United States
Environmental Protection
Agency
Office of Policy
(2111)
EPA 236-F-99-002
May 1999
Climate Change And Tennessee
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
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 10 warmestyears in this century all
have occurred in the last 15 years. Of these, 1998 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)
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
-1 | | | | | | | | | | | | | |
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 2 100, 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 Nashville.
Tennessee, has increased nearly 1°F, and precipitation has
increased by up to 10% in many parts of the state. These
past trends may or may not continue into the future.
Over the next century, climate in Tennessee 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 Tennessee could increase by 2-3°F (with a
range of 1-5°F) in all seasons (slightly less in summer, slightly
more in fall). Precipitation is estimated to increase only slightly in
winter (with a range of 0-10%), by 20% in spring and fall (with a
range of 10-30%), and by 30% (with a range of 10-50%) in summer.
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 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 summer
thunderstorms is possible.
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. Although Tennessee is exposed to regular.
intense heat during a typical summer, one study suggests that the
population could still be sensitive to heat waves.
Precipitation Trends From 1900 To Present
Trends/100 years
+20%
+10% %
+5% •
-5% 0
-10% O
-20% Q
Source: Karl et al. (1996)
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In Memphis, a city historically vulnerable to heat-related deaths.
a warming of 3-4°F during a typical summer is projected to cause
heat-related deaths to increase by about 60% from the current 40
to 65 (although increased air conditioning use may not have been
fully accounted for). The elderly, especially those living alone, are
at greatest risk. This study also projects little change in winter-
related deaths in Tennessee.
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. 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
will most likely increase.
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, thus increasing the
potential for transmission of diseases such as malaria and dengue
("break bone") fever. Infected individuals can bring malaria to
places where it does not occur naturally. Warmer temperatures
could increase the incidence of Lyme disease and other tick-borne
diseases in Tennessee, 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
Surface and groundwater resources in Tennessee are abundant.
The Tennessee and Cumberland rivers are the major rivers in the
eastern and central regions of the state, where they are the
principal source of water. These rivers contain a well-developed
system of dams and lakes that provide flood control, navigation.
power generation, recreation, and minimum flows for water quality
maintenance. In western Tennessee, the Mississippi River forms
the border between Tennessee and Arkansas. Most public and
industrial water supplies in this part of the state, however, depend
on groundwater sources.
Snow accumulation is minimal in Tennessee, so in a warmer
climate, runoff would be influenced primarily by higher tempera-
tures, increased evaporation, and changes in precipitation. If
runoff decreases, the reservoir systems of the Tennessee and
Cumberland rivers could experience declines in hydropower
generation, disruptions to navigation, degraded recreational
opportunities, and decreased water availability for water supplies.
Lower flows and higher water temperatures also could degrade
water quality by lowering dissolved oxygen levels and concen-
trating pollutant levels. This could be problematic for urban areas
such as Knoxville, Chattanooga, Nashville, and Memphis, which
discharge their treated municipal and industrial wastes into
rivers. Higher water temperatures could also impair the cold water
fisheries that have been established below many dams. In
addition, higher water temperatures could reduce the efficiency of
industrial and power plant cooling systems. They also could
make it increasingly difficult to meet regulatory standards for
acceptable downstream water temperatures, particularly during
extremely warm periods.
If rainfall and runoff increase in the Tennessee region, then
higher streamflows and lake levels could benefit hydropower
production, enhance recreational opportunities, and improve
water availability for water supplies. Although higher flows
would dilute pollutants, erosion and levels of pesticides and
fertilizers in runoff from agricultural areas could increase. It also
could increase pollution in runoff from mining areas. Many river
basins in western Tennessee are susceptible to sedimentation
and nutrient enrichment from farming activities. Increased rainfall
also could increase flooding, which is currently a problem in the
steep terrain in eastern Tennessee, along the many unregulated
streams throughout the state, and in growing urban areas such as
Chattanooga-Hamilton, Nashville-Davidson, and Memphis-
Shelby counties. Increased rainfall also could disrupt navigation
during periods of high flow.
Agriculture
The mix of crop and livestock production in a state is influ-
enced 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
evaporation 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
Dryland Yield Production
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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 adaption 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 Tennessee, production agriculture is a $2 billion annual
industry, almost split evenly between crops and livestock. Very
few of the farmed acres are irrigated. The major crops in the state
are corn, soybeans, hay, and tobacco. Corn yields could increase
1-15% as a result of climate change. Hay and pasture yields could
rise by 30%, and soybean yields could fall by 5%. Estimated
changes in yield vary, depending on whether land is irrigated.
Farmed acres are estimated to remain fairly constant. Livestock
and dairy production may not be affected, unless summer
temperatures rise significantly and conditions become signifi-
cantly 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 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 warmer condi-
tions, such as oaks and pines, would prevail. 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 themselves be
worsened by a warmer and drier climate. Commercial timber
production could also be affected by resulting changes in growth
rates, plantation acreage and management, and market conditions.
With changes in climate, the extent of forested areas in Tennessee
could change little or decline by as much as 5-15%. However, the
types of trees dominating those forests and woodlands are likely
to change. Forested areas could be increasingly dominated by
pine and scrub oaks, replacing many of the eastern hardwoods
common throughout Tennessee. The forests in and around the
Great Smoky Mountains National Park support a rich variety of
plants and animals, and they are important recreation areas.
Composition changes in these forests could adversely affect
diversity and recreation. In areas where richer soils are prevalent.
southern pines could increase their range and density, and in
areas with poorer soils, which are more common in Tennessee's
forests, scrub oaks of little commercial value (e.g., post oak and
blackjack oak) could increase their range. As a result, the charac-
ter of forests in Tennessee could change. Climate change could
also affect the success of tree plantings to stabilize open-face
mining sites.
Changes In Forest Cover
Current +10°F, +13% Precipitation
• Conifer Forest
• Broadleaf Forest
Savanna/Woodland
Sources: VEMAP Participants (1995); Neilson (1995)
Ecosystems
Tennessee contains diverse ecosystems, including wetlands.
high-elevation forests and glades, oak-hickory forest, grasslands.
cedar glades, mussel shoals, and caves. The waterways of the
Mississippi Delta reach into the western part of the state and
contain remnants of rich bottomland hardwood forests, a habitat
that supports almost five times the biodiversity of upland areas.
Migratory and wintering waterfowl frequent these areas, which
also support the greatest diversity and number of freshwater
mollusk and fish species in the country. Grasslands in the
Highland Rim and Central Basin are home to hundreds of spe-
cially adapted plants and animals, including several rare plants.
The Smoky Mountains have long been recognized as a global
center of biodiversity, including the southern limit of spruce-fir
forests found in the highest elevations. The southern Appala-
chians also contain a diverse array of salamanders, which are
very sensitive to climatic factors.
Exotic species invasions, excess nutrient and toxic loading, and
sedimentation in freshwater systems of the state are expected to
increase as a result of climate change. If increased evaporation
exceeds any increase in rainfall during the summer months.
streamflows could become intermittent, and thus favor plants and
animals adapted to ephemeral conditions (e.g., chironomids and
mayflies), rather than those with relatively long life cycles
(e.g., caddisflies and mollusks). Under a warmer climate, the
habitat available to coldwater fish species such as trout is
expected to decrease, thus limiting their abundance and range.
Habitat for warmwater fish could also be reduced by hotter
temperatures. Higher flood peaks, a result of greater clustering
of storms, could increase erosion and sediment loading to stream
channels. The Appalachian spruce-fir forests already are threat-
ened by air pollution (acid rain and ground-level ozone) and
exotic pests (hemlock wooly adelgid). Climate change could add
significantly to the stresses of these forests as conditions
suitable for the growth of red spruce and Fraser fir disappear
under warmer and drier conditions.
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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