What Climate Change Means for Wisconsin and the Upper Midwest

Wisconsin has what is called a continental climate, modified somewhat in coastal areas by two of the largest lakes in the world. Averaging about 1,000 feet above sea level and located halfway between the equator and the North Pole, our state historically has had cold, snowy winters and warm summer days with cool summer nights.

In northern parts of the state, temperatures 30 degrees below zero or colder occur almost every winter. Usually snow covers the ground and the lakes are frozen-over statewide all winter long. In southern parts of the state, average daytime high temperatures are generally below freezing from early December through late February. We expect temperatures to top 90 degrees fewer than 14 times a year.

Our annual precipitation averages about 30 inches, about two-thirds of it falling as rain during the growing season. We average three dozen thunderstorms most years, sometimes accompanied by tornadoes. Ice storms are relatively rare, occurring somewhere in the state less than once every three years or so.

That’s been Wisconsin’s climate since the state was created in 1848, and it’s what makes Wisconsin a special place for enjoying a wide variety of winter sports, including ice fishing, cross-country skiing, snowmobiling, sled dog racing, tobogganing, snowshoeing and ice hockey. It’s an ideal climate for dairy farming and growing vegetables, corn, hay and soybeans. It’s why trout and other cold-water species of fish inhabit our lakes and streams, and white and red pine and quaking aspen thrive in the North Woods. It’s what makes Wisconsin, well, Wisconsin.

Now it is clear our climate is changing, and the forecast for our part of the world says our grandchildren will likely be living in a Wisconsin that’s very different from the one we live in now. In fact, our climate is likely to become noticeably different within the lifetimes of most adults living here today.


Mean temperatures in the upper Great Lakes region have gone up nearly four degrees over the last century. About two-thirds of that increase was recorded just within the last 30 years—which by definition means we are already living in a different climate.

Perhaps the single most elegant proof of this four-degree change comes from the Center for Limnology (the study of lakes) at the University of Wisconsin-Madison, which maintains a record of the dates each year when Lake Mendota freezes over and the ice cover breaks up that spans more than 150 years. This record shows that the 10 longest periods of ice cover all occurred more than 100 years ago, while seven of the 10 shortest ice covers all happened inside the last 50 years—the four shortest ever within the last 25 years. When averaged, this record shows a long-term downward trend in the length of time that Lake Mendota is ice covered to where it is now19 days shorter than a century ago. In a typical winter these days, the ice on Lake Mendota lasts only three months compared to four months 150 years ago.

Similar records show almost identical trends in the freeze and break-up dates of the ice cover on lakes across the entire state, from Lake Geneva in southeastern Wisconsin to Shell Lake in the northwestern part of the state. Much older ice cover records in Finland, Russia and Japan show the same thing is happening on lakes all across the Northern Hemisphere.

Plenty of other evidence—both scientific and anecdotal—indicates our Midwestern climate is changing. Numerous scientific studies report many species of cold-climate mammals breaking hibernation earlier and expanding their ranges northward. Records kept at Aldo Leopold’s cabin near Baraboo show that migratory geese are returning a month sooner and plants are blooming over a week earlier as compared to what Leopold recorded there 70 years ago. Residents of the Duluth-Superior area say they were unaccustomed to seeing nesting cardinals and tomatoes turning red before the first killing frost of fall—but no longer.


In the coming decades, Wisconsin’s climate is expected to become noticeably warmer. Before the century ends, average summer temperatures are projected to increase by as much as eight to 18 degrees and average winter temperatures will rise six to 11 degrees. That may not seem like much, but in southern parts of Wisconsin an eight-degree increase in average temperatures would push daytime highs from the low 80s to 90 degrees or higher for 31 days each summer and nudge the average daily high above freezing all winter long.

Wisconsin’s average annual amount of precipitation is not expected to change much, but our summers are expected become drier as warmer temperatures increase evaporation and seasonal precipitation patterns shift. Winter precipitation is projected to increase by as much as 30 percent, while summer precipitation may decline as much as 20 percent. As warmer temperatures increase evaporation and the amount water vapor in the atmosphere rise worldwide, the air will become more saturated, increasing humidity levels year round. This means when it does rain or snow, it’s likely to be in very large amounts.

All of this means Wisconsin can expect an increase in extreme heat waves and more frequent droughts in summer. At the same time, severe thunderstorms may double in frequency, increasing the amounts of damage caused by heavy rainfall, flashfloods, hail and strong tornadoes. The winter season is likely to be punctuated with increasingly frequent mid-winter thaws, freezing rains, ice storms and flooding. We may expect heavier snowfalls, especially in the near term, yet the average length of time the ground stays snow-covered and our lakes remain ice-covered will shrink with each decade.


On the plus side, a warming climate during the first half of this century could mean lower winter heating costs, a longer frost-free growing season and better yields of some crops. It is also expected to improve forest growth, and enlarge resident populations of birds, warmwater fishes, reptiles and small mammals, especially nuisance animals like mice, bats, rabbits, squirrels, raccoons and opossums. Waterborne commerce will enjoy longer ice-free shipping seasons on the Great Lakes and Upper Mississippi River. Winter recreation may suffer, but summer recreation could enjoy a boom.

On the minus side, as the climate continues to warm, it will bring higher summer cooling costs, more frequent ozone alerts, and longer, more intense heat waves. Over time, the benefits of a warming climate for agriculture will likely be outweighed by the adverse effects of declining soil moisture and more frequent droughts, severe storm and erosion damage, and a northward invasion of various warm-climate crop and livestock pests and pathogens. The need to irrigate crops and greater urban demands for water will strain groundwater supplies in some areas. Warmer, damp conditions will cause populations of disease-carrying insects to swell and spread, and outbreaks of infectious diseases like West Nile virus may increase.

Greater evaporation due to generally warmer temperatures and less winter ice cover are expected to cause Great Lakes water levels to decline several feet, threatening coastal drinking water supply systems as well as waterborne commerce, and causing shipping, dredging and harbor maintenance costs to rise. Barge and train traffic through the Upper Mississippi River Valley could be interrupted alternately by low summer-autumn stream flows and winter-spring floods. Warmer water temperatures and increased stormwater runoff will reduce the water quality of many inland lakes and rivers as well as Great Lakes coastal waters.

Longer, hotter, drier summers and increasing evaporation will result in warmer and shallower rivers, shrinking wetlands, and dried-up streams, flowages and wild rice beds. Algal blooms will create anoxic conditions for aquatic life in ponds and many lakes. These conditions will reduce the amount of suitable habitat available for trout and other cold-water fishes, amphibians and waterfowl. A two-degree rise in temperature could wipe out half of Wisconsin’s 2,700 trout streams. Hot dry conditions, coupled with more frequent thunderstorms and lightning, will increase the chance of forest fires. Red pine, aspen and spruce trees will disappear from our northern forests.


These projections for Wisconsin’s future climate are but a microcosm of the most recent global climate forecast of the Intergovernmental Panel on Climate Change. The IPCC’s 2007 report concluded that “warming of the climate systems is unequivocal” and “sea level rise under warming is inevitable.”

The report presents the consensus findings of nearly 4,000 of the world’s leading experts on climate and climate change, the product of more than 450 authors and 800 contributing authors from universities, environmental organizations and industries throughout the world, whose work was reviewed by 2,500 other scientific experts to ensure that it represented an objective and complete assessment of the latest scientific information available. “Consensus” means general agreement on every finding presented in the report, so as alarming as many of the report’s conclusions are, it is a conservative assessment and most likely understates the problem.


The ability of people, plants, animals, ecosystems and civilizations to adapt to changes in climate largely depends on how much and how rapidly change occurs. Until human carbon dioxide emissions are minimized, global temperatures are certain to continue rising, as all of the carbon dioxide added to the atmosphere each day will remain there for the next 50 to 100 years. Immediate, significant reductions in carbon dioxide and other greenhouse gas emissions will help slow down the rate of climate change, reduce the magnitude of change in the future, and help improve our ability to adapt.

The first thing Wisconsin must do is to begin greatly reducing its own greenhouse gas emissions. Next, we must anticipate and prepare for the possibility of severe summer droughts, extreme heat waves, more frequent severe storms and strong tornadoes, heavy rains and snowfalls, ice storms, and record flooding.

We also need to be prepared for any disruption to power, water and food supplies that climatic events may cause. It has always been wise to make such emergency preparations, but the expected—and especially the unforeseen—consequences of a changing climate will make such preparations increasingly important in the years ahead.