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Historic Variability of Lake Ice
Lake ice freeze-up and break-up data provide useful information on temperature changes. On average, ice freeze-up and break-up are observed to change ~1 day for a 0.2°C change in air temperature, thus lake ice information can provide a valuable proxy record of climate change, particularly in data sparse areas. Several recent studies (e.g. Magnuson et al, 2000) have shown that lake ice in many regions of the Northern Hemisphere is beginning to form later and melt earlier, and there has been a demonstrated relationship between "anomalous" lake ice years and certain ENSO events.
Below is a map showing the network of Canadian lake ice sites (1822-1995) prepared by Frédéric Lenormand from Centre d'études nordiques, Université Laval. The numbers correspond to lake sites on which studies of their ice freeze-up and ice break-up dates have been undertaken. Click on each numbered lake on the map to view the variability of that lake's ice freeze-up, break-up, ice duration and ice thickness over the past century or more.
Alternatively, click on the links below to view the same illustrations (each image file is about 120kb in size):
Recent Case Studies
Analysis of trends in the dates of river freeze-up, river ice break-up, and periods of ice-cover in Canada was recently carried out by Zhang et al. (2001) using data from the Canadian Reference Hydrometric Basin Network. The trend results are presented for three different periods: 1969-1996, 1957-1996 and 1947-1996. The results show an interesting regional difference with rivers over western Canada generally showing trends toward earlier break-up, and rivers over the maritimes showing later break-up.
 A study of 81 selected lakes and reservoirs in southern Canada and the upper-midwest USA over the period 1980 to 1994 (Wynne et al, 1998) has revealed a significant (probability < 0.001%) trend toward earlier ice breakup dates. A much larger historical survey of rivers and lakes across the whole of the Northern Hemisphere from 1846 to 1995 by Magnuson et al. (2000) revealed significant trends towards earlier break-up and later formation of lake ice providing further evidence for sytematic global warming over the past 150 years.
The records for this latest study came from nine countries (Canada, USA, Russia, Japan and several European countries). The sources used were as diverse as transportation ledgers, newspaper articles and religious observances. The data set consists of ice records for 746 water bodies.  The average rate of change over the 150-year period was nearly nine days later for freeze dates and almost 10 days earlier for ice break-up dates, according to the study. The importance of these records is that they come from direct human observations, making them difficult to refute in any general way.
Another important finding from the same database (using 184 ice records from 1950 to 1995) was an increase in the interannual variability in freeze and breakup rates over the past three decades (possibly due to the increasing influence of El Nino and La Nina events in the Pacific).
References
- John J. Magnuson, Dale M. Robertson, Barbara J. Benson, Randolph H. Wynne, David M. Livingstone, Tadashi Arai, Raymond A. Assel, Roger G. Barry, Virginia Card, Esko Kuusisto, Nick G. Granin, Terry D. Prowse, Kenton M. Stewart, Valery S. Vuglinski, 2000: Historical trends in lake and river ice cover in the Northern Hemisphere. Science, 289, 1743-1746.
- Wynne, R.H., T.M. Lillesand, M.K. Clayton, and J.J. Magnuson, 1998: Satellite monitoring of lake ice breakup on the Laurentian Shield (1980-1994). Photogrametric Engineering and Remote Sensing (64): 607-617.
- Zhang, X., K.D. Harvey, W.D. Hogg, and T.R. Yuzyk, 2001: Trends in Canadian streamflow. Water Resources Research, 37, 987-998.
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