An airplane is silhouetted at sunrise, seen from the suburb of Saint-Cloud, near Paris, France, 08 December 2016. Paris is undergoing a third day pollution spike, prompting the city to limit vehicle circulation. (Photo by Ian Langsdon/EPA)

A Maasai moran athlete has his face smeared with red ocher paint during preparations for the 2016 Maasai Olympics at the Sidai Oleng Wildlife Sanctuary, at the base of Mt. Kilimanjaro, near the Kenya-Tanzania border in Kimana, Kajiado, Kenya December 10, 2016. (Photo by Thomas Mukoya/Reuters)

Framed by the setting sun, an American Bison grazes at the Tallgrass Prairie National Preserve on Tuesday, April 28, 2015, near Strong City, Kan. The buffalo herd at Tallgrass is one of the few herds of wild bison left in the United States. (Photo by Travis Heying/The Wichita Eagle via AP Photo)

Paul, 9, dumps a bucket of water over his head at a fountain near government buildings during hot weather on July 1, 2015 in Berlin, Germany. Temperatures across northern Europe are rising and in Germany a high of 36 degrees is forecast for the weekend. (Photo by Sean Gallup/Getty Images)

Fires approach a home near Lower Lake, Calif., Friday, July 31, 2015. A series of wildfires were intensified by dry vegetation, triple-digit temperatures and gusting winds. The golden hills of California were being blackened Friday by a series of wildfires egged on by bone-dry vegetation, triple-digit temperatures and gusting winds. (Photo by Jeff Chiu/AP Photo)

A partially burned American flag lies on the street near the spot where Michael Brown was killed before an event to mark the one year anniversary of his killing in Ferguson, Missouri August 9, 2015. (Photo by Rick Wilking/Reuters)

A man checks his mobile phone near overturned shipping containers after explosions hit the Binhai new district, Tianjin, August 13, 2015. A huge explosion hit an industrial area in the northeastern Chinese city of Tianjin late on Wednesday evening, triggering a blast wave felt several kilometres away and injuring at least 50 people, domestic media reported. (Photo by Reuters/Stringer)

Combine harvesters work on a wheat field of the Solgonskoye farming company near the village of Talniki, southwest from Siberian city of Krasnoyarsk, Russia, August 27, 2015. Russia, one of the world's top wheat exporters, will harvest its third-largest grain crop in post-Soviet history this year, leading Russian consultancy SovEcon said on August 27 after upgrading its forecast. (Photo by Ilya Naymushin/Reuters)