United States
Environmental Protection
Agency
Office of Policy, Planning
and Evaluation
(2111)
EPA 236-F-96-001
May 1999
oEPA Climate Change And Wisconsin
The earth's climate is predicted to change because human
activities arc altering the chemical composition of the atmosphere
through the buildup of greenhouse gases — primarily carbon
dioxide, methane, nitrous oxide, and chlorofluorocarbons. The
heat-trapping property of these greenhouse gases is undisputed.
Although there is uncertainty about exactly how and when the
earth's climate will respond to enhanced concentrations of
greenhouse gases, observations indicate that detectable changes
are under way. There most likely will be increases in temperature
and changes in precipitation, soil moisture, and sea level, which
could have adverse effects on many ecological systems, as well
as on human health and the economy.
The Climate System
Energy from the sun drives the earth's weather and climate.
Atmospheric greenhouse gases (water vapor, carbon dioxide,
and other gases) trap some of the energy from the sun, creating
a natural "greenhouse effect." Without this effect, temperatures
would be much lower than they are now, and life as known today
would not be possible. Instead, thanks to greenhouse gases, the
earth's average temperature is a more hospitable 60°F. However,
problems arise when the greenhouse effect is enhanced by
human-generated emissions of greenhouse gases.
Global warming would do more than add a few degrees to today's
average temperatures. Cold spells still would occur in winter, but
heat waves would be more common. Some places would be drier,
others wetter. Perhaps more important, more precipitation may
come in short, intense bursts (e.g., more than 2 inches of rain
in a day), which could lead to more flooding. Sea levels would
be higher than they would have been without global wanning,
although the actual changes may vary from place to place because
coastal lands are themselves sinking or rising.
The Greenhouse Effect
Solar
radiation
passes
through
the clear
atmosphere
Some solar radiation
is reflected by the
earth and the
atmosphere
Some of the infrared radiation passes
through the atmosphere, and some is
absorbed and re-emitted in all
directions by greenhouse gas
molecules. The effect of this is to warm
the earth's surface and the lower
atmosphere.
Source: U.S. Department of State (1992)
Emissions Of Greenhouse Gases
Since the beginning of the industrial revolution, human activities
have been adding measurably to natural background levels of
greenhouse gases. The burning of fossil fuels — coal, oil, and
natural gas — for energy is the primary source of emissions.
Energy burned to run cars and trucks, heat homes and businesses,
and power factories is responsible for about 80% of global
carbon dioxide emissions, about 25% of U.S. methane emissions,
and about 20% of global nitrous oxide emissions. Increased
agriculture and deforestation, landfills, and industrial production
and mining also contribute a significant share of emissions. In
1994, the United States emitted about one-fifth of total global
greenhouse gases.
Concentrations Of Greenhouse Gases
Since the pre-industrial era, atmospheric concentrations of carbon
dioxide have increased nearly 30%, methane concentrations have
more than doubled, and nitrous oxide concentrations have risen
by about 15%. These increases have enhanced the heat-trapping
capability of the earth's atmosphere. Sulfatc aerosols, a common
air pollutant, cool the atmosphere by reflecting incoming solar
radiation. However, sulfates are short-lived and vary regionally,
so they do not offset greenhouse gas warming.
Although many greenhouse gases already are present in the
atmosphere, oceans, and vegetation, their concentrations in the
future will depend in part on present and future emissions.
Estimating future emissions is difficult, because they will depend
on demographic, economic, technological, policy, and institu-
tional developments. Several emissions scenarios have been
developed based on differing projections of these underlying
factors. For example, by 2100, in the absence of emissions
control policies, carbon dioxide concentrations are projected to
be 30-150% higher than today's levels.
Current Climatic Changes
Global mean surface temperatures have increased 0.6-1.2°F since
the late 19th century. The 10 warmest years in this century all
have occurred in the last 15 years. Of these, 1998 was the
warmest year on record, suggesting the atmosphere has re-
bounded from the temporary cooling caused by the eruption of
Mt. Pinatubo in the Philippines.
Several pieces of additional evidence consistent with warming,
such as a decrease in Northern Hemisphere snow cover, a
decrease in Arctic Sea ice, and continued melting of alpine
glaciers, have been corroborated. Globally, sea levels have risen
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Global Temperature Changes (1861-1996)
0.6
O./l
0.2
n
--0.2
-0.4
-0.6
-0.6
-1
AA/W
t
/y/SA „,
/ ^ \f
Year
Source: IPCC (1995), updated
4-10 inches over the past century, and precipitation over land has
increased slightly. The frequency of extreme rainfall events also
has increased throughout much of the United States.
A new international scientific assessment by the Intergovern-
mental Panel on Climate Change recently concluded that "the
balance of evidence suggests a discernible human influence
on global climate."
Future Climatic Changes
For a given concentration of greenhouse gases, the resulting
increase in the atmosphere's heat-trapping ability can be pre-
dicted with precision, but the resulting impact on climate is more
uncertain. The climate system is complex and dynamic, with
constant interaction between the atmosphere, land, ice, and
oceans. Further, humans have never experienced such a rapid rise
in greenhouse gases. In effect, a large and uncontrolled planet-
wide experiment is being conducted.
General circulation models are complex computer simulations
that describe the circulation of air and ocean currents and how
energy is transported within the climate system. While uncertain-
ties remain, these models arc a powerful tool for studying
climate. As a result of continuous model improvements over the
last few decades, scientists arc reasonably confident about the
link between global greenhouse gas concentrations and tempera-
ture and about the ability of models to characterize future climate
at continental scales.
Recent model calculations suggest that the global surface temper-
ature could increase an average of 1.6-6.3°F by 2100, with signif-
icant regional variation. These temperature changes would be far
greater than recent natural fluctuations, and they would occur
significantly faster than any known changes in the last 10,000
years. The United States is projected to warm more than the
global average, especially as fewer sulfate aerosols are produced.
The models suggest that the rate of evaporation will increase as
the climate warms, which will increase average global precipita-
tion. They also suggest increased frequency of intense rainfall as
well as a marked decrease in soil moisture over some mid-
continental regions during the summer. Sea level is projected to
increase by 6-38 inches by 2100.
Calculations of regional climate change are much less reliable
than global ones, and it is unclear whether regional climate will
become more variable. The frequency and intensity of some
extreme weather of critical importance to ecological systems
(droughts, floods, frosts, cloudiness, the frequency of hot or cold
spells, and the intensity of associated fire and pest outbreaks)
could increase.
Local Climate Changes
Over the last century, the average temperature in Stanley,
Wisconsin, has remained virtually unchanged, and precipitation
has increased by 5-10% in some areas of the state.
Over the next century, Wisconsin's climate may change signifi-
cantly. Based on projections given by the Intergovernmental
Panel on Climate Change and results from the United Kingdom
Hadley Centre's climate model (HadCM2), a model that has
accounted for both greenhouse gases and aerosols, by 2100
temperatures in Wisconsin could increase by about 4°F
(with a range of 2-7°F) in winter, spring, and fall, and by some-
what less in summer. Precipitation is projected to increase by
15-20% in winter, summer, and fall, with little change projected
for spring.
The amount of precipitation on extremely wet days in summer
most likely would increase. The frequency of extremely hot days
in summer is expected to increase along with the general warming
trend. It is not clear how severe storms would change.
Precipitation Trends From 1900 To Present
Trends/ 1 00 years
+20% •
+ 10% •
-5%o
-10%O
-20% O
Source: Karl et al. (1996)
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Climate Change Impacts
Global climate change poses risks to human health and to
terrestrial and aquatic ecosystems. Important economic resources
such as agriculture, forestry, fisheries, and water resources also
may be affected. Warmer temperatures, more severe droughts and
floods, and sea level rise could have a wide range of impacts. All
these stresses can add to existing stresses on resources caused by
other influences such as population growth, land-use changes,
and pollution.
Similar temperature changes have occurred in the past, but the
previous changes took place over centuries or millennia instead
of decades. The ability of some plants and animals to migrate and
adapt appears to be much slower than the predicted rate of
climate change.
Human Health
Higher temperatures and increased frequency of heat waves
could increase the number of heat-related deaths and the inci-
dence of heat-related illnesses. Wisconsin, with its irregular,
intense heat waves, seems somewhat susceptible.
In Milwaukee, one study projects that a 3°F warming could
almost double heat-related deaths during a typical summer from
30 per summer to about 55 (although increased air conditioning
use may not have been fully accounted for). The elderly, particu-
larly those living alone, are at greatest risk.
There is concern that climate change could increase concentra-
tions of ground-level ozone. For example, high temperatures,
strong sunlight, and stable air masses tend to increase urban
ozone levels. Air pollution also is made worse by increases in
natural hydrocarbon emissions during hot weather. If a warmed
climate causes increased use of air conditioners, air pollutant
emissions from power plants also will increase.
A 4°F warming in the Midwest, with no other change in
weather or emissions, could increase concentrations of ozone,
a major component of smog, by as much as 8%. Perhaps more
important, however, is that the area exceeding national health
standards for ozone could almost triple. Currently, Door, Mara-
thon, and Oneida counties do not meet national standards for
ozone. Ground-level ozone has been shown to aggravate existing
respiratory illnesses such as asthma, reduce lung function, and
induce respiratory inflammation. In addition, ambient ozone
reduces crop yields and impairs ecosystem health.
Warming and other climate changes could expand the habitat of
disease-carrying insects or alter the life-cycle dynamics of the
infective parasites they may carry, thus increasing the potential
for transmission of diseases such as malaria and dengue ("break
bone") fever. Mosquitoes flourish in Wisconsin, and some carry
LaCrosse encephalitis. The number of mosquitoes that carry this
disease could increase with climate change. Also, the mosquitoes
that carry yellow fever, dengue fever, and Eastern equine en-
cephalitis recently have spread as far north as Chicago. Global
warming could shift the region where these mosquitoes breed and
Changes In Forest Cover
Current +10°F, +13% Precipitation
Conifer Forest
Broadleaf Forest
Savanna/Woodland
Grassland
Source: VEMAP Participants (1995); Neilson (1995)
overwinter farther north. If conditions become warmer and
wetter, mosquito populations could increase, increasing the risk
of transmission of these diseases.
Forests
Trees and forests arc adapted to specific climate conditions, and
as climate warms, forests will change. These changes could
include changes in species, geographic extent, and health and
productivity. If conditions also become drier, the current range
and density of forests could be reduced and replaced by grass-
lands and pasture. Even a warmer and wetter climate would lead
to changes; trees that arc better adapted to these conditions, such
as oaks and southern pines, would thrive. Under these conditions,
forests could become more dense. These changes could occur
during the lifetimes of today's children, particularly if they are
accelerated by other stresses such as fire, pests, and diseases.
Some of these stresses would themselves be worsened by a
warmer and drier climate.
With changes in climate, the extent of forested areas in Wisconsin
could change little or decline by 55-75%. The uncertainties
depend on many factors, including whether soils become drier
and, if so, by how much drier. Significant summer droughts with
increased tree loss and wildfire frequency could be expected with
hotter and drier weather. The mixed aspen, birch, beech, maple,
and pine forests found in the north would shrink in range and
would be replaced by a combination of grasslands and hardwood
forests consisting of more oak, elm, ash, and pines. Grasslands
and savanna eventually could replace much of the forest and
woodland in the state. These changes would affect the character
of Wisconsin forests and the activities that depend on them.
Water Resources
Water resources arc affected by changes in precipitation as well
as by temperature, humidity, wind, and sunshine. Changes in
strcamflow tend to magnify changes in precipitation. Water
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resources in drier climates tend to be more sensitive to climate
changes. Because evaporation from streams and lakes is likely to
increase with warmer climate, it could result in lower river flow
and lower lake levels, particularly in the summer. In addition,
more intense precipitation could increase flooding. If streamflow
and lake levels drop, groundwater also could be reduced.
About one-third of Wisconsin lies within the headwaters of the
Mississippi River basin. The remainder contains numerous small
rivers and streams, most of which drain to either Lake Michigan
or Lake Superior. Earlier spring snowmelt under climate change
could cause seasonal flows to peak sooner in most streams.
Increased summer evaporation probably would reduce summer
streamflows.
In the northern part of the state, as much as one-third of precipita-
tion currently goes to groundwater. This groundwater recharge
would almost certainly decrease in a warmer climate because of
increased evaporation. This would reduce the amount of water in
many, if not most, of the state's aquifers. In addition, unless the
evaporation were counteracted by increased precipitation, the
reduction in groundwater could harm the health of Wisconsin's
lakes and streams.
The water temperatures of the Great Lakes could increase
because of the warmer summer air temperatures and longer ice-
free season. This could increase evaporation and degrade water
quality through decreases in dissolved oxygen and increases in
the growth of algae. Perhaps more importantly, increased lake
evaporation could decrease lake levels by a foot or more for a
4°F warming. This could increase shore erosion from wind and
rain, increase water pollutant concentrations, and result in
increased dredging and other problems for Great Lakes shipping.
Flood damages, however, could be lessened.
Agriculture
The mix of crop and livestock production in a state is influenced
by climatic conditions and water availability. As climate warms,
production patterns will shift northward. Increases in climate
variability could make adaptation by farmers more difficult.
Warmer climates and less soil moisture due to increased evapora-
tion may increase the need for irrigation. However, these same
conditions could decrease water supplies, which also may be
needed by natural ecosystems, urban populations, and other
economic sectors.
Understandably, most studies have not fully accounted for
changes in elimate variability, water availability, and imperfect
responses by farmers to changing climate. Including these factors
could substantially change modeling results. Analyses based on
changes in average climate and which assume farmers effectively
adapt suggest that aggregate U.S. food production will not be
harmed, although there may be significant regional changes.
In Wisconsin, agriculture is about a $6 billion annual industry, of
which three-quarters comes from livestock. The principal crops
arc corn, silage, and hay. About 3% of the state's farmed acres is
irrigated. The effects of climate change arc difficult to predict,
Changes In Agricultural Yield And Production
Yield Production
Corn Silage Hay
• AT = 8'F; Aprecip. = 7%
Corn Silage Hoy
I AT = 10°F; Aprecip. = 19%
Source: Mendelsohn and Neumann (in press); McCarl (personal
communication)
however, potential impacts for Wisconsin might include: corn and
silage yields unchanged, or they could decrease by up to 34%.
Hay yields could remain unchanged or could decrease by 17%.
Acreage use could remain largely unchanged, and farm income
could remain unchanged or could increase up to 100%. Irrigated
acreage could increase. This could further stress water supplies,
and water quality could be further degraded.
Ecosystems
Wisconsin has diverse ecosystems that support a variety of
wildlife. Wisconsin's aquatic wildlife includes brown trout,
walleye, musky, largemouth bass, crayfish, snails, mussels, and
freshwater sponges. These species rely on the state's vast water
resources, which include more than 43,000 miles of flowing waters,
15,000 inland lakes, 800 miles of coastline, and wetlands covering
approximately 5 million acres. Wisconsin is also home to a variety
of birds and animals, including the bald eagle, osprcy, deer, black
bear, and gray wolf. One of the largest populations of Karncr blue
butterfly, an endangered species, is found in Wisconsin.
Climate change could influence many of Wisconsin's ecosystems.
Brown trout could lose a majority of their habitat as a result of
climate change. Prolonged drought from climate change could
decrease the number of lakes with suitable habitat for organisms
such as crayfish and snails. Drought also could decrease ground-
water supplies of silica, an essential nutrient for freshwater
sponges and diatoms. Climate change could affect the habitat and
population of many endemic species, and cause the disappear-
ance of some endangered species. Because of the fragmentation
of ecosystems from natural and human-caused barriers, many of
Wisconsin's animals could have difficulty migrating in response
to the effects of climate change.
For further information about the potential impacts of climate
change, contact the Climate and Policy Assessment Division
(2174), U.S. EPA, 401 M Street SW, Washington, DC 20460.
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