An Afghan journalist takes a “selfie” as U.S. President Barack Obama (R) holds a joint news conference with Afghanistan's President Ashraf Ghani (C) at the White House in Washington March 24, 2015. (Photo by Jonathan Ernst/Reuters)

“The Amazon river has a newly discovered source. Completed last year and led by West Hansen and documented by award-winning freelance photographer Erich Schlegel, this is the first expedition to paddle from the furthest source of the earth's largest river to the ocean”. – zReportage. Photo: August 19, 2012 – Alpamarca, Peru – Amazon Express white water members Juan Antonio De Ugarte, of Peru, Rafael Ortiz, of Mexico, West Hansen, of the U.S., and Tino Specht, of the U.S., paddle down the Rio Gashan after leaving Lago Acucocha. Lago Acucocha is possibly the dry season source of the Amazon River. (Photo by Erich Schlegel/zReportage via ZUMA Press)

A woman walks in front of an art installation made of artificial fruits and vegetables during the “Moscow Autumn” festival in central Moscow, September 14, 2015. (Photo by Maxim Zmeyev/Reuters)

A girl uses her mobile phone during the evening at the National Park in Khartoum, Sudan, April 24, 2015. (Photo by Mohamed Nureldin Abdallah/Reuters)

Arnaq Egede walks to the potato field on her family's farm on July 31, 2013 in Qaqortoq, Greenland. The farm, the largest in Greenland, has seen an extended crop growing season due to climate change. (Photo by Joe Raedle/Getty Images)

A woman photographs a Norwegian spruce Christmas tree from Oslo after it was lit at Trafalgar Square in central London, December 4, 2014. (Photo by Toby Melville/Reuters)

U.S. Secretary of State John Kerry stands inside the historic Shackleton hut near McMurdo Station, Antarctica, Friday, November 11, 2016. Kerry became the highest-ranking American official to visit Antarctica when he landed for a two-day trip on Friday. He's been hearing from scientists about the impact of climate change on the frozen continent. Kerry's aides described the trip as a learning opportunity for the secretary of state. He has been receiving briefings from scientists working to understand the effects of climate change on Antarctica. Kerry has made climate change an intensive focus of American diplomacy during his term, and had previously spent decades working on the issue as a U.S. senator. Trump has called climate change a hoax and said he would “cancel” U.S. involvement in the landmark Paris Agreement on global warming. (Photo by Mark Ralston/Pool Photo via AP Photo)

Ngorongoro Crater (Tanzania). At 610m deep and 260 sq km, this is the largest unflooded caldera in the world. A blue-green vision from above it's a haven for engangered wildlife and Maasai livestock. The crater was formed three million years ago when a giant volcano, which could have been as high as Kilimanjaro, exploded and collapsed. The caldera formed the concentric fractures in the crust cracked down to a magma reservoir deep underground. (Photo by John Bryant/Getty Images)