DULUTH - After days of frigid weather, a brave angler could be seen testing Lake Superior ice midweek near the Twin Ports, where snow-covered ice and open water co-exist in the slender finger of the lake that ends where the St. Louis River begins.

Coming off two years of low Lake Superior ice cover, this winter is again expected to clock in below average, which could threaten aquatic life that depends on ice cover and increase shoreline erosion. The National Oceanic and Atmospheric Administration (NOAA) projects the lake to be 52.3% covered by ice at its peak, with a long-term average of 62.3%. Lake Superior ice cover was roughly 12% late last week, compared to a long-term average of 20%.

While below average, those numbers are better than they have been in recent years. A year ago, just 6% of the lake had ice cover.

"This year isn't as bad, and we're still not yet to February, when most ice forms," said Jia Wang, an ice climatologist for NOAA's Great Lakes Environmental Research Laboratory.

The Great Lakes as a whole is expected to see lower than average ice cover at about 48%, with an average maximum ice cover of 54.5%.

While it varies year to year and is driven by global weather patterns, ice cover is decreasing over time, Wang said. For the five Great Lakes overall, maximum ice cover has shrunk by 5% per decade since NOAA began collecting such data in 1973. That year ice cover for all Great Lakes was about 64%. Since then, the percentage has gone as high as 94.7% in 1979, and as low as 11.9% in 2002, with some extreme variation in recent years. Nearly 81% of the Great Lakes was covered by ice in 2019, and the following year that percentage sank to 19.5.

Last year on Lake Superior, ice cover peaked at about 50%, but didn't stay there long. More open water, and the warmer lake that comes with it, can delay ice formation, Wang said, along with a host of other ecological effects. At the start of January, Lake Superior was a couple of degrees warmer than average, although that's evened out with the recent spate of freezing days.

Because of its depth and far north location, ice cover on Lake Superior varies more wildly than the rest of the Great Lakes, said Jay Austin, a professor with the University of Minnesota Duluth's Large Lakes Observatory.

That's why it sees high ice years like 2009 and 2014, when adventurers safely hiked out to the ice caves near the Apostle Islands, and low ice years like 2012, when coverage was less than 10%, Austin said.

And the winter air temperature difference that can signal a little ice on the big lake or a lot can be as narrow as 3-4 degrees.

Climate change can be hard to communicate because "the differences we talk about are relatively small," he said, making it easy to dismiss. "But here is this major piece of our landscape that is very sensitive to those relatively small changes."

Several harmful algae blooms were spotted on western Lake Superior in 2021, a sign of a warming lake. Low ice leads to a longer warming period, creating higher summer surface temperatures, said Bob Sterner, director of the Large Lakes Observatory.

Algae blooms, which are actually bacteria, can produce toxins that make both humans and animals sick, according to the Minnesota Pollution Control Agency. Typically, they thrive in warm, nutrient-rich water and can give off a swampy odor.

"So far, no cyano [algae] blooms have occurred in Lake Superior in cold summers," Sterner said, but whether this year's ice forecast could mean more algae blooms is too soon to tell.

For Lake Superior, climate change probably doesn't mean an annually declining amount of ice. It will continue to fluctuate, Austin said, but there will likely be fewer ice-heavy years to come.

"How we perceive the lake will change over time," he said. "An icy, icy year will be an amazing event 50 years from now."