LANSING — The amount of ice on the Great Lakes has declined rapidly over the past four decades, but a warming climate might not be the only explanation for freezing fluctuations during the last century.
Those are the findings of a new study that reported, for the first time, 125 years of historical air temperature and ice data on the Great Lakes.
Researchers discovered that the amount of ice dropped 10 times faster over the past 30 to 40 years. But the lakes also have experienced repeated cycles of ice increases and decreases since 1898 due to a variety of factors.
The findings matter because “ice cover on large lakes regulates regional weather and aquatic ecosystems, and understanding lake ice responses to climate change is critical for environmental management,” the study said.
“When the lakes are covered with ice, they are more protected from waves generated by strong winter storms,” said David Cannon, a researcher at the Cooperative Institute for Great Lakes Research at the University of Michigan and one of the study’s lead authors. “Ice can help prevent coastal erosion, and there’s even evidence that some fish species rely on ice cover to protect their spawning habitats.”
He added that the results will help climate researchers separate century-scale trends related to global climate change from shorter-term variability.
“This is especially important for climate projections, since our results suggest that rates of ice cover loss may slow down, at least temporarily, over the next several decades,” he said. “This is important in the context of lake management, since Great Lakes fisheries, shipping and recreation all rely on ice in some capacity.”
Researchers reconstructed changes in Great Lakes ice cover from 1898 to 2022. They measured daily air temperature records to determine how cold each winter was and how warm the previous summer was, according to Cannon.
Long-term data showed that changes in ice cover occurred not only against a backdrop of overall warming, but also under the influence of fluctuations that repeated roughly every 60 years.
“The 60-year cycle means that over the last 100-plus years, there have been periods when ice cover decreased, followed by periods when it increased or, at least, remained about the same,” Cannon said. “So ice cover didn’t change constantly in one direction but went through recurring periods of increase and decline.”
Researchers found that these long-term changes in Great Lakes ice cover were closely linked to the Atlantic Multidecadal Oscillation, known as the AMO. It’s a climate indicator that is calculated based on the surface temperature of the Atlantic Ocean.
What they found: The phases of the AMO are linked to the amount of ice on the Great Lakes. During warm periods, there was less ice cover on the lake. During colder phases, there was more.
“We see the same pattern of changes in the Atlantic and in the Great Lakes region,” Cannon said. “The Great Lakes are influenced by climate conditions from both the Atlantic and Pacific oceans. That is what makes the Great Lakes unique.”
Researchers were particularly surprised by the data on Lake Ontario.
“Over the last 40 years, the maximum ice cover on the lake was about 20 percent,” he said. “I found it interesting that Lake Ontario has such low ice cover.”
“Since we don’t have direct records of what happened with ice 100 years ago, we can’t see that directly. But the data reconstructed using our model show that Lake Ontario has always been a lake with relatively little ice cover.”
Cannon noted that the current study considers only the overall ice cover of each of the five Great Lakes.
“Right now, we’re estimating the overall ice cover of each of the five Great Lakes without separating them into individual areas,” he said. “In the future, we hope to use this approach to estimate how ice is distributed across different parts of the lakes. Then, for example, we could look at what ice cover was like in Green Bay or Saginaw Bay over the last 100 years. I think that would be a really interesting way to study more regional changes and see how they may have affected how people use the lakes.”
Kyrmyzy Turebayeva writes for Great Lakes Echo.
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