Glaciers are sentinels of climate change. Ice that took centuries to develop can vanish in just a few years. A glacier doesn't melt slowly and steadily like an ice cube on a table. Once glacial ice begins to break down, the interaction of meltwater with the glacier's structure can cause increasingly fast melting and retreat.
Widespread loss of glaciers would likely alter climate patterns in complex ways. Glaciers have white surfaces that reflect the Sun's rays. This helps keep our current climate mild. When glaciers melt, darker surfaces are exposed, which absorb heat. This raises temperatures even more.