What is the largest environmental killer of people?

The answer here is easy.  Dirty, smokey air.  More than 2 million people die annually from the effects of indoor cooking fires.  Another two million people die annually from other dirty air sources or disease processes associated with reduced vigor as a result of smoke and air pollution.  Left uncounted are the horrific burn all too often suffered by children as a result of open cooking fires.  Sadly, these deaths and injuries are easily avoidable using techniques that also help our environment, forests and watersheds.  Fuel-efficient safe stoves are an important answer . . . but not just any stove!