United States
Environmental Protection
Agency
Office of Policy, Planning
and Evaluation
(2111)
EPA 230-F-97-008W
September 1997
&EPA Climate Change And Minnesota
The earth's climate is predicted to change because human
activities are 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 enhancedby
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 warming.
although the actual changes may vary from place to place because
coastal lands are themselves sinking or rising.
The Greenhouse Effect
Some solar radiation
is reflected by the
earth and the
k 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. Sulfate 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 9 warmest years in this century all have
occurred in the last 14 years. Of these, 1995 was the warmest
year on record, suggesting the atmosphere has rebounded 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
1
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Global Temperature Changes (1861-1996)
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 are a powerful tool for studying
climate. As a result of continuous model improvements over the
last few decades, scientists are 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 Minneapolis.
Minnesota, has increased slightly from 43.9°F (1888-1917
average) to 44.9°F (1963-1992 average), and precipitation in
some areas of the state has increased by up to 20%, especially in
the southern half.
Over the next century, Minnesota's climate may change even
more. 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, it is projected that by
2100, temperatures in Minnesota 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
around 15% in winter, summer, and fall, with little change
projected for spring.
The amount of precipitation on extreme wet days in summer most
likely would increase. The frequency of extreme hot days in
summer is expected to increase along with the general warming
trend. It is not clear how severe storms would change.
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
Precipitation Trends From 1900 To Present
Trends/100 years
+20% •
+10% •
+5% •
-5%o
-10%0
-20% O
Source: Karl et al. (1996)
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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 may
increase the number of heat-related deaths and the incidence of
heat-related illnesses. Minnesota, with its irregular, intense heat
waves, seems somewhat susceptible.
In Minneapolis, one study projects that a 3°F warming could
triple heat-related deaths from 60 during a typical summer to
about 180 (although increased air conditioning use may not have
been fully accounted for). The elderly, particularly those living
alone, are at greatest risk.
Warming and other climate changes could expand the habitat and
infectivity of disease-carrying insects, increasing the potential for
transmission of diseases such as malaria and dengue ("break
bone") fever. Mosquitoes flourish in Minnesota, and some carry
St. Louis encephalitis. The mosquito populations that carry this
disease could increase with climate change. Also, the mosquitoes
that carry yellow fever, dengue fever, Eastern equine encephalitis.
and La Crosse encephalitis recently have spread as far north as
Chicago. Global warming could shift the region where these
mosquitoes breed and overwinter farther north. If conditions
become warmer and wetter, mosquito populations can increase.
thereby increasing the risk of transmission of these diseases.
Forests
Trees and forests are 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 are better adapted to warmer conditions.
such as oaks and southern pines, would prevail. 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 Minnesota
could change little or decline by as much as 50-70%. The
uncertainties depend on many factors, including whether soil
Changes In Forest Cover
Current +10°F, +13% Precipitation
Conifer Forest
Broadleaf Forest
Savanna/Woodland
Grassland
Arid Lands
Source: VEMAP Participants (1995); Neilson (1995)
becomes drier and, if so, by how much drier. Hotter, drier
weather could increase the frequency and intensity of wildfires.
The unique boreal forests in the northern part of the state and in
the Boundary Waters Canoe Area could be replaced by mixed
forests better adapted to warmer conditions. The mixed aspen.
birch, beech, maple, and pine forests in the northern and eastern
areas of the state would shrink in range and be replaced by a
combination of grasslands and hardwood forests consisting of
oak, elm, and ash. Grasslands and savanna eventually could
replace much of the forests and woodlands in the state. These
changes would significantly affect the character of Minnesota
forests and the activities that depend on them.
Water Resources
Water resources are affected by changes in precipitation as well
as by temperature, humidity, wind, and sunshine. Changes in
streamflow tend to magnify changes in precipitation. Water
resources in drier climates tend to be more sensitive to climate
changes. Because evaporation 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.
Minnesota is known as the "Land of 10,000 Lakes." About two-
thirds of the state lies within the headwaters of the Mississippi
River. The remainder is drained by the Red River and small
tributaries of Lake Superior. If climate warms, the ice cover on
Minnesota's lakes and streams would not last as long as it does
today. Streamflows could peak sooner in the spring because of
earlier snowmelt and ice breakup. Reduced summer flows could
decrease water quality. Lake surface temperatures would be
warmer in the summer, although the temperature changes
generally would be less than the increase in air temperature. As a
result, lake evaporation would increase considerably, perhaps by
as much as 20% for a 4°F warmer climate.
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Shorter ice-cover seasons and increased lake evaporation could
have major effects on Lake Superior. Fresh water flowing into
Lake Superior could decrease with global warming, potentially
reducing lake levels and degrading water quality. Flood damage
could be reduced, but shorelines could be more susceptible to
erosion damage from wind and rain. Reduced fresh water in the
Great Lakes could negatively affect shipping to and from Duluth.
for example, primarily because of lower water levels in the
shipping channels connecting the lower Great Lakes. However.
this could be offset by a longer ice-free season.
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 climate 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 Minnesota, agriculture is about a $7 billion annual industry.
50% of which comes from crops. About 5% of all farm acres in
the nation is in Minnesota. The principal crops are corn, soy-
beans, and wheat. About 2% of the state's farm acres are irri-
gated. If climate warms, corn yields could remain unchanged or
could decrease by up to 34%. Wheat yields could increase by 6-
10%, and projected soybean yields are mixed: they could
increase by up to 28% or decrease by 12%. The number of acres
farmed could fall by 12-18%, and farm income could decrease by
Changes In Agricultural Yield And Production
Yield
Production
Corn Wheat
Soybeans
• DT = 8°F;Dprecip. = £
Corn Wheat
Soybeans
DT = 9°F; Dprecip. = 17%
Source: Mendelsohn and Neumann (in press); McCarl (personal
communication)
10-25%. Irrigated acreage could increase. This could further
stress water supplies, which could be lower in the summer, and
water quality could be degraded further.
Ecosystems
The prairie potholes of Minnesota are the single most important
breeding area for North American waterfowl such as mallards.
pintails, and blue-winged teals. The drying effects of climate
change could reduce the size and number of prairie potholes, with
damaging effects to the waterfowl.
The forest ecosystems in the Boundary Waters Canoe Area are an
important habitat for Kirtland's warblers. If the birch, balsam fir.
white cedar, and quaking aspen found there were replaced by
sugar maples, Kirtland's warblers could disappear in Minnesota.
Aquatic ecosystems also could be affected by climate change; for
example, brown trout could lose most of their habitat.
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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