In its heyday, the Pastoruri glacier in central Peru drew daily throngs of tourists, packed into dozens of double-decker buses 5,000 metres high into the Andes to ski, build snowmen and scale its dizzying peaks.

It was so bright with ice and snow that sunglasses were mandatory.

But in less than 20 years, including at least 10 of the hottest on record, Pastoruri has shrunk in half, and now spans over a third of a square kilometre.

Melting ice has given way to slabs of black rock, two small lakes gathering the glacial runoff have swollen together and officials have banned climbing on the unstable formation.

“There isn’t much left of our great tourist attraction,” said local guide Valerio Huerta, squinting at Pastoruri. “Tourists now always leave totally disappointed.”

The dwindling number of visitors to Pastoruri – 34,000 last year compared to an estimated 100,000 per year in the 1990s – has eroded tourism earnings that support thousands in the Cordillera Blanca, Peru’s most popular cluster of snowy peaks.

Now, locals are making a bid to lure tourists back to Pastoruri before it is gone completely – likely in a decade.

Instead of marketing Pastoruri as the pristine Andean winter wonderland it once was – visible in outdated pictures that still hang in hotels and restaurants in nearby towns – the peak is being rebranded as a place to see climate change in action.

The “climate change route”, to officially launch in March, is the latest offbeat answer to rising temperatures that have eaten up 30 to 50 per cent of Andean glaciers in recent decades.

Peruvians have insulated ice with sawdust to stave off melting and painted exposed rock white to reflect sunlight. Those experiments curb glacial retreat on a small scale, but cannot bring ice blocks like Pastoruri back from the brink, said Selwyn Valverde with the Huascaran National Park, home to Pastoruri and more than 700 other shrinking Peruvian glaciers.