Amplifiers: Clouds
Like aerosols, clouds can either warm or cool the Earth, depending on their density and altitude. Their behavior demonstrates the intricate interactions at work within the climate system.
Very small differences in clouds may produce large feedbacks. An increase in high, thin clouds produced by greenhouse warming would further increase the warming. This is because high, thin clouds are relatively effective in trapping infrared radiation (heat) while allowing the Sun’s energy to pass through. In contrast, an increase in thick, low clouds could lessen the warming because these clouds reflect sunlight efficiently.
 |
 |
Clouds Can Have Different Effects
Although not completely understood, differences in clouds may produce large feedbacks in the climate. High thin clouds, such as cirrus clouds (left), may increase warming by trapping infrared radiation, while thick low-level clouds (right) may cool the Earth by reflecting sunlight. |
Changes in clouds result from changes in the distribution of water vapor, temperature, and winds. The effects of global warming on these factors are complex and not well understood.
In addition, aerosols may also play a role in cloud formation. Tiny aerosol particles can “seed” clouds by providing the “nuclei” around which cloud droplets are formed. High concentrations of some aerosol types may affect the character of clouds by causing many tiny droplets to form rather than a few big ones. Clouds with more tiny droplets reflect more solar energy and tend to produce less rainfall.
| 
