...are as scary as they sound. From the United Nations Environment Program

Cities from Beijing to New Delhi are getting darker, glaciers in ranges like the Himalayas are melting faster and weather systems becoming more extreme, in part, due to the combined effects of man-made Atmospheric Brown Clouds (ABCs) and greenhouse gases in the atmosphere.

These are among the conclusions of scientists studying a more than three km-thick layer of soot and other manmade particles that stretches from the Arabian Peninsula to China and the western Pacific Ocean.

The New York Times is on the story.

The byproduct of automobiles, slash-and-burn agriculture, wood-burning kitchen stoves and coal-fired power plants, these plumes of carbon dust rise over southern Africa, the Amazon basin and North America. But they are most pronounced in Asia, where so-called atmospheric brown clouds are dramatically reducing sunlight in many Chinese cities and leading to decreased crop yields in swaths of rural India, say a team of more than a dozen scientists who have been studying the problem since 2002...

The brownish haze, sometimes more than a mile thick and clearly visible from airplanes, stretches from the Arabian Peninsula to the Yellow Sea. During the spring, it sweeps past North and South Korea and Japan. Sometimes the cloud drifts as far west as California.

The report identified 13 cities as brown-cloud hotspots, among them Bangkok, Cairo, New Delhi, Seoul and Tehran. In some Chinese cities, the smog has reduced sunlight by as much as 20 percent since the 1970s, it said.

Rain can cleanse the skies, but some of the black grime that falls to earth ends up on the surface of the Himalayan glaciers that are the source of water for billions of people in China, India and Pakistan. As a result, the glaciers that feed into the Yangtze, Ganges, Indus and Yellow rivers are absorbing more sunlight and melting more rapidly, researchers say.

NASA has some photos of Atmospheric Brown Clouds, like the one above, taken from outer space. That photo shows an Atmospheric Brown Cloud over eastern China.