Students stand on the roof of a wooden boat as haze blankets the Musi River while they travel to school in Palembang, on Indonesia's Sumatra island, September 10, 2015. Indonesia is investigating 10 firms over worsening forest fires that have created a blanket of smog over Southeast Asia, threatening them with sanctions if they are found responsible, a government minister said on Tuesday. The thick haze from Indonesia's Sumatra and Kalimantan islands has forced the repeated cancellation of flights in the area and pushed air quality to unhealthy levels in neighbouring Singapore and Malaysia. (Photo by Reuters/Beawiharta)

Dancers of the Moulin Rouge cabaret adjust their boots prior to a show on April 22, 2014 in Paris. Since 1945, the “Maison Clairvoy” is specialised in the creation of luxury shoes and started in 1960 a collaboration with the famous Moulin Rouge to create boots and shoes for French Cancan dancers. (Photo by Franck Fife/AFP Photo)

Collided passenger train cars are seen in Taebaek, South Korea, Tuesday, July 22, 2014. Two passenger trains collided head-on in eastern South Korea on Tuesday afternoon, killing one passenger and injuring dozens, fire officials said. (Photo by AFP Photo/Yonhap)

A house built on a rock on the river Drina is seen near the western Serbian town of Bajina Basta, about 160km (99 miles) from the capital Belgrade May 22, 2013. The house was built in 1968 by a group of young men who decided that the rock on the river was an ideal place for a tiny shelter, according to the house's co-owner, who was among those involved in its construction. (Photo by Marko Djurica/Reuters)

A reveller wearing a golden cape celebrates as the sun rises during the winter solstice at Stonehenge on Salisbury plain in southern England December 22, 2014. The winter solstice is the shortest day of the year, and the longest night of the year. (Photo by Dylan Martinez/Reuters)

A member of India’s Dongria tribe faints in trance during the two-day long Niyamraja Festival atop the Niyamgiri hills near Lanjigarh in Kalahandi district, Orissa state, India, Sunday, February 22, 2015. Every year, members of this indigenous group celebrate this festival sacrificing animals and birds in worship of their deity. (Photo by Biswaranjan Rout/AP Photo)

Overlooking qingshuitan Wetland Park in the air, thousands of Chinese fir trees turn green. Gaoyou City, Jiangsu Province, China, April 20, 2020. April 22 is world earth day. (Photo credit should read Costfoto/Barcroft Media via Getty Images)