United States
Environmental Protection
Agency
Office of Policy
(2111)
EPA 236-F-98-007f
Septmeber 1998
SEPA Climate Change And Idaho
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 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
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 near Boise, Idaho.
has increased nearly 1°F, and precipitation has increased by
nearly 20% in many parts of the state, and has declined in other
parts of the state by more than 10%. These past trends may or
may not continue into the future.
Over the next century, climate in Idaho may experience additional
changes. For example, based on projections made by the Inter-
governmental 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 Idaho could increase by 5°F (with a range of
2-9°F) in winter and summer and 4°F (with a range of 2-7°F) in
spring and fall. Precipitation is estimated to change little in sum-
mer, to increase by 10% in spring and fall (with a range of 5-20%).
and to increase by 20% in winter (with a range of 10-40%). Other
climate 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/100 years
+20%
+10%
+5%
-5% O
-10% O
-20%
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.
Climate change could increase concentrations of ground-level
ozone. For example, high temperatures, strong sunlight, and
stable air masses tend to increase urban ozone levels. Although
Idaho is in compliance with current ozone air quality standards.
increased temperatures could make remaining in compliance more
difficult. Ground-level ozone is associated with respiratory
illnesses such as asthma, reduced lung function, and respiratory
inflammation. Air pollution also is made worse by increases in
natural hydrocarbon emissions such as emissions of terpenes by
trees and shrubs during hot weather. If a warmed climate causes
increased use of air conditioners, air pollutant emissions from
power plants also could increase.
Upper and lower respiratory allergies also are influenced by
humidity. A 2°F warming and wetter conditions could increase
the incidence and severity of respiratory allergies.
Warming and other climate changes could expand the habitat
and infectivity of disease-carrying insects. Mosquitoes in Idaho
can carry malaria, and some can carry western equine encephali-
tis, which can be lethal or cause neurological damage. 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 Idaho, 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
Idaho relies primarily on surface, but groundwater is also an
important source of supply. Most of Idaho is drained by tributar-
ies to the Columbia River, including the Spokane, Pend Oreille.
Kootenai, and Snake rivers. These rivers are regulated by dams
and reservoirs to reduce spring flooding and augment summer
flows. Runoff in the state is strongly affected by winter snow
accumulation and spring snowmelt. A warmer climate could mean
less snowfall, more winter rain, and a faster, earlier snowmelt. This
could result in lower reservoirs and water supplies in the summer
and fall. Additionally, without increases in precipitation, higher
summer temperatures and increased evaporation also would
contribute to lower streamflows and lake levels in the summer.
Drier summer conditions would intensify competition for water
among the diverse and growing demands in Idaho. Traditionally.
the largest water withdrawals have been for irrigated agriculture.
and hydroelectric power production has been an important
instream user of water. Recently, water demands to support
manufacturing and tourism have increased. Higher instream
flows are now required to augment flows in the lower Snake
and Columbia rivers to improve conditions for threatened and
endangered salmon. The public has demanded improved recre-
ational opportunities, and tribal water rights also must be
satisfied. In areas such as the Snake River Plain aquifer, ground-
water levels are declining because of increased pumpage.
changes in irrigation practices, and a prolonged drought (1987-
1994). Lower streamflows and runoff could reduce rates of
groundwater recharge and exacerbate water supply problems.
Lower flows and increased temperatures could impair water
quality by reducing the assimilation of wastes and concentrating
pollutants from irrigation return flows, mine tailings, and munici-
pal and industrial wastes.
Wetter conditions could benefit hydropower production and
ease competition for water, but they could also increase flooding
in some areas. In snow-dominated river basins such as the
Columbia, less snow accumulation could reduce the risk of spring
floods. However, more rain during the traditional flood season
could increase the frequency of flooding at lower elevations. In a
warmer climate, storm intensity could increase. Near Boise.
intense storms and warm rain on snowpack cause severe flooding
and mud and debris flows. More intense rains could increase
other hazards associated with high flows in Idaho, such as
landslides on steep roadcuts, erosion and stream sedimentation.
levels of pesticides and fertilizers in runoff from agricultural lands.
and pollution in runoff from urban lands.
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.
Changes In Agricultural Yield And Production
Irrigated Yield Production
50
40
30
Si 2°
a 10
s «
-10
-20
-30
-40
Wheat Hay
Barley Potatoes
• AT = 9°F; Aprecip. = 22%
Wheat Hay
Barley Potatoes
• AT = 7°F; Aprecip. = 29%
Sources: Mendelsohn and Neumann (in press); McCarl
(personal communication)
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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 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 Idaho, production agriculture is a $2.8 billion annual industry.
60% of which comes from crops. Almost 70% of the farmed acres
are irrigated. The major crops in the state are wheat, hay, barley.
and potatoes. Climate change could increase wheat yields by
9-18%. Barley and hay could increase by 12%, and potato yields
could fall by 18% under severe conditions where temperatures
rise beyond the tolerance levels of the crop. Farmed acres could
rise or fall by 10%, depending on how climate changes.
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 Idaho
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, threaten-
ing both property and forests. Drier conditions would 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 rangeland
could expand into previously forested areas along the eastern
slope of the Rocky Mountains and into some of the western
valleys. Warmer conditions could increase the elevation of the
timberline, resulting in a reduction or the disappearance of alpine
tundra and its unique (and in some cases already endangered)
species. 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 Idaho forests and the activities that depend on them.
Ecosystems
Idaho is very rich in ecological diversity. Major forest ecosystems
include grand fir-Douglas fir forest, cedar-hemlock-pine forest.
Douglas fir forest, western ponderosa pine forest, and western
spruce-fir forest. While the northern part of the state is dominated
by forests, most of the southern part of the state is covered by
sagebrush steppe, interspersed with islands of desert and
saltbush-greasewood shrublands. Many areas in the state are
nearly pristine and include some of the largest areas in the United
States without paved roads. Significant fish resources include
salmon and steelhead. Fire plays an important role in several
ecosystems, including sagebrush steppe, western juniper
woodlands, and ponderosa and lodgepole pine. In many of these
ecosystems, fire suppression and other land use policies have
resulted in significant changes in forest composition and struc-
ture. 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 park-like
conditions in ponderosa pine stands. 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. Significant changes are also occurring in whitebark pine
populations of high-elevation forests. In northern Idaho, stands
have decreased by anywhere between 50 and 100%, due in part to
fire suppression and white pine blister rust, a non-native fungus
that has defied control. Fewer than 1 in 10,000 trees is resistant.
Loss of this forest type may be catastrophic for grizzlies. Even a
modest warming and drying could reduce whitebark pine habitat
by up to 90%. Whitebark pine nuts and the army cutworm moth
caterpillars found in southeastern forests provide vital food for
grizzly bears. Yellowstone National Park is the most famous of the
region's protected areas. Its intact grizzly bear habitat, rangelands
for buffalo, elk, and moose, and spectacular hot springs and
geysers attract millions of visitors per year.
Climate change could exacerbate many of the problems facing
ecosystems in Idaho. Although wildfires are a natural and
necessary part of the ecology of western forests, changes in
fire regimes under climate change have significant implications.
Climate change poses a threat to high alpine systems, and
could lead to their significant decline .Local extinctions of alpine
species such as arctic gentian, alpine chaenactis, rosy finch and
water pipit have resulted from habitat loss and fragmentation.
both of which could worsen under climate change. Whitebark
pine forest could be replaced with Douglas fir. On the lower
slopes, forests would give way to treeless landscapes dominated
by sagebrush, Idaho fescue, 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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