United States
Environmental Protection
Agency
Office of Policy
(2111)
EPA 236-F-98-007n
September 1998
©EPA Climate Change And Wyoming
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 underway. 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 warming,
although the actual changes may vary from place to place
because coastal lands are themselves sinking or rising.
The Greenhouse Effect
Solar
radiation
passes
throi
the dear
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 busi-
nesses, 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. Forexample, 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
between 1890 and 1996. The 9 warmestyears 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
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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 uncertainties
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 temperature
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 Laramie.
Wyoming, has increased 1.5°F, and precipitation has decreased
by up to 20% in many parts of the state. These past trends may
or may not continue into the future.
Over the next century, climate in Wyoming may change
even more. For example, based on projections made by the
Intergovernmental Panel on Climate Change and results from
the United Kingdom Hadley Centre's climate model (HadCM2), a
model that accounts for both greenhouse gases and aerosols, by
2100 temperatures in Wyoming could increase by 4°F in spring
andfall (witharange of 2-7°F), 5°F in summer (with a range of 2-
8°F), and 6°F in winter (witharange of 3-11°F). Precipitation is
estimated to decrease slightly in summer (with a range of 0-10%).
increase by 10% in spring and fall (with a range of 5-20%), and
increase by 30% in winter (with a range of 10-50%). Otherclimate
models may show different results, especially regarding estimated
changes in precipitation. The impacts described in the sections
that follow take into account estimates from different models. The
amount of precipitation on extreme wet or snowy days in winter is
likely to increase. The frequency of extreme hot days in summer
would increase because of the general warming trend. It is not
clear how the severity of storms might be affected, although an
increase in the frequency and intensity of winter storms is
possible.
Precipitation Trends From 1900 To Present
Trends/1 00 years
+20% Q
+10% £
+5% •
-5% O
-10% O
-20% O
0 0
0 0
0
0 °
o
0 °
Cheyenne ^
Source: Karl et al. (1996)
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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. The elderly, particularly those living alone.
are at greatest risk. These effects have been studied only for
populations living in urban areas; however, even those in rural
areas may be susceptible.
Upper and lower respiratory allergies are influenced by humidity.
A 2°F warming and wetter conditions could increase respiratory
allergies.
Warming and other climate changes could expand the habitat
and infectivity of disease-carrying insects. Infected individuals
can bring malaria to places where it does not occur naturally.
Also, some mosquitoes in Wyoming can carry malaria. If condi-
tions become warmer and wetter, mosquito populations could
increase, thus increasing the risk of transmission if this and other
diseases are introduced into the area. Warmer temperatures could
increase the incidence of Lyme disease and other tick-borne
diseases in Wyoming, because populations of ticks, and their
rodent hosts, could increase under warmer temperatures and
increased vegetation. Increased runoff from heavy rainfall could
increase water-borne diseases such as giardia, cryptosporidia.
and viral and bacterial gastroenteritides. Developed countries
such as the United States should be able to minimize the impacts
of these diseases through existing disease prevention and control
methods.
Water Resources
The headwaters of several rivers originate in Wyoming and
flow in all directions into the Missouri, Snake, Great, and Colo-
rado river basins. Within the state, water is plentiful in some parts
and scarce in others. The mountains receive abundant precipita-
tion, mostly as snow, which support perennial streams. The plains
and intermountain areas are semiarid, and most of the rain there
comes during summer thunderstorms. The streams in these areas
tend to be intermittent and are not dependable water sources;
hence, reservoir storage is required to ensure reliable year-round
supplies. Surface water is the primary source of water, and
irrigation is the largest user. Groundwater is used where surface
supplies are inadequate or need to be supplemented.
Winter snow accumulation and spring snowmelt strongly affect
many of Wyoming's rivers. A warmer climate could result in less
winter snowfall, more winter rain, and faster, earlier spring
snowmelt. In the summer, without increases in rainfall of at least
15-20%, higher temperatures and increased evaporation could
lower streamflows and lake levels. Less water would be available
to support irrigation, hydropower generation, public supply, fish
and wildlife habitat, recreation, and mining. Competition for water
could increase on the plains, where agricultural and industrial
users compete for available water. Similarly, in northeastern
Wyoming, which has large deposits of minerals, coal, and
petroleum, competition between mining, energy, and other users
could intensify for the meager summer streamflows. Groundwater
levels in several areas of the state are declining because of
increased pumpage for irrigation and urban development. Less
spring and summer recharge could lower groundwater levels.
Tourism and recreation, important components of Wyoming's
economy, also depend on adequate supplies of clean water.
Higher temperatures and lower flows could impair water quality
by concentrating pollutants and reducing assimilative capacity.
Major water quality concerns such as the saline content of
irrigation return flows and eutrophication also could be aggra-
vated by a warmer climate. Many streams in Wyoming are fully
appropriated for offstream uses. Much of the water in the state
belongs to downstream users through interstate compacts and
court decrees. Reductions in water availability could complicate
water rights issues and interstate agreements. Changes in the
timing and accumulation of snow could affect skiing conditions in
positive and negative ways, such as the timing and length of
season and snow depth.
More rain could ease water competition, but it also could
increase flooding. Earlier, more rapid snowmelt would contribute
to winter and spring flooding. In a warmer climate, more intense
rains are expected, which could increase flash floods.
Agriculture
The mix of crop and livestock production in a state is influenced
by climatic conditions and water availability. As climate warms.
production patterns could 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, industry, and
other users.
Understandably, most studies have not fully accounted for
changes in climate variability, water availability, crop pests.
changes in air pollution such as ozone, and adaptation by farmers
to changing climate. Including these factors could change
modeling results substantially. Analyses that assume changes
Changes In Agricultural Yield And Production
Irrigated Yield Production
50
40
S> 30
O
5? 20
10
Wheat Hay Wheat Hay
• AT = 9°F; Aprecip. = 11% • AT = 8°F; Aprecip. = 1 %
Sources: Mendelsohn and Neumann (in press); McCarl (per-
sonal communication)
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in average climate and effective adaptation by farmers suggest
that aggregate U.S. food production would not be harmed,
although there may be significant regional changes.
In Wyoming, production agriculture is an $800 million annual
industry, 80% of which comes from livestock, mainly cattle.
Almost 70% of the farmed acres are irrigated. The major crops in
the state are wheat and hay. Climate change could increase wheat
yields by 35-48%. Hay and pasture dry land yields could fall by
13 % or rise by 12% with irrigation, depending on how climate
changes and whether irrigation is used. Farmed acres could
remain fairly constant or could increase by as much as 12%, with
an increased share of acres under irrigation. Livestock production
may not be affected, unless summer temperatures rise signifi-
cantly and conditions become significantly drier. Under these
conditions, livestock tend to gain less weight and pasture yields
decline, limiting forage.
Forests
Trees and forests are adapted to specific climate conditions.
and as climate warms, forests will change. These changes could
include changes in species composition, geographic range, and
health and productivity. If conditions also become drier, the
current range and density of forests could be reduced and
replaced by grasslands and pasture. Even a warmer and wetter
climate could lead to changes; trees that are better adapted to
these conditions, such as fir and spruce, would thrive. Under
these conditions, forests could become more dense. These
changes could occur during the lifetimes of today's children.
particularly if the change is accelerated by other stresses such as
fire, pests, and diseases. Some of these stresses would them-
selves be worsened by a warmer and drier climate.
With changes in climate, the extent of forested areas in
Wyoming could change little or decline by as much as 15-30%.
The uncertainties depend on many factors, including whether
soils become drier and, if so, how much drier. Hotter, drier weather
could increase the frequency and intensity of wildfires, threaten-
ing both property and forests. Drier conditions would reduce the
range and health of ponderosa and lodgepole forests, and
increase their susceptibility to fire. Grasslands and rangeland
could expand into previously forested areas in the western part of
the state. Milder winters could increase the likelihood of insect
outbreaks and of subsequent wildfires in the dead fuel left after
such an outbreak.
Ecosystems
Wyoming straddles the Continental Divide, and its abrupt
topographic relief includes alternating basins and mountain
ranges. Major mountain ranges include the Beartooth, Gros
Ventre, Teton, Wind River, Bighorn, Sierra Madre, and Medicine
Bow. Internal basins and eastern plains are rolling to flat, and in
the east are the Great Plains. Typical vegetation includes sage-
brush, greasewood, and saltbush shrubs in the intermountain
basins, grasses on the Great Plains, juniper and mountain
mahogany in the foothills, and forest and alpine meadows in the
mountains. Fire plays an important role in several Wyoming
ecosystems, including sagebrush steppe, western juniper
woodlands, and ponderosa pine forests. In sagebrush steppe, a
greater frequency of fires in the last 50 years has resulted in
invasion by annual grasses such as cheatgrass and medusahead.
In western juniper woodlands, continued grazing and 50 years of
attempted fire exclusion have allowed juniper expansion to
continue unchecked. Historically, frequent low intensity surface
fires perpetuated ponderosa pine stands with grassy under-
growth. Today, after 60 years of fire suppression, many of these
forests, along with lodgepole pine forests, have high densities of
trees, are plagued by epidemics of insects and diseases, and are
subject to severe stand-destroying fires. Whitebark pines have
suffered extensive diebacks in Idaho in part because of fire
suppression and the introduced white pine blister rust, a non-
native fungus that has defied control. This disease is now
expanding into northwest Wyoming.
Since the massive fires of 1988, whennearly half of Yellowstone
National Park burned, scientists have been paying close attention
to the possible threats from climate change. Experts agree that the
fires of 1988 came about as result of a winter drought, a hot dry
summer, and unusually strong winds. Also important were the
large areas of highly flammable, old growth lodgepole pine forest.
Under normal conditions, large fires like those of 1988 occur only
once in every few generations. But, with approximately 40% of
the Yellowstone still vulnerable to large-scale burns, any in-
creased fire risk due to climate change would pose a significant
problem. The replacement of old-growth forest stands by
younger stands could threaten northern twinflower, fairy slipper.
pine martin, and goshawk. Outbreaks of defoliating attacks by
western spruce budworms could occur more frequently and
become much more damaging for the conifer forests.
Climate change also poses a threat to the high alpine systems.
and this zone could disappear in many areas. Local extinctions of
alpine species such as arctic gentian, alpine chaenactis, rosy
finch, and water pipit could be expected as a result of habitat loss
and fragmentation. Even a modest warming and drying could
reduce whitebark pine habitat by up to 90% within 50 years.
Whitebark pine nuts and army cutworm moth caterpillars, which
are found in these forests, provide vital food for Wyoming's
grizzly bear population. Whitebark pine forest may be replaced
with Douglas fir, and on the lower slopes, forest would give way
to treeless landscapes dominated by big sagebrush, Idaho fes-
cue, and bluebunch wheatgrass.
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, or
visit http://www. epa.gov/globalwarming/impacts.
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