Police in riot gear hold back demonstrators against U.S. Republican presidential candidate Donald Trump outside the Hyatt hotel where Trump is set to speak at the California GOP convention in Burlingame, California, U.S., April 29, 2016. (Photo by Noah Berger/Reuters)

The Aletsch Glacier is pictured at dusk in Fiesch, Switzerland, August 11, 2015. One of Europe's biggest glaciers, the Great Aletsch coils 23 km (14 miles) through the Swiss Alps – and yet this mighty river of ice could almost vanish in the lifetimes of people born today because of climate change. The glacier, 900 metres (2,950 feet) thick at one point, has retreated about 3 km (1.9 miles) since 1870 and that pace is quickening. (Photo by Denis Balibouse/Reuters)

The six-months-old female koala cub holds on to the back of zoo keeper Lena at the zoo in Duisburg, Germany, 23 October 2015. The yet unnamed baby weighs 580 grams. (Photo by Roland Weihrauch/EPA)

A couple watches the sunset over a sea of fog covering the Geneva Lake from Chardonne, Switzerland, 28 December 2015. (Photo by Jean-Christophe Bott/EPA)

A reveller is seen smoking at the annual gay pride parade in Santo Domingo in the Dominican Republic July 03, 2016. (Photo by Ricardo Rojas/Reuters)

Nepalese Hindu priests perform rituals during Janai Purnima festival at Pashupatinath temple in Kathmandu, Nepal, Thursday, August 18, 2016. During this festival Hindus take holy baths and perform annual change of the Janai, a sacred cotton string worn around their chest or tied on the wrist, in the belief that it will protect and purify them. (Photo by Niranjan Shrestha/AP Photo)

People take part in a snowball fight in front of the Colosseum covered by snow during a snowfall in Rome, Italy, 26 February 2018. Media reports on 26 February state that extreme cold weather is forecast to hit many parts of Europe with temperatures plummeting to a possible ten year low. (Photo by Angelo Carconi/EPA/EFE)

Athlete: Aaron Chase Location: Brooklyn, NY, United States. Image is from the Red Bull Illume Image Quest 2016 contest. Category Winner: New Creativity. (Photo by Ale Di Lullo/Red Bull Illume)