page_title: Glacier mass balance
section_title: Measurement methods
hierarchical_section_title: Glacier mass balance / Measurement methods
caption_attribution_description: Glacier de Grinnell 1850-1981
context_page_description: Crucial to the survival of a glacier is its mass balance or surface mass balance, the difference between accumulation and ablation. Climate change may cause variations in both temperature and snowfall, causing changes in the surface mass balance. Changes in mass balance control a glacier's long-term behavior and are the most sensitive climate indicators on a glacier. From 1980–2012 the mean cumulative mass loss of glaciers reporting mass balance to the World Glacier Monitoring Service is −16 m. This includes 23 consecutive years of negative mass balances.
  A glacier with a sustained negative balance is out of equilibrium and will retreat, while one with a sustained positive balance is out of equilibrium and will advance. Glacier retreat results in the loss of the low elevation region of the glacier. Since higher elevations are cooler than lower ones, the disappearance of the lowest portion of the glacier reduces overall ablation, thereby increasing mass balance and potentially reestablishing equilibrium. However, if the mass balance of a significant portion of the accumulation zone of the glacier is negative, it is in disequilibrium with the local climate.
caption: Grinnell Glacier in Glacier National Park (U.S.) showing recession since 1850 of 1.1 km USGS
exif: {}