Dark clouds bearing down on the city on April 17, 2011 in Foshan, Guangdong Province of China. According to flood control authorities on Monday, gales as strong as 45.5 meters per second, accompanied by hailstorm, cloudburst and strong wind battered cities including Guangzhou, Foshan, Zhaoqing and Dongguan of south China's Guangdong Province on Sunday, has killed at least 17 people and injured 118. (Photo by ChinaFotoPress/Getty Images)

Mazda Motor introduces the company's concept vehicle, Taiki during the press day of the 40th Tokyo Motor Show at Makuhari Messe, on October 24, 2007 in Chiba Prefecture, Japan. (Photo by Koichi Kamoshida/Getty Images)

Color dyed rabbits are seen in the markets of the Souq Waqif on January 12, 2011 in Doha, Qatar. (Photo by Robert Cianflone/Getty Images)

Three secondary schoolboys smoking an illicit cigarette in Hyde Park, London. (Photo by Evening Standard/Getty Images). May 1972

“Contrails (short for “condensation trails”) or vapour trails are artificial clouds that are the visible trails of condensed water vapour made by the exhaust of aircraft engines. As the hot exhaust gases cool in the surrounding air they may precipitate a cloud of microscopic water droplets or, if the air is cold enough, tiny ice crystals”. – Wikipedia

Photo: An airplane leaves a vapor trail as it flies in front of he moon on January 17, 2007 above Hanover, Germany. (Photo by Alexander Hassenstein/Getty Images)

“Not for the faint of heart”. Casa Milà, better known as La Pedrera, is a building designed by the Catalan architect Antoni Gaudí and built during the years 1905–1910, being considered officially completed in 1912. It is located at 92, Passeig de Gràcia in the Eixample district of Barcelona, Catalonia, Spain. (Photo by Stefano Scarselli)

Two women look at a mobile phone as they stand on Tiananmen Square during a sand storm in heavily polluted weather in Beijing on February 28, 2013. Beijing residents were urged to stay indoors as pollution levels soared before a sandstorm brought further misery to China's capital. (Photo by Ed Jones/AFP Photo)