Clouds - (n.)
Clouds consist of fine water particles floating in air and which are dense enough to prevent the direct transmission of light. The particles can be frozen, as with ice clouds. Condensation of water occurs when the moisture in the air exceeds the capability of the air to hold the water vapor (upon cooling moist air or mixing it with cold air) and when microscopic particles called aerosols are present on which the vapor can condense. Clouds come in many different types, depending on particle size and density, temperature and phase, thickness and elevation, cloud size and dynamics of change. The properties and the response of different types of clouds is crucial to the improvement of prediction of how the Earth's climate will respond to global warming. On the whole, higher temperature will produce greater moisture in the air, which will favor the formation of clouds in the cool regions of the atmosphere, which may move upward as the surface warms. The general increase of pollution of the atmosphere that is associated with increased human activity (e.g. burning, agriculture, and diesel engines) should favor the availability of cloud nuclei. Clouds also provide for "cloud albedo," since they reflect much of the sunlight into space, but they also trap infrared radiation. How the balance between these two effects will shift is uncertain. From a geological viewpoint (considering the climate patterns on a warm Earth, before the presence of large glaciers) it seems reasonable to expect that increasing clouds in the tropics will cool the tropics and increasing clouds in high latitudes will warm the cold regions.