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164 Role of Glaciers and Ice Sheets in Climate and the Global Water Cycle

Part 14. Snow and Glacier Hydrology

  1. Martin J Siegert

Published Online: 15 APR 2006

DOI: 10.1002/0470848944.hsa170

Encyclopedia of Hydrological Sciences

Encyclopedia of Hydrological Sciences

How to Cite

Siegert, M. J. 2006. Role of Glaciers and Ice Sheets in Climate and the Global Water Cycle. Encyclopedia of Hydrological Sciences. 14:164.

Author Information

  1. University of Bristol, Bristol Glaciology Centre, School of Geographical Sciences, Bristol, UK

Publication History

  1. Published Online: 15 APR 2006


Glaciers and ice sheets store nearly 70% of the world's freshwater and would raise sea level by around 70 m if they melted. They are, thus, an important component of the global water cycle. Their role in climate can be assessed through current responses to global warming and their influence on the environment during periods of glaciation. At the Last Glacial Maximum, ∼21 000 years ago, the glacial cover caused sea level to be 115 to 130 m lower than at present. The climate of Ice Age Earth was affected in many ways by ice sheets. First, the expansion of ice sheets caused huge changes to the surface albedo and, hence, the radiation budget of the planet. Second, the orography of North America and Eurasia was altered significantly by large ice sheets, which had implications for atmospheric flow. Third, as the ice sheets grew and decayed, the influx of freshwater to the oceans, and in particular the North Atlantic, affected the ocean circulation, which in turn affected climate. The result of this ice–ocean–atmosphere interaction was large-scale short-term oscillations in air temperatures, which have been recorded in Greenland ice cores. The ice and climate processes identified for the glacial cycle are relevant today. For example, the Greenland ice sheet is currently melting at its southern margin, and releasing freshwater to the North Atlantic. Importantly, global temperatures were a few degrees higher in the previous interglacial, and the Greenland ice sheet was about half its current size. As global warming continues, the response of the Greenland ice sheet could be to return to its Eemian configuration. Although far smaller in volume, glaciers respond much quicker to climate change than do ice sheets. In the last century, most have experienced decay, and the runoff generated has been estimated to account for at least 10% of the 15 to 20 cm of sea-level rise measured (see Mass and Energy Balances of Glaciers and Ice Sheets,). In combination, glacier and ice-sheet melting may send large quantities of water into the oceans, some of it rapidly. This could have serious implications for the climate of the North Atlantic and, through teleconnection, the world.


  • glaciers;
  • ice sheets;
  • oceans;
  • climate;
  • glaciation;
  • feedback processes