United States
Environmental Protection
Agency
Office of Policy, Planning
and Evaluation
(2111)
EPA 230-F-97-008qq
September 1997
Climate Change And Texas
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 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
passes
through
the clear
Some solar radiation
is reflected by the
earth and the
k 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.
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 businesses.
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, common
air pollutants, cool the atmosphere by reflecting incoming solar
radiation. However, sulfates are short-lived and vary regionally.
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. 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.
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
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.
Source: U.S. Department of State (1992)
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Global Temperature Changes (1861-1996)
Year
Source: IPCC (1995), updated
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 uncertain-
ties remain, these models are a powerful tool for studying
climate. Scientists are reasonably confident 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 annual temperature in
San Antonio, Texas, has decreased 0.5°F, and precipitation has
decreased by up to 20% in some parts of the state.
Over the next century, climate in Texas could experience addi-
tional 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 Texas could increase by about 3°F in spring
(with a range of 1-6°F) and about 4°F in other seasons (with a
range of 1-9°F). Precipitation is estimated to decrease by 5-30%
in winter and increase by about 10% in the other seasons.
Increases in summer could be slightly larger (up to 30%) than in
spring and fall. Other climate models may show different results.
The amount of precipitation on extreme wet or snowy days in
winter is likely to decrease, and 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 severe storms such as
hurricanes would change.
Climate Change Impacts
Global climate change poses risks to human health and to
terrestrial and aquatic ecosystems. Important economic resources
such as agriculture, forestry, fisheries, and water resources also
may be affected. Warmer temperatures, more severe droughts and
floods, and sea level rise could have a wide range of impacts. All
these stresses can add to existing stresses on resources caused by
other influences such as population growth, land-use changes.
and pollution.
Similar temperature changes have occurred in the past, but the
previous changes took place over centuries or millennia instead
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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of decades. The ability of some plants and animals to migrate and
adapt appears to be much slower than the predicted rate of
climate change.
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. Texas, with its intense heat waves, could
be especially susceptible.
In Dallas, one study projects that by 2050 heat-related deaths
during a typical summer could triple, from about 35 heat-related
deaths per summer to over 100 (although increased air condition-
ing use may not have been fully accounted for). Winter-related
deaths are expected to change very little. The elderly, particularly
those living alone, are at greatest risk.
Climate change could increase concentrations of ground-level
ozone. Currently, ground-level ozone concentrations exceed
national ozone health standards in some areas across the state.
The Houston-Galveston area is classified as a "severe"
nonattainment area, and the El Paso area is classified as in
"serious" non-attainment. Ground-level ozone has been shown to
aggravate respiratory illnesses such as asthma, reduce existing
lung function, and induce respiratory inflammation. In addition.
ambient ozone reduces crop yields and impairs ecosystem health.
Air pollution also is made worse by increases in natural hydrocar-
bon emissions during hot weather. If a warmed climate causes
increased use of air conditioners, air pollutant emissions from
power plants also will increase.
Warming and other climate changes may 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. Recently reported cases of
malaria and dengue fever in Texas demonstrate the continued
risk of these diseases. If conditions become warmer and wetter.
mosquito populations could increase, thereby increasing the risk
of transmission.
In addition, warmer seas could contribute to the increased
intensity, duration, and extent of harmful algal blooms. These
blooms damage habitat and shellfish nurseries and can be toxic
to humans. About two-thirds of the Texas coastline was closed
to shellfish harvesting in 1996 because of contamination by an
unusually large bloom of marine algae, or "red tide." Consump-
tion of contaminated shellfish can cause neurotoxic shellfish
poisoning. Warming in the Caribbean may have contributed to
this problem; future warming combined with local pollution most
likely would continue to damage fish and shellfish and thus affect
human health.
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.
The Texas coastline is over 1,400 miles long. The coastline is
composed of wind tidal flats, sandy marshes, salt marshes, and
beaches. The Laguna Madre has over 350 square miles of wind
tidal flats that provide nesting areas or rookeries for sea birds.
The sandy marsh shoreline provides critical habitat for shore-
birds, wading birds, endangered brown pelicans, and other birds.
About 75% of the ducks and geese found in the United States
move through the Texas coastal wetlands. The salt marshes
provide a home for oysters and clams, and serve as nursery
grounds for young shrimp, crab, and fish. These marshes
protect the shorelines from erosion and also act as a purification
system by filtering out many pollutants added to the waters by
human activities.
At Galveston, sea level already is rising by 25 inches per century.
and it is likely to rise another 38 inches by 2100. Brown shrimp
catch in the U.S. Gulf Coast could fall 25% with only a 10-inch
rise in sea level. 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. 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 replenish-
ment to protect the coast of Texas from a 20-inch sea level rise
by 2100 is estimated at $4.2-$ 12.8 billion.
Water Resources
Water resources are affected by changes in precipitation as well
as by temperature, humidity, wind, and sunshine. Changes in
streamflow tend to magnify changes in precipitation. Water
resources in drier climates tend to be more sensitive to climate
changes. Because evaporation is likely to increase with warmer
climate, it could result in lower river flow and lower lake levels.
particularly in the summer. If streamflow and lake levels drop.
groundwater also could be reduced. In addition, more intense
precipitation could increase flooding.
Several major river basins lie in part, or entirely, within Texas.
Most of the state is drained by several south-flowing rivers.
including the Neches, Trinity, Brazos, Colorado, San Antonio.
and Nueces. Western Texas drains into the Rio Grande or its
major tributary, the Pecos River. Unless increased temperatures
are coupled with a strong increase in rainfall, water could become
more scarce. A warmer and drier climate would lead to greater
evaporation, as much as a 35% decrease in streamflow, and less
water for recharging groundwater aquifers. Increased rainfall
could mitigate these effects, but also could contribute to localized
flooding. Additionally, climate change could give rise to more
frequent and intense rainfall, resulting in flash flooding.
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
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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 sectors.
Understandably, most studies have not fully accounted for
changes in climate variability, water availability, and imperfect
responses 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 Texas, agriculture is a $12.6 billion annual industry, two-thirds
of which comes from livestock, especially cattle. About 25% of
the crop acreage is irrigated. The major crops in the state are
cotton, wheat, and sorghum. Climate change could reduce cotton
and sorghum yields by 2-15% and wheat yields by 43-68%.
leading to changes in acres farmed and production. For example.
cotton yields could fall while production rises because of an
increase in cotton acres farmed. Irrigated acreage could decline
slightly because of decreased water availability.
Forests
Trees and forests are adapted to specific climate conditions, and
as climate warms, forests will change. These changes could
include changes in species, 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
southern pines, would spread. Under these conditions, forests
could become more dense. These changes could occur during the
lifetimes of today's children, particularly if change is accel-
erated 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
Changes In Agricultural Yield And Production
I Conifer Forest
I Broadleaf Forest
Savanna/Woodland
Shrub/Woodland
Grassland
Arid
Irrigated Yield
Production
Cotton
Sorghum
Cotton
Sorghum
Wheat
Wheat
Source: VEMAP Participants (1995); Neilson (1995)
• AT = 8°F; Aprecip. = -7% • AT = 7°F; Aprecip. = 3%
Source: Mendelsohn and Neumann (in press); McCarl (personal
communication)
With changes in climate, the extent and density of forested areas
in east Texas could change little or decline by 50-70%. Hotter.
drier weather could increase wildfires and the susceptibility of
pine forests to pine bark beetles and other pests, which would
reduce forests and expand grasslands and arid shrublands. With
increased rainfall, however, these effects could be less severe. In
some areas, the types of trees dominating Texas forests would
change; for example, longleaf and slash pine densities could
increase in the deciduous forests of east Texas.
Ecosystems
The vast area within Texas includes a great diversity of ecosys-
tems, from forests to grasslands to semiarid shrublands to
extensive coastal and inland wetlands. In Texas, climate change
could weaken and stress trees, making them more susceptible to
pine bark beetle outbreaks. Semi-arid grasslands and shrublands
are very sensitive to changes in rainfall season and in the amount
of rainfall, and could be affected adversely by warmer, drier
conditions.
The Balcones Canyonlands National Wildlife Refuge in central
Texas provides nesting grounds for the golden-cheeked warbler
and the black-capped vireo, two endangered songbirds. Warmer
and drier conditions could reduce critical habitat in the refuge
and further stress sensitive plant and animal populations. The
coastal wetlands, which support important fisheries and provide
vital wildlife habitat, are also vulnerable to climate change. For
example, Brazoria National Wildlife Refuge, a 43,388 acre
coastal estuarine and coastal prairie habitat on the Gulf Coast.
provides winter habitat for 30,000-40,000 ducks and 40,000
snow geese. The refuge also contains about 4,000 acres of native
coastal bluestem prairie. Changes in rainfall and runoff from
upland regions could adversely affect sensitive coastal systems.
and sea level rise would accelerate loss of wetlands and estuaries.
eliminating breeding and foraging habitat for commercial, game.
and threatened and endangered species.
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.
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