Cloud feedback
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Cloud feedback is the coupling between cloudiness and surface air temperature in which a change in surface air temperature could lead to a change in volume of clouds, which could then amplify or diminish the initial temperature perturbation.
This effect is currently known to have a negative impact on the climate system. However, a changing climate may involve changes in the clouds with both positive and negative effects on the radiative balance. It is not known whether the overall effect of Cloud feedback will become a negative or positive feedback, depending on whether and how cloud cover changes. Cloud feedback could almost halve or double the surface air temperature.
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[edit] Negative feedback
An increase in surface air temperature could increase evaporation; this in turn might increase the extent of cloud cover. Increased cloud cover would reduce the solar radiation reaching the Earth's surface, thereby lowering the surface temperature. However, the cloud that is produced may not have ability to block sunlight as low clouds tend to cool, while high clouds tend to warm.
[edit] Positive feedback
Likewise, an increase in surface air temperature would have more water vapor present in the atmosphere. The amount of water vapor that the atmosphere can contain increases exponentially with temperature. Therefore, increases in temperature will yield increases in atmospheric water vapor. The increased water vapor will act as a greenhouse gas, enhances the greenhouse effect and could lead to further warming. However, this positive feedback could be modified by an increase in cloudcover that could lead to a negative feedback.
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[edit] References
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