A haze has periodically wafted over Southeast Asia for 20 years. It is especially bad in the Asia-Pacific region, which has a population of over 4.2 billion and high population density. Pictured, smog hovers above the Kuala Lumpur skyline in June 2013.
Smoke billowing from fires in areas surrounded by plantations in Riau province, on Indonesia's Sumatra island, about 173 miles west of Singapore on June 17 2013. On June 20, Singapore demanded "definitive" action by Indonesia on forest fires raging in Sumatra as the nations prepared for emergency talks to ease the severe smog enveloping Singapore.