Measuring glacier change
Melt runoff from glaciers in mountain environments provides 50 - 75% of the world’s fresh water supply. Glaciers gain and lose mass through snowfall, melting and sublimation (when water evaporates directly from solid ice). Glaciers that terminate in a lake or the ocean also lose mass through iceberg calving. Those that end in the ocean are called tidewater glaciers, and they have more complex cycles of advance and retreat than glaciers that terminate on land, at least on annual and decades-long time scales. (climate.gov ) Global climate has changed rapidly with an average increase of 1.5°F over the past 100 years. While this number may seem insignificant, noticeable changes have occurred in the glaciers in the park. In 1850, glaciers numbered around 150. By 1966, the number dropped to 50 named and unnamed glaciers. As of 2009, according to USGS, 26 glaciers remained. Glaciers are no longer considered glaciers when their area diminishes to 25 acres