United States
Environmental Protection
Agency
Office of Policy, Planning
and Evaluation
(2111)
EPA 230-F-97-008Z
September 1997
Climate Change And Montana
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
Solar
radiation
passes
through
the clear
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.
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, common
air pollutants, cool the atmosphere by reflecting incoming solar
radiation. However, sulfates are short-lived and vary regionally.
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
between 1890 and 1996. 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 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
Source: U.S. Department of State (1992)
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Global Temperature Changes (1861-1996)
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
-1
±
r^ \ /
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 Helena.
Montana, has increased 1.3°F, and precipitation has decreased
by up to 20% in many parts of the state.
Over the next century, climate in Montana 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 Montana could increase by about 4°F
in spring and summer (with a range of 1-8°F) and 5°F in fall and
winter (with a range of 2-10°F). Precipitation is estimated to
increase by roughly 10% in all seasons except winter, when the
range of estimated increase is 15-40%. The amount of precipita-
tion 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. Although it is not clear
how severe storms would change, an increase in the frequency
and intensity of winter storms is possible.
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
Precipitation Trends From 1900 To Present
Trends/100 years
+20%
+10% %
+5% •
-5% O
-10% O
-20%
Source: Karl et al. (1996)
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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. Montana, with its irregular, intense heat
waves, could be susceptible. The elderly, particularly those living
alone, are at greatest risk.
Warming and other climate changes may expand the habitat and
infectivity of disease-carrying insects, thus increasing the
potential for transmission of diseases. A recent study has con-
cluded that a 5-9°F temperature increase would cause a signifi-
cant northern shift in Western equine encephalitis outbreaks.
Mosquitos capable of transmitting this disease already are present
in Montana. If Montana's climate becomes warmer and wetter.
mosquito populations could increase and conditions may become
more favorable for disease transmission.
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. If streamflow and lake levels drop.
groundwater also could be reduced. In addition, more intense
precipitation could increase flooding.
Western Montana drains into the Columbia River system, and
most of the remaining areas of the state drain to the east into the
Missouri River or its major tributary, the Yellowstone River.
Winter snow accumulation and spring melt are key processes that
affect the runoff of all rivers within the state. A warmer climate
would lead to earlier spring snowmelt, resulting in higher
streamflows in winter and spring and lower streamflows in
summer and fall. Earlier spring snowmelt could reduce the
performance of the reservoir system in western Montana, thus
reducing summer and fall runoff, which is critical for power
generation, fisheries protection, recreation, and other uses.
Increased rainfall could mitigate some of these effects, but it also
could lead to increased flooding.
Changes In Agricultural Yield And Production
Irrigated Yield Production
Wheat Barley Hay
• AT = 9°F; Aprecip. = 19%
Wheat Barley Hay
AT = 7°F; Aprecip. = 19%
Source: Mendelsohn and Neumann (in press); McCarl (personal
communication)
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 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 change modeling results substantially. Analyses that
assume changes 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 Montana, agriculture is a $1.8 billion annual industry, one-half
of which comes from livestock, mainly cattle. Just over 20% of
the crop acreage is irrigated. The major crops in the state are
wheat, barley, and hay. In a warmer climate wheat yields could
increase by more than a third, and changes in barley and hay
yields could vary between -8% and +13%, depending on whether
irrigation is used, leading to changes in acres farmed and produc-
tion. For example, barley yields could rise while production falls
because of a decrease in barley acres farmed. An increased
dependence on irrigation is possible, depending on the relative
balance between rainfall and increased evaporation.
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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 range, 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 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 change is
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 Montana
may change little or could 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, threat-
ening both property and forests. Drier conditions could reduce
the range and health of lodgepole and Douglas fir forests, and
increase their susceptibility to fire. With increases in rainfall.
however, these effects could be less severe. Grass and range-
land could expand into previously forested areas along the
eastern slope of the Rocky Mountains and into some of the
western valleys. Milder winters could increase the likelihood
of insect outbreaks and of subsequent wildfires in the dead fuel
left after such an outbreak. These changes would significantly
affect the character of Montana forests and the activities that
depend on them.
Ecosystems
Ecosystems in Montana are diverse, ranging from grasslands and
deserts to mountain shrublands, forests, meadows, and alpine
tundra. They also include numerous wetlands and streams.
Because of elevation changes and human land use, many habitats
are fragmented and restricted in area. Changes in temperature and
precipitation caused by climate change could affect the location
and productivity of these ecosystems.
Warming and changes in precipitation could affect alpine areas.
causing tree lines to rise by roughly 350 feet for every degree
Fahrenheit of warming. Mountain ecosystems such as those found
in Glacier National Park could shift upslope, reducing habitat for
many subalpine species. Alpine animals and species, many of
which are unique to the region, could disappear from the highest
elevations. Mountain glaciers such as those found in Glacier
National Park are expected to shrink, possibly leading to higher
stream temperatures and decreased runoff. This would adversely
affect aquatic biota, including trout species. Changes in rainfall
and snowfall also could alter streamflows and wetlands, affecting
wildlife and possibly accelerating the invasion of non-native
plants into streamside habitats. Aquatic species that are sensitive
to water temperature could be affected adversely by climate
change. Brown trout and rainbow trout could lose habitat.
Glacier National Park
Glacier National Park is located in a pristine mountainous
area in northwest Montana. The park provides habitat for an
abundance of wildlife, including the most dense population
of grizzly bears (an endangered species) in the United
States. Other endangered animal species found in the park
include the bald eagle and the gray wolf. Over 1,400
different plants live in Glacier Park, 28 of which are found
nowhere else in Montana.
Climate change could have a serious impact on Glacier
National Park. The park has approximately 50 glaciers
today, down from an estimated 150 glaciers in 1850. The
recession of Sperry Glacier illustrates the impact of recent
warming temperatures in the park. If these warming trends
continue, it is estimated that no glaciers will be found in the
park by 2030. Without glaciers, stream temperatures are
expected to rise, which could affect aquatic ecosystems in
the park, including trout species. Climate change also could
affect the types of trees found in the forests. Lodgepole pine
and western cedar forests could yield to forests dominated
by spruce and western hemlock. Six rare alpine plants that
are at the southern border of their geographic range would
be especially vulnerable to climate change.
Sperry Glacier Recession
1850-1993
Alberta
-Sperry Glacier
•
Glacier
National /• Montana
Park
Continental
Divide
r
1 kilometer
Source: USGS Biological Resources Division, Glacier
Field Station. Carl H. Key, provisional data (1997)
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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