is deflected by the intrinsic magnetic field of a planet or similar body. Earth is surrounded by a magnetosphere, as are the other planets with intrinsic magnetic fields: Mercury, Jupiter,...

 or the solar wind
Solar wind
The solar wind is a stream of charged particles ejected from the upper atmosphere of the Sun. It mostly consists of electrons and protons with energies usually between 1.5 and 10 keV. The stream of particles varies in temperature and speed over time...

.

Thermosphere



Temperature increases with height in the thermosphere from the mesopause up to the thermopause
Thermopause
The thermopause is the atmospheric boundary of Earth's energy system, located at the top of the thermosphere.Below this, the atmosphere is defined to be active on the insolation received, due to the increased presence of heavier gases such as monoatomic oxygen. The solar constant is thus expressed...

, then is constant with height. Unlike in the stratosphere, where the inversion is caused by absorption of radiation by ozone, in the thermosphere the inversion is a result of the extremely low density of molecules. The temperature of this layer can rise to 1500 °C (2,732 °F), though the gas molecules are so far apart that temperature in the usual sense
Kinetic theory
The kinetic theory of gases describes a gas as a large number of small particles , all of which are in constant, random motion. The rapidly moving particles constantly collide with each other and with the walls of the container...

 is not well defined. The air is so rarefied, that an individual molecule (of oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

, for example) travels an average of 1 kilometer between collisions with other molecules. The International Space Station
International Space Station
The International Space Station is a habitable, artificial satellite in low Earth orbit. The ISS follows the Salyut, Almaz, Cosmos, Skylab, and Mir space stations, as the 11th space station launched, not including the Genesis I and II prototypes...

 orbits in this layer, between 320 and 380 km (198.8 and 236.1 mi). Because of the relative infrequency of molecular collisions, air above the mesopause is poorly mixed compared to air below. While the composition from the troposphere to the mesosphere is fairly constant, above a certain point, air is poorly mixed and becomes compositionally stratified. The point dividing these two regions is known as the turbopause
Turbopause
The turbopause marks the altitude in the Earth's atmosphere below which turbulent mixing dominates. The region below the turbopause is known as the homosphere, where the chemical constituents are well mixed and display identical height distributions; in other words, the chemical composition of the...

. The region below is the homosphere, and the region above is the heterosphere. The top of the thermosphere is the bottom of the exosphere, called the exobase. Its height varies with solar activity and ranges from about 350 km (217.5 mi; 1,148,294 ft).

Mesosphere



The mesosphere extends from the stratopause to 80 km (49.7 mi; 262,467.2 ft). It is the layer where most meteor
METEOR
METEOR is a metric for the evaluation of machine translation output. The metric is based on the harmonic mean of unigram precision and recall, with recall weighted higher than precision...

s burn up upon entering the atmosphere. Temperature decreases with height in the mesosphere. The mesopause
Mesopause
The mesopause is the temperature minimum at the boundary between the mesosphere and the thermosphere atmospheric regions. Due to the lack of solar heating and very strong radiative cooling from carbon dioxide, the mesopause is the coldest place on Earth with temperatures as low as -100°C...

, the temperature minimum that marks the top of the mesosphere, is the coldest place on Earth and has an average temperature around -85 C. At the mesopause
Mesopause
The mesopause is the temperature minimum at the boundary between the mesosphere and the thermosphere atmospheric regions. Due to the lack of solar heating and very strong radiative cooling from carbon dioxide, the mesopause is the coldest place on Earth with temperatures as low as -100°C...

, temperatures may drop to -100 C. Due to the cold temperature of the mesosphere, water vapor is frozen, forming ice clouds (or Noctilucent cloud
Noctilucent cloud
Night clouds or Noctilucent clouds are tenuous cloud-like phenomena that are the "ragged-edge" of a much brighter and pervasive polar cloud layer called polar mesospheric clouds in the upper atmosphere, visible in a deep twilight. They are made of crystals of water ice. The name means roughly night...

s). A type of lightning referred to as either sprites
Sprite (lightning)
Sprites are large-scale electrical discharges that occur high above thunderstorm clouds, or cumulonimbus, giving rise to a quite varied range of visual shapes flickering in the night sky. They are triggered by the discharges of positive lightning between an underlying thundercloud and the...

 or ELVES, form many miles above thunderclouds in the troposphere.

Stratosphere



The stratosphere extends from the tropopause to about 51 km (31.7 mi; 167,322.8 ft). Temperature increases with height due to increased absorption of ultraviolet radiation by the ozone layer
Ozone layer
The ozone layer is a layer in Earth's atmosphere which contains relatively high concentrations of ozone . This layer absorbs 97–99% of the Sun's high frequency ultraviolet light, which is potentially damaging to the life forms on Earth...

, which restricts turbulence and mixing. While the temperature may be -60 C at the tropopause, the top of the stratosphere is much warmer, and may be near freezing. The stratopause
Stratopause
The stratopause is the level of the atmosphere which is the boundary between two layers, stratosphere and the mesosphere...

, which is the boundary between the stratosphere and mesosphere, typically is at 50 km (31.1 mi; 164,042 ft). The pressure here is 1/1000 sea level.

Troposphere



The troposphere begins at the surface and extends to between 9 km (29,527.6 ft) at the poles and 17 km (55,774.3 ft) at the equator, with some variation due to weather. The troposphere is mostly heated by transfer of energy from the surface, so on average the lowest part of the troposphere is warmest and temperature decreases with altitude. This promotes vertical mixing (hence the origin of its name in the Greek word "τροπή", trope, meaning turn or overturn). The troposphere contains roughly 80% of the mass of the atmosphere. The tropopause
Tropopause
The tropopause is the atmospheric boundary between the troposphere and the stratosphere.-Definition:Going upward from the surface, it is the point where air ceases to cool with height, and becomes almost completely dry...

 is the boundary between the troposphere and stratosphere.

Other layers


Within the five principal layers determined by temperature are several layers determined by other properties.
  • The ozone layer
    Ozone layer
    The ozone layer is a layer in Earth's atmosphere which contains relatively high concentrations of ozone . This layer absorbs 97–99% of the Sun's high frequency ultraviolet light, which is potentially damaging to the life forms on Earth...

     is contained within the stratosphere. In this layer ozone
    Ozone
    Ozone , or trioxygen, is a triatomic molecule, consisting of three oxygen atoms. It is an allotrope of oxygen that is much less stable than the diatomic allotrope...

     concentrations are about 2 to 8 parts per million, which is much higher than in the lower atmosphere but still very small compared to the main components of the atmosphere. It is mainly located in the lower portion of the stratosphere from about 15 km (9.3 mi; 49,212.6 ft), though the thickness varies seasonally and geographically. About 90% of the ozone in our atmosphere is contained in the stratosphere.

  • The ionosphere
    Ionosphere
    The ionosphere is a part of the upper atmosphere, comprising portions of the mesosphere, thermosphere and exosphere, distinguished because it is ionized by solar radiation. It plays an important part in atmospheric electricity and forms the inner edge of the magnetosphere...

    , the part of the atmosphere that is ionized by solar radiation, stretches from 50 km (31.1 mi; 164,042 ft) and typically overlaps both the exosphere and the thermosphere. It forms the inner edge of the magnetosphere. It has practical importance because it influences, for example, radio
    Radio
    Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...

     propagation on the Earth. It is responsible for aurora
    Aurora (astronomy)
    An aurora is a natural light display in the sky particularly in the high latitude regions, caused by the collision of energetic charged particles with atoms in the high altitude atmosphere...

    s.

  • The homosphere and heterosphere are defined by whether the atmospheric gases are well mixed. In the homosphere the chemical composition of the atmosphere does not depend on molecular weight because the gases are mixed by turbulence. The homosphere includes the troposphere, stratosphere, and mesosphere. Above the turbopause
    Turbopause
    The turbopause marks the altitude in the Earth's atmosphere below which turbulent mixing dominates. The region below the turbopause is known as the homosphere, where the chemical constituents are well mixed and display identical height distributions; in other words, the chemical composition of the...

    at about 100 km (62.1 mi; 328,084 ft) (essentially corresponding to the mesopause), the composition varies with altitude. This is because the distance that particles can move without colliding with one another
    Mean free path
    In physics, the mean free path is the average distance covered by a moving particle between successive impacts which modify its direction or energy or other particle properties.-Derivation:...

     is large compared with the size of motions that cause mixing. This allows the gases to stratify by molecular weight, with the heavier ones such as oxygen and nitrogen present only near the bottom of the heterosphere. The upper part of the heterosphere is composed almost completely of hydrogen, the lightest element.

  • The planetary boundary layer
    Planetary boundary layer
    The planetary boundary layer , also known as the atmospheric boundary layer , is the lowest part of the atmosphere and its behavior is directly influenced by its contact with a planetary surface. On Earth it usually responds to changes in surface forcing in an hour or less...

     is the part of the troposphere that is nearest the Earth's surface and is directly affected by it, mainly through turbulent diffusion
    Turbulence
    In fluid dynamics, turbulence or turbulent flow is a flow regime characterized by chaotic and stochastic property changes. This includes low momentum diffusion, high momentum convection, and rapid variation of pressure and velocity in space and time...

    . During the day the planetary boundary layer usually is well-mixed, while at night it becomes stably stratified with weak or intermittent mixing. The depth of the planetary boundary layer ranges from as little as about 100 m on clear, calm nights to 3000 m or more during the afternoon in dry regions.


The average temperature of the atmosphere at the surface of Earth is 14 °C (57.2 °F; 287.2 K) or 15 °C (59 °F; 288.2 K), depending on the reference.

Pressure and thickness


The average atmospheric pressure at sea level
Sea level
Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...

 is about 1 atmosphere (atm) = 101.3 kPa (kilopascals) = 14.7 psi (pounds per square inch) = 760 torr = 29.92 inches of mercury (symbol Hg). Total atmospheric mass is 5.1480×1018 kg (1.135×1019 lb), about 2.5% less than would be inferred from the average sea level pressure and the Earth's area of 51007.2 megahectares, this portion being displaced by the Earth's mountainous terrain. Atmospheric pressure is the total weight of the air above unit area at the point where the pressure is measured. Thus air pressure varies with location and weather.

If atmospheric density were to remain constant with height the atmosphere would terminate abruptly at 8.5 km (27,887.1 ft). Instead, density decreases with height, dropping by 50% at an altitude of about 5.6 km (18,372.7 ft). As a result the pressure decrease is approximately exponential with height, so that pressure decreases by a factor of two approximately every 5.6 km (18,372.7 ft) and by a factor of e = 2.718… approximately every 7.64 km (25,065.6 ft), the latter being the average scale height
Scale height
In various scientific contexts, a scale height is a distance over which a quantity decreases by a factor of e...

 of Earth's atmosphere below 70 km (43.5 mi; 229,658.8 ft). However, because of changes in temperature, average molecular weight, and gravity throughout the atmospheric column, the dependence of atmospheric pressure on altitude is modeled by separate equations for each of the layers listed above. Even in the exosphere, the atmosphere is still present. This can be seen by the effects of atmospheric drag on satellite
Satellite
In the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavour. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon....

s.

In summary, the equations of pressure by altitude in the above references can be used directly to estimate atmospheric thickness. However, the following published data are given for reference:
  • 50% of the atmosphere by mass is below an altitude of 5.6 km (18,372.7 ft).
  • 90% of the atmosphere by mass is below an altitude of 16 km (52,493.4 ft). The common altitude of commercial airliners is about 10 km (32,808.4 ft) and Mt. Everest's summit is 8848 m (29,028.9 ft) above sea level.
  • 99.99997% of the atmosphere by mass is below 100 km (62.1 mi; 328,084 ft), although in the rarefied region above this there are aurora
    Aurora (astronomy)
    An aurora is a natural light display in the sky particularly in the high latitude regions, caused by the collision of energetic charged particles with atoms in the high altitude atmosphere...

    s and other atmospheric effects. The highest X-15
    North American X-15
    The North American X-15 rocket-powered aircraft/spaceplane was part of the X-series of experimental aircraft, initiated with the Bell X-1, that were made for the USAAF/USAF, NACA/NASA, and the USN. The X-15 set speed and altitude records in the early 1960s, reaching the edge of outer space and...

     plane flight in 1963 reached an altitude of 108 km (354,330.7 ft).

Density and mass




The density of air at sea level is about 1.2  kg/m3 (1.2 g/L). Density is not measured directly but is calculated from measurements of temperature, pressure and humidity using the equation of state for air (a form of the ideal gas law
Ideal gas law
The ideal gas law is the equation of state of a hypothetical ideal gas. It is a good approximation to the behavior of many gases under many conditions, although it has several limitations. It was first stated by Émile Clapeyron in 1834 as a combination of Boyle's law and Charles's law...

). Atmospheric density decreases as the altitude increases. This variation can be approximately modeled using the barometric formula
Barometric formula
The barometric formula, sometimes called the exponential atmosphere or isothermal atmosphere, is a formula used to model how the pressure of the air changes with altitude.-Pressure equations:...

. More sophisticated models are used to predict orbital decay of satellites.

The average mass of the atmosphere is about 5 quadrillion (5) tonne
Tonne
The tonne, known as the metric ton in the US , often put pleonastically as "metric tonne" to avoid confusion with ton, is a metric system unit of mass equal to 1000 kilograms. The tonne is not an International System of Units unit, but is accepted for use with the SI...

s or 1/1,200,000 the mass of Earth. According to the American National Center for Atmospheric Research
National Center for Atmospheric Research
The National Center for Atmospheric Research has multiple facilities, including the I. M. Pei-designed Mesa Laboratory headquarters in Boulder, Colorado. NCAR is managed by the nonprofit University Corporation for Atmospheric Research and sponsored by the National Science Foundation...

, "The total mean mass of the atmosphere is 5.1480 kg with an annual range due to water vapor of 1.2 or 1.5 kg depending on whether surface pressure or water vapor data are used; somewhat smaller than the previous estimate. The mean mass of water vapor is estimated as 1.27 kg and the dry air mass as 5.1352 ±0.0003 kg."

Optical properties


Solar radiation
Radiation
In physics, radiation is a process in which energetic particles or energetic waves travel through a medium or space. There are two distinct types of radiation; ionizing and non-ionizing...

 (or sunlight) is the energy the Earth receives from the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

. The Earth also emits radiation back into space, but at longer wavelengths that we cannot see. Part of the incoming and emitted radiation is absorbed or reflected by the atmosphere.

Scattering


When light passes through our atmosphere, photon
Photon
In physics, a photon is an elementary particle, the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation. It is also the force carrier for the electromagnetic force...

s interact with it through scattering. If the light does not interact with the atmosphere, it is called direct radiation and is what you see if you were to look directly at the Sun. Indirect radiation is light that has been scattered in the atmosphere. For example, on an overcast
Overcast
Overcast or overcast weather, as defined by the World Meteorological Organization, is the meteorological condition of clouds obscuring all of the sky. Overcast, written as "OVC" in the METAR observation, is reported when the cloud cover is observed to equal eight oktas .Sometimes clouds can be...

 day when you cannot see your shadow there is no direct radiation reaching you, it has all been scattered. As another example, due to a phenomenon called Rayleigh scattering
Rayleigh scattering
Rayleigh scattering, named after the British physicist Lord Rayleigh, is the elastic scattering of light or other electromagnetic radiation by particles much smaller than the wavelength of the light. The particles may be individual atoms or molecules. It can occur when light travels through...

, shorter (blue) wavelengths scatter more easily than longer (red) wavelengths. This is why the sky looks blue, you are seeing scattered blue light. This is also why sunset
Sunset
Sunset or sundown is the daily disappearance of the Sun below the horizon in the west as a result of Earth's rotation.The time of sunset is defined in astronomy as the moment the trailing edge of the Sun's disk disappears below the horizon in the west...

s are red. Because the Sun is close to the horizon, the Sun's rays pass through more atmosphere than normal to reach your eye. Much of the blue light has been scattered out, leaving the red light in a sunset.

Absorption



Different molecules absorb different wavelengths of radiation. For example, O2 and O3 absorb almost all wavelengths shorter than 300 nanometers. Water (H2O) absorbs many wavelengths above 700 nm. When a molecule absorbs a photon, it increases the energy of the molecule. We can think of this as heating the atmosphere, but the atmosphere also cools by emitting radiation, as discussed below.

The combined absorption spectra of the gases in the atmosphere leave "windows" of low opacity
Opacity (optics)
Opacity is the measure of impenetrability to electromagnetic or other kinds of radiation, especially visible light. In radiative transfer, it describes the absorption and scattering of radiation in a medium, such as a plasma, dielectric, shielding material, glass, etc...

, allowing the transmission of only certain bands of light. The optical window
Optical window
The meaning of this term depends on the context:* In astronomy, the optical window is the optical portion of the electromagnetic spectrum that passes through the atmosphere all the way to the ground...

 runs from around 300 nm (ultraviolet
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...

-C) up into the range humans can see, the visible spectrum
Visible spectrum
The visible spectrum is the portion of the electromagnetic spectrum that is visible to the human eye. Electromagnetic radiation in this range of wavelengths is called visible light or simply light. A typical human eye will respond to wavelengths from about 390 to 750 nm. In terms of...

 (commonly called light
Light
Light or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...

), at roughly 400–700 nm and continues to the infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...

 to around 1100 nm. There are also infrared and radio window
Radio window
The radio window is the range of frequencies of electromagnetic radiation that the earth's atmosphere lets through. The wavelengths in the radio window run from about one centimetre to about eleven-metre waves.-See also:*Astronomical window...

s that transmit some infrared and radio waves
Radio waves
Radio waves are a type of electromagnetic radiation with wavelengths in the electromagnetic spectrum longer than infrared light. Radio waves have frequencies from 300 GHz to as low as 3 kHz, and corresponding wavelengths from 1 millimeter to 100 kilometers. Like all other electromagnetic waves,...

 at longer wavelengths. For example, the radio window runs from about one centimeter to about eleven-meter waves.

Emission



Emission is the opposite of absorption, it is when an object emits radiation. Objects tend to emit amounts and wavelengths of radiation depending on their "black body
Black body
A black body is an idealized physical body that absorbs all incident electromagnetic radiation. Because of this perfect absorptivity at all wavelengths, a black body is also the best possible emitter of thermal radiation, which it radiates incandescently in a characteristic, continuous spectrum...

" emission curves, therefore hotter objects tend to emit more radiation, with shorter wavelengths. Colder objects emit less radiation, with longer wavelengths. For example, the Sun is approximately 6000 K, its radiation peaks near 500 nm, and is visible to the human eye. The Earth is approximately 290 K, so its radiation peaks near 10,000 nm, and is much too long to be visible to humans.

Because of its temperature, the atmosphere emits infrared radiation. For example, on clear nights the Earth's surface cools down faster than on cloud
Cloud
A cloud is a visible mass of liquid droplets or frozen crystals made of water and/or various chemicals suspended in the atmosphere above the surface of a planetary body. They are also known as aerosols. Clouds in Earth's atmosphere are studied in the cloud physics branch of meteorology...

y nights. This is because clouds (H2O) are strong absorbers and emitters of infrared radiation. This is also why it becomes colder at night at higher elevations. The atmosphere acts as a "blanket" to limit the amount of radiation the Earth loses into space.

The greenhouse effect is directly related to this absorption and emission (or "blanket") effect. Some chemicals in the atmosphere absorb and emit infrared radiation, but do not interact with sunlight in the visible spectrum. Common examples of these chemicals are CO2 and H2O. If there are too much of these greenhouse gases, sunlight heats the Earth's surface, but the gases block the infrared radiation from exiting back to space. This imbalance causes the Earth to warm, and thus climate change
Climate change
Climate change is a significant and lasting change in the statistical distribution of weather patterns over periods ranging from decades to millions of years. It may be a change in average weather conditions or the distribution of events around that average...

.

Refractive index


The refractive index
Refractive index
In optics the refractive index or index of refraction of a substance or medium is a measure of the speed of light in that medium. It is expressed as a ratio of the speed of light in vacuum relative to that in the considered medium....

 of air is close to, but just greater than 1. Systematic variations in refractive index can lead to the bending of light rays over long optical paths. One example is that, under some circumstances, observers onboard ships can see other vessels just over the horizon
Horizon
The horizon is the apparent line that separates earth from sky, the line that divides all visible directions into two categories: those that intersect the Earth's surface, and those that do not. At many locations, the true horizon is obscured by trees, buildings, mountains, etc., and the resulting...

 because light is refracted in the same direction as the curvature
Curvature
In mathematics, curvature refers to any of a number of loosely related concepts in different areas of geometry. Intuitively, curvature is the amount by which a geometric object deviates from being flat, or straight in the case of a line, but this is defined in different ways depending on the context...

 of the Earth's surface.

The refractive index of air depends on temperature, giving rise to refraction effects when the temperature gradient is large. An example of such effects is the mirage
Mirage
A mirage is a naturally occurring optical phenomenon in which light rays are bent to produce a displaced image of distant objects or the sky. The word comes to English via the French mirage, from the Latin mirare, meaning "to look at, to wonder at"...

.

Circulation



Atmospheric circulation is the large-scale movement of air through the troposphere, and the means (with ocean circulation) by which heat
Heat
In physics and thermodynamics, heat is energy transferred from one body, region, or thermodynamic system to another due to thermal contact or thermal radiation when the systems are at different temperatures. It is often described as one of the fundamental processes of energy transfer between...

 is distributed around the Earth. The large-scale structure of the atmospheric circulation varies from year to year, but the basic structure remains fairly constant as it is determined by the Earth's rotation rate and the difference in solar radiation between the equator and poles.

Earliest atmosphere


The outgassings of the Earth were stripped away by solar winds early in the history of the planet until a steady state was established, the first atmosphere. Based on today's volcanic evidence, this atmosphere would have contained 60% hydrogen, 20% oxygen (mostly in the form of water vapor),

10% carbon dioxide, 5 to 7% hydrogen sulfide, and smaller amounts of nitrogen, carbon monoxide, free hydrogen, methane and inert gases.

A major rainfall led to the buildup of a vast ocean, enriching the other agents, first carbon dioxide and later nitrogen and inert gases. A major part of carbon dioxide exhalations were soon dissolved in water and built up carbonate sediments.

Second atmosphere


Water-related sediments have been found dating from as early as 3.8 billion years ago. About 3.4 billion years ago, nitrogen was the major part of the then stable "second atmosphere". An influence of life has to be taken into account rather soon in the history of the atmosphere, since hints of early life forms are to be found as early as 3.5 billion years ago. The fact that this is not perfectly in line with the 30% lower solar radiance (compared to today) of the early Sun has been described as the "faint young Sun paradox
Faint young Sun paradox
The faint young Sun paradox or problem describes the apparent contradiction between observations of liquid water early in the Earth's history and the astrophysical expectation that the Sun's output would be only 70% as intense during that epoch as it is during the modern epoch. The issue was raised...

".

The geological record however shows a continually relatively warm surface during the complete early temperature record
Temperature record
The temperature record shows the fluctuations of the temperature of the atmosphere and the oceans through various spans of time. The most detailed information exists since 1850, when methodical thermometer-based records began. There are numerous estimates of temperatures since the end of the...

 of the Earth with the exception of one cold glacial phase about 2.4 billion years ago. In the late Archaean eon an oxygen-containing atmosphere began to develop, apparently from photosynthesizing algae which have been found as stromatolite
Stromatolite
Stromatolites or stromatoliths are layered accretionary structures formed in shallow water by the trapping, binding and cementation of sedimentary grains by biofilms of microorganisms, especially cyanobacteria ....

 fossils from 2.7 billion years ago. The early basic carbon isotopy (isotope ratio proportions) is very much in line with what is found today, suggesting that the fundamental features of the carbon cycle
Carbon cycle
The carbon cycle is the biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of the Earth...

 were established as early as 4 billion years ago.

Third atmosphere


The accretion of continents about 3.5 billion years ago added plate tectonics
Plate tectonics
Plate tectonics is a scientific theory that describes the large scale motions of Earth's lithosphere...

, constantly rearranging the continents and also shaping long-term climate evolution by allowing the transfer of carbon dioxide to large land-based carbonate storages. Free oxygen did not exist until about 1.7 billion years ago and this can be seen with the development of the red beds and the end of the banded iron formations. This signifies a shift from a reducing atmosphere to an oxidising atmosphere. O2 showed major ups and downs until reaching a steady state of more than 15%. The following time span was the Phanerozoic
Phanerozoic
The Phanerozoic Eon is the current eon in the geologic timescale, and the one during which abundant animal life has existed. It covers roughly 542 million years and goes back to the time when diverse hard-shelled animals first appeared...

 eon, during which oxygen-breathing metazoan life forms began to appear.

Currently, anthropogenic greenhouse gases are increasing in the atmosphere. According to the Intergovernmental Panel on Climate Change
Intergovernmental Panel on Climate Change
The Intergovernmental Panel on Climate Change is a scientific intergovernmental body which provides comprehensive assessments of current scientific, technical and socio-economic information worldwide about the risk of climate change caused by human activity, its potential environmental and...

, this increase is the main cause of global warming
Global warming
Global warming refers to the rising average temperature of Earth's atmosphere and oceans and its projected continuation. In the last 100 years, Earth's average surface temperature increased by about with about two thirds of the increase occurring over just the last three decades...

.

Air pollution


Air pollution is the introduction of chemicals, particulate matter, or biological material
Biological material
Biological material may refer to:* Tissue , or just tissue* Biomass, living or dead biological matter, often plants grown as fuel* Biomass , the total mass of living biological matter* Biomaterials...

s that cause harm or discomfort to organisms into the atmosphere. Stratospheric
Stratosphere
The stratosphere is the second major layer of Earth's atmosphere, just above the troposphere, and below the mesosphere. It is stratified in temperature, with warmer layers higher up and cooler layers farther down. This is in contrast to the troposphere near the Earth's surface, which is cooler...

 ozone depletion
Ozone depletion
Ozone depletion describes two distinct but related phenomena observed since the late 1970s: a steady decline of about 4% per decade in the total volume of ozone in Earth's stratosphere , and a much larger springtime decrease in stratospheric ozone over Earth's polar regions. The latter phenomenon...

 is believed to be caused by air pollution (chiefly from chlorofluorocarbons).

See also



  • Aerial perspective
    Aerial perspective
    Aerial perspective or atmospheric perspective refers to the effect the atmosphere has on the appearance of an object as it is viewed from a distance. As the distance between an object and a viewer increases, the contrast between the object and its background decreases, and the contrast of any...

  • Air glow
  • Air (music)
    Air (music)
    Air , a variant of the musical song form, is the name of various song-like vocal or instrumental compositions.-English lute ayres:...

  • Airshed
    Airshed
    An airshed is a part of the atmosphere that behaves in a coherent way with respect to the dispersion of emissions. It typically forms an analytical or management unit.Also: A geographic boundary for air quality standards.-External links:*...

  • Atmosphere
    Atmosphere
    An atmosphere is a layer of gases that may surround a material body of sufficient mass, and that is held in place by the gravity of the body. An atmosphere may be retained for a longer duration, if the gravity is high and the atmosphere's temperature is low...

     (for information on atmospheres in general)
  • Atmospheric dispersion modeling
    Atmospheric dispersion modeling
    Atmospheric dispersion modeling is the mathematical simulation of how air pollutants disperse in the ambient atmosphere. It is performed with computer programs that solve the mathematical equations and algorithms which simulate the pollutant dispersion...

  • Atmospheric electricity
    Atmospheric electricity
    Atmospheric electricity is the regular diurnal variations of the Earth's atmospheric electromagnetic network . The Earth's surface, the ionosphere, and the atmosphere is known as the global atmospheric electrical circuit...

  • Atmospheric models
    Atmospheric models
    Static atmospheric models describe how the ideal gas properties of an atmosphere change, primarily as a function of altitude....

  • Atmospheric Radiation Measurement
    Atmospheric Radiation Measurement
    The United States Department of Energy's Atmospheric Radiation Measurement Program was created in 1989 to develop several highly instrumented ground stations to study cloud formation processes and their influence on radiative transfer...

     (ARM) (in the U.S.)
  • Atmospheric stratification
  • Aviation
    Aviation
    Aviation is the design, development, production, operation, and use of aircraft, especially heavier-than-air aircraft. Aviation is derived from avis, the Latin word for bird.-History:...

  • Biosphere
    Biosphere
    The biosphere is the global sum of all ecosystems. It can also be called the zone of life on Earth, a closed and self-regulating system...

  • Carbon dioxide in the Earth's atmosphere
    Carbon dioxide in the Earth's atmosphere
    The concentration of carbon dioxide in Earth's atmosphere is approximately 392 ppm by volume and rose by 2.0 ppm/yr during 2000–2009. 40 years earlier, the rise was only 0.9 ppm/yr, showing not only increasing concentrations, but also a rapid acceleration of concentrations...

  • Compressed air
    Compressed air
    Compressed air is air which is kept under a certain pressure, usually greater than that of the atmosphere. In Europe, 10 percent of all electricity used by industry is used to produce compressed air, amounting to 80 terawatt hours consumption per year....

  • Environmental impact of aviation
  • Global dimming
    Global dimming
    Global dimming is the gradual reduction in the amount of global direct irradiance at the Earth's surface that was observed for several decades after the start of systematic measurements in the 1950s. The effect varies by location, but worldwide it has been estimated to be of the order of a 4%...

  • Historical temperature record
  • Hydrosphere
    Hydrosphere
    A hydrosphere in physical geography describes the combined mass of water found on, under, and over the surface of a planet....

  • Hypermobility (travel)
    Hypermobility (travel)
    The term hypermobility in regard to travelers arose around 1980 and is a concept that has increased in useage since the early 1990s: Damette ; Hepworth and Ducatel ; Whitelegg ; Lowe ; van der Stoep ; Shields ; Cox ; Adams ; Khisty and Zeitler ; Gössling et al. ; and Mander & Randles...

  • Kyoto Protocol
    Kyoto Protocol
    The Kyoto Protocol is a protocol to the United Nations Framework Convention on Climate Change , aimed at fighting global warming...

  • Lithosphere
    Lithosphere
    The lithosphere is the rigid outermost shell of a rocky planet. On Earth, it comprises the crust and the portion of the upper mantle that behaves elastically on time scales of thousands of years or greater.- Earth's lithosphere :...

  • Standard Dry Air
  • COSPAR international reference atmosphere
    COSPAR international reference atmosphere
    The COSPAR International Reference Atmosphere is an empirical model of the atmosphere of Earth. It consists of a set of tables of average air pressures, altitudes and temperatures...

     (CIRA)
  • U.S. Standard Atmosphere
  • Warm period
  • Water vapor in Earth's atmosphere


External links