The world’s largest postcard was displayed on the shrinking Aletsch Glacier in the Swiss Alps on Friday.
Organisers set the challenge to raise awareness of climate change.
The huge mosaic postcard is actually made from 125,000 drawings and messages about climate change.
They measure 2,500 sq m and were created by children from all over the world.
Seen from above, the whole picture read: “STOP GLOBAL WARMING #1.5 DEGREES C” – echoing scientists’ calls to limit the rise in Earth’s temperature.
The Aletsch Glacier is visible from space, but is shrinking by up to 12m a year. It is the largest in Western Europe at 23km, but experts have warned that it could disappear altogether by 2100.