I walked the Alps largest glacier. It felt like last-chance tourism

A trek on the Aletsch glacier in Switzerland’s Bernese Alps is dazzling, but also a stark example of the damage caused by global warming

Seven of us are roped in a line, with hiking poles in our hands and crampons on our boots. Led by our guide, David, we take it in turns to step from rock into the marbled grey ice beyond. I hesitate before taking my step; the act feels oddly disrespectful. It takes a few minutes to trust that the spikes will hold their grip, but I get used to the crunching rhythm and the occasional tug of the rope. The summer sunshine is warm but a coldness radiates from below. It is a six-hour hike to the hut we will sleep in tonight.

This is the Aletsch glacier in Switzerland’s Bernese Alps. It is 15 miles long and up to 800 metres deep, the largest and longest glacier in the Alps. From above, its mass looked uniform, but up close it is creased and contorted, speckled with browns, blacks and greys, and glimpses into its deep crevasses reveal a startling turquoise. Two gritty parallel lines follow its long curve downhill, moraines that act as conveyor belts bearing rocks and rubble. As David reminds us, the ice is not static but a dynamic system, a frozen river in a constant state of (very slow) motion.