Ice coverage on Great Lakes has been declining for decades

Northwest Indiana's shoreline has been affected by erosion in recent years. Beaches have shrunk and gotten less sandy. Roads have suffered damage. Wooden stairs to beaches, protective barrier stones and other infrastructure have washed away into Lake Michigan.

A recent study in the journal Environmental Research Letters found that warming temperatures caused the Great Lakes to lose an average of 14 days of winter conditions each decade since 1995.

"For this study, we considered winter days from the lake’s perspective to be days with ice cover or when surface water temperature was less than 2 degrees Celsius. Those criteria help us distinguish what might be happening in the lakes in the spring and fall. We find that the lakes are seeing decreases over time based on these metrics, and the biggest driver is warmer air temperatures," said the study's lead author Eric Anderson, a professor with the Colorado School of Mines. "From a physical standpoint, it means that important processes related to how the water mixes from top to bottom could be changing. Mixing is important to water chemistry and ecology. Less ice can also mean increased lake-effect snow and less shoreline protection in the winter."

Ice coverage on the Great Lakes can swing from year to year due to cold air outbreaks but has been declining since 1973.

"Ice cover was part of how we counted winter days, so the decreases report include declines in ice cover," he said. "There is a lot of spatial variability in how and why the lakes are losing winter days. In general, we see that winter days are being lost to both spring and fall, with no notable transition to one over the other."

Both air and water temperatures have been rising in the Great Lakes region over the last few decades.

"Most of the change in Lake Michigan is found along the coastline, as well as in Green Bay and the northern end of the lake," he said. "Temperatures, ice cover, and lake mixing all play important roles in how the lakes function. Loss of coastal ice can lead to increased erosion or degradation of habitats. While generally less ice means more possibility for shipping, it’s important to note that we didn’t specifically look at ice changes in ports."

Great Lakes shipping is seasonal because ice chokes northern passageways like the Straits of Mackinac, making them impassable for months. The winter season has been shortening with the first ice cover happening six to 11 days later than in the 19th century and ice breaking up about two to 13 days earlier in the spring, according to the NOAA.

The NOAA forecasts ice coverage on the Great Lakes will continue to shrink, which could lead to more lake-effect snow and rain and affect aquatic plants like plankton and fish species like whitefish and lake trout. It could lead to depleted oxygen, dead zone, extreme precipitation, runoff and toxic algal bloom formations, among other consequences.