United States
Environmental Pn
Agency
itton
Office of Policy
(2111)
tit
September 1998
&EPA Climate Chaise And Mississippi
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 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
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
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 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 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)
0.6
0.4
0.2
0
fc-0-2
-0.4
-0.6
-0.8
-1
J_
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 1.6-63°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 Jackson,
Mississippi, has decreased 2.1°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 Mississippi could experience
additional changes. 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 Mississippi could increase by 2°F in winter
and summer (with a rarige of 1-4°F), 3°F in spring (with a range of
1-5°F), and 4°F in fall (with a range of 2-6°F). Precipitation is
estimated to change little in winter, increase by 10% in spring
(with a range of 5-20%), and 15% in summer and fall (with a range
of 5-25%). 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 such as hurri-
canes 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. The elderly, particularly those living alone,
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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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.
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 Mississippi can
carry malaria, and others can carry eastern 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
introduced into the area. Increased runoff from heavy rainfall
could increase water-borne diseases such as giardia, crypto-
sporidia, and viral and bacterial gastroenteritides. Rodent
populations that carry hantavirus aiid leptospirosis (a bacterium)
are sensitive to climatic factors. Drought can reduce rodent
predators (owls, snakes, coyotes), and sudden rains can bring
new food supplies to rodents. These conditions could be
associated with upsurges in rodent populations. 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 addition, warmer seas could contribute to the increased
intensity, duration, and extent of harmful algal blooms, that is,
red tides. These blooms damage habitat and shellfish nurseries,
can be toxic to humans, and can carry bacteria like those causing
cholera.
Coastal Areas
Sea level rise could lead to flooding of low-lying property, loss
of coastal wetlands, erosion of beaches, saltwater contamination
of drinking water, and decreased longevity of low-lying roads,
causeways, and bridges. In addition, sea level rise could
increase the vulnerability of coastal areas to storms and
associated flooding.
Mississippi has a 360-mile tidally influenced shoreline along
the Gulf of Mexico. The shoreline consists of alow-lying coastal
plain, narrow barrier islands, and low terraces. AC Pass Christian,
sea level already is rising by 5 inches per century, and it is likely
to rise another 15 inches by 2100. Possible responses to sea level
rise include building walls to hold back the sea, allowing the'sea
to advance and adapting to it, and raising the land (e.g., by
replenishing beach sand, elevating houses and infrastructure).
Each of these responses will be costly, either in out-of-pocket
costs or in lost land and structures. For example, the cumulative
cost of sand replenishment to protect the coast of Mississippi
from the estimated sea level rise by 2100-is $70-$ 140 million.
However, sand replenishment may not be cost-effective for
all coastal areas in the state, and therefore some savings
could be possible.
Water Resources
In a warmer climate, runoff in Mississippi would primarily be
influenced by higher temperatures, increased evaporation, and
changes in precipitation. Lower streamfiows, lake levels, and
groundwater levels in the summer could affect water availability
an'd increase competition among domestic, industrial, and
agricultural uses of water.
Declining groundwater levels are a matter of concern throughout
the state. Increased rice irrigation and fish farming in the north-
western Delta region have reduced groundwater levels in the
Mississippi alluvial aquifer. Increased municipal and industrial
withdrawals in the metropolitan Jackson area, along the Gulf
Coast, and in northeastern Mississippi also have lowered
groundwater levels. Additionally, in the southern half of the
state, saline water has begun to intrude into freshwater aquifers
because of declining groundwater levels along the coast as well
as from saline waste water injection into oil-field production
zones. Warmer and drier conditions, particularly if accompanied
by sea level rise, could compound these types of problems due
to higher demand and lower flows.
Higher rainfall and streamflow would alleviate water supply
problems, but could increase flooding. Floodplains along the
Pearl River, including areas near Jackson, Columbia, Picayune,
and along the lower reaches to the Gulf of Mexico, are vulnerable
to flooding. Reaches of the Yazoo, Big Black, Tombigbee, and
Leaf rivers near Hattisburg, as well as low-lying agricultural lands,
also are subject to periodic inundation. Higher rainfall could
increase erosion and levels of pesticides and fertilizers in runoff
from agricultural lands, a major cause of degraded water quality.
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
Dryland Yield Production
Cotton Soybeans Hay Cotton Soybeans Hay
• AT = 8°F; Apreoip. = -1% BB AT = 7°F; Aprecip. = -7%
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.
In Mississippi, production agriculture is a $2.6 billion annual
industry, 60% of which comes from livestock, mainly poultry.
Almost 20% of the farmed acres are irrigated. The major crops in
the state are cotton, soybeans and hay. Irrigated soybean yields
could rise by 4-18%; without irrigation soybean yields could fall
9-22%. Cotton yields could rise by 3% or fall by 25%, depending
on how climate changes. Farmed acres are projected to remain
fairly constant; however, an increased share of this acreage could
become irrigated. 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 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 subtropical evergreens, would prevail over tune.
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
• Conifer Forest
• Broadleaf Forest
3 Savanna/Woodland
Sources: VEMAP Participants (1995); Neilson (1995)
In Mississippi, longleaf and slash pine forests could expand
northward and replace loblolly and shortleaf pine forests. Wetter
conditions would favor expansion of southern pine forests as
well as oak and hickory forests and the gum and cypress forests
found along the Gulf Coast. In contrast, under drier conditions,
50-75% of forests in the east-central part of the state could be
replaced by grasslands and pasture. Warmer and drier conditions
could increase the frequency and intensity of fires, which could
result in increased losses to important commercial timber areas
and speed the transition to grassland. Even warmer and wetter
conditions could stress forests by increasing the winter survival
of insect pests.
Ecosystems
Most of Mississippi is made up of habitats associated with
either the coastal plain or the Mississippi Delta. The coastline is
separated from the Gulf of Mexico by a shallow sound and is
paralleled by a series of barrier islands. Farther inland are tracts
of wet savanna habitat, home to the critically endangered
nonmigratory Mississippi sandhill crane. Only small remnants are
left of the formerly extensive Black Belt and Jackson Prairies, in
which several species of endemic crayfish are found. Bald eagles,
a threatened species, use the Upper Mississippi River valley as a
winter migration corridor and for summer nesting habitat. The
Mississippi flatlands in the alluvial plain attract hundreds of
thousands of migrating snow geese, Canada geese, and ducks in
the winter. About 55% of the land area of Mississippi is covered
with forests, including bottomland hardwoods, pine woods, and
oak-hickory forests.
Wetlands play a major role in basin hydrology and serve as
wildlife habitats. Changes in water levels brought about by a
changing climate can dramatically alter the extent of these
ecosystems. Wet savanna habitats are already under threat from
conversion into pine plantations. Coastal wetlands are among the
ecosystems most vulnerable to climate change. The low-lying
Mississippi Delta is particularly vulnerable to the effects of sea
level rise — inundation of coastal lands, intrusion of saltwater
into coastal freshwater ecosystems, increase in erosion rates and
storm damage with increasing wave force and storm frequency. If
runoff along the Gulf Coast increases, estuarine flushing rates
would increase, leading to reduced yields in shrimp and other
species favoring high salinities. Increasing runoff rates and
outflow into the Gulf of Mexico could increase nutrient loads and
alter water temperatures, exacerbating the already serious
eutrophication and low oxygen levels. Loss of coastal wetlands
and marshes with rapid sea level rise would reduce estuarine
health because many estuarine species depend on wetlands as
nursery areas and sources of organic matter. Warmer tempera-
tures could lead to reduced stream flow and warmer water
temperatures, which would significantly impair reproduction of
fish and other animals and favor the spread of exotic species that
exhibit a high tolerance for extreme environmental 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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