A dense blanket of pollution that is hovering over South Asia could cause millions of deaths in the region and pose a threat to the world at large, a group of 200 scientists announced today. Known as the “Asian Brown Cloud,” the smog is an estimated two miles thick and covers the entire Indian subcontinent, from Sri Lanka to Afghanistan. The cloud is responsible for hundreds of thousands of deaths from respiratory disease every year, and is also altering the regional climate by trapping heat and blocking sunlight. The cloud is composed of aerosols, ash, soot, and other particles, and stems from forest fires, vegetation clearing, fossil fuels, and industrial pollution. A U.N. report found that the smog blanket could cut rainfall in the region by up to 40 percent and travel halfway around the world in just one week. If there’s a silver lining to this particular cloud, it’s that it could disappear relatively quickly with the use of more efficient technologies and cleaner energy sources, scientists said.