We had several threads (now closed) about global warming, for instance this, so some of you might be interested to hear about global dimming:

Look forward to a darker world (Nature, May 19th, 2004)

I don't know whether you have access, so I'll give you the first two paragraph that tell the amin thing:

It's official: the world is getting darker. Scientists now agree that as cloud cover and particles in the atmosphere increase, the amount of radiation reaching us from the Sun is falling. And although they are nervous about raising the idea, they think the effect may help protect us from global warming.

The phenomenon, called global dimming, has been quietly discussed in scientific circles for the past decade or so. Since the late 1950s, scientists have observed a 2-4% reduction each decade in the amount of solar radiation reaching the Earth's surface, which is thought to be caused by particles and clouds in the atmosphere scattering the light.

Wolfgang