Today the air pollution was so thick in Harbin, in northern China, that visibility was reduced to fewer than 33 feet in some parts of the city. In response to the conditions -- which are equivalent to levels that exceed “hazardous” on the air-pollution measurement system used by the U.S. State Department in major Chinese cities -- Harbin shut down some schools, canceled flights and sent out relevant officials to stop polluting behavior.

That’s hardly sufficient.

Last week, the World Health Organization’s International Agency for Research on Cancer announced that “outdoor air pollution” would henceforth be classified as “carcinogenic to humans.” The designation is shared with -- among other inhalable carcinogens -- tobacco smoke; the IARC’s news release notes “sufficient evidence that exposure to outdoor air pollution causes lung cancer,” as well as “a positive association with an increased risk of bladder cancer.”

None of this comes as any surprise in Beijing, another northern Chinese city, where cancer is the leading cause of death. Lung cancer is apparently the country’s leading, fast-growing variety of the disease: In 2008, an official with China’s Ministry of Health claimed that Chinese lung-cancer rates had risen 465 percent over the previous three decades -- a period that corresponds with both China’s economic revival and the transformation of its cities into some of the world’s most polluted places. (Reports from the IARC and others consistently point to Asia -- specifically, China and India -- as having among the world’s most serious air-pollution problems.)

Despite the fact that people in China’s cities instinctively know that the air is slowly killing them, there’s been precious little quality data showing a direct correlation between the opaque smog and mortality rates. A 2007 report by the World Bank was allegedly stripped of its more damning conclusions at the request of Chinese government departments. (The bank reportedly determined that up to 760,000 premature deaths related to air and water pollution occur in China annually.) Meanwhile, a spring 2013 report on global mortality trends estimated 1.2 million premature Chinese deaths in 2010 due to air pollution alone. Yet, for all of the benefit these studies may have brought, neither is the comprehensive, on-the-Chinese-ground study of pollution’s impact on human health.

The IARC’s decision to classify air pollution as a carcinogen isn’t a study, either. But its importance is less what it reveals, than the debate it opens up. Not so long ago Beijing’s government regularly labeled China’s choking smog as “fog” (a tradition revived by the Ladies Professional Golf Association during an October tournament) and thus circumvented the ability of its own people -- much less well-intentioned officials and researchers -- to even discuss the health effects. To be sure, some of those consequences were already well-known, including respiratory problems. But it’s one thing to look out the window, see gray skies and think, “I might have a respiratory problem,” and another entirely to think, “That’s giving me lung cancer.”

To its modest credit, the Chinese government -- and not just the city of Beijing -- is starting to take its air-pollution problems seriously. In September, it announced a comprehensive plan to control and slowly reduce air pollution across the country. On Oct. 16, Beijing announced emergency measures to reduce air pollution on particularly polluted days. On Saturday, Shanghai announced a similar program that includes school closings. (Harbin’s program is probably due any day.) So far these plans have not been designed to return China’s air to a consistently non-carcinogenic state. Thanks to the IARC, the Chinese public might start to demand that they do.

(Adam Minter is the Shanghai correspondent for the World View blog and a contributor to the Ticker. Follow him on Twitter.)