United States
Environmental Protection
Agency
Office of Policy
(2111)
EPA 236-F-98-0070
September 1998
v>EPA Climate Change And Nevada
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.
•ared radiation is emitted
om the earth's surface
radiation is absorbed by
urface and.warms Jt
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
institutional developments. Several emissions scenarios have
been developed based on differing projections of these under-
lying 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 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 Elko, Nevada.
has increased 0.6°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 Nevada 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
Nevada 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 in summer by 10%
(with a range of -5% to -20%), to increase by 15% in spring (with
a range of 5-25%), to increase by about 30% in fall (with a range
of 10-50%), and to increase by about 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, 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. Currently.
the Reno area is classified as a "marginal" nonattainment area for
ozone. Increased temperatures could make attaining compliance
more difficult. Ground-level ozone is associated with respiratory
illnesses such as asthma, reduced lung function, and respiratory
inflammation.
Upper and lower respiratory allergies also 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 Nevada can carry
malaria, and others can carry St. Louis and California 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
introduced into the area. Increased runoff from heavy rainfall
could increase water-borne diseases such as giardia.
cryptosporidia, and viral and bacterial gastroenteritides. Devel-
oped 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 sustained streamflow in Nevada largely results from spring
and summer snowmelt in the mountains. At lower altitudes,
intense storms can contribute to streamflow, but because of high
evaporation, most smaller streams run dry in the summer. A
warmer climate could lead to more winter rainfall and an earlier.
more rapid snowmelt. This could result in higher winter and
spring flows, and the inability to store flood waters for use later in
the summer. Additionally, without large increases in rainfall.
higher temperatures and increased evaporation could lower lake
levels and streamflows in the summer. In western Nevada, the
Truckee and Carson rivers serve the rapidly growing population
of the Reno-Sparks-Carson City area, as well as irrigated agricul-
ture. Competition for water between agricultural, municipal.
industrial, and instream uses could intensify. In north-central
Nevada, competition for water is acute on the Humbolt River, and
when snowpacks are meager, demand for irrigation greatly
exceeds supply. The expanding metropolitan area of Las Vegas
uses a large portion of Nevada's allotment of the Colorado River.
Under current conditions, without significant increases in either
reuse of water or alternative supplies, future development could
be limited by this allotment. In several areas of the state, particu-
larly near large urban areas, groundwater has been withdrawn at
rates that exceed natural replenishment, and groundwater levels
have seriously declined. Less spring and summer recharge could
exacerbate this situation.
Lower streamflows and higher temperatures could also impair
water quality by concentrating pollutant levels and reducing the
assimilative capacity of streams. Sewage effluent and pollutants
from agricultural and urban runoff are concerns in the Truckee
and Carson rivers, Lake Tahoe, and Lake Mead. Nevada's surface
waters are fully appropriated. Changes in water availability would
complicate the complex water-rights and interstate compacts that
govern water allocation.
More rain could ease competition for water, but it also could
increase flooding. Earlier, more rapid snowmelts could contribute
to winter and spring flooding, and more intense summer storms
could increase the likelihood of flash floods. Although Nevada is
extremely dry, intense rains can produce torrents of water and
debris. Residential and industrial developments on the valley
floors and near the foothills are especially vulnerable. Increased
rain also could increase erosion and pollution from runoff from
mining areas, and exacerbate levels of pesticides and fertilizers
from runoff from agricultural lands. The Las Vegas Wash, which
drains into Lake Mead, is susceptible to erosion. Sediment and
urban runoff from Las Vegas have affected the water quality of
Lake Mead. Similarly, sediment and fertilizer runoff from develop-
ing areas on the quality of Lake Tahoe is a matter of concern.
Fertilizer runoff from agricultural lands has also adversely
affected water quality in the Truckee and Carson rivers.
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.
Changes In Agricultural Yield And Production
Irrigated Yield
Production
I
6
s?
Hay Potatoes
• AT = 9°F; Aprecip. = 18%
Hay Potatoes
I AT = 8°F; Aprecip. = 30%
Sources: Mendelsohn and Neumann (in press); McCarl
(personal communication)
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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.
InNevada, production agriculture is a $300 million annual
industry, two-thirds of which comes from livestock, mainly cattle.
Almost all of the farmed acres are irrigated. The major crops in the
state are hay and potatoes. Climate change could have a small
impact on crop production reducing potato yields by about 12%.
and hay and pasture yields increasing by about 7%. Farmed acres
could rise by 9% or fall by 9%, depending on how climate
changes. Livestock 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.
With changes in climate, the extent of forested areas in Nevada
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
Changes In Forest Cover
Current +10°F, +13% Precipitation
Tundra
Conifer Forest
Savanna/Woodland
Shrub/Woodland
Grassland
Arid Lands
Sources: VEMAP Participants (1995); Neilson (1995)
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 in the
northern and western areas of the state, and increase their
susceptibility to fire. Grasslands, 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 Nevada
forests and the activities that depend on them. However, in-
creased rainfall could reduce the severity of these effects.
Ecosystems
Nevada supports a great variety of ecosystems, including the
Mojave Desert and more than 300 mountain ranges. The Great
Basin region, situated between the Rockies and the Sierra Nevada
and Cascades, contains a rich array of ecosystems: playas.
alkaline flats that are home to salt-tolerant plants, salt lakes, sand
dunes, marshes that are crucial habitat for migratory waterfowl.
vast expanses of sagebrush, the pi-on-juniper woodlands, the
alpine islands of isolated mountain peaks that are home to
remnant plant populations, the aspen glens, and the subalpine
forest that is home to 4,000-year-old bristlecone pines, the oldest
living trees on earth. Springs and stream-riparian ecosystems
support a great diversity of plant and animal life that depends on
these oases of water and food resources. These isolated aquatic
ecosystems are unique, and they contain many rare plants and
animals, including White River springfish, Railroad Valley
springfish, White River mountainsucker, White River spinedace.
Pahranagat spinedace, White River Colorado gila, and White
River speckled dace. Marshes such as Ruby Lake and Stillwater
are important for migratory birds in both the Central and Pacific
flyways. Hundreds of thousands of waterfowl such as canvas-
back and redhead ducks, long-billed dowitchers, snowgeese.
tundra swans, white-faced ibis, and great and snowy egrets
overwinter or breed in these areas.
The region's inherently variable and unpredictable hydrological
and climatic systems could become even more variable with
changes in climate, putting additional stress on wetland ecosys-
tems. The streams and rivers in Nevada are entirely spring-fed or
derived from runoff from the mountains. A warmer climate would
increase evaporation and shorten the snow season in the
mountains, resulting in earlier spring runoff and reduced summer
streamflow. This would exacerbate fire risk in the late summer.
These threats, coupled with increasing human demands on water
resources, could severely reduce the number and quality of
wetland habitats, which are already stressed and ephemeral. This
would degrade habitat essential for migrating and breeding birds.
and could further stress rare and endangered fish species. Many
desert-adapted plants and animals already live near their toler-
ance limits, and could disappear under the hotter conditions
predicted under global warming.
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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