United States
Environmental Protection
Agency
Office of Policy, Planning
and Evaluation
(2111)
EPA 230-F-97-008r
September 1997
©EPA Climate Change And Louisiana
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
Some solar radiation
is reflected by the
earth and the
L 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 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, 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. 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 since
the late 19th century. 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
-0.6
Year
Source: IPCC (1995), updated
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, average temperatures in New Orleans.
Louisiana, have remained virtually unchanged, but precipitation
has increased by 5-20% in some locations of the state.
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 uncertain-
ties 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 tempera-
ture 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
Over the next century, Louisiana's climate may change signifi-
cantly. Based on projections given by the Intergovernmental
Panel on Climate Change and results from the United Kingdom
Hadley Centre's climate model (HadCM2), a model that has
accounted for both greenhouse gases and aerosols, it is projected
that by 2100, temperatures in Louisiana could increase about 3°F
(with a range of 1-5°F) in spring and summer, slightly less in
winter, and slightly more in fall. Little change is projected for
seasonal precipitation totals in winter and spring, with an increase
of around 10% in summer and fall.
The frequency of extreme hot days in summer is expected to
increase along with 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.
Precipitation Trends From 1900 To Present
Trends/ 100 years
+20% •
+ 10%*
-5%o
-10%0
-20% O
Source: Karl et al. (1996)
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Similar temperature changes have occurred in the past, but the
previous changes took place over centuries or millennia instead
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
Warming and other climate changes could expand the habitat
and infectivity of disease-carrying insects, increasing the poten-
tial for transmission of diseases such as malaria and dengue
("break bone") fever. Mosquitoes flourish in Louisiana. Some can
carry malaria, while others can carry Eastern equine encephalitis.
which can be lethal or cause neurological damage. If conditions
become warmer and wetter, mosquitoes could increase, thereby
increasing the risk of transmission of these diseases. For example.
the lack of a killing frost between 1990 and 1995 caused a
proliferation of mosquitoes, cockroaches, and termites in
Louisiana.
At Grand Isle, Louisiana, sea level already is rising by 41 inches
per century, and is likely to rise another 55 inches by 2100.
Louisiana currently is losing coastal wetlands at a more rapid rate
(approximately 50 square miles a year) than any other coastal
state or region in the United States. Louisiana's low-lying delta
coastal wetlands are a unique case — these wetlands receive large
deposits of sediment from the outflow of the Mississippi River.
These deposits provide wetlands with a natural defense against
the effects of sea level rise. However, because the surface is
subsiding faster than sedimentation is occurring, Louisiana
wetlands could be flooded extensively even by relatively small
changes in sea level. A 1-3 foot increase in sea level over the
next century is projected to submerge at least 70% of Louisiana's
remaining salt marshes. Even freshwater marshes located far
inland may convert to brackish or salt marsh.
Cumulative costs of sand replenishment to protect Louisiana's
coast from a 20-inch sea level rise by 2100 could be $2.6-
$6.8 billion.
In addition, warmer seas could contribute to the increased
intensity, duration, and extent of harmful algal blooms. These
blooms damage habitat and shellfish nurseries, can be toxic to
humans, and can carry bacteria like those causing cholera.
Brown algal tides and toxic algal blooms already are prevalent in
the Atlantic. Warmer ocean waters could increase their occur-
rence and persistence. Along Louisiana's coast, viral and bacte-
rial contamination of shellfish has repeatedly caused illness.
Warming in the Caribbean may have contributed to these ill-
nesses; future warming combined with local pollution most likely
would continue to damage fish and shellfish and thus affect
human health.
There is concern that climate change could increase concentra-
tions of ground-level ozone. For example, high temperatures.
strong sunlight, and stable air masses tend to increase urban
ozone levels. Air pollution also is made worse by increases in
natural hydrocarbons emissions during hot weather. If a warmed
climate causes increased use of air conditioners, air pollutant
emissions from power plants also will increase.
Increased emissions and higher temperatures could slow progress
being made in Louisiana to provide healthy and clear air. Cur-
rently, ground-level ozone concentrations in the Baton Rouge and
Lake Charles areas exceed the national standards. Ground-level
ozone has been shown to aggravate existing respiratory illnesses
such as asthma, reduce lung function, and induce respiratory
inflammation. In addition, ambient ozone reduces agricultural
crop yields and impairs ecosystem 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.
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 extent, and health and
productivity. If conditions also become drier, the current range
and density of forests could be reduced and replaced by grass-
lands and pasture. Even a warmer and wetter climate would lead
to changes; trees that are better adapted to these conditions, such
as oaks and redwoods, would thrive. Under these conditions.
forests could become more dense. These changes could occur
during the lifetimes of today's children, particularly if they are
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 forested areas
in Louisiana could change little or decline by 5-15%. Hotter.
drier weather could increase wildfires, particularly in the impor-
tant timber producing regions in the northern part of the state. In
some areas, the types of trees dominating Louisiana forests are
likely to change. Long-leaf and slash pine densities could
Changes In Forest Cover
Current +10°F, +13% Precipitation
• Conifer Forest
Broadleaf Forest
Savanna/Woodland
Source: VEMAP Participants (1995); Neilson (1995)
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increase, as would the extent of cypress and gum dominated
forests in southeastern Louisiana. Loblolly and shortleaf pines
would continue to thrive over much of the state; however, drier
conditions could result in increased areas of grassland and
savanna in the western part of the state.
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. In addition, more intense precipitation
could increase flooding. If streamflow and lake levels drop.
groundwater also may be reduced.
Most of Louisiana drains to the lower Mississippi and Red rivers.
both of which have headwaters thousands of miles from their
mouths. Streamflow in these rivers is affected mostly by condi-
tions outside Louisiana's borders. Because much of the runoff of
the Red and Mississippi rivers comes from areas where there is
little snowfall, streamflow is affected by changes in precipitation
and temperature. Summer flows of these rivers could be reduced
by the increased evaporation that would occur in a warmer
climate.
The part of Louisiana that is not in the Red or Mississippi River
basins is drained by smaller rivers and streams that flow directly
to the Gulf of Mexico. Because of the relatively flat topography.
the groundwater and surface water systems are either indistin-
guishable (e.g., in the bayous) or closely connected. Changes in
the flow of these rivers in a warmer climate would depend largely
on precipitation changes. However, evaporation probably would
increase, which could reduce water levels in freshwater wetlands
as well as in groundwater supplies.
Agriculture
The mix of crop and livestock production in a state is influenced
by climatic conditions and water availability. As climate warms.
production patterns will 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, and other
economic 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 substantially change modeling results. Analyses based on
changes in average climate and which assume farmers effectively
adapt suggest that aggregate U.S. food production will not be
harmed, although there may be significant regional changes.
Changes In Agricultural Yield And Production
Yield Production
o
a?
Cotton Soybeans Rice
• AT = 7°F; Aprecip. = -2%
Cotton Soybeans Rice
• AT = 6°F; Aprecip. = -0.5%
Source: Mendelsohn and Neumann (in press); McCarl (personal
communication)
In Louisiana, agriculture is about a $2 billion annual industry.
one-third of which comes from livestock. About 25% of the acres
farmed is irrigated. The principal crops are cotton, soybeans, and
rice. Cotton yield under climate change could remain unchanged
or fall by 15%. Rice yields could increase, and soybean yields
could fall by up to 28%. Acres farmed could fall by 2%, and farm
income could be as much as 80% lower. The number of irrigated
acres could increase. This could further limit water supplies, and
water quality could be further degraded.
Ecosystems
Louisiana's Mississippi River delta contains the largest wetlands
in the nation. These coastal wetlands support 30% of national
commercial fish and shellfish harvests. They are also the winter
home of 20-25% of the ducks that frequent ponds in North
America. These wetlands are among the most commercially and
ecologically productive in the United States. The coastal marshes
in Louisiana, for example, generate over $2 billion worth of
commercial species such as oysters, crabs, fish, and shrimp each
year. They also are an invaluable buffer against storm surges.
The wetlands of Louisiana are highly vulnerable to climate
change effects, particularly sea level rise. Louisiana is already
losing many of its wetlands because of levees and other structures
along the Mississippi River. Sea level rise most likely will
accelerate wetland loss, reducing important habitats for migratory
birds, crayfish, sport fish, and other species. Some warm water
fish species such as black crappie could lose all of their habitat in
Louisiana as a result of the effects of climate change. In addition.
spotted sea trout, oyster larvae, pinfish, and flounder would lose
much, if not all, of their habitat.
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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