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
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.
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
Cold weather that kills invasive bugs allows local ecosystems to rebound with their absence.
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.
Frozen Lake Michigan seashore.
“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.
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.
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
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.
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