The skies are dimming, for most of the world.
Increases in airborne pollution have dimmed the skies by blocking sunlight over the past three decades, researchers report in Friday's edition of the journal Science.
While decreases in atmospheric visibility — known as global dimming — have been reported in the past, the new study compiles satellite and land-based data dating back to 1973 for a longer period than had been available.
"Creation of this database is a big step forward for researching long-term changes in air pollution and correlating these with climate change," Kaicun Wang, assistant research scientist in the University of Maryland, said in a statement. "And it is the first time we have gotten global long-term aerosol information over land to go with information already available on aerosol measurements over the world's oceans."
They reported that dimming is occurring everywhere except Europe, where declines in pollution have resulted in brighter skies.
Changes in aerosols can affect weather and also may have an impact on climate, though past studies have been inconclusive. These pollutants can result in cooling by reflecting sunlight back into space, but they also can absorb solar energy, warming the atmosphere.
Aerosols include soot, dust and sulfur dioxide particles, and typically come from burning fossil fuels and tropical rainforests.
Separate study on 'sunshade' idea
Researchers at the U.S. National Oceanic and Atmospheric Administration, meanwhile, warned that suggestions for a high-atmosphere "sunshade" of particles to battle global warming could reduce energy production from solar power plants.
Those proposals are aimed at blocking sunlight that can be absorbed by so-called greenhouse gases like carbon dioxide, warming climate.
But airborne particles also scatter light that does get through, and that diffuse light cannot be used by solar energy concentrating systems that produce electricity, Daniel Murphy, a scientist at NOAA's Earth System Research Laboratory in Boulder, Colo., reported in the journal Environmental Science and Technology.
Flat photovoltaic and hot water panels, commonly seen on household roofs, use both diffuse and direct sunlight, so they would be less affected.
