The skies over most land areas are not, as previous studies have suggested, becoming cleaner.
Aerosol pollution has in fact increased most everywhere since 1973, a team reports in Science today (Abstract). Only over Europe have skies brightened, they found.
Kaicun Wang of the University of Maryland, and his colleagues, looked at a 35-year record of clear-sky transparency from 3,250 stations around the world. At many stations visibility had notably decreased – the skies have dimmed.
Air pollution is worst In India, China, Africa and South America, where hundreds of millions are breathing air thick with soot and smog. Clean-air technologies are lacking, or have not yet had much effect, in these regions.
Previous studies concluded that the skies are getting cleaner, and that as a result more sunlight is reaching the surface. Atmospheric scientists believe that aerosols and dust have been shielding us from the worst of global warming.
But the overall cooling effect of aerosols has lately been questioned. The connection between different types of aerosol particles, clouds and solar radiation is more complicated than previously thought. Now it appears as if darker skies don’t necessarily mean less warming, and vice versa. My story
over at Nature News has more about these disturbing uncertainties.
Meanwhile, China is trying hard to reduce air pollution in its most populated cities. Strict regulations aimed at curbing pollution from cars have been set up last year in Beijing and Shanghai.