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.
A woman walks through haze as a forest fire burns bushes and fields, June 27, 2013 in Riau province, Indonesia. The fires on Sumatra caused record smog levels in Malaysia and Singapore. Sumatra was forced to step up efforts to fight the fires to relieve conditions, with eight farmers arrested for starting the fires.
Burned trees and clearing in protected peatland in Riau province, June 29 2013. Environmentalists say that illegal slash and burn method is a widespread method of clearing land.
Indonesian motorists travel under a blanket of haze in Dumai town, Riau province, March 3, 2014.
March 1 2014, In Medan, Indonesia, construction workers toil in the setting sun as smoke from fires in Riau province covers the region. The province was at the heart of a Southeast Asian smog crisis in 2013 and declared a state of emergency in February 2014 after being blanketed in a thick haze from forest fires.
Singapore's skyscrapers enveloped in smog, 16 October 2006, from forests fire in Indonesia. The annual recurrence of carbon-rich haze caused by fires in Indonesia's vast tropical peatlands may help fuel global warming if left unchecked, experts have warned.