United States
Environmental Protection
What Climate Change
/Weansfor Wisconsin
Wisconsin's climate is changing. In the past century,
most of the state has warmed about two degrees (F).
Heavy rainstorms are becoming more frequent, and
ice cover on the Great Lakes is forming later or melting
sooner. In the coming decades, the state will have more
extremely hot days, which may harm public health in
urban areas and corn harvests in rural areas.
Our climate is changing because the earth is warming.
People have increased the amount of carbon dioxide
in the air by 40 percent since the late 1700s, Other
heat-trapping greenhouse gases are also increasing.
These gases have warmed the surface and lower
atmosphere of our planet about one degree during the
last 50 years. Evaporation increases as the atmosphere
warms, which increases humidity, average rainfall, and
the frequency of heavy rainstorms in many places—but
contributes to drought in others.
Greenhouse gases are also changing the world's oceans
and ice cover. Carbon dioxide reacts with water to
form carbonic acid, so the oceans are becoming more
acidic. The surface of the ocean has also warmed about
one degree during the last 80 years. Although warmer
temperatures cause sea level to rise, the impact on
water levels in the Great Lakes is not yet known. Warmer
air also melts ice and snow earlier in spring.
Temperature change (F):
-1 -0.5 0 0.5 1 1.5 2 2.5 3 3.5
Rising temperatures in the last century. All regions of
Wisconsin have warmed. Source: EPA, Climate Change
Indicators in the United States.
Heavy Precipitation and Flooding
Changing the climate is likely to increase the frequency of floods in
Wisconsin. Over the last half century, average annual precipitation in
most of the Midwest has increased by 5 to 10 percent. But rainfall
during the four wettest days of the year has increased about
35 percent. During the next century, spring rainfall and annual
precipitation are likely to increase, and severe rainstorms are likely
to intensify. Each of these factors will tend to further increase the
risk of flooding.
blooding in Menominee County in 2014, caused by an ice jam in the Wolf
River. Credit: National Weather Seivice.
Great Lakes
Changing the climate is also likely to harm water quality in Lake
Michigan. Warmer water tends to cause more algal blooms,
which can be unsightly, harm fish, and degrade water quality.
Severe storms also increase the amount of pollutants that run off
from land to water, so the risk of algal blooms will be greater if
storms become more severe. Increasingly severe rainstorms
could also cause sewers to overflow into the lake more often,
threatening beach safety and drinking water supplies.
One advantage of climate change is that warmer winters reduce
the number of days that ice prevents navigation. Between 1994 and
2011, the decline in ice cover lengthened the shipping season on the
Great Lakes by eight days. The lakes are likely to warm another
3° to 7°F in the next 70 years, which will further extend the shipping

Winter Recreation
Warmer winters are likely
to shorten the season for
recreational activities like
ice fishing, snowmobiling,
skiing, and snowboarding,
which could harm the local
economies that depend on
them. Small lakes are freezing
later and thawing earlier
than a century ago, which
shortens the season for ice
fishing and ice skating. Since
the early 1970s, winter ice
coverage in the Great Lakes
has decreased by 63 percent. The warmer climate is likely to
shorten the season when the ground is covered by snow, and
thereby shorten the season for activities that take place on snow.
Nevertheless, annual snowfall has increased in much of the
Great Lakes region, which could benefit winter recreation at
certain times and locations.
Changing the climate is likely to shift the ranges of plants and
animals. For example, rising temperatures could change the
composition of Wisconsin's forests. As the climate warms, the
populations of paper birch, quaking aspen, balsam fir, and black
spruce may decline in the North Woods, while oak, hickory, and
pine trees may become more numerous. Climate change will also
affect habitat for animals such as fish. Rising water temperatures
will increase the available habitat for warmwater fish such as
bass, while shrinking the available habitat for coldwater fish
such as trout. Declining ice cover and increasingly severe storms
would harm fish habitat through erosion and flooding.
Warming could also harm ecosystems by changing the timing of
natural processes such as migration, reproduction, and flower
blooming. Migratory birds are arriving in the Midwest earlier
in spring today than 40 years ago. Along with range shifts,
changes in timing can disrupt the intricate web of relationships
between animals and their food sources and between plants and
pollinators. Because not all species adjust to climate change in
the same way, the food that one species eats may no longer be
available when that species needs it (for example, when migrat-
ing birds arrive). Some types of animals may no longer be able to
find enough food.
The changing climate may reduce the output of Wisconsin's
multi-billion-dollar dairy industry, which generates more than
half of the state's farm revenue. Higher temperatures cause
cows to eat less and produce less milk. Climate change may
also pose challenges for crops, but it could also have some
benefits; the net effect is unknown. Longer frost-free growing
seasons and higher concentrations of atmospheric carbon
dioxide would increase yields of soybeans and wheat during an
average year. But increasingly hot summers are likely to
reduce yields of corn. Seventy years from now, much of
Wisconsin is likely to have 5 to 10 more days per year with
temperatures above 95°F than it has today. More severe
droughts or floods would also hurt crop yields.
Air Pollution and Human Health
Changing the climate can harm air quality and amplify existing
threats to human health. Higher temperatures increase the
formation of ground-level ozone, a pollutant that causes lung and
heart problems. Ozone also harms plants. In some rural parts
of Wisconsin, ozone levels are high enough to reduce yields of
soybeans and winter wheat. EPA and the Wisconsin Department
of Natural Resources have been working to reduce ozone
concentrations. As the climate changes, continued progress
toward clean air will become more difficult.
Climate change may also increase the length and severity of the
pollen season for allergy sufferers. For example, the ragweed
season in Madison and La Crosse is two weeks longer than in
1995, because the first frost in fall is later. The risk of some
diseases carried by insects may also increase. The ticks that
transmit Lyme disease are active when temperatures are above
45°F, so warmer winters could lengthen the season during which
ticks can become infected or people can be exposed to the ticks.
Hot days can be unhealthy—even dangerous. High temperatures
can cause heat stroke and dehydration, and affect people's
cardiovascular and nervous systems. Northern cities like
Milwaukee are vulnerable to heatwaves, because many houses
and apartments lack air conditioning, and urban areas are
typically warmer than their rural surroundings. For example,
heatwaves killed 91 people in Milwaukee County in 1995, and
11 people in 1999. Heat stress is likely to increase as climate
change brings hotter summer temperatures and more humidity.
Certain people are especially vulnerable, including children, the
elderly, the sick, and the poor.
Ducks on Lake Mendota in
Madison on a mild January day
in 2015. Mendota is one of many
lakes in the region that are freezing
later and thawing earlier than
they used to. Credit: Jeff Miller,
University of Wisconsin-Madison.
The sources of information about climate and the impacts of climate change in this publication are: the national climate assessments by the U.S. Global Change Research
Program, synthesis and assessment products by the U.S. Climate Change Science Program, assessment reports by the Intergovernmental Panel on Climate Change, and
EPA's Climate Change Indicators in the United States. Mention of a particular season, location, species, or any other aspect of an impact does not imply anything about
the likelihood or importance of aspects that are not mentioned. For more information about climate change science, impacts, responses, and what you can do, visit EPA's
Climate Change website at www.epa.gov/climatechanae.