United States
Environmental Protection
Agency
Office of Policy
(2111)
EPA 236-F-98-007t
September 1998
Climate Change And Oklahoma
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
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
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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 Stillwater.
Oklahoma, 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 Oklahoma 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 Oklahoma could increase by 2°F (with a
range of 1 -4°F) in spring, 3 °F in summer and fall (with a range of
1-5°F), and 4°F in winter (with a range of 2-6°F). Precipitation is
estimated to change little in winter, to increase slightly in fall (with
a range of 0-10%), and to increase by 20% in spring and summer
(with a range of 10-30%). 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 days in summer 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 such as tornados might be affected.
although an increase in the frequency and intensity of summer
thunderstorms is possible.
Precipitation Trends From 1900 To Present
Trends/100 years
+20% Q
+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. This study projects little change in
winter-related deaths.
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
Oklahoma 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 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. Also, some
mosquitoes in Oklahoma 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
introduced into the area.
Warmer temperatures could increase the incidence of Lyme
disease and other tick-borne diseases in Oklahoma, 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.
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
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
10
5 "10
5s -20
-30
-40
Wheat Hay Wheat Hay
• AT = 9°F; Aprecip. = -5% • AT = 7°F; Aprecip. = 14%
Sources: Mendelsohn and Neumann (in press); McCarl (per-
sonal communication)
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 Oklahoma, production agriculture is a $3.9 billion annual
industry, 70% of which comes from livestock, mainly cattle. Very
few of the farmed acres are irrigated. The major crops in the state
are wheat and hay. Climate change could reduce wheat yields by
27-37% as temperatures rise beyond the tolerance levels of the
crop. Hay and pasture yields could remain constant or could rise
by 10%, depending on how climate changes. Farmed acres could
remain fairly 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.
Water Resources
Oklahoma lies entirely within the Arkansas, White, and Red river
basins. The water resources of the state, however, are unevenly
distributed. The eastern part of Oklahoma has plentiful surface
water, which is used primarily for the municipal supplies of
Oklahoma City and Tulsa, for thermoelectric power generation.
and for pulp and paper manufacturing. The western part of the
state relies primarily on groundwater, which is used principally for
irrigation. The largest groundwater withdrawals are in the
panhandle, which overlies the High Plains, orOgallala, aquifer.
Oklahoma's water resources are characterized by long droughts
and frequent floods. This situation could be exacerbated by a
warmer climate. Runoff in the state is determined largely by
rainfall and to a small degree by spring snowmelt. A warmer
climate would lead earlier to snowmelt, resulting in higher
streamflows in winter and spring. In the summer, without large
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increases in precipitation, higher temperatures and increased
evaporation could lower streamflows and lake levels. Less
recharge also would reduce groundwater levels. Less water
would be available to support important uses of the numerous
reservoirs in eastern Oklahoma, such as navigation, hydropower
generation, water supply, recreation, and fish and wildlife habitat.
In the central area of the state, the higher water demands result-
ing from population growth, increasing urbanization, and industri-
alization would become increasingly difficult to meet. In western
Oklahoma, water withdrawals exceed recharge in some areas and
groundwater levels are declining. Surface waters are also unde-
pendable and often unusable because of high concentrations of
chloride and dissolved minerals. Many urban areas in western
Oklahoma have water demands that exceed their supply, and
they continually acquire additional surface-water rights as they
become available or explore the possibility of water transfer
from surplus areas to the east. Lower flows would compound
water shortages in the west. Increased temperatures and lower
streamflows also could impair water quality by concentrating
pollutant levels and reducing the ability of streams to assimilate
wastes. Increased pollution is a concern in streams downstream
of large urban areas such as Oklahoma City and in scenic rivers
such as the Illinois River where development has expanded.
More rain could ameliorate these impacts, but it also could
increase flooding. Flooding in urban areas and along tributary
streams is a recurring problem in Oklahoma. More intense rains
are also expected with climate change, which would increase
erosion and sedimentation and exacerbate levels of pesticides
and fertilizers in runoff from agricultural areas. It also would
increase pollution in runoff from mining areas and oil and
gas exploration areas.
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 southern pines, would spread. Under these
Changes In Forest Cover
Current +10°F, +13% Precipitation
Conifer Forest
Broadleaf Forest
Savanna/Woodland
Shrub/Woodland
Grassland
Sources: VEMAP Participants (1995); Neilson (1995)
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.
With changes in climate, the extent and density of the forested
areas in eastern Oklahoma could change. Hotter, drier weather
could increase wildfires and the susceptibility of pine forests to
pine bark beetles and other pests, leading to reduced forests and
expanded grasslands and arid shrublands. However, with
increased rainfall (shown in some studies), the area! extent of
Oklahoma forests could rise. In some areas, the types of trees
dominating eastern Oklahoma forests would change; for example.
southern pines and oaks could increase in some of the hardwood
forests of eastern Oklahoma.
Ecosystems
Few states encompass as much natural diversity as Oklahoma. In
the southeast, the forests of the Mississippi River floodplain are
home to bald cypresses. In the extreme west, pinon and ponde-
rosa pines are found at elevations approaching 4,500 feet.
Between these extremes, oak woodlands historically transitioned
into tallgrass and shortgrass prairies. Today, in the face of
agricultural development, many of these native ecosystems are
endangered. The tallgrass prairie ranks as one of the most
threatened plant communities in the Midwest and the world.
Extensive agriculture, demand for irrigation, and dam construction
on the Arkansas River have degraded habitats of prairie fishes.
Historically, frequent, low-intensity surface fires
perpetuated park-like ponderosa pine stands with grassy under-
growth. Today, after 60 years of fire suppression, many of the
ponderosa pine forests have high densities of trees, are plagued
by epidemics of insects and diseases, and are subject to severe
stand-destroying fires. Climate change could exacerbate the
stresses and threats to these sensitive ecosystems.
Warmer temperatures and precipitation increases could alter
the balance of freshwater ecosystems. The physical impacts on
streams in the Ozarks are likely to 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 water flow, 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 trans-
port processes and habitat availability in these riparian systems.
A warming climate with less rain could increase pressure on
aquifers such as the Ogallala, which in turn may affect the
Arkansas river basin.
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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