Ask the experts: mild winters

UMD specialists weigh in on the lasting impacts of winters with warmer temperatures and less snow.

Turn the clock back to the end of December, 2023: rain and warm weather, and no snow on the ground. Northern Minnesota had a unique start to the winter season to say the least. And while snow and cold finally reached the northland, we wanted to find out from University of Minnesota Duluth experts what these warming temps mean, and what sort of lasting effects they might have. From water temps to the growing season, the answers might surprise you.

We asked experts in several different areas to speak to their specialties, to find out how we can expect the season's warm temperatures to impact the coming year and beyond.

Lake ice and water:

Lake ice formation is remarkably sensitive to winter air temperature. While on the face of it, this may seem obvious, it is still remarkable that almost all year-to year variability in the amount of ice can be explained simply in terms of whether we are having a warm or cold winter. What’s more, a difference of just a few degrees in seasonal air temperature can result in the difference between a largely ice-free year (when there may be ice in the Duluth Superior Harbor, Chequamegon Bay, and other fringing bays, but essentially no ice on the open lake) and a high ice year, with all of the consequences of that: visits to the Apostle Islands ice caves, ice fishing along the North Shore, impacts to the shipping season, and a host of ecological impacts as well. 

Lake ice is also a useful predictor (though perhaps not the primary driver) of conditions later in the year, driving the onset of summer conditions and determining mean and maximum summer water temperatures. This has important implications for other ecological processes, like the formation of Harmful Algal Blooms, which have become more prevalent in the last several years. While it’s too early to make definitive predictions about what we should expect this summer, it is becoming more likely that this summer will be a warm one in Lake Superior. 

  • Jay Austin, professor in the department of Physics and Astronomy and the Large Lakes Observatory


While Minnesota’s wildlife have adapted to the cold weather, there's no question that for many of them, the length and intensity of our winters is a challenge. So when we see a warm spell like we experienced in December of 2023, the impact on wildlife is a mixed bag, and we see a number of species that actually benefit, at least in the short term.

Animals like deer and terrestrial predators were happy to have the warmer temps, largely because of increased access to their food sources, and their increased ability to move around in an environment where they're normally hindered by snow accumulations. But when we look at smaller rodents and shrews, they would be negatively impacted for the exact opposite reason: their shelter and cover was gone, making them easier for predators to find, and they don’t have the thermal benefits that accumulating snow provides. In contrast, warmer temperatures mean that larger animals need to expend less energy to maintain their body temperature.

  • Ron Moen, senior wildlife biologist at UMD's Natural Resources Research Institute and associate professor in the Swenson College of Science and Engineering


Minnesota is warming. Today, forests in northeastern Minnesota experience a climate that is more like that of the Twin Cities a few decades ago. This is some of the most extreme climate change recorded in the continental USA. Both winter and summer temperatures are expected to continue to trend higher for the foreseeable future and climate patterns will become more erratic, with increasing frequencies of heat waves, extended periods of drought, and deluges of rainfall. Increased warming and extreme events are stressful for our forests and could lead to declines of common tree species such as paper birch, quaking aspen, balsam fir, and white spruce. This happens because the climate exceeds the conditions to which the trees are adapted, either killing them directly or making them weaker and more vulnerable to pests and diseases.

But, there is cause for optimism. As a state, we have a tremendous opportunity to take proactive steps to tackle these problems through climate-smart forest restoration. Recent research shows that planting more southern populations of native tree species into northern forests can increase tree survival and growth compared to local populations that are adapted to climates of the past.  If we can transition to a mindset where we consider how much the climate has already changed and source our tree seedlings for reforestation accordingly, we are more likely to preserve forest cover in our state into the future, to the benefit of people and the planet.

  • Julie Etterson, Distinguished McKnight University Professor in the Swenson College of Science and Engineering


Plants in the northland are adapted to cold, snowy winters. Therefore, when we have a warm, low snowfall winter, it can impact their life cycle and health. If temperatures stay mild during the winter, it could lead to early leaf out and/or flowering in the spring. Although a shorter winter seems great on many levels, it can cause problems for plants if warming happens before the risk of frost has passed. If plants start growing prematurely, cold temperatures can damage and stunt growth, which can impact forest health and regeneration in the future. It is also possible that warming can lead to mismatch between the activity of pollinators and flowers.

Low snowfall can have additional impacts. Plants (and many other organisms) in the northland rely on snowpack for insulation. Snow can protect plants from the wind and ice, and keep them warmer than the air. Plants and roots that are covered in snow are less likely to be damaged by freezing temperatures. Snow is also critical to our regional hydrology, and many plants rely on water in the early spring that comes from snow melt.

The long-term impact of a warm, low snowfall winter will largely depend on what happens next. One year that is record-breaking may have short-term impacts on our northern forests. The bigger concern is an increase in the frequency of these types of years because of their potential cumulative impact on our plant life.

  • Jessica Savage, botanist and associate professor in the Swenson College of Science and Engineering


While some of us may enjoy a reprieve from shoveling and snowblowing, the lack of snow and warmer-than-average temperatures aren’t always appreciated by all.

Many may be surprised to know that the winter season represents a significant share of our region’s tourism revenue. In December 2022, the northeast region of Minnesota saw nearly 1.5 million visitor days (number of visitors times their length of stay), making it the busiest of the winter months for tourism that year and nearly as popular as September and October. And a 2012 study by the Natural Resources Defense Council found that, in 2010, more than 8,500 jobs were supported by winter tourism in Minnesota.

Many local businesses struggled due to the mild winter start we experienced in 2023. Ski resorts like Spirit Mountain—which contributed $22 million in economic impacts to the region in 2020—were forced to close during what are typically some of their busiest days in order to make snow. The famous John Beargrease Sled Dog Marathon was canceled due to lack of snow. And businesses that cater to snowmobiling and ice suffered as well, with millions of dollars each year spent on bait, lures, and ice fishing equipment. All of this amounts to millions of dollars in lost revenue for the local economy.

There is one industry, however, that benefits from warmer temperatures: shipping. With unseasonably warm conditions slowing ice formation, in November the St. Lawrence Seaway approved its latest seasonal closure ever: January 5, 2024. As a result, the port set a record for its latest-departing saltie since the St. Lawrence Seaway opened in 1959—the Canadian-flagged Nordika Desgagnes sailed out of Duluth on Dec. 29, 2023. Overall, the Port saw a 3.9% increase in total tonnage through Nov. 30, compared with the previous year.

  • Monica Haynes, director of the Bureau of Business and Economic Research and adjunct professor in the Labovitz School of Business and Economics