Ingles

Global dimming
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Dozens of fires burning on the surface (red dots) and a thick pall of smoke and haze (greyish pixels) filling the skies overhead in Eastern China. Smoke, pollution and other air particles are linked to global dimming. Photo taken by MODIS aboard NASA's Aqua satellite.
Global dimming is the gradual reduction inthe amount of global direct irradiance at the Earth's surface that was observed for several decades after the start of systematic measurements in the 1950s. The effect varies by location, but worldwide it has been estimated to be of the order of a 4% reduction over the three decades from 1960–1990. However, after discounting an anomaly caused by the eruption of Mount Pinatubo in 1991, a veryslight reversal in the overall trend has been observed.[1]
Global dimming is thought to have been caused by an increase in particulates such as sulfate aerosols in the atmosphere due to human action.
It has interfered with the hydrological cycle by reducing evaporation and may have reduced rainfall in some areas. Global dimming also creates a cooling effect that may have partially masked the effectof greenhouse gases on global warming.
Deliberate manipulation of this dimming effect is being considered as a geoengineering technique to reduce the impact of global warming.[citation needed]
Contents * 1 Causes and effects * 2 Research * 3 Pan evaporation data * 4 Probable causes * 5 Recent reversal of the trend * 6 Relationship to hydrological cycle * 7 Relationship to globalwarming * 8 Possible use to mitigate global warming * 9 See also * 10 References * 11 External links |
Causes and effects
Further information: Albedo, irradiance, and insolation
It is thought that global dimming is probably due to the increased presence of aerosol particles in the atmosphere caused by human action.[2] Aerosols and other particulates absorb solar energy and reflectsunlight back into space. The pollutants can also become nuclei for cloud droplets. Water droplets in clouds coalesce around the particles.[3] Increased pollution causes more particulates and thereby creates clouds consisting of a greater number of smaller droplets (that is, the same amount of water is spread over more droplets). The smaller droplets make clouds more reflective, so that more incomingsunlight is reflected back into space and less reaches the Earth's surface. In models, these smaller droplets also decrease rainfall.[4]
Clouds intercept both heat from the sun and heat radiated from the Earth. Their effects are complex and vary in time, location, and altitude. Usually during the daytime the interception of sunlight predominates, giving a cooling effect; however, at night there-radiation of heat to the Earth slows the Earth's heat loss.
Oscurecimiento global es un término que describe la reducción gradual de la cantidad de luz solar observada que alcanza la superficie terrestre desde los años cincuenta.

Fotografía de la NASA que muestra estelas de aeronaves y nubes naturales. Las estelas podrían estar implicadas en el oscurecimiento global.
Se piensa que ha sidoprovocado por un incremento de partículas de hollín (negro de carbón, carbonilla) en la atmósfera debido a las actividades humanas, principalmente la combustión, tanto industrial como en el transporte. El efecto varía con la localización, pero globalmente la reducción de luz ha sido del orden de un 4% en tres décadas (1970-1990). El oscurecimiento global ha interferido con el ciclo hidrológicoreduciendo la evaporación y ha podido provocar sequías en algunas zonas. La tendencia se ha revertido durante los años noventa. El oscurecimiento global crea un efecto de enfriamiento que ha podido llevar a los científicos a subestimar los efectos de los gases de efecto invernadero enmascarando parcialmente el calentamiento global.
Contenido * 1 Causa y efectos * 1.1 Trabajos de investigación...