A tourist takes a picture of the Aletsch Glacier near the Eggishorn in Fiesch, Switzerland, August 22, 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)





A close-up view of ice is pictured inside a glacier cave on the Aletsch Glacier in Fiesch, Switzerland, August 29, 2015. (Photo by Denis Balibouse/Reuters)





Ice melts on the Aletsch Glacier in Fiesch, Switzerland, August 12, 2015. (Photo by Denis Balibouse/Reuters)





Mountain guide Christian Pletscher stands in a cave on the Aletsch Glacier in Fiesch, Switzerland, August 29, 2015. (Photo by Denis Balibouse/Reuters)





The Aletsch Glacier is pictured at dusk in Fiesch, Switzerland, August 11, 2015. (Photo by Denis Balibouse/Reuters)





Goats stand on rocks at the Platta viewpoint on the Aletsch Glacier in Fiesch, Switzerland, August 12, 2015. (Photo by Denis Balibouse/Reuters)





Hikers walk on the Aletsch Glacier near the Eggishorn in Fiesch, Switzerland, August 22, 2015. (Photo by Denis Balibouse/Reuters)





The Aletsch Glacier is pictured from the Eggishorn summit in Fiesch, Switzerland, August 22, 2015. (Photo by Denis Balibouse/Reuters)





Hikers begin their descent to the Aletsch Glacier in the early morning from the Konkordia Hut, Switzerland, August 29, 2015. (Photo by Denis Balibouse/Reuters)





Hikers get ready under the full moon at the Konkordia Hut above the Aletsch Glacier at Konkordia Place, Switzerland, August 29, 2015. (Photo by Denis Balibouse/Reuters)





Mountain guide Christian Pletscher looks towards the Aletsch Glacier from the Jungfraufirn Glacier, Switzerland, August 28, 2015. (Photo by Denis Balibouse/Reuters)





A group of hikers (top L) walk on the Aletsch Glacier in Fiesch, Switzerland, August 12, 2015. (Photo by Denis Balibouse/Reuters)





Hikers climb the 460 steps up to the Konkordia Hut on the Aletsch Glacier, Switzerland, August 28, 2015. (Photo by Denis Balibouse/Reuters)





A close-up view of ice on the Aletsch Glacier is pictured in Fiesch, Switzerland, August 12, 2015. (Photo by Denis Balibouse/Reuters)





Hikers walk on the south side of the Aletsch Glacier in Riederalp, Switzerland, August 23, 2015. (Photo by Denis Balibouse/Reuters)





Hikers stand on the side of the Aletsch Glacier in Fiesch, Switzerland, August 12, 2015. (Photo by Denis Balibouse/Reuters)





Marks left by ice are pictured on a rock with the Aletsch Glacier in the background in Fiesch, Switzerland, August 12, 2015. (Photo by Denis Balibouse/Reuters)





Hikers walk on the south side of the Aletsch Glacier in Riederalp, Switzerland, August 23, 2015. (Photo by Denis Balibouse/Reuters)





The Aletsch Glacier is pictured in Riederalp, Switzerland, August 23, 2015. (Photo by Denis Balibouse/Reuters)





Hikers walk down steps onto the Aletsch Glacier, Switzerland, August 29, 2015. (Photo by Denis Balibouse/Reuters)





Goats and sheep rest at the Platta viewpoint on the Aletsch Glacier in Fiesch, Switzerland, August 12, 2015. (Photo by Denis Balibouse/Reuters)





A man takes a picture of his family at the Eggishorn Summit with the Aletsch Glacier in the background in Fiesch, Switzerland, August 22, 2015. (Photo by Denis Balibouse/Reuters)





Hikers walk on the Aletsch Glacier near the Eggishorn in Fiesch, Switzerland, August 22, 2015. (Photo by Denis Balibouse/Reuters)





A helicopter takes off after delivering supplies to the Konkordia Hut near the Aletsch Glacier, Switzerland, August 28, 2015. (Photo by Denis Balibouse/Reuters)





A roped team of hikers descend from the Jungfraufirn Glacier towards the Aletsch Glacier at the Jungfrau, Switzerland, August 28, 2015. (Photo by Denis Balibouse/Reuters)





A goat rests at the Platta viewpoint as a group of hikers (background on R) trek in the distance on the Aletsch Glacier in Fiesch, Switzerland, August 12, 2015. (Photo by Denis Balibouse/Reuters)