Inside the highest glaciers of the Alps lies an invaluable archive of data revealing the Earth's historic climate. However, as the atmosphere warms due to climate change, so does the glaciers' internal temperature, threatening the future longevity of these records. Using our customised Python model, validated by on-site measurements, we show how a doubling in surface melt has caused a warming of 1.5 °C in the past 21 years and explore the challenges of modelling in complex mountainous terrain.