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Why can mountains have permanent snow and ice near their peaks?

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A car drives along the Trans-Canada Highway with Mount Sir Donald's sharp, snow-capped peak rising above forested slopes in the Selkirk Mountains, British Columbia. — mountain Mount Sir Donald in the Selkirk Mountains, British Columbia, looms above a segment of the Trans-Canada Highway.

Mountains can maintain permanent snow and ice near their peaks primarily due to the effects of altitude on temperature and atmospheric pressure.

As air rises to higher elevations, it encounters lower atmospheric pressure, causing it to expand. This expansion leads to adiabatic cooling, a process where the air cools as it uses its own energy to expand, resulting in significantly lower temperatures at higher altitudes compared to lower elevations. Because atmospheric temperature drops by approximately 0.5 to 0.6 °C per 100 metres of ascent, high-altitude regions often remain cold enough to prevent snow from melting throughout the year.12

When a mountain is sufficiently high, it reaches an elevation known as the snow line, above which the climate is cold enough to collect and sustain permanent snow and ice. The specific elevation of this line varies globally based on latitude and local climatic conditions.3