A handout picture of the Aletsch Glacier in Fieschertal, Switzerland taken between 1860 and 1890 and released by Library of Congress, is displayed at the same location on September 4, 2019. Picture taken September 4, 2019. REUTERS/Denis Balibouse and Library of Congress/Handout via REUTERS

The Trient Glacier is pictured in 1891 in Trient, Switzerland in this handout picture released by the ETH Library Zurich. Glaziologische Kommission der Akademie der Naturwissenschaften Schweiz/ETH Library Zurich/Handout via REUTERS

The Eiger, Guggi and Giesen Glaciers are pictured near the Jungfrau in the Swiss Alps in Wengen, Switzerland August 27, 2019. Picture taken August 27, 2019.

People sit above the Aletsch Glacier in the Swiss Alps at the Eggishorn in Fieschertal, Switzerland September 4, 2019.

The Aletsch Glacier is pictured from the Eggishorn between 1860 and 1877 in Fieschertal, Switzerland in this handout picture released by the ETH Library. Adolphe Braun/Glaziologische Kommission der Akademie der Naturwissenschaften Schweiz/ETH Library Zurich/Handout via REUTERS

The Rhone Glacier and Belvedere Hotel are seen in the Swiss Alps in Obergoms, Switzerland August 21, 2019.

The Rhone Glacier and Belvedere hotel are pictured before 1938 in Obergoms, Switzerland in this handout picture released by the ETH Library Zurich. ETH Library Zurich/Handout via REUTER

The Aletsch Glacier pictured in 1865 is seen in Belalp, Switzerland in this handout picture released by the ETH Library Zurich. Adolphe Braun/Glaziologische Kommission der Akademie der Naturwissenschaften Schweiz/ETH Library Zurich/Handout via REUTERS

The Eiger, Guggi and Giesen Glaciers are pictured near the Jungfrau between 1890 and 1900 in Wengen, Switzerland in this handout picture released by the Library of Congress. Library of Congress/Handout via REUTERS

The Rhone Glacier is pictured in Furka, Switzerland August 21, 2019.

The Rhone Glacier pictured in 1849 is seen in this handout image released by the ETH Library Zurich. Leo Wehrli/Verein Schweizerischer Geographie-Lehrer/ETH Library Zurich/Handout via REUTERS

The Trient Glacier is seen in the Swiss Alps in Trient, Switzerland August 26, 2019.

The Aletsch Glacier is pictured in the Swiss Alps in Belalp, Switzerland September 3, 2019.

A handout picture of the Gorner Glacier taken in 1863 in Zermatt, Switzerland and released by ETH Library Zurich, is seen displayed at the same location on August 25, 2019. Picture taken August 25, 2019. REUTERS/Denis Balibouse

A handout picture of the Trient Glacier taken in 1891 and released by ETH Library Zurich, is seen displayed at the same location on August 26, 2019. Picture taken August 26, 2019. REUTERS/Denis Balibouse and Glaziologische Kommission der Akademie der Naturwissenschaften Schweiz/ETH Library Zurich/Handout via REUTERS