Annual premature deaths from poor air quality are estimated to rise from three million today to 4.5 million by 2040 if steps aren't taken to reform global energy combustion, according to a recent report by the International Energy Agency. Air quality is the fourth-largest threat to human health, after high blood pressure, poor diet, and smoking.

As many as 18,000 people die each day from air quality-related health problems, including lung disease, asthma, tuberculosis, and throat cancer. And each year, the number of air pollution-related deaths outnumber deaths caused by HIV/AIDS, tuberculosis, and road injuries combined. If the global energy sector were to increase clean energy investment by 7 percent  —  or $4.7 trillion  —  by 2040, premature deaths caused by outdoor air pollution could fall from 4.5 million to 2.8 million a year, the report states.

Although global greenhouse gas emissions are projected to decline throughout industrialized countries like China, energy policies will need to account for rising emissions — and an increase in air pollution-related deaths  —  in countries like India, Southeast Asia, and Africa, according to the IEA's report. Asia's air quality alone will account for nearly 90 percent of the rise in premature deaths.

Investing in better access to clean cooking stoves, tighter emissions controls on the global power sector, renewable energy, urban planning, and public transportation could decrease global energy demand by as much as 13 percent by 2040. Currently, just 8 percent of the world's energy production is entirely combustion-free.

"As a result, the share of India's population exposed to air with a high concentration of fine particles (higher than the least stringent of the World Health Organization's interim targets) falls to less than 20 percent in 2040 from more than 60 percent today," the report states. "In China, this figure shrinks below one-quarter (from well over half), and in Indonesia and South Africa it falls almost to zero."

Human energy use is responsible for about 85 percent of all the particulate matter and nearly all of the sulfur oxides and nitrogen oxides released into the atmosphere. Inefficient fuel combustion from factories, power plants, and cars are largely to blame. Cooking stoves powered by wood, charcoal, and other biomass also release huge amounts of pollutants into the atmosphere, like particulate matter. When inhaled, those pollutants can travel deep into the lungs, leading to lung cancer, chronic obstructive pulmonary disease, and heart disease.

As many as 2.7 billion people worldwide still rely on cooking stoves, which are linked to 3.5 million premature deaths each year, the majority of them coming in Asia and sub-Saharan Africa, according to the report. In developing countries, biomass burning is responsible for half of all particulate matter emissions.

"We need to revise our approach to energy development so that communities are not forced to sacrifice clean air in return for economic growth," IEA Executive Director Fatih Birol said in a statement. "Implementing the IEA strategy in the Clean Air Scenario can push energy-related pollution levels into a steep decline in all countries. It can also deliver universal access to modern energy, a rapid peak and decline in global greenhouse-gas emissions and lower fossil-fuel import bills in many countries."

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