"The phenomenon, called global dimming, has been quietly discussed in scientific circles for the past decade or so."

Well, that corresponds closely to the eruption of Mt. Pinatubo in 1991. That event is said to have produced more pollution, both gas and particulate, than cars have produced in 100 or so years of their existance. Although "greenhouse gases" are supposed to let light in, then block the reflected energy (heat) from leaving the atmosphere, particulates block the light before it can get to the earth. Result is "global cooling". Trouble is, all discussions I have heard on the subject of global warming/cooling/dimming are overshadowed by politics and posturing.

Here are some facts and pictures of the mountain:

   Mt. Pinatubo