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Frozen Lakes: Two UTSC researchers discuss the cold winter and ice coverage on the Great Lakes

It doesn't happen very often, but the Great Lakes were almost completely covered in ice this winter. (Photo by Bill Gough)

The long cold winter has resulted in an unusual occurrence: almost all of the Great Lakes have completely frozen over. It’s been 20 years since we’ve last seen this happen.

Cheryl Robertson, an Environmental Science doctoral student at UTSC, researches the impact of climate change on the Great Lakes shipping industry. She recently spoke with UTSC climatologist Bill Gough about this year’s lake ice coverage.

Robertson: I have been hearing a lot of discussion over the Great Lakes ice coverage lately. Do you know why this has become a news topic?

Gough: Almost complete ice coverage of the Great Lakes, as you know, does not happen very often. Last time we saw this much ice was in 1994 and before that, 1979.

It’s not unusual for Georgian Bay and Lake Erie to freeze over, as they are considerably shallower than the other Lakes. But it’s rare to see Lake Superior and Lake Ontario freeze over.

Robertson: Why is it uncommon for those two lakes to freeze over?

Gough: Lake Superior doesn’t usually freeze completely because it is so large.

Although Lake Ontario is the smallest in surface area, it’s very deep, with an average depth of 86 metres and a maximum depth of 244 metres. By comparison, Lake Erie’s average depth is 19 metres, and it’s only 64 metres at its deepest. Lake Ontario, together with Lake Erie, is a southern lake and therefore is warmer than the other three. Finally, Lake Ontario is the final lake of the series, so it has the greatest upstream inflow through the Niagara River providing more turbulent mixing. This churning inhibits the formation of ice.

Robertson: What about historically? You mentioned that 1979 and 1994 also had significant ice coverage on the Great Lakes and now this winter we are experiencing another event. Is this happening more or less often?

Gough: We looked at this in the Climate Lab recently. Records of sea ice coverage are difficult to determine prior to the advent of useable satellite data in the early 1970s. But we’ve found that we can use a thermal index to “hindcast” [recreate] the ice record for the Great Lakes.

 We total up the “ice degree-days” for December, January and February: these are the sum of days weighted by the degrees below zero Celsius for these three months, offset by a similar count of days above zero Celsius.

The climate station on the St. George campus at U of T has temperature records that go all the way back to the 1840s – that’s the longest temperature record in all of Canada. We were able to use data from 1841 to the present.

Robertson: What were the results of the hindcast?

Gough: We looked at return rates, the average period of time between major heavy ice events.

From 1841 to today, we found 23 heavy ice years, likely 90% or more coverage at some point during the winter. For that time period (174 years) the return period (average number of years between events) is 7.6 years.

However, when we divided those 174 years into three sub periods, we got a return rate of 4.6 years for the period 1841-1900, 10 years for the period 1901-1950 and 12.8 years for the period 1951-2014. So it’s happening almost three times less frequently now than it did in the 19th century.

Now I have a question for you. From your research perspective, why are these changes important? How important is lake ice to the shipping industry.

Robertson: During the winter months, the shipping of goods by vessels on the Great Lakes is dependent on ice conditions. When the locks close due to ice conditions at St. Mary’s River, the Welland Canal and the St. Lawrence Seaway, the official navigation season is over, and it doesn’t start again until the locks open again in the spring.

Although these locks may be closed during the main winter season, some shipping activity normally continues to occur within the lakes to allow transport of goods between ports. However, ice conditions, such as this year, have increased the restrictions and delays of the delivery of commodities.

The impacts on vessels and on the industry as a whole are two of the main focuses of my PhD. I plan to use this past winter season as a “worst case” study scenario to determine potential future impacts. My next steps are to see if the projected ice event return rates will increase or decrease in the future, in hopes that this information can help the shipping industry to better prepare for navigating the Great Lakes in the winter.

© University of Toronto Scarborough