Owing to the mountains' latitude near the Tropic of Cancer, the permanent snow line is among the highest in the world at typically around 5,500 m (18,000 ft).[30] In contrast, equatorial mountains in New Guinea, the Rwenzoris and Colombia have a snow line some 900 m (2,950 ft) lower.[31] The higher regions of the Himalayas are snowbound throughout the year, in spite of their proximity to the tropics, and they form the sources of several large perennial rivers.
In recent years, scientists have monitored a notable increase in the rate of glacier retreat across the region as a result of climate change.[32][33] For example, glacial lakes have been forming rapidly on the surface of debris-covered glaciers in the Bhutan Himalaya during the last few decades. Although the effect of this will not be known for many years, it potentially could mean disaster for the hundreds of millions of people who rely on the glaciers to feed the rivers during the dry seasons.[34][35][36] The global climate change will affect the water resources and livelihoods of the Greater Himalayan region.