PBS’ Nova is running a new episode on a phenomenon they’ve dubbed, “Global Dimming”—the reduction of the sun’s intensity due to atmospheric pollution. On its surface this might seem like a perfectly obvious consequence of pollution, but, as the documentary demonstrates, scientists are making astonishing discoveries about its true scope.
Via a clever experiment in the Maldives, researchers were able to measure the actual reduction caused by human pollution. They expected to find something on the order of a half of one percent. Instead, they discovered man-made pollution caused as much as a ten percent reduction in the intensity of the sun’s rays reaching the ground.
How, you ask? First, plainly, simply putting particulates in the air blocks sunlight. But—and here’s the tricky part—pollution particulates tend to be much smaller than ordinary dust in our atmosphere. Consequently, they create clouds (as water vapor condenses around the particulates) that are vastly more reflective than ordinary clouds. These pollution-enhanced clouds have a profoundly greater cooling effect on the Earth below.
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