Environment: Cloud Cover: Is Earth Getting Darker?

The sun is not growing weaker, yet its light appears to be dimming. Between 1960 and 1990, some scientists believe, the amount of solar radiation reaching Earth's surface may have declined as much as 10%--and in some places, Hong Kong, for example, more than 35%.

What was going on? Well, it appears that increased air pollution during those 30 years--over Asia, in particular--with the help, perhaps, of some increased cloudiness, may have exerted a cooling influence on the surface of the planet even as carbon dioxide and other greenhouse gases were encouraging the atmosphere to warm. The impacts of that tug-of-war...

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