People on motor bikes celebrate American President Barack Obama's visit to Kenya by holding up a photo, center top, of the president and First Lady Michelle Obama in Kisumu, Kenya, Saturday, July 25, 2015. President Barack Obama heralded Africa as a continent “on the move” Saturday as he opened a U.S.-sponsored business summit in Kenya, the East African nation where he has deep family ties. (Photo by AP Photo)

An art installation formed with milk churns, made by land art artist Gerard Benoit a la Guillaume, is seen at the Chenau de Mayen in the resort of Leysin, Switzerland August 7, 2015. More than 80 milk churns were placed between the Tour d'Ai and the Tour de Mayen summits at an altitude of 2,000 meters (6,561 feet) above sea level under the direction of the artist, to be photographed for his ongoing art project entitled “Milk churns without borders”. (Photo by Denis Balibouse/Reuters)

Roped up climbers leave the summit of Breithorn at 4,164 metres (13,661 feet) on the ridge marking the border with Switzerland (left) and Italy in the Alpine resort of Zermatt August 4, 2014. Switzerland will vote on November 30 on an initiative from the group Ecopop which proposes a cap on the number of immigrants. The group says it is motivated by concerns about a lack of living space exerting too much pressure on the land and natural resources, rather than by opposition to foreigners. (Photo by Denis Balibouse/Reuters)

People try to catch offerings thrown off the summit of Mount Bromo volcano by Tengger tribe members and local tourists in Probolinggo, East Java province on July 18, 2019, as part of the Yadnya Kasada Festival. During the annual Yadnya Kasada festival, the Tenggerese climb Mount Bromo, an active volcano, and seek the blessing from the main deity by presenting offerings of rice, fruit, livestock and other items. (Photo by Juni Kriswanto/AFP Photo)

Nguyen Thi Vui paddles her boat in the flooded streets of Hoi An, Vietnam, Monday, November 6, 2017. A powerful typhoon that rocked Vietnam has killed dozens of people and caused extensive damage to the country's south-central region ahead of the APEC summit that will draw leaders from around the world, the government said Monday. (Photo by Hau Dinh/AP Photo)

Young Japanese women pose with a green bear costumed person during the 'Earth Parade 2015' in Tokyo, Japan, Saturday, November 28, 2015. Ahead of the U.N. climate change summit in Paris starting this week, about 1,000 citizens and environmental activists took to the streets of Tokyo on Saturday, calling for strong actions to combat global warming. (Photo by Franck Robichon/EPA)

A group of around 400 demonstrators participate in a protest by burying their heads in the sand at Sydney's Bondi Beach November 13, 2014. Hundreds of protesters participated in the event, held ahead of Saturday's G20 summit in Brisbane, which was being promoted as a message to Australian Prime Minister Tony Abbott's government that, “You have your head in the sand on climate change”. (Photo by David Gray/Reuters)

This is a portion of the first color 360-degree panorama from NASA's Curiosity rover, made up of thumbnails, which are small copies of higher-resolution images. The mission's destination, a mountain at the center of Gale Crater called Mount Sharp, can be seen in the distance, to the left, beginning to rise up. The mountain's summit will be imaged later. (Photo by NASA/JPL-Caltech/MSSS)