Air pollution is linked to 7 million premature deaths worldwide every year, according to the World Health Organization (WHO). This figure is more than double what was previously thought, according to the global health agency.

The report said more than half of the deaths caused by air pollution are linked to indoor sources such as cooking over coal, wood or biomass stoves. Air pollution is now the world’s greatest single environmental risk, according to WHO.

Examples from history

The “Great Smog of London” is an example of the impact of air pollution on premature death rates. During a single weekend in 1952, pollution from coal-burning fireplaces was trapped over the city during a cold-weather inversion. The pollution exposure during that one single weekend caused more than 12,000 premature deaths and 100,000 cases of serious respiratory illness.

In ancient times, air quality was also a cause of premature death. Researchers from the University of Manchester (U.K.) studied 15 lungs from ancient Egyptian mummies. They found high levels of particulates and lung scarring in all of them. The source of the particulates is believed to have been sandstorms and burning fossil fuels.

Air pollution and premature death today

More than 3,500 years later, air pollution is still a growing cause of premature death in many parts of the world. But the primary sources of air pollution today are traffic and industrial processes.

Scientists say air pollution is responsible for the rising rate of premature death in China and India. In those countries, pollution levels far exceed the pollution levels of even the most traffic-clogged cities of North America. One study in northern China determined that incremental increases of 100 micrograms per cubic meter in airborne particulates shorten life expectancy by three years.

How does air pollution kill?

There are at least four specific ways air pollution contributes to premature death rates:

Heart Disease.A study published late last year by researchers at the University of California, Berkeley, linked air pollution exposure to premature death from ischemic heart disease, which is reduced blood supply to the heart. Heart disease is the #1 cause of death in the U.S.

Cancer.Studies estimate that 223,000 people worldwide die each year from lung cancer caused by air pollution, according to the American Lung Association. The International Agency for Research on Cancer has classified particulate pollution as carcinogenic.

Asthma.More than 250,000 annual deaths worldwide are caused by asthma, and almost all of them preventable, according to the World Health Organization. That number includes 3,000 asthma deaths each year in the U.S. Air pollution is a major cause of asthma attacks.

COPD.Air pollution is a leading cause of chronic obstructive pulmonary disease (COPD). The two most common forms of the disease are emphysema and bronchitis. COPD killed 133,965 Americans in 2009, according to the U.S. Centers for Disease Control and Prevention.

Take action against air pollution

The most important strategy for controlling air pollution is to reduce the sources of air pollution – especially pollution from traffic and power generation. Here are a few suggested steps you can take, from the California Air Resources Board:

On the road:

• Walk or ride a bike whenever possible.
• Take public transportation.
• When purchasing a new car, choose a low-polluting or zero-emission vehicle.

At home:

• Turn off the lights when you leave a room.
• Replace incandescent lights with compact florescent light bulbs.
• Use a programmable thermostat and set it to 78 degrees in summer and 68 degrees in winter.

At work:

• Join a carpool.
• Telecommute.
• Open the blinds and turn off the lights whenever possible.

For more information about air pollution and what you can do about it, visit the Air Resources Board or the American Lung Association.