JUNGFRAUJOCH, Switzerland (Reuters) - Switzerland’s Aletsch glacier is western Europe’s largest expanse of ice, but Swiss scientists say it’s receding at an unprecedented pace, losing up to 12 meters (13 yards) of ice a year.

That vanishing act made the Alpine glacier the site of a publicity stunt on Friday: the creation of what organizers say is the world’s largest postcard. Climate change activists hope it will convince more young people to get involved in keeping rising temperatures in check.

In all, 125,000 postcards with messages against climate change and sent by young people from all over the world have been assembled around 3,400 meters up on the Jungfraufirn, the upper reaches of the Aletsch glacier.

This collection, organized by the Swiss government’s Agency for Development and Cooperation among other groups, includes the message “WE ARE THE FUTURE GIVE US A CHANCE”.

Another message on the snow -- “STOP GLOBAL WARMING #1.5 DEGREES C” -- refers to a U.N. report released last month.

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Its scientists concluded limiting the increase in the Earth’s temperature to 1.5 degrees Celsius -- rather than the 2C target agreed at the 2015 Paris climate talks -- would provide clear benefits, but it would requires rapid, unprecedented changes in how people use energy.

Glaciology experts at the University of Zurich fear the Great Aletsch glacier, visible from space, could disappear by 2100. It still measures 23 kilometers (14.3 miles), but it has receded about 3 km since 1870, and the pace is accelerating. [reut.rs/2Bbtc0U]

The Aletsch glacier has melted so much that in 2012 the receding ice laid bare the remains of three mountain climbers, brothers who had disappeared nearly 90 years earlier on an ill-fated mountain expedition.

That is a far cry from the situation back in 1678, Swiss historians say, when residents of the valley below the Aletsch glacier prayed to the Vatican in Rome for the ice mass to stop its inexorable expansion that was threatening their lives.

Organizers of the postcard say the project will be climate- neutral.