Temperature and precipitation are the main ingredients for a glacier to form and keep going. The temperature must be cold enough so that more ice accumulates than is lost. The precipitation must be in the form of snow. Today, huge ice sheets exist in the polar regions of the Arctic and Antarctic, where even summer temperatures stay well below freezing. There is little ablation of material in these regions.
Glaciers also can exist in areas that most people consider warm.
New Zealand, Chile, and the northwest of the United States support quite large valley glacial systems. However, the same equation holds true. Most of these glaciers have very high accumulation rates in the winter to balance the ice they lose in the summer melting period.