China's air pollution has cut life expectancy by an average of 5.5 years in the north of the country and caused higher rates of lung cancer, heart attacks and strokes, according to a groundbreaking study.
The worsening toxic smog in northern China became an issue of national concern after air pollution spiked to record levels in Beijing in January, prompting worried citizens to stock up on air filters and face masks. Pollution domes, which provide filtered air for sports activities, are also increasingly common.
But the body of scientific research on the health impact is slim because there is little historical precedent for prolonged exposure to such high levels of air pollution.
Using decades of pollution data from across China, the new study, co-authored by professors from Massachusetts Institute of Technology in the U.S., Tsinghua University and Peking University in Beijing, and the Hebrew University of Jerusalem, calculates that air pollution in the north caused the loss of 2.5bn years of aggregate human life expectancy during the 1990s.
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"This is the first time anyone has got the data to show how severe long-term pollution affects human health, both in terms of life expectancy and the types of disease," said Li Hongbin, an economics professor at Tsinghua University and a co-author of the study.
"It shows how high the cost of pollution is in terms of human life – and that it is worth it for the government to spend more money to solve the pollution issue, even if we have to sacrifice growth."
Mr Li estimates the shorter life expectancy identified by the study in northern China is equivalent to reducing the workforce there by one-eighth.
China's breakneck economic development during the past three decades has been accompanied by the widespread degradation of air, soil and water. Environmental worries are now a growing source of social unrest and public protest, particularly because of health concerns. In response, Beijing has tightened environmental laws and regulations but these efforts have so far had little impact in reversing decades of damage.
The study, published in Proceedings of the National Academy of Sciences, the prestigious U.S. journal, compares populations north and south of the Huai River, which runs through central China. Air pollution is much worse north of the river because of a government policy to distribute free coal for heating in winter.
Using pollution data from 1981-2000 and health data from 1991-2000, the study found that an increase of 100 micrograms of total particulate matter per cubic metre, a common measure of air pollution, corresponded to a three-year reduction in average life expectancy. The difference between the north and south of the river was about 185 micrograms per cubic metre.
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"What we found is that people who live just north of the river have life expectancy of five and a half years [less]," said Michael Greenstone, a professor of environmental economics at MIT and a co-author of the study.
"Part of the novelty of this study is that this was conducted with data on actual pollution measurements in China, and actual health and life expectancy in China. It is not an extrapolation," he said.
Most previous calculations of the health cost of Chinese pollution are extrapolated from research conducted in the U.S., where overall pollution levels are much lower.