United States
Environmental Protection
Agency
Office of Policy
(2111)
EPA 236-F-98-007Z
September 1998
Climate Change And Utah
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
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
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 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 out-
breaks) could increase.
Local Climate Changes
Over the last century, the average temperature in Logan.
Utah, has increased 1.4°F, and precipitation has increased 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 Utah 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 Utah could increase by
3 -4°F in spring and fall (with a range of 1-6°F), and by 5-6°F in
winter and summer (with a range of 2-10°F). Precipitation is
estimated to decrease by 10% in summer (with a range of -5 to
-20%), to increase by 10% in spring (with a range of 5-20%), to
increase by 30% (with a range of 10-50%) in fall, and to increase
by 40% in winter (with a range of 20-70%). 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, especially 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. In Salt Lake City, one study estimates
little change in heat-related deaths during the summer given a
3-4°F warming (the current population appears to be accustomed
to intense, dry heat). This study also shows a slight increase in
winter-related deaths. However, the exact reasons for this
increase are unknown.
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.
Currently, the Salt Lake City area is classified as a "moderate"
nonattainment area for ozone. Warming could worsen air
quality further. Ground-level ozone is associated with
respiratory illnesses such as asthma, reduced lung function.
and respiratory inflammation.
Upper and lower respiratory allergies are influenced by humidity.
A 2°F warming and wetter conditions could increase respiratory
allergies.
Infected individuals can bring malaria to places where it does
not occur naturally. Also, some mosquitoes in Utah can carry
malaria, and others can carry western equine encephalitis, which
can be lethal or cause neurological damage. If conditions become
warmer and wetter, mosquito populations could increase, thus
increasing the risk of transmission if these diseases are intro-
duced into the area. 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.
In 1993, hantavirus pulmonary syndrome emerged in Utah, and
the deer mice that are the primary reservoir for the hantaviruses
are prevalent in Utah. Long droughts punctuated by heavy rains
can decrease the predators (owls, snakes, and coyotes) of
rodents, and the heavy rains can provide the rodents with added
food supplies (grasshoppers and pinon nuts).
Water Resources
Winter snow accumulation and spring snowmelt strongly affect
Utah'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 spring and summer recharge
also could lower groundwater levels. Less water would be
available to support irrigation, hydropower generation, public
supply, fish and wildlife habitat, recreation, and mining. Concerns
about adequate water supplies could be exacerbated along the
highly populated and industrialized Wasatch Front, which runs
fromOgdento Provo. Groundwater levels, which are declining
because of large withdrawals for public supply and for irrigation
in southwestern Utah, could be lowered further. Energy develop-
ment and mining operations in the eastern part of the state
depend on adequate water supplies. Major water quality con-
cerns such as the saline content of irrigation return flows and
pollutant levels in urban streams would be aggravated by lower
flows and higher temperatures. Surface and groundwater have
been fully allocated in many parts of Utah. Reductions in water
availability could complicate water rights issues and interstate
compacts. 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.
In a warmer climate, earlier and more rapid snowmelt, heavier
rains, and the possibility of more rain could all contribute to
flooding, particularly in the winter and spring. Densely
populated urban areas in the Wasatch Front are susceptible to
springmelt floods, and high lake levels around Utah and Great
Salt lakes have caused considerable damage to farmland.
wildlife habitats, industries, transportation routes, recreation
facilities, and residential areas. Increased and more intense rains
also could increase landslides and mudslides in the state's
mountainous regions, as well as pollution in runoff from urban
and mining areas.
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 Agricultural Yield And Production
Irrigated Yield Production
(D
Dl
c
CO
6
10
-10
-20
-30
-40
Wheat Barley Hay Wheat Barley Hay
• AT = 9°F; Aprecip. = 19% • AT = 8°F; Aprecip. = 27%
Sources: Mendelsohn and Neumann (in press); McCarl (per-
sonal communication)
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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 Utah, production agriculture is an $800 million annual industry.
three-fourths of which comes from livestock, mainly cattle. About
80% of the farmed acres are irrigated. The major crops in the state
are wheat, barley, and hay. Climate change could significantly
affect agricultural production, for example, reducing wheat yields
by 10-30% as temperatures rise beyond the tolerance level of the
crop. Irrigated barley, hay, and pasture yields, however, could rise
by about 7%; unirrigated yields of those crops could rise by 3%
or fall by 9%, depending on how climate changes. One model
estimates that agricultural production of grain and forage crops
could decline 5-30%. Farmed acres are projected to remainfairly
constant. Livestock and dairy production may not be affected.
unless summer temperatures rise significantly 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.
Changes In Forest Cover
Current +10°F, +13% Precipitation
Tundra
Conifer Forest
Broadleaf Forest
Savanna/Woodland
Shrub/Woodland
Grassland
Arid Lands
Sources: VEMAP Participants (1995); Neilson (1995)
With changes in climate, the extent of forested areas in Utah
could change little or decline by as much as 15-30%. The uncer-
tainties 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, threatening
both property and forests. Drier conditions would reduce the
range and health of ponderosa and lodgepole forests, and
increase their susceptibility to fire. Grassland, rangeland, and
even desert could expand into previously forested areas. 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 Utah
forests and the activities that depend on them. However, in-
creased rainfall could reduce the severity of these effects.
Ecosystems
Utah is at the intersection of four unique regions: the basin and
range country of the Great Basin, the alpine peaks of the Rocky
Mountains, the canyon country of the Colorado Plateau, and the
Mojave Desert. This variety of habitats supports over 3,500
species of native plants and animals, making Utah the fifth-ranked
state in the nation in terms of biodiversity. The Great Basin region
alone contains a rich array of ecosystems, including playas and
alkaline flats that are home to salt-tolerant plants, salt lakes and
dunes, marshes that are crucial habitat for migratory waterfowl.
vast expanses of sagebrush, the pinon-juniper woodlands, the
mountain islands of the Great Basin, aspen glens, and the
subalpine forests that are home to the oldest living trees on the
planet, 4,000-year-oldbristlecone pines. The Great SaltLake, the
world's 33rd largest waterbody, is a migratory stopover and
breeding site of international importance for a myriad of bird
species, including Wilson's phalaropes, American avocets, white-
faced ibis, white pelicans, and the world's largest colony of
California gulls.
The Great Salt Lake may be one of the most vulnerable wetlands
in the United States to changing climate. A warmer climate would
increase evaporation and, without offsetting increases in rainfall.
the lake would shrink and the salinity levels would increase.
These changes would have adverse impacts for migratory bird
populations for which this ecosystem is crucial. The rangelands
of the Great Basin are already threatened by the expansion of
non-native weedy species such as European cheatgrass. Climate
change could exacerbate such threats, because opportunistic
exotic species are well-suited to take advantage of the ecosystem
disturbances caused by warming temperatures, such as increases
in the frequency and severity of wildfires. Climatic variability also
could lead to increased susceptibility of rangelands to droughts.
insect pest outbreaks, and floods. Streams, rivers, and other
freshwater oases situated in this arid landscape are highly
vulnerable to climate change, particularly to warmer and drier
conditions. Coupled with increasing human demands on water
resources, these changes could destroy or seriously degrade the
few wetland habitats that exist in this state.
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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