An employee of the National Park Service takes a selfie with President Barack Obama, left, in the background meeting with the crowd after a tour of Everglades National Park on Earth Day, Wednesday, April 22, 2015, in Florida. Obama used the visit to warn of the damage that climate change is already inflicting on the nation's environmental treasures. (Photo by Lynne Sladky/AP Photo)

A remote-controlled plane in the form of a witch flies over a neighborhood as the sun sets during Halloween in Encinitas, California, U.S. October 31, 2016. (Photo by Mike Blake/Reuters)

A vehicle leaves light trails in a long exposure photograph as it drives beneath the 500-metre Aperture Spherical Radio Telescope in Pingtang county, China. Construction on the device began in 2011 and is nearing completion. (Photo by Liu Xu/AP Photo)

An Afghan man rides on his donkey, holding balloons for sale during Newroz Day celebrations, a festival marking their spring and new year, in Kabul, Afghanistan March 21, 2017. (Photo by Omar Sobhani/Reuters)

A lemur licks a block of ice containing fruit at Rome's Bioparco zoo, Wednesday, July 5, 2017. Zookeepers at the Bioparco often give animals ice blocks with either fruit or meat on hot summer days. (Photo by Gregorio Borgia/AP Photo)

Convicted murderer Hector Alvarado Mazariegos, right, drops to the ground as he is hit by bullets of a Guatemala firing squad in the public cemetery at Mazatenango, June 28, 1975. His companion, Rocael Ortiz, met the same fate a few seconds later. Both were convicted of murder. (Photo by AP Photo/Anzueto)

A man steers with his legs while riding a motorcycle on a road in Vietnam's northern Hoa Binh province, outside Hanoi, October 15, 2015. (Photo by Reuters/Kham)

A man watches a wave hit a rock pool at Curl Curl beach as large swell hits the East Coast of Australia on June 6, 2016 in Sydney, Australia. Torrential rain over the weekend saw streets and homes flooded while wind gusts up to 120km per hour brought down trees and powerlines. A king tide has also seen beachside homes evacuated on Sydney's northern beaches as large waves erode the coast. (Photo by Cameron Spencer/Getty Images)