File:Glacier Mass Balance.png

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Description

Map of glacier thickness changes since 1970.

This figure shows the change in average thickness of mountain glaciers around the world. This information, known as the glaciological mass balance, is found by measuring the annual snow accumulation and subtracting surface ablation driven by melting, sublimation, or wind erosion. These measurements do not account for thinning associated with iceberg calving, flow related thinning, or subglacial erosion. All values are corrected for variations in snow and firn density and expressed in meters of water equivalent (Dyurgerov 2002).

Measurements are shown as both the annual average thickness change and the accumulated change during the fifty years of measurements presented. Years with a net increase in glacier thickness are plotted upwards and in red; years with a net decrease in glacier thickness (i.e. positive thinning) are plotted downward and in blue. Only three years in the last 50 have experienced thickening in the average.

Systematic measurements of glacier thinning began in the 1940s, but fewer than 15 sites had been measured each year until the late 1950s. Since then more than 100 sites have contributed to the average in some years (Dyurgerov 2002, Dyurgerov and Meier 2005). The percentage of measurement sites at which net thinning has been observed averages two-thirds over this interval, and reached a maximum of 96% in 2003 (Dyurgerov 2005). Error bars indicate the standard error in the mean.

Other observations, based on glacier length records, suggest that glacier retreat has occurred nearly continuously since the early 1800s and the end of the little ice age, but variations in rate have occurred, including a significant acceleration during the twentieth century that is believed to have been a response to global warming (Oerlemans 2005).

Further information: Retreat of glaciers since 1850

Data

These measurements are described in Dyurgerov (2002), updated in Dyurgerov and Meier (2005), and archived at the World Glacier Monitoring Service at the National Snow and Ice Data Center. [1] [2]

Copyright

This figure was prepared by Robert A. Rohde from published data.

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References

• [abstract] [full text] Dyurgerov, Mark B. (2002). Glacier Mass Balance and Regime: Data of Measurements and Analysis. Occasional Paper 55. 
• [abstract] [full text] Dyurgerov, Mark B. and Mark F. Meier (2005). Glaciers and the Changing Earth System: A 2004 Snapshot. Institute of Arctic and Alpine Research. Occasional Paper 58. 
• [abstract] [DOI] Oerlemans, J.H. (2005). "Extracting a Climate Signal from 169 Glacier Records". Science 308: 675-677. 

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File history

Click on a date/time to view the file as it appeared at that time.

	Date/Time	Thumbnail	Dimensions	User	Comment
current	10:06, 29 July 2006		658×500 (24 KB)	Robert A. Rohde (Talk | contribs)	(invert scales, more intelligible)
	09:09, 29 July 2006		650×499 (23 KB)	Robert A. Rohde (Talk | contribs)