Decades of research on Great Lakes ice cover reveal trends
March 9, 2012
Contact: Linda Joy, 301-734-1165
As longtime Great Lakes region residents know, some winters choke the lakes with ice and others leave wide areas of open water, as the winter of 2012 has done. The amount of ice affects not only shipping and water and electric utilities, but also the region’s weather. NOAA’s Great Lakes Environmental Research Laboratory in Ann Arbor, Mich., has monitored ice cover on the lakes for several decades. Their measurements have documented wide variations from winter to winter and made possible discoveries about climate links to variation in ice cover.
To learn more, read the following Q&A interview with Great Lakes Environmental Research Lab researchers George Leshkevich and Jia Wang on ice cover on the Great Lakes. Also, see a new GLERL fact sheet on Great Lakes ice at http://www.glerl.noaa.gov/pubs/brochures/ice/ice.pdf (opens a pdf).
1 Why is the amount of winter ice cover on the Great Lakes important to the region?
The amount of winter ice cover on the Great Lakes is important for several reasons, including:
· Ice cover can reduce the amount of evaporation from the lakes, contributing to higher water levels
· Stable ice cover is needed for ecosystem health, and is especially important for some fish species’ spawning and recruitment
· Reduced ice cover can contribute to increased lake effect snowfall
· Reduced ice cover can contribute to increased water temperature
· Reduced ice cover can lead to more coastal erosion
· Ice cover is important to the economy, impacting navigation and recreation
2. Does the amount of ice on the Great Lakes vary much from winter to winter?
The amount of ice cover on the Great Lakes can vary widely from winter to winter. For example, over the past two decades, the maximum percent ice concentration on Lake Erie varied from approximately 100 percent in 1996 to only 4.4 percent in 1998.
How do climate patterns like El Niño and the North Atlantic Oscillation affect Great Lakes ice cover?
The combination of these climate patterns, ENSO (El Niño and Southern Oscillation) and NAO/AO (Arctic Oscillation), can significantly affect lake ice cover by influencing the circulation of warm and cold air. Generally speaking, the positive or warm phase of the NAO causes less lake ice, and the negative or cold phase causes more ice. Lake ice response to ENSO is a bit more complicated, and the interaction between the two climate patterns can make lake ice hard to predict. The combined effects of ENSO and NAO on temperature and lake ice are described in the following matrix: 
Does Great Lakes ice cover have implications for weather and climate beyond the Great Lakes states? An example could be lake effect snow that falls outside the Great Lakes basin in some areas.
Yes, lake effect snow may affect areas outside the Great Lakes basin such as upper New York State.
How do you measure ice cover on the five Great Lakes?
The amount of ice cover on the Great Lakes is currently observed and measured with the aid of satellite observations. For example, Great Lakes Ice Analysis charts showing ice concentration, produced by the National Ice Center, are composed largely from observations of several different satellites.
Other technologies are being used to measure ice on the Great Lakes. GLERL has several ice profilers that sit on the bottom of Lake Erie and use sound waves to measure ice thickness. A ground penetrating radar unit, attached to a helicopter, is being tested in cooperation with the Canadian Coast Guard to measure transects of ice thickness across a lake. This adds spatial dimension to ice thickness measurements.
Have you observed any trends in Great Lakes ice cover in recent decades?
Yes, there is an overall decrease in Great Lakes ice cover over the past 40 years, with a decrease in variability as well. This graph shows the downward trend in ice cover area (in square kilometers) since 1973. The total loss in area was 71 percent for all of the Great Lakes.
What are we learning from research on Great Lakes ice cover?
We are learning that two factors are contributing to changes in Great Lakes ice cover: 1) natural variability of air temperature in response to ENSO and NAO/AO patterns as described above; and 2) increases in air temperature due to anthropogenic effects. Surface air temperature has increased 0.4-0.6 degrees Celsius per decade over the past four decades in the Great Lakes region. Changes in ice cover in turn can affect the ecosystem, local weather, regional climate, and the economy. GLERL currently uses the results of our basic research to project the amount of ice cover that will form. We are also working on joining our projections with models of ice circulation to develop ice forecasts that will provide important information for navigation and to others users such as the U.S. Coast Guard, the wind energy industry, the ice fishing community, planners, and resource managers.
You can see the GLERL Great Lakes Coastal Forecasting System, which includes Great Lakes ice cover, online at http://www.glerl.noaa.gov/res/glcfs.
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