Each year about 6.5 million deaths worldwide are linked to air pollution, a number that could grow in coming decades unless the energy sector steps up its efforts to slash emissions, the International Energy Agency warned Monday.

In the Paris-based agency's first report on the subject, the IEA said air pollution is the fourth biggest threat to human health, after high blood pressure, bad diets and smoking.

"Without changes to the way that the world produces and uses energy, the ruinous toll from air pollution on human life is set to rise," the report said.

Outdoor air pollution comes mainly from power plants, factories and cars while household pollution stems from dirty cook stoves, primarily in developing countries. About 3 million premature deaths are linked to outdoor air pollution and 3.5 million premature deaths to inhaling smoke from stoves in the household, the report said.

The latter number is projected to fall to 3 million in 2040 as access to cleaner-burning stoves improves in poor countries, IEA said. But it projected that the death toll linked to outdoor air quality would rise to 4.5 million, mainly in Asia, as growing demand for energy results in higher emissions.

"Air pollution in many of the region's growing cities continues to be a major public health hazard and, indeed, to affect a larger share of an increasingly urban population," the report said.

However, the IEA said sharp health improvements could be achieved with a seven per cent increase in total energy investment over the period to 2040. That would entail additional reductions of household emissions, stricter fuel standards for cars and trucks, improving energy efficiency and accelerating a shift in power generation from high-polluting sources such as coal to renewable alternatives.

The report said energy production is the biggest source of man-made air pollution, accounting for 85 per cent of the particulate matter and nearly all of the sulfur oxides and nitrogen oxides.

Energy production is also a key source of carbon dioxide emissions linked to global warming.