Choked with smog that shut down roads, schools, and its main airport, the city of Harbin (map) this week offered a striking reminder that China has a long way to go in addressing the hazards caused by its dependence on coal.

Visibility in the northeastern city of more than 10 million people reportedly was reduced in places to less than 65 feet (20 meters) as coal-fired heating systems ramped up for the winter months. Officials also pointed to farmers burning crop stubble and low winds as additional causes for the pollution crisis.

Harbin, also known as the Ice City, hosts an ice and snow festival every year that features displays of elaborate ice sculptures. But the city's frigid temperatures, which can reach -40ºF (-40º C) in winter, mean that residences usually need heating for six months of the year. As part of a national effort to reduce energy intensity, Harbin in 2010 spent $1.1 million to retrofit 21 million square feet (2 million square meters) of residential buildings—adding five new layers of wall insulation, as well as better windows and roofing. (See related story: "In China's Icy North, Outfitting Buildings to Save Energy.")

But building retrofits can go only so far in a country where coal fuels 70 percent of the energy consumption. China, the world's largest consumer of coal, is also the world's leader in carbon emissions. (See related interactive map: "Four Ways to Look at Global Carbon Footprints.") Those emissions have stark consequences for the country's residents, a fact highlighted in two recent studies that measured the health impacts of fossil fuel emissions.

Deadly Pollution Problems

The level of fine particulate matter, or PM2.5, in Harbin's air this week reportedly reached 1,000 micrograms per cubic meter, exceeding the World Health Organization's daily target level by a factor of 40. While Harbin's predicament is alarming, it is not isolated; many cities in Northern China, including the capital Beijing and neighboring Tianjin, rank among the most polluted in the world. In January, Beijing made headlines when its air quality got so bad that it went beyond the very top of the U.S. Environmental Protection Agency's Air Quality Index.

Research published in the Proceedings of the National Academy of Sciences (PNAS) in July found that air pollution has caused the loss of more than 2.5 billion years of life expectancy in China. Because of a government policy that provided free coal for home and office heating to residents of the north from 1950 to 1980, life expectancy there was 5.5 years shorter than in southern China in the 1990s. That disparity persists today, researchers say, almost entirely because of heart and lung disease related to air pollution from the burning of coal. (See related story: "Coal Burning Shortens Lives in China, New Study Shows.")

Bill Chameides of Duke University's Nicholas School for the Environment led two air quality studies in China's Yangtze Delta between 1995 and 2004. "Hearing about Harbin's smog problems, I couldn't help but think back [to those studies]," Chameides said via e-mail Tuesday. "It was really bad then. Everywhere I went in China the sky was covered with a smoggy, foggy gray blanket. A cab driver told me, tongue in cheek, that while dogs howl once a month at night at the moon, in China they howl once a month during the day-because that's how often the sun comes out."

A separate study released last month found that if the world took action to reduce greenhouse gas emissions, more than 500,000 lives could be saved globally each year. The air and health quality benefits for East Asia alone would add up to between 10 and 70 times the cost of reducing emissions by 2030, researchers said. (See related story: "Climate Change Action Could Save 500,000 Lives Annually, Study Says.")

Growth, at a Cost

The challenge to improve heating infrastructure and improve efficiency for millions of square feet within existing buildings is made even more formidable by the fact that China is currently adding some 22 billion new square feet (2 billion square meters) of construction per year. At the same time, living standards are increasing, creating demand for ever more power; and coal remains subsidized, meaning that consumers don't see the fuel's true cost in their heating prices. (See related quiz: "What You Don't Know About Home Heating.")

China did earlier this year announce a ban on new coal plants in three industrial regions near Beijing, Shanghai, and Guangzhou, citing air quality problems. (See related blog post by Chameides: "China Puts Kibosh on New Coal Plants (in Three Regions).")

The government has also approved at least nine large-scale projects that would turn coal into synthetic natural gas (SNG), a strategy that may help ease China's air pollution woes but create more environmental problems than it solves. "In terms of mitigating smog in eastern China, replacing coal with SNG indeed can help quite a bit," said Chi-Jen Yang, a researcher at Duke, in an e-mail Tuesday. Yang co-authored a recent paper on the topic in Nature Climate Change, noting that SNG produces greenhouse gas emissions seven times that of conventional natural gas while requiring vast amounts of water.

"I understand that to the Chinese government, smog is probably more urgent than global warming, which explains their policy [favoring SNG]," Yang said. "I am just warning that their near-sighted policy will lock them into a long-term unsustainable path of development."

Yang's warning underscores a larger truth echoed by Chameides: Though China's energy decisions are being felt most keenly right now by those in Harbin and cities like it, the longer-term effects reverberate far beyond its borders. "When you think about how important China's economy is to the U.S. consumer, indeed to the whole world," said Chameides, "China's pollution is a threat to us all."

—Additional reporting by Marianne Lavelle and Te-Ping Chen

This story is part of a special series that explores energy issues. For more, visit The Great Energy Challenge.

This story has been changed from a previous version to correct the conversion of -40ºF to Celsius.