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Calcite is a form of calcium carbonate (*CaCO*_{3}). It is one of the most widely distributed
minerals on Earth and is a constituent of sedimentary rocks, in particular limestone. See section 2.3.2.2.

The calcite compensation depth (CCD) is the depth at which the input of calcite from sedimentation exactly balances the dissolution at the top of the sediments. At the CCD there is thus very little calcite left in the old sediment, because it has all dissolved. See section 4.3.1.

Calibration is the adjustment of the numerical or physical parameters in a model to improve the agreement between the results of the model and observations.

The canopy is the above-ground portion of a plant community formed by plant crowns.

Carbonate compensation is a negative feedback between the oceanic carbon cycle
and the underlying sediments that tends to reduce the variations in the
alkalinity in the ocean and thus to stabilise the atmospheric CO_{2}
over long timescales. See section 4.3.1.

The carbonate pump is a net downward flux of carbon associated with the transport of calcium carbonate from the surface layer, where it is produced because of biological activity, to the deeper layers where it could be dissolved. See sections 2.3.2.2, 4.3.1 and 5.4.3 and see also soft tissue pump.

The celestial equator is the projection of the Earth's equator onto the celestial sphere. See section 2.1.3.2.

The celestial equator. Source: NASA. Following the policy of U.S. government agencies, this figure is not subject to copyright protection.

The celestial sphere is an imaginary sphere with a very large radius whose centre is the centre of the Earth. See section 2.1.3.1.

Chlorofluorocarbons (or CFCs) are gases derived from alkanes (e.g., methane or ethane) in which all the hydrogen atoms have been replaced by chlorine or fluorine. They are a subset of the halocarbons. Chlorofluorocarbons have been widely used in refrigerators, insulation and aerosol spray cans. However, because they have been shown to contribute to stratospheric ozone depletion, their use is now banned.

The Clausius-Clapeyron equation gives the relationship between the
latent heat associated with a transition from Phase 1 to Phase 2 (${L}_{1\to 2}$
(*T*)) at the equilibrium temperature *T*, the volume
*V*_{1}(*T*, *P*) of the matter in Phase 1, the volume
*V*_{2}(*T*, *P*) of the matter in
Phase 2 and the slope of the line separating the two phases in a T-P diagram (i.e.
*dP*/*dT*)

$${L}_{1\to 2}\left(T\right)=T\left({V}_{2}\left(T,P\right)-{V}_{1}\left(T,P\right)\right)\frac{dP}{dT}$$

For the transition between the liquid and vapour phase in the atmosphere, the Clausius- Clapeyron equation can be written as:

$${L}_{v}\left(T\right)=T\left({V}_{\mathrm{vapour}}-{V}_{\mathrm{liquid}}\right)\frac{d{e}_{s}}{dT}$$
where *V*_{vapour} and *V*_{liquid} are the volumes of the water in the
vapour and liquid phases, and e_{s} is the saturation vapour pressure.
This relationship can be used to compute the variation of es as a function of temperature:

If we consider water vapour as a perfect gas, the volume of the vapour is much larger
than that of the liquid, and if we also assume that *L*_{v} is a constant (which is a strong approximation),
we can express *e*_{s} as a function of the
temperature *T* by integrating this equation between
273.15*K* (for which *e*_{s} = 611 Pa) and the
temperature *T* :

where *R*_{v} is the gas constant for water
vapour (461.39J.kg^{-1}.K^{-1}). This
relationship can be used to compute the specific humidity at saturation
*q*_{sat}, using the relationship between the
saturation vapour pressure and
humidity and knowing the air pressure p (*q*_{sat}
$\simeq $ 0.622 *e*_{sat}/*p*). See sections 2.1.6, 2.2 and 4.2.1.

Climate is traditionally defined as the description, in terms of the mean and variability over a 30-year reference period, of the relevant atmospheric variables (temperature, precipitation, winds). In a wider sense, it is the statistical description of the climate system. See section 1.1.

A climate model is a simplified representation of the climate system, generally in the form of a set of mathematical equations. See section 3.1.1.

See equilibrium climate sensitivity.

The climate system consists of five major components: the atmosphere, the hydrosphere, the cryosphere, the land surface and the biosphere. See section 1.1.

Climatic precession ( ecc sin $\tilde{\omega}$) is related to the distance between the Earth and the Sun at the summer solstice. See section 5.4.1.

The climatological value of a variable is its mean over a reference period (generally 30 years). See section 1.1.

Cloud microphysics describes the physical processes that occur in clouds at scales smaller than a few centimetres. See section 4.2.2.

The cloud radiative forcing (CRF) is a measure of the effect of clouds on the Earth’s
radiation budget. It could be evaluated by computing the difference of the radiative fluxes
at the top of the atmosphere with and without clouds. CRF is often separated in a
longwave
and a shortwave
contribution. Clouds reduce the longwave losses from the Earth because their
tops emit at a lower temperature than the Earth surface. On the shortwave part of the spectrum,
clouds reflect a part of the incoming solar radiation because of their relatively high
albedo
and thus tend to cool the Earth. The sum of those two effects is negative and presently
amounts to a net cloud
radiative forcing of around -20 Wm^{-2}.
See section 4.2.2.

In thermal convection, some of a fluid (liquid or gas) receives heat. It thus warms, becomes less dense and rises. It is continuously replaced by colder fluid which is subsequently heated and thus also rises, forming a convection loop or convection current. Convection stops when the temperature differences between different parts of the fluid are too small to create any movement. See sections 1.2.2 and 1.3.3.1.

The Coriolis force causes an apparent deflection of moving objects towards the right in the Northern Hemisphere and towards the left in the Southern Hemisphere when viewed from a frame of reference attached to the Earth (or equivalently when viewed by an observer who is standing on the Earth). This occurs because of the Earth's rotation, and the Coriolis effect is actually present whenever a rotating frame of reference is used. See section 1.2.2, 3.3.1 and 3.3.3.

A correlation is a measure of the strength of a linear
relationship between two variables. It is often estimated by the Pearson correlation coefficient *r*.

Cosmogenic isotopes are created when elements in the atmosphere or on Earth are bombarded by cosmic rays.

Cosmic rays are high energy particles coming from outer space. See section 5.5.2.1.

The cryosphere is the portion of the Earth's surface where water is in solid form (sea ice, lake and river ice, snow cover, glaciers, ice caps and ice sheets). See section 1.4.1.

A cyclone is a low pressure system in the atmosphere. See sections 1.2.2 and 1.2.3.