Travelling on ice is an important part of life in the North. We skate on frozen water, skidoo on it, drive dog teams on it and even drive on it. A Carleton University professor is concerned that climate change could mean thinner ice on lakes and rivers, making winter travel more hazardous in some places.

Chris Burn has been studying permafrost in the Mayo area since 1982, and is interested in how climate change could affect permanently frozen ground. He also sees ice as an important indicator of climate, and has enlisted the help of students in Mayo to figure out the relationship between winter conditions and the thickness of ice on lakes in the central Yukon.

"I have always thought of lake ice as a fundamental variable that responds to seasonal changes," he says.

Burn has set up a project on four large lakes in the Mayo area. Students from the J.V. Clark School will measure ice thickness on the lakes once a month through the winter, and correlate their findings with weather information gathered at the Mayo airport.

Burn explains that ice thickness is related to the intensity of a particular winter, a variable that is measured in something called freezing degree days. Each day of the winter receives a score based on the number of degrees below zero to which the temperature falls that day. For example, if the temperature is -10 degrees C., the score for that day is minus 10.

The daily scores are added up for the winter to get the cumulative measurement. In Whitehorse, for example, the average winter total is 2106, while Inuvik scores 4719.

Snow depth also helps determine how much ice forms. Ice grows very quickly early in the winter when there is not much snow, but then the rate slows down as snow accumulates and insulates the ice from the cold air.

The Inuvik area, for example, about 30-40 centimetres of snow accumulate on lakes over the winter and the average ice thickness is about one metre. Along the coast, where the wind blows snow inland, only about 10-20 centimetres of snow accumulates on the lakes and the ice is twice as thick.

Scientists are now predicting that climate change could mean not only warmer temperatures in the North, but more snowfall. Burn says the insulating effects of snow could compound problems with thinner ice.

"If snow piles up in drifts along the sides of rivers, the ice will be thinner at the edges. You could have people in the embarrassing situation of driving down an ice road in the middle of the river and coming to the edges and breaking through," he says.

The thickness of the ice is not the only issue. "The problem is having the same thickness everywhere," he says. "You can land a Twin Otter on just 25 centimetres of ice, but that is the minimum. When it comes time to load up you have to know that you have that minimum amount everywhere."

The ice bridges on the Dempster Highway at the Peel and Mackenzie Rivers are opened to private vehicles when the ice is about 25 centimetres thick; another 15 centimetres is needed for heavier commercial vehicles.

Problems with overflow could also arise later in the season because of the pattern of break-up along northern rivers. "Most Yukon rivers flow from south to north, so they will melt first in southern areas and later in the north," Burn explains. As water levels rise in the spring, running water can spill over downstream sections of the river that are still frozen, making ice bridges and roads impassable.

Burn says that ice thickness is one area where climate change could have a real impact on the daily lives of northerners. He says the information students are gathering in the Mayo area will establish a baseline of information, against which any future changes can be measured.

For more information on this subject, contact Chris Burn at crburn@ccs.carleton.ca.