DULUTH – As the sun rose over this corner of Lake Superior on Wednesday morning, the windchill was nearly 30 below. Open water at last disappeared under a thin layer of ice after stubbornly sticking it out through an unseasonably warm January. But just over the horizon, the waves remained.
For the second season in a row, Lake Superior and the Great Lakes as a whole are expected to have below-average ice, which could increase shoreline erosion and threaten organisms that depend on ice cover, sending ripples through an ecosystem already challenged by warming waters.
Even with the recent cold spell, just 6% of Lake Superior had ice cover at the start of the week, below the average of about 20% for this time of year. Last week's ice coverage was the lowest on those dates since the federal government started keeping track in 1973.
The National Oceanic and Atmospheric Administration projects ice coverage on Lake Superior will peak at 30% this year after topping out at 22.6% last year.
"At this time I'm not that worried, but if next year is another low ice year, the whole lake will warm up," said Jia Wang, a NOAA Great Lakes Environmental Research Laboratory research scientist and ice climatologist. "What concerns me is if these kinds of lows continue for several years — that will have a bigger impact."
While fluctuations in ice coverage on the Great Lakes are normal and driven by global weather patterns, which in turn are influenced by climate change, the highs and lows have started to vary wildly.
"It's been a while since we've had an ice cover year that was close to the average," said James Kessler, a physical scientist with the NOAA Great Lakes Lab. Average maximum ice cover on Lake Superior is close to 50%, but "in the last decade we haven't had anything close to that," he said, referring to the extreme highs and lows in recent years.
Ice cover typically peaks between late February and early March. In 2020, Lake Superior maxed out at 22.6% ice coverage on Feb. 17, while the lake was 94.9% covered with ice on March 8, 2019.
Researchers will be updating their ice projections every two weeks through the season.
The Great Lakes as a whole are expected to have 30% ice coverage this year, well below the average of 53%. Since record-keeping began, ice cover has on average been declining about 5% per decade, according to Wang.
"When there is less ice, the surface absorbs more solar radiation in the wintertime," he said. "Superior has the largest decline in sea ice and the largest warming trend."
For Lake Superior, the coldest and the deepest of the Great Lakes, increased temperatures could lead to potentially harmful algae blooms more commonly associated with the lower lakes. Superior saw its first known large-scale bloom in 2018.
One benefit to low ice cover is an easier start to the shipping season, which typically reopens at the end of March. The Lake Carriers' Association has been urging the federal government to add another icebreaker to get ships moving faster in icy years.
"In 2014 and 2015 there was a combined two-year loss of $1 billion and another 5,800 jobs due to inadequate icebreaking resources," the shipping group said last April. "With a shortened season of nine and a half months, every shipment is vitally important. Unfortunately, delays due to ice have stressed the supply chain to the breaking point."
Congress has allocated about $18 million toward a new icebreaker over the past five years.
For those hoping to explore the ice caves along the Apostle Islands National Lakeshore near Bayfield, Wis., where until the late 1990s safe ice was reliably present, this year may disappoint. Given the recent trend in ice coverage fluctuations, next year could be more promising, however.
"You don't have to go back very far to find high ice cover years, so I would expect to see another high ice cover year soon," Kessler said. "Three years in a row with low ice cover would be concerning."