Here's a stunning statistic: A government policy to promote coal use in Northern China may have cut the life expectancy of 500 million people by more than five years on average.
That comes from a big new study in the Proceedings of the National Academies of Sciences, which uses a quasi-natural experiment to quantify the effects of air pollution from China's coal use in recent decades.
The study concluded that nearly 500 million people living north of the Huai River will lose an estimated 2.5 billion life years because of pollution from widespread coal burning, compared with those south of the river. The study is based on analyses of health and air-quality data from 1981 to 2000.
"I was surprised by the magnitude of the effect," says MIT economist Michael Greenstone, who co-authored the paper with Yuyu Chen, Avraham Ebenstein and Hongbin Li.
Researchers have long known that the fine particles released when coal is burned can have adverse health effects. But it's always been difficult to measure the exact effects of particulate pollution. After all, scientists can't just subject ordinary people to trials in which a few people are exposed to heavy pollution at random. And it's difficult to find proper controls occurring naturally.
Until now, that is. Greenstone and his colleagues found an excellent quasi-natural experiment in China. Starting in the 1950s, the Chinese government began providing free winter heating via coal boilers to people living north of the Huai River. Yet those living south of the Huai River didn't get the free boilers. That gave the researchers a way to isolate the effects of air pollution. They then analyzed official data on both air quality and health between 1981 and 2000 to get a sense for the effects.
What they found was surprising. Concentrations of "total suspended particulates" were about 55 percent higher in the north, thanks to the heavy coal burning. And life expectancy for those living in the north was also about 5.5 years shorter — an effect due entirely to differences in cardio-respiratory problems, which is exactly what you'd expect if pollution was the cause. (There's a long appendix detailing all the different controls they applied.)
"The original policy to provide free heating was obviously very well-intentioned," says Greenstone. "But it had a large unintended consequences that were unpredictable" — not least since so few people at the time realized the large health impacts of pollution.
The authors were also able to get a more precise estimate of the impacts of particulate pollution. An extra 100 micrograms per cubic meter of "total suspended particulates" is associated with a drop in life expectancy of about three years. (In 2001, particulate levels across China were about 400 μg/m3.)
"These results may help explain why China's explosive economic growth has led to relatively anemic growth in life expectancy," the paper concludes.
The findings could also help the country craft environmental rules to limit air pollution in the future. At the moment, China currently burns nearly as much coal as the rest of the world combined — and its officials have long maintained that coal is utterly necessary for the country's economic growth. But a more precise estimate of the health toll inflicted by air pollution could help Chinese regulators tally up all those costs and benefits — and act accordingly.