Lightning strikes the Willis Tower (formerly Sears Tower) in downtown on June 12, 2013 in Chicago, Illinois. (Photo by Scott Olson/Getty Images)

Julian, left, is photographed by his mother with friend Gianluca, right, under water at a public pool in Gelsenkirchen, Germany, on a hot Friday, July 3, 2015. Germany faces a heat wave with temperatures up to 38 degrees Celsius (100 degrees Fahrenheit) at the weekend. (Photo by Martin Meissner/AP Photo)

A combination photo shows various popular street foods under $6 from various hawker food stalls and eateries in Singapore, taken between July 28 to 31, 2016. Top row (L to R) bak chor mee, soya sauce chicken; Middle row (L to R) laksa, hokkien mee, nasi lemak, ice kachang; Bottom row (L to R) rojak, roti prata and satay. (Photo by Edgar Su/Reuters)

Netapp Endura team rider Slovenian Blaz Jarc (R) crashes into Katusha team rider Russian Viacheslav Kuznetsov (ground) during the 112th Paris Roubaix cycling race, in Roubaix, France, 13 April 2014. (Photo by Nicolas Bouvy/EPA)

“The Challenge!” Young boy relishes in a game of tug of war before school. Photo location: Lake Titicaca, Peru. (Photo and caption by Paul Heyman/National Geographic Photo Contest)

A competitor walks on tightrope during a performance in Taizhou, Zhejiang Province, China, May 7, 2016. (Photo by Reuters/China Daily)

A boat is stranded on Poyang Lake in Lushan City, China during low-water season on November 3, 2016. (Photo by Xinhua/Barcroft Images)

Filipino beauty candidates hide from the sun before a group photo during the media presentation of the Miss Philippines Earth 2017 held at a hotel in Manila, Philippines, 05 July 2017. A total of 40 environmentally aware and concerned Filipino young ladies will compete to represent the Philippines at the Miss Earth beauty pageant. Miss Earth is a pioneering beauty pageant that serves as a vehicle for environmental advocacy. (Photo by Mark R. Cristino/EPA)