Water vapor

Clouds, formed by condensed water vapor
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Evidence for increasing amounts of stratospheric water vapor over time in Boulder, Colorado.
MODIS/Terra global mean atmospheric water vapor in atm-cm (centimeters of water in an atmospheric column if it condensed)
Cryogeyser erupting on Jupiter's moon Europa (artist concept)
Artist's illustration of the signatures of water in exoplanet atmospheres detectable by instruments such as the Hubble Space Telescope.

Gaseous phase of water.

- Water vapor

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Greenhouse gas

Gas that absorbs and emits radiant energy within the thermal infrared range, causing the greenhouse effect.

The greenhouse effect of solar radiation on the Earth's surface caused by emission of greenhouse gases.
Radiative forcing (warming influence) of different contributors to climate change through 2019, as reported in the Sixth IPCC assessment report.
Atmospheric absorption and scattering at different wavelengths of electromagnetic waves. The largest absorption band of carbon dioxide is not far from the maximum in the thermal emission from ground, and it partly closes the window of transparency of water; hence its major effect.
Concentrations of carbon monoxide in the Spring and Fall of 2000 in the lower atmosphere showing a range from about 390 parts per billion (dark brown pixels), to 220 parts per billion (red pixels), to 50 parts per billion (blue pixels).
Increasing water vapor in the stratosphere at Boulder, Colorado
Schmidt et al. (2010) analysed how individual components of the atmosphere contribute to the total greenhouse effect. They estimated that water vapor accounts for about 50% of Earth's greenhouse effect, with clouds contributing 25%, carbon dioxide 20%, and the minor greenhouse gases and aerosols accounting for the remaining 5%. In the study, the reference model atmosphere is for 1980 conditions. Image credit: NASA.
The radiative forcing (warming influence) of long-lived atmospheric greenhouse gases has accelerated, almost doubling in 40 years.
Top: Increasing atmospheric carbon dioxide levels as measured in the atmosphere and reflected in ice cores. Bottom: The amount of net carbon increase in the atmosphere, compared to carbon emissions from burning fossil fuel.
400,000 years of ice core data
Recent year-to-year increase of atmospheric.
Major greenhouse gas trends.
The US, China and Russia have cumulatively contributed the greatest amounts of since 1850.

The primary greenhouse gases in Earth's atmosphere are water vapor, carbon dioxide , methane , nitrous oxide , and ozone.

Atmosphere of Earth

Layer of gases retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere.

NASA photo showing Earth's atmosphere at sunset, with Earth silhouetted
Composition of Earth's atmosphere by molecular count, excluding water vapor. Lower pie represents trace gases that together compose about 0.0434% of the atmosphere (0.0442% at August 2021 concentrations ). Numbers are mainly from 2000, with and methane from 2019, and do not represent any single source.
Mean atmospheric water vapor
The mole fraction of the main constituents of the Earth's atmosphere as a function of height according to the MSIS-E-90 atmospheric model.
Earth's atmosphere Lower 4 layers of the atmosphere in 3 dimensions as seen diagonally from above the exobase. Layers drawn to scale, objects within the layers are not to scale. Aurorae shown here at the bottom of the thermosphere can actually form at any altitude in this atmospheric layer.
orbiting in the thermosphere. Because of the angle of the photo, it appears to straddle the stratosphere and mesosphere that actually lie more than 250 km below. The orange layer is the troposphere, which gives way to the whitish stratosphere and then the blue mesosphere.
Temperature trends in two thick layers of the atmosphere as measured between January 1979 and December 2005 by microwave sounding units and advanced microwave sounding units on NOAA weather satellites. The instruments record microwaves emitted from oxygen molecules in the atmosphere. Source:
Temperature and mass density against altitude from the NRLMSISE-00 standard atmosphere model (the eight dotted lines in each "decade" are at the eight cubes 8, 27, 64, ..., 729)
Rough plot of Earth's atmospheric transmittance (or opacity) to various wavelengths of electromagnetic radiation, including visible light.
Distortive effect of atmospheric refraction upon the shape of the sun at the horizon.
An idealised view of three pairs of large circulation cells.
Oxygen content of the atmosphere over the last billion years

Air also contains a variable amount of water vapor, on average around 1% at sea level, and 0.4% over the entire atmosphere.

Precipitation

Mean precipitation based on global high resolution climate data (CHELSA)
Countries by average annual precipitation
A thunderstorm with heavy precipitation
Late-summer rainstorm in Denmark
Lenticular cloud forming due to mountains over Wyoming
Condensation and coalescence are important parts of the water cycle.
Puddle in the rain
An accumulation of ice pellets
A large hailstone, about 6 cm in diameter
Snowflake viewed in an optical microscope
Convective precipitation
Orographic precipitation
Lake-effect snow bands near the Korean Peninsula in early December 2008
Rainfall distribution by month in Cairns showing the extent of the wet season at that location
Standard rain gauge
Updated Köppen-Geiger climate map
Rainfall estimates for southern Japan and the surrounding region from July 20 to 27, 2009.
Extreme precipitation events have become more common in the U.S. over recent decades.
Image of Atlanta, Georgia, showing temperature distribution, with hot areas appearing white
Example of a five-day rainfall forecast from the Hydrometeorological Prediction Center

In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds.

Humidity

Paranal Observatory on Cerro Paranal in the Atacama Desert is one of the driest places on Earth.
A hygrothermograph for humidity and temperature recording
Hygrometer for domestic use, wet/dry psychrometer type
Thermo hygrometer displaying temperature and relative humidity
Hygrostat set to 50% relative humidity
Humidor, used to control humidity of cigars
Average humidity around Australia year-round at 9 am
Tillandsia usneoides in Tropical house, Royal Botanic Gardens, Kew. It is growing where the climate is warm enough and has a relatively high average humidity.
Effects of high humidity level in a building structure (primary efflorescence)
Desiccant bag (silica gel), commonly included in packages containing electronic products to control humidity

Humidity is the concentration of water vapour present in the air.

Sublimation (phase transition)

Transition of a substance directly from the solid to the gas state, without passing through the liquid state.

Dark green crystals of nickelocene, sublimed and freshly deposited on a cold finger
Comparison of phase diagrams of carbon dioxide (red) and water (blue) showing the carbon dioxide sublimation point (middle-left) at 1 atmosphere. As dry ice is heated, it crosses this point along the bold horizontal line from the solid phase directly into the gaseous phase. Water, on the other hand, passes through a liquid phase at 1 atmosphere.
Dry ice subliming in air
Experimental set up for the sublimation reaction of naphthalene Solid naphthalene sublimes and form the crystal-like structure at the bottom of the watch glass
Solid compound of naphthalene sublimed to form a crystal-like structure on the cool surface.
Camphor subliming in a cold finger. The crude product in the bottom is dark brown; the white purified product on the bottom of the cold finger above is hard to see against the light background.
Crystals of ferrocene after purification by vacuum sublimation

Similarly the combustion of candles, containing paraffin wax, to carbon dioxide and water vapor is not sublimation but a chemical reaction with oxygen.

Hydrosphere

Combined mass of water found on, under, and above the surface of a planet, minor planet, or natural satellite.

The Pacific Ocean, part of Earth's hydrosphere
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At any given time, about 2 × 1013 tonnes of this is in the form of water vapor in the Earth's atmosphere (for practical purposes, 1 cubic metre of water weighs 1 tonne).

Ice

Water frozen into a solid state, typically forming at or below temperatures of 0 degrees Celsius or 32 degrees Fahrenheit.

The three-dimensional crystal structure of H2O ice Ih (c) is composed of bases of H2O ice molecules (b) located on lattice points within the two-dimensional hexagonal space lattice (a).
Pressure dependence of ice melting
Log-lin pressure-temperature phase diagram of water. The Roman numerals correspond to some ice phases listed below.
An alternative formulation of the phase diagram for certain ices and other phases of water
Frozen waterfall in southeast New York
Feather ice on the plateau near Alta, Norway. The crystals form at temperatures below −30 °C (−22 °F).
Ice on deciduous tree after freezing rain
A small frozen rivulet
Ice formation on exterior of vehicle windshield
An accumulation of ice pellets
A large hailstone, about 6 cm in diameter
Snowflakes by Wilson Bentley, 1902.
Harvesting ice on Lake St. Clair in Michigan, c. 1905
Layout of a late 19th-Century ice factory
Loss of control on ice by an articulated bus
Channel through ice for ship traffic on Lake Huron with ice breakers in background
Rime ice on the leading edge of an aircraft wing, partially released by the black pneumatic boot.
Skating fun by 17th century Dutch painter Hendrick Avercamp
Ice pier during 1983 cargo operations. McMurdo Station, Antarctica

It may also be deposited directly by water vapor, as happens in the formation of frost.

Dew point

This graph shows the maximum percentage, by mass, of water vapor that air at sea-level pressure across a range of temperatures can contain. For a lower ambient pressure, a curve has to be drawn above the current curve. A higher ambient pressure yields a curve under the current curve.
Graph of the dependence of the dew point upon air temperature for several levels of relative humidity.

The dew point is the temperature to which air must be cooled to become saturated with water vapor, assuming constant air pressure and water content.

Frost

A patch of grass showing crystalline frost in the below-freezing shade (blue, lower right); frost in the warming but still below freezing strip most recently exposed to sunlight (white, center); and a frost-free region: here, the previous frost has melted from a more prolonged exposure to sunlight (green, upper left.)
Frost in the highest town in Venezuela, Apartaderos: Because of its location in an alpine tundra ecosystem called páramo, a daily freeze-and-thaw cycle, sometimes described as "summer every day and winter every night", exists.
A spider web covered in air hoar frost
Hoar frost on the snow
Depth hoar, imaged with optical (left) and scanning electron (right) microscopy
A flower with advection frost on the edges of its petals
Frost patterns that developed on glass of a cold frame.
Dead plant leaves during Winter Storm Uri in a backyard in Northern Mexico, with below freezing temperatures.
Frost on the grass of a public park in November
Map of average first killing frost in Ohio from "Geography of Ohio," 1923
Roses with protection against frost - Volksgarten, Vienna
Curitiba (Southern Brazil) is the coldest of Brazil's state capitals; the greenhouse of the Botanical Garden of Curitiba protects sensitive plants.
Frost on a nettle
Large feathery crystals
Fern frost on a window
Window frost
Frost on plant leaves in the Himalayas
Surface hoar in Alaska
Hoar frost in Julian Alps
Frost on birch tree in Stockholm
Frost on grass in Ranu Pani, East Java, Indonesia
Frost on birch stem in Norway
Frost on grass in Sydney
An oak leaf with frost in Sweden

Frost is a thin layer of ice on a solid surface, which forms from water vapor in an above-freezing atmosphere coming in contact with a solid surface whose temperature is below freezing, and resulting in a phase change from water vapor (a gas) to ice (a solid) as the water vapor reaches the freezing point.

Hygrometer

A hair tension dial hygrometer with a nonlinear scale.
Deluc's hair tension whalebone hygrometer (MHS Geneva)
The interior of a Stevenson screen showing a motorized psychrometer
Psychrometer probably made in Switzerland circa 1850 by Kappeller (MHS Geneva)
A sling psychrometer for outdoor use

A hygrometer is an instrument used to measure the amount of water vapor in air, in soil, or in confined spaces.