nited States
Environmental Protection
Agency
Office of Policy
(2111)
EPA 236-F-98-007d
September 1998
Climate Change And Arkansas
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
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 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)
0.6
0.4
0.2
-0.2
-0.4
-0.6
-0.8
-1 I I I I I I I I I I I I I I
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 Fayetteville.
Arkansas, has increased 0.4°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 Arkansas may change even
more. For example, based on projections made by the Intergov-
ernmental Panel on Climate Change and results from the United
KingdomHadley Centre's climate model (HadCM2), a model that
accounts for both greenhouse gases and aerosols, by 2100
temperatures in Arkansas could increase by 2°F in winter and
summer (with a range of 1 -4°F), and 3 °F in spring and fall (with a
range of 1-5°F). Precipitation is estimated to change little in
winter, increase by 15% in spring and fall (witharange of 5-25%).
and increase by 25% in summer (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 frequency of extreme hot days in summer
is expected to increase along with 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. 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.
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 Arkansas is in compliance with current 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 will 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. Infected individuals
can bring malaria to places where it does not occur naturally.
Also, mosquitoes in Arkansas can carry malaria. If conditions
become warmer and wetter, mosquito populations could increase.
thus increasing the risk of transmission if this and other
mosquito-borne diseases are introduced into the area. Warmer
temperatures could increase the incidence of Lyme disease and
other tick-borne diseases in Arkansas, 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.
rainfall, higher temperatures and evaporation in the summer also
could cause drier summer conditions. This could result in lower
streamflows, lake levels, and groundwater levels at a time when
water demand, particularly for irrigation, is often the highest.
Many of the tributaries of the Arkansas River currently go dry
during dry periods. Lower summer flows could also affect water-
based recreation such as fishing, boating, and canoeing. Per
capita boat ownership in Arkansas is one of the highest in the
nation. Warmer, drier summer conditions could also increase
water quality problems such as low dissolved oxygen and lake
eutrophication, and could adversely affect wetlands.
In a warmer climate, rainfall could increase. Higher rainfall
could alleviate water supply problems and recharge groundwater
aquifers, but also could increase flooding. Intense rainfalls
currently cause localized flooding problems throughout the state.
Much of the farmland in eastern Arkansas is in the floodplains of
major streams, and widespread flooding in low-lying areas is a
continuing concern. Higher rainfall and streamflow also could
increase erosion and levels of pesticides and fertilizers in runoff
from farming areas. It also could increase pollution in runoff from
urban and mining areas. The pollution of water and the accumula-
tion of pesticides in bottom sediments of streams, lakes, and
ponds in agricultural areas have been important water quality
issues in the state.
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.
Water Resources
Arkansas has abundant surface and groundwater resources.
About two-thirds of the runoff from the state flows into the
Mississippi River through the Arkansas, White, and St. Francis
rivers. Aquifers in the eastern part of the state are a major source
of groundwater. Agriculture is the economic base of Arkansas.
and the availability of water for irrigation of crops and mainte-
nance offish farms in the eastern part of the state is a primary
concern. Because of large withdrawals, groundwater levels have
declined rapidly in recent years, and saline water from underlying
rocks has begun to intrude into the freshwater aquifers. Farmers
have resorted to drilling deeper wells and exploring the use of
surface waters from the Arkansas, White, and Little Red rivers as
an alternative source.
In a warmer climate, these problems could be exacerbated.
Winter runoff could increase and spring and summer runoff could
decrease in the northwestern Highlands and headwater areas
outside the state. In other areas of the state, without increases in
Changes In Agricultural Yield And Production
Dryland Yield
Production
Soybeans Rice Hay
Soybeans Rice Hay
• AT = 9°F; Aprecip. = -2% • AT = 7°F; Aprecip. = 12%
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 Arkansas, production agriculture is a $4 billion annual
industry, three-fourths of which comes from livestock, mainly
poultry. Almost one-half of the farmed acres are irrigated. The
major crops in the state are soybeans, rice, and hay. Soybean
yields could rise by 11% with adequate irrigation or fall by 16%.
depending on how climate changes. In contrast, rice, hay, and
pasture yields are projected to increase by about 30%. Farmed
acres are projected to remain fairly constant in response to
offsetting changes in estimated farm production and prices.
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
conditions, such as subtropical evergreens, would prevail over
time. 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.
Changes In Forest Cover
Current +10°F, +13% Precipitation
• Conifer Forest
• Broadleaf Forest
• Savanna/Woodland
Grassland
Sources: VEMAP Participants (1995); Neilson (1995)
In Arkansas, longleaf and slash pine forests could expand
northward and replace loblolly and shortleaf pine forests.
Wetter conditions would favor expansion of southern pine, oak.
and hickory forests. In contrast, under drier conditions, scrub and
other noncommercial oaks and shrubs could increase their range.
and 40-60% of the forests in 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. Even
warmer and wetter conditions could stress forests by increasing
the winter survival of insect pests.
Ecosystems
The Arkansas landscape is divided between highland ecosys-
tems in the north and lowland habitats in the south. The Ozark
and Ouachita plateaus are covered by oak, hickory, maple, and
beech forests and host several endemic animal species, including
fish and salamanders. The Mississippi alluvial plain region, the
delta, contains the remnants of a once-extensive bottomland
hardwood forests and meandering flatland rivers. The flood-
plains of the White and Cache rivers contain the most important
breeding areas for mallard ducks in the world — as much as
10% of the continent's population may winter in this area. Loess
ridges are found within the delta region, and they contain several
plant species that are uncommon elsewhere in the state. The
sandy soils of the Gulf coastal plain are dominated by pine
woods, including loblolly, longleaf, and shortleaf, and provide
old-growth habitat for endangered red-cockaded woodpeckers
and other animals.
Scientists working in the Cache River have already documented
a steady decline in magnitude and predictability of base flow
during low flow periods since the 1920s, which they have
attributed largely to intensive agriculture. Direct and indirect
effects of climate change would exacerbate these and other
threats to riparian ecosystems, including exotic species inva-
sions, excess nutrient and toxin loading, and sedimentation.
Habitat for warm water fish could also be reduced by hotter
temperatures. The physical impacts on stream channels in
the Ozarks could be significant. Because of extensive land use
changes, coarse gravel (with low water retention capacity) has
been accumulating along riparian shores at the expense of fine
sediment. Research has demonstrated that changes in hydrology.
which could be exacerbated by climate change in the future, affect
the ability of willows and sycamores to germinate, which in turn
is expected to affect sediment transport processes and habitat
availability in these riparian systems. A warming climate with less
midcontinental rainfall would increase pressure on aquifers such
as the Ogallala, which in turn could affect the Arkansas river
basin. Increased air temperatures could have an adverse effect
on the hydrology and productivity of loblolly pine stands, which
in western Arkansas are at the limit of their range.
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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