China's capital city and dozens of other metropolitan areas this week are facing air pollution so thick and toxic that it could be seen from space (See comparison photos below). English-speaking people living in Beijing have taken to calling it "Airpocalypse," according to a report from Time, which blamed the smog on a combination of coal-fired power plants — China burned half of the coal used worldwide in 2011 — as well as vehicles, heavy industry and an extended windless period that has kept emissions floating over the city.

NASA view of Beijing air qualityThe smog is so bad that it is literally off the charts. The U.S. embassy recorded levels of fine particulates known as PM 2.5 (particles less than 2.5 micrometers in diameter) as high as 886 micrograms per cubic meter. The group's measuring process normally stops at 500. Anything above 25 per cubic meter is considered unsafe, while anything above 301 is considered "hazardous." According to the U.S. Environmental Protection Agency, "health studies have shown a significant association between exposure to fine particles and premature death from heart or lung disease." The U.S. standard for air quality is 15 micrograms of PM 2.5 per cubic meter.

Reuters reports that China has warned residents to stay indoors and has ordered some factories to temporarily close and some vehicles to stay off the road, but Xinhua, the official Chinese news agency, used the smog cloud as a way to promote the country's economy, which it says is expected to grow up to 8.2 percent in 2013 after a weak 2012. "Beijingers have felt probably the worst air pollution on record over the last couple of days," analyst Martina Fuchs told the agency. "But finally, the sun is slowly shining through again. The same might apply to the Chinese economy this year."

Even if the skies above Beijing and other cities do clear up in the coming weeks, the effects of this smog could be long-felt. A new 232-page study published this week in the Journal of Geophysical Research identifies soot (aka black carbon) as one of the biggest contributors to global warming, second only to carbon dioxide (CO2). This new assessment of soot shows it to be two times as bad as previously estimated.

Black carbon traps heat into the atmosphere several different ways, according to the study. When mixed with clouds, it can cause clouds to evaporate or to grow, depending on their altitude. When it mixes with rain and snow, it darkens the precipitation, increasing its heat absorption, which both increases melting and reduces the ability of snow and ice to bounce sunlight back out of the atmosphere. The scientists behind the study say that even eliminating all black carbon emissions today might not make a difference in global warming, since soot has a very short lifespan in the atmosphere compared to CO2. They also say that the study "sets a baseline from which to improve future climate forcing estimates."

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Air quality photos as seen from above: NASA Earth Observatory