Cloud forcing (sometimes described as 'cloud radiative forcing') is the difference between the radiation budget components for average cloud conditions and cloud-free conditions. Cumulus of fair weather Different cloud types A cloud is a visible mass of condensed droplets or ice crystals suspended in the atmosphere above the surface of the Earth or another planetary body. ...

Roughly speaking, clouds increase the albedo from 15 to 30%, which results in a reduction of absorbed solar radiation of about 44 W/m². This cooling is offset somewhat by the greenhouse effect of clouds which reduces the OLR by about 31 W/m², so the net cloud forcing of the radiation budget is a loss of about 13 W/m² (source: IPCC '90, table 3.1). Were the clouds to be removed with all else remaining the same, the Earth would gain this last amount in net radiation and begin to warm up. These numbers should not be confused with the usual radiative forcing concept, which is for the change in forcing related to climate change: clouds remain one of the largest uncertainties in future projections of climate change by global climate models. Albedo is a ratio of scattered to incident electromagnetic radiation power, most commonly light. ... Solar irradiance spectrum at top of atmosphere. ... A schematic representation of the exchanges of energy between outer space, the Earths atmosphere, and the Earth surface. ... OLR (Outgoing long-wave radiation) is, in climatology, the upwards component of the infra-red (long wave) radiation. ... The generalised concept of radiative forcing in climate science is any change in the radiation (heat) entering the climate system or changes in radiatively active gases. ... Variations in CO2, temperature and dust from the Vostok ice core over the last 400 000 years Climate change refers to the variation in the Earths global climate or regional climates over time. ... ...

Without the inclusion of clouds, water vapor alone contributes between 36-70% of the greenhouse effect on Earth. When considering water vapor and clouds together, the contribution is between 66-85%. In these estimates, the lower bounds are the amount of change if water vapor and clouds are removed, and the upper bounds are the remaining greenhouse effect if everything but water vapor and clouds are removed. [1]

Trapping of the long-wave radiation due to the presence of clouds reduces the radiative forcing of the greenhouse gases compared to the clear-sky forcing. However, the magnitude of the effect due to clouds varies for different greenhouse gases. Relative to clear skies, clouds reduce the global mean radiative forcing due to CO₂ by about 15% (Pinnock et al., 1995; Myhre and Stordal, 1997), that due to CH₄ and N₂O is reduced by about 20% (derived from Myhre et al., 1998b), and that due to the halocarbons is reduced by up to 30% (Pinnock et al., 1995; Christidis et al., 1997; Myhre et al., 1998b) [2].

See also

• Climate change