How Climate Change Affects Wisconsin Winters

Excerpted from: Climate Change in the Midwest

Across the United States, winters are already growing warmer and shorter as a result of climate change, and that trend is expected to continue in the future.

If you’re a winter-hater, that might sound like fantastic news. But bitterly cold temperatures, snow, and ice are more useful than you might think. Wintry weather — for now — is keeping invasive Burmese pythons confined to South Florida, providing a natural store of drinking water in the West, and reducing the spread of insect pests, among many other useful services.

But think of a Minnesota with almost no ice fishing. A Missouri that is as hot and dry as Texas. River and lake communities where catastrophic flooding happens almost every year, rather than every few generations.

To kill off infestations of Asian insects we need at least -20°F or colder of morning low temperatures to cut in half these hibernating populations.

  Why Wisconsin Needs Sub-zero Days

Cold air might not be enjoyable but it's necessary and desperately needed for our local ecosystems. Why is this a good thing?

There are many invasive species in Wisconsin but some of the most sensitive to extreme cold are insects like the Emerald Ash Borer and the Brown Marmorated Stink Bug.

While most of these invasive insects come from a similar climate to the United States, they can't handle the extremes quite as well as Wisconsin's native insects and plants. Our native species have evolved to withstand arctic air outbreaks and can handle dangerous cold no problem. Survival rates for native species are even higher with adequate snow cover like we currently have.

Generally, to kill off significant populations of invasive Asian insects you need prolonged stretches of 4 days or more of extreme cold. For Wisconsin's infestation, we need at least -20°F or colder of morning low temperatures to half these hibernating populations, and the more days in a row the better odds their numbers are reduced.

Cold weather that kills invasive bugs allows local ecosystems to rebound with their absence.

  Wisconsin Climate

Although winter can still bring bitterly cold weather to the Wisconsin, the season has been gradually warming, enabling new insect pests and crop diseases to spread farther north in this agriculture-dependent region. In the future, climate change could cause a litany of problems, such as increasing the risk of winter and spring flooding, adding stress to forests, and altering the timing of seasonal water turnover in the Great Lakes — which could unleash cascading changes in the lake ecosystems.

Wisconsin climate conditions are largely determined by the region’s location, in the center of the North American continent. They are also affected by its relatively flat topography, carved out by the glaciers that covered the region for thousands of years during the last Ice Age.

Far from the moderating effects of the oceans, Wisconsin weather conditions can vary widely over the course of a year. Sudden changes of weather, large daily temperature ranges, and unpredictable precipitation patterns are all staples of regional weather.

Wisconsin typically experiences four distinct seasons, although those seasons can be highly variable and year-to-year variations can be large. In the winter, the absence of significant mountain barriers to the north allows bitterly cold air masses from the Arctic to move southward into the region. The polar jet stream is often located near or over the region during the winter, with frequent storm systems bringing cloudy skies, windy conditions, and precipitation.

In contrast, Wisconsin summers are characteristically hot and humid due to a semi-permanent high pressure system in the subtropical Atlantic that draws warm, humid ocean air into the area. Summer also tends to be the rainiest season, with short-lived rainfall and thunderstorms.

  Climate Change Impacts

“Climate” refers to the average conditions in a given location over time scales of decades to centuries. Year-to-year weather patterns average out to give a picture of what a typical or “climatological” year might look like. Over longer time scales, however — on the order of centuries to millennia — climate or “average” conditions in Wisconsin have been very different than today.

18,000 years ago, when temperatures were an estimated 10 to 15° F cooler than they are today (Petit et al., 1999), the region was covered by a mile-thick ice sheet. By 10,000 years ago, the climate had warmed and the glaciers retreated, depositing layers of soil and rock debris that characterize the southern part of the region, and scouring out the many lakes and rocky shores typical of the more northern states.

Atmospheric levels of carbon dioxide are now higher than they have been at any time in at least the last 800,000 years. Average surface temperatures in the Northern Hemisphere have risen by 1.3° F over the past 150 years. It is very likely that most of the climate changes observed over the last 50 years have been caused by emissions of heat trapping or greenhouse gases from human activities.

  Indicators Of Recent Changes

Although definitive attribution of regional-scale climate change to human causes is still difficult due to the relatively large year-to-year variability in local climate, changes that are at least consistent with global, human-induced warming are already under way across Wisconsin. Since 1970, the region has been warming at a rate of more than 0.4o° F per decade. Winter temperatures have risen even faster, at a rate of 0.9° F per decade from 1970 to 2000. This warming has been correlated with many noticeable changes, including:

  Increases of 2.6° F in annual average temperatures since 1980, with the greatest increases of almost 4° F occurring in winter
  A scarcity of cold waves during the 1990s, accompanied by several major heat waves, particularly those in 1995, 1999, and 2006
  A progressive advance in the date of last spring freeze, with current dates approximately 1 week earlier than the beginning of the 1900’s.
  A lengthening of the growing season, by about one week during the twentieth century
  An increase in rain days and a doubling in the frequency of heavy rainfall events since the early 1900s, increasing the risk of flooding in Iowa, Missouri and Illinois
  Shifts in the hydrological cycle, with decreasing spring snow cover leading to earlier dates for spring melt, peak streamflow, and high lake levels.
  Later formation of ice on the Great Lakes and inland lakes, and a shorter overall duration of winter lake ice, with some years being nearly entirely ice-free
  An increase in Great Lakes near-shore water temperatures of almost 0.2° F per decade since 1920 (measured at Sault Ste. Marie and Put-In-Bay), accompanied by an increase of more than 2 weeks in the duration of summer stratification.

  Climate Predictions

As climate changes, precipitation patterns over the Wisconsin are also expected to change. These changes range from shifts in seasonal distributions to changing proportions of rain vs. snow. In particular:

  Although relatively little change in annual average precipitation is expected, relatively large seasonal shifts are likely.
  Winter and spring precipitation is likely to increase, by about 20% by the end of the century under lower emissions and 30% under higher.
  Little change in summer and fall precipitation is expected under lower emissions, but summer decreases and fall increases on the order of 10% are expected by the end of the century under higher emissions.
  The frequency of heavy precipitation events—measured in terms of number of days per year with more than 2 inches of rain, and annual maximum 24-hr, 5-ady and 7-day rainfall totals—is likely to continue to increase, with slightly greater increases for regions closer to the Great Lakes.
  More precipitation will fall as rain and less as snow, particularly in southern Midwest states and towards the end of the century, when reductions of 30 to 50% in annual snow days are expected under lower emissions, and 45 to 60% under higher. By the end of the century, all states can expect no more than an average of 20 snow days per year under lower emissions; for Illinois, Indiana, and Missouri, less than 10 snow days per year on average.

Although some future changes are unavoidable because of past emissions, the greatest of the projected changes do not have to happen if prompt action is taken to significantly reduce emissions. Through reducing our energy use and preparing for future change, we can help protect our communities, economy, and ecosystems.

Further Reading on Climate Change:

 Climate Change Impacts On Wisconsin
 Climate Change Impacts On The Great Lakes
 Climate Change Impacts On Bees and Food Production
 Lake Michigan Warming: Climate Threats
 Growing Corn Is Changing The Climate
 How Climate Change Affects Butterflies