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Contributions to Sea Level Rise
Glaciers respond to slight but prolonged changes in climate. At least some aspects of these climate changes may be deduced from observations of glacier fluctuations. This useful relationship was the basis for scientific activity beginning in the 18th and 19th centuries, and led directly to the formation of the International Commission of Snow and Ice in 1894.
The study of glacier fluctuations is relevant to an understanding of climate and climate change over temporal scales from years to a century or more, and at regional to global spatial scales. As glaciers wax and wane, they store or release water; this "natural regulation" of runoff from glacierized areas is critical to water supply and use in many mountain areas. This storage or release of water also affects global sea level; at least one third of the observed sea level rise in the last 100 years has come from the melting of glaciers exclusive of the Greenland and Antarctic Ice Sheets.
We live in a time of increasing greenhouse gas concentrations with an attendant warming of the climate. Understanding how glaciers of the world react is vital to better defining the regional pattern of climate change, and to project future changes in water resources and sea level. The critical link between glaciers and climate is the glacier mass balance. Mark Dyurgerov of INSTAAR has produced an updated global synthesis of existing mass balance data aimed at improving our understanding of glacier-climate interactions.
One of the most serious consequences of global warming is rising sea level. With so much human activity concentrated along coastlines and areas only a few meters above sea level, modest flooding will likely cause societal and economic distress. Contributing to global sea level rise are thermal expansion of ocean water and melting glaciers, ice caps and ice sheets. Other causes may be important locally but are not significant on a global basis. The contributions to sea level rise due to changes in the Antarctic and Greenland ice sheets, although not well understood, are thought to be smaller than the contributions from mountain glaciers and smaller ice caps.
The World Glacier Monitoring Service (WGMS) publications are the main sources of data used in this data set. The goal of this work is less ambitious than that of the WGMS (which aims to create and make accessible a complete database of all characteristics of glaciers, including fluctuations) but goes beyond the WGMS mass balance publications. A similar effort has been made at Trent University in Canada.
This data set presents measurements of glacier mass balance from records collected over the history of mass balance measurement activity. Until now, these data were spread through many publications, which may explain why glaciological data have not been used as fully as they could be. Mass balance data have not been appropriately organized, i.e. digitized, quality checked, made accessible electronically, and compiled as a continuous series of variables. It has taken many years to gather, organize, and present the mass balance and related data contained in this data set. This time series of the main parameters of glacier regime is available for use by the climate and hydrological communities and other scientific disciplines.
Changes in glacier mass balance must be estimated accurately to compare with other components of the water balance of the Earth, such as changes in the amount of water stored in the ground and changes in mass of the Greenland and Antarctic ice sheets. The critical link between glaciers and climate is the glacier mass balance. Mass balances of more than 300 glaciers have been measured at one time or another since 1946. All of these data are included, but the short analysis represented in these tables and graphs emphasizes the 1961-2001 time period.
This analysis is focused on mountain glaciers and smaller ice caps, which have a total area at least 785x103 km2. Although they make up only 4% of the total land ice area, they may have contributed to as much as 30% of sea level change in the 20th century due to rapid ice volume reduction connected with global warming.
|Largest Contributors to Global Water Cycle and Sea Level Rise|
|Region||Percentage of Total Area||Percentage of Contribution to Volume Change
|High Mountain Asia||19.4||23.9|
|Alaska and Coastal Mountains||15.0||23.0|
|NW USA and SW Canada||6.5||16.6|
|Patagonia Ice Fields||3.3||4.7|
Measurements of Glacier Change
Annual change in global glacier thickness (left axis, meters of water equivalent, m/yr) and cumulative value (right axis, m), based on surface area-weighted mass balance observations. Dates of major volcanic eruptions are shown, since stratospheric aerosols have a cooling effect on climate. Red arrow highlights volume rate change.
Contributions to Sea Level
Annual glacier contribution to sea level change (left axis, mm/yr), and cumulative value (right axis, mm) based on area-weighted averaged mass balance.
Supporting article: Glacier Mass Balance and Regime (PDF file, 2 MB)
Glaciology at Trent
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