It's easy to feel small standing on the shore of Lake Superior.
It was mid-February, and the lake was roaring like a freight train. Awestruck visitors to Split Rock Lighthouse State Park watched a mesmerizing display of icy tectonics as the lake's frozen surface slowly crashed into the shore, splintering into thousands of gleaming shards like an enormous shattered mirror. A sense of the lake's ancient power hung in the air.
Even the old lighthouse, which has spent more than a century rooted to the billion-year-old bedrock, scarcely registers as a footnote in the lake's long story. Superior's age and immensity make it seem eternal, immovable. But below the frigid waters and along its evergreen shore, a sea change is coming for North America's largest lake.
At 31,700 square miles and over 1,300 feet deep, Lake Superior is the largest freshwater lake in the world by surface area, and the third largest by water volume. Approximately 150 miles of its 2,700-plus miles of shoreline make up Minnesota's exquisite North Shore, a stretch of inland coast known for its severe cliffs, coursing rivers and waterfalls, stretches of iconic north woods, and breathtaking vistas.
According to the State Climatology Office, northeastern Minnesota's climate is changing in a few clear-cut ways. Temperatures are rising faster in northern Minnesota than just about anywhere else in the state, but especially from the bottom up—meaning winter low temperatures are rising much faster than summer high temperatures. The area is also getting wetter, with a 15 percent increase in precipitation across the historical record—meaning an extra four inches of annual precipitation each year.
"That's a lot of water," says Kenny Blumenfeld, DNR senior climatologist at the office. "It's the equivalent of over 70 million gallons of water per square mile, per year, coming out of the sky that didn't used to be."
All this extra moisture could mean more snow falling on the northeastern Arrowhead region, which Blumenfeld calls "the capital of winter in Minnesota." However, rising winter temperatures can also mean mushy, patchy snow from unexpected February rains and earlier thaws.
In other words, the North Shore's climate is becoming less reliable, with implications for the big lake and its environs. Says Blumenfeld: "You have to be able to withstand disruption now."
In the decades to come, that ability to withstand disruption—or not—will determine the fate of Lake Superior's waters, surrounding lands, and the human and non-human inhabitants who depend on both.
In the Water
Climate change is affecting everything from the physics to the biology of Lake Superior's waters.
For starters, winter ice cover has been decreasing on Lake Superior, especially in the past 20 years or so. There are exceptions, such as the winters of 2014, when the lake froze over completely for about two months, and 2019, when ice cover briefly neared 100 percent. But according to University of Minnesota Duluth's Jay Austin, a physicist who works with the Large Lakes Observatory, winters like those are becoming increasingly rare.
"It's not as if there's never going to be ice again. … We're still going to have years with lots of ice," says Austin. "We're just going to have more and more years with no ice."
Austin and colleagues have published research on the link between winter and summer conditions in the lake, noticing that low-ice winters were followed by warmer summer waters. Summer surface water temperatures in Lake Superior have increased about 4 degrees Fahrenheit in the past three or four decades, which Austin says is part of a warming trend among large lakes globally.
This warming is having an unusual impact on the physics of the lake. Temperate zone lakes like Superior "turn over" during the transition months between cold and warm seasons, when shifting temperatures change the density of surface waters, causing them to mix with waters below. During summer, deeper, colder water tends not to mix with overlying warmer water. This summer condition—Lake Superior's aquatic growing season—is about 25 days longer today than it was a century ago, according to Austin.
"You're twiddling all kinds of biological knobs when you change the temperature regime of the lake like this," he says.
Robert Sterner, director of the Large Lakes Observatory, and Euan Reavie, a researcher at the Natural Resources Research Institute, are among the experts keeping an eye on those spinning dials.
Sterner studies blue-green algal blooms, which have been increasing near Duluth-Superior and along the south shore of the lake. These goopy, unpleasant-looking surface scums can occur in typically cooler places that have become warmer, as is occurring in Lake Superior.
"We strongly suspect a climate connection, but it is not yet proven," says Sterner. While blue-green algae can become toxic under certain conditions, this hasn't yet been observed in Lake Superior.
Reavie and his colleagues have seen changes in population levels of diatoms, the tiny creatures that make up much of the base of the lake's food web.
"We saw quite clearly that there was this rise in a particular group of diatoms, the cyclotelloids, that corresponded with the rise in atmospheric temperature," Reavie says. At the same time, other types of diatoms are seeing a decline. Reavie predicts that this is a result of decreased ice cover on the lake, as the cyclotelloids thrive in open water.
"It's concerning that we see this underlying long-term shift in the base of the food web, because it's undoubtedly going to have some kind of domino effect upward at some point," says Reavie, referring to potential impacts on invertebrate and fish populations in the lake. "It's likely that it's already happening; we just haven't detected it yet."
Meanwhile, at the top of the native food web, things are currently looking up for Lake Superior's lake trout.
"Right now our lake trout population is very healthy. … Rehabilitation has been successful," says Cory Goldsworthy, DNR area fisheries supervisor for Lake Superior. He's referring to a decades-old program to restore native lake trout populations after commercial fishing and sea lamprey, an invasive parasite, devastated trout numbers.
Unfortunately, warmer temperatures are a boon for sea lampreys, which seem to be increasing in size. Larger lampreys are hungrier, and they lay more eggs, both of which bode ill for lake trout. Further, warmer waters may favor other invasive species that can negatively affect native fish.
The lake's introduced sportfish like salmon and rainbow trout prefer warmer waters and may also benefit from increasing temperatures. While that may provide a silver lining for anglers, Goldsworthy says it's not a net win: "I don't think the positives outweigh the negatives of warmer water temperatures being a benefit to invasive species."
Along the North Shore and throughout the Arrowhead region, the forest has a distinct cold climate feel. Dark evergreens blend with snow-white stems of paper birch and aspen. Unique plants usually found in the Arctic, like cloudberry and bird's-eye primrose, hide out in cooler pockets near the lake.
"It's a different mix of forests than you'll find in other areas of the state," says Katie Frerker, ecologist and climate change coordinator for the Superior National Forest.
These woods are accustomed to hardship. Regular historic wildfire in combination with poor, rocky soils make for interesting growing conditions. However, the North Shore's cold-hardy tree species may not fare well in a warmer world.
"There are a lot of projections that indicate that some of those southern boreal species are predicted to decline—specifically balsam fir, black spruce, paper birch, quaking aspen, tamarack, and white spruce," Frerker says. "And that's a huge bulk of what our forests are made of."
Shifts in forest composition may be just the tip of the iceberg for the changes coming to the North Shore. The lake is a cultural icon for Minnesotans and visitors to the state, who flock year-round to popular destinations along its jagged coastline, such as Gooseberry Falls, Palisade Head, and the Superior Hiking Trail. The shore's magnetism fuels a thriving outdoor recreation–based tourism industry for outfitters, resorts, bed-and-breakfasts, and restaurants that serve those who come to hike, bike, fish, camp, ski, snowmobile, paddle, and explore.
But residents and visitors alike may experience a "new normal" in coming years.
According to survey research led by Mae Davenport at the University of Minnesota, both groups are worried about climate change. Fish and wildlife impacts, forest health, and the spread of invasive species top the list of concerns. Over 85 percent of surveyed residents reported personally observing a change in local weather patterns over time. And after meeting in focus groups, community leaders, business owners, and local officials identified threats to the tourism economy as a top concern.
Despite these concerns, Davenport notes, surveyed visitors didn't think that climate change will affect their trip planning. However, a look at recreation data from the last decade suggests otherwise. Factors such as high heat index and fire risk in the summer and thin ice or low snow cover in the winter did match up with lower visitation rates. This has some local tourism businesses worried. In focus groups, business leaders said they think about climate change "almost every day," says Davenport. "They're worried about how it's going to affect their business and their communities."
Tom Rider, co-owner of Lutsen Mountains Ski and Summer Resort, is one of those anxious business leaders.
The resort, which opened in 1948, attracts thousands of visitors year-round, but it makes most of its revenue in winter.
"It's a real concern in our industry, as you can imagine," says Rider. "We're a winter industry. Winters are getting warmer and shorter. Shorter winter seasons directly correlate to less revenue for ski resorts."
In recent years, the resort has increased its artificial snow-making to ensure adequate cover throughout the ski season. Another concern for Rider is that heavier rains outside of the growing-season months are saturating the area's thin soils, leading to landslides on the slopes and expensive repairs for the resort. He worries about the long-term consequences of these costly climate impacts. "It's a very negative paradigm for us, and one that will potentially see a decline and ultimately destruction of our business."
The lake's cultural significance long predates its parks and resorts, as both the waters and the shore hold great importance to northeastern Minnesota's Native American communities.
Tansey Moore is the climate change specialist for the 1854 Treaty Authority, an intertribal natural resource management organization in northeastern Minnesota. She points out that the tribes, with their fixed boundaries of ceded territories and reservation lands, are especially vulnerable to climate impacts. If culturally important species such as wild rice, sugar maple, paper birch, or moose die out or shift north, it's a serious problem.
"That's part of their culture, their life ways," says Moore. "They really depend on these resources to be there."
The scope of change coming for the lake and its shore is certainly daunting. But Tom Beery, former resilience specialist for Minnesota Sea Grant in Duluth, encourages Lake Superior enthusiasts to take heart—and to take action.
"These projections can guide how we manage our resources," he says. "People are already thinking creatively. So I'm somewhat hopeful … that there is an engagement and awareness of the problem. And I think that is a good sign for what kind of changes might be made."
Examples of adaptive responses abound. Foresters in the Superior National Forest are working with partners to monitor forests and brainstorm ways to keep them healthy, such as planting trees in areas that are most resilient to change and sourcing seeds from further south. Lutsen Mountains Ski and Summer Resort is investigating "snow farming," whereby late spring snow is mounded and protected with an insulating cover for reuse the following winter. The 1854 Treaty Authority is implementing an adaptation plan with more than 250 strategies for responding to climate impacts on culturally important species.
Minnesotans who love the outdoors may even be discovering more climate-proof methods of recreating. For example, "We're seeing an increase in the popularity of fat-tire bikes," says Beery. "You can do it in really low snow conditions or crusty snow. If ski trails get rained on and they're just destroyed for skiing, if you have some studded tires on your fat bike, you can get through anything."
While northeastern Minnesota communities must learn to adapt to climate change, many are also thinking about how to reduce the greenhouse gas emissions that are fueling these changes. Says Beery: "Those of us who are looking down the road at … the change that is here and the change that is coming, we also have to say, 'And how do we slow that change?'"
The answer will inform the next chapter of the big lake's ongoing story.