In this Wednesday, August 20, 2014 photo released by Red Bull, Maikel Melero of Spain warms up prior to the fifth stage of the Red Bull X-Fighters World Tour in the South African savanna of Pretoria, South Africa. (Photo by Joerg Mitter/AP Photo/Red Bull)

Labourers walk near trucks loaded with logs, which are trapped on a muddy road, near an unreserved forest in the village of Igbatoro, southwest Nigeria, August 28, 2014. Wood, a form of biomass, is the sole source of energy for hundreds of millions of Africans who lack access to modern sources of power, and logging, both legal and illegal, remains a lucrative business that has contributed to the rapid shrinking of Africa's rainforests and woodlands. (Photo by Akintunde Akinleye/Reuters)

A man takes pictures at the finish line during the Colour Run at Centennial Park in Sydney August 25, 2013. According to organizers, 15,000 runners registered to complete the 5km (3 miles) course in Centennial Park on Sunday, being covered in blue, pink, orange and yellow powder on their way to the finish line. (Photo by Daniel Munoz/Reuters)

Twenty five life-size donkeys have been given pride of place in St Paul's Cathedral as part of an interfaith exhibition. They've been painted by Egyptian and Western artists, to show solidarity for the people of Egypt. Photo: Artist painted donkey statues are displayed in the “Caravan” exhibition on August 30, 2013 in London, England. (Photo by Peter Macdiarmid)

A man covered in motor oil, poses for a picture next to a girl dress a traditional clothes during a festivities in honor of Santo Domingo de Guzman in Managua, Nicaragua, Saturday, August 1, 2015. Some of the faithful coat their bodies in a black motor oil, red paint and wear traditional clothes as a promise for a prayer or miracle they believe was performed or answered by Managua's patron saint, Santo Domingo de Guzman. (Photo by Esteban Felix/AP Photo)

A former paratrooper demonstrates his strength and skills while lifting a chair during the celebrations for the Paratroopers Day at the Central park in the Siberian city of Krasnoyarsk, Russia, August 2, 2015. Paratroopers are an elite unit of the Soviet Army, and everyone in the country recognize their blue berets. (Photo by Ilya Naymushin/Reuters)

Stefan Dobrovolny of Austria and Inigo Munoz Elorza of Spain (R) stand in front of a quad bike during a simulated Mars mission on Tyrolean glaciers in Kaunertal, Austria, August 7, 2015. The Austrian Space Forum is sending some of its researchers to practice weight-less walking in spacesuits on a glacier which resembles the terrain on Mars. (Photo by Dominic Ebenbichler/Reuters)

An exhausted and frustated migrant holds his head after he missed to get a place on a train heading to the Serbian border at the train station in Gevgelija, The Former Yugoslav Republic of Macedonia, August 13, 2015. From the beginning of the year to mid-June 2015, nearly 160,000 migrants landed in the southern European countries, mainly Greece and Italy, on their way to wealthier countries in Western and Northern Europe, according to estimates by the International Organization for Migration (IOM). (Photo by Georgi Licovski/EPA)