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How times change Records show ice is forming later in fall, melting earlier in spring Natures Notebook Ice has been in the headlines far and near, from massive sea ice that's broken off in both the Arctic and Antarctic to melting pack ice to vehicles plunging through lake ice. We've heard sad stories about polar bears and penguins that have been stranded, Inuit communities that have been affected and people who have perished.
Over the past month I've listened to the groaning and moaning of the lake ice as it has expanded and contracted with the changing temperatures. When it booms the sound sends shivers down my back and reinforces my commitment to ice safety.
Lake ice monitoring takes place locally and informally, statewide and formally and globally in both ways. "How's the ice?" is a common question from first ice in the fall to ice out in the spring. Some folks keep records on their own or nearby lakes.
In researching this topic I was impressed with data documented by Canada. The Meteorological Service of Canada's State of the Canadian Cryosphere (SOCC) is the storehouse of historic, as well as current information. I've gleaned and rearranged most of the following from their web site. In some cases, it is presented verbatim.
Manual observations of lake freeze-up and break-up (phenology) have been made at an extensive network of Canadian sites since the 1800s. In addition, the Canadian Ice Service (CIS) monitors Canadian lakes via remote sensing on a regular basis. The CIS also keeps tabs on several lakes in the United States, including three in Minnesota: Rainy, Red and Mille Lacs. A total of 71 lakes are studied.
Although the Canadian network has decreased substantially in recent years, it is increasingly using satellite data, particularly NOAA, AVHRR and Radarsat, to monitor lake ice cover.
The advantage of satellite data is that it provides a complete image of lake ice cover, unlike manual observations that are limited to the local scale. Satellite data also allows lake ice monitoring to be carried out over vast uninhabited areas of Canada, thus providing useful climate information in areas without surface-based observations. Investigations to use passive microwave to collect lake ice processes are being undertaken too.
Ice coverage is measured in tenths, and from this the freeze-up and break-up dates can be determined within a one-week range of accuracy. Monitoring lake ice dynamics provides a useful seasonally-integrated index of climatic change, as well as information on temperature changes.
On average, ice freeze-up and break-up are observed to change plus-minus one day for a 0.2¡ Celsius change in air temperature. Thus, lake ice information can provide a valuable proxy record of climate change, particularly in data-sparse areas.
A study of 81 selected lakes and reservoirs in southern Canada and the upper-Midwest of the U.S. over the period 1980 to 1994 has revealed a significant trend toward earlier ice break-up dates. John Magnuson and other researchers conducted a much larger historical survey of rivers and lakes across the whole of the northern hemisphere from 1846 to 1995. It revealed significant trends towards earlier break-up and later formation of lake ice providing further evidence for systematic global warming over the past 150 years.
The records for this latest study came from nine countries (Canada, U.S., 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. 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 inter-annual variability in freeze and break-up rates over the past three decades. This is also possibly due to the increasing influence of El Nino and La Nina events in the Pacific.
So while we are witnesses to localized observations of lake ice, it is easy to see there is a much broader picture. We have a choice to be part of the problem or part of the solution when it comes to global warming. There may be little we can do to the forces that are natural, but there is plenty we can do to curb our contributions to global warming and to come to the aid of the polar bears, penguins and people affected by it.
ANDREA LEE LAMBRECHT, naturalist and outdoors photographer, can be reached at andreal@umn.edu.
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