By Michael Greenstone / Source: nytimes

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Back in 1970, Los Angeles was known as the smog capital of the world — a notorious example of industrialization largely unfettered by regard for health or the environment. Heavy pollution drove up respiratory and heart problems and shortened lives.

But 1970 was also the year the environmental movement held the first Earth Day and when, 45 years ago this month, Congress passed a powerful update of the Clean Air Act. (Soon after, it was signed by President Richard Nixon, and it was followed by the formation of the Environmental Protection Agency and passage of the Clean Water Act, making him one of the most important, though underappreciated, environmentalists in American history.)

Since that time, the Clean Air Act has repeatedly been challenged as costly and unnecessary. As a fight brews over President Obama’s new use of the law to address global warming, it’s worth re-examining the vast difference the law has already made in the quality of the air we breathe, and in the length of our lives.

Numerous studies have found that the Clean Air Act has substantially improved air quality and averted tens of thousands of premature deaths from heart and respiratory disease. Here, I offer new estimates of the gains in life expectancy due to the improvement in air quality since 1970 — based on observations from the current “smog capital” of the world, China. (To learn more about how this was calculated, click here.)

For several decades starting in the 1950s, China’s government gave residents in the northern half of the country free coal for winter heating, effectively creating a natural experiment in the health impact of pollution. My colleagues and I recently compared pollution and mortality rates between the north and south of China and calculated the toll of airborne particulate matter, widely believed to be the most harmful form of air pollution, on life expectancy.

Applying that formula to E.P.A. particulate data from 1970 to 2012 yields striking results for American cities.

In Los Angeles, particulate pollution has declined by more than half since 1970. The average Angeleno lives about a year and eight months longer. Residents of New York and Chicago have gained about two years on average. With more than 42 million people currently living in these three metropolitan areas, the total gains in life expectancy add up quickly.

But some of the greatest improvements occurred in smaller towns and cities where heavy industries appeared to operate with few restrictions on pollution.

In 1970, the Weirton, W.Va.–Steubenville, Ohio, metropolitan area had particulate concentrations similar to current-day Beijing. A child born there today can expect to live about five years longer than one born in 1970.

More than 200 million people currently live in places monitored for particulates in 1970 and today. (The E.P.A. focuses on the most heavily populated or polluted areas of the country, which is why these calculations exclude approximately 115 million people.) On average, these people can expect to live an additional 1.6 years, for a total gain of more than 336 million life-years.

Not all of these benefits came from Clean Air Act regulations. Other factors include local regulations and the shifting of relatively dirty industries abroad. But the Clean Air Act was a primary cause.

The history and impact of the Clean Air Act can serve as a valuable case study for countries that are struggling today with the extraordinary pollution that we once faced. In Northern China, where pollution is curtailing lives by an average of five years, the government has at last declared a “war on pollution.” While enforcement is not perfect, the government has improved transparency and amended environmental protection laws to impose stricter punishments against polluters.

In India, pollution is abridging the average person’s life by about three years. But the growing outrage has not yet coalesced into forceful action, although it’s possible that pressure to take steps against climate change will also have an effect on improving air quality.

The hundreds of millions of life-years saved from improved air quality in our country didn’t happen by accident or overnight. This happened because a collective voice for change brought about one of the most influential laws of the land.

As the United States and other nations continue to debate the costs of environmental regulation, they can do so with the knowledge that the benefits can be substantial. As proof, we need look no further than the five extra years residents of Weirton-Steubenville are living and the hundreds of millions of years gained by Americans throughout the nation.

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