(Newser) – Almost an eighth of all deaths worldwide last year were caused by air pollution, which is now the world's biggest environmental health risk, the World Health Organization warns. A new study released by the agency finds that around 3.7 million deaths in 2012 were caused by outdoor air pollution, the Guardian reports, but even more deaths—4.3 million—were caused by indoor air pollution, mainly from coal or dung-powered stoves in some of the world's poorest countries.

The report found that pollution-caused deaths, especially from heart disease and strokes, are soaring in fast-developing Asian nations like China. The WHO's public health chief says he hopes the report, by exposing the "astronomical costs" of air pollution, will spur governments to do more about dirty air. "What's needed is collective action," he tells the New York Times. "The air you are polluting is the same air you breathe." (Read more pollution stories.)

