United States
Environmental Protection
Agency
Office of Policy, Planning
and Evaluation
(2111)
EPA 230-F-97-008I
September 1997
Climate Change And Florida
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
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.
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)
. -0.2
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 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
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 have increased in
Florida. At Ocala, the 1892-1921 average temperature was
almost 67°F; the 1966-1995 average temperature was over 69°F
Precipitation over the last hundred years has decreased in the
Keys and parts of south Florida, and increased in central Florida
and the panhandle.
Over the next century, Florida's climate may change even more.
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, by 2100 temperatures in
Florida could increase by 3-4°F (with a range of 1-6°F) in spring.
summer, and fall, and by somewhat less in winter. Little change is
projected for precipitation.
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.
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.
Precipitation Trends From 1900 To Present
Trends/ 100 years
+20%0
+10% •
-5%o
-10%0
-20%O
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. Recent scientific work suggests that 28
people die every year in Tampa from heat-related causes during
the summer. Even if people adjust to climate change, a 3°F
warming could more than double this figure; as many as 68
additional heat-related deaths could occur every year in Tampa
during the summer. The elderly, particularly those living alone.
are at greatest risk.
There is concern that climate change could increase concentra-
tions of ground-level ozone. For example, specific weather
conditions — strong sunlight, stable air masses — tend to
increase urban ozone levels. While Florida is in compliance with
current air quality standards, increased temperatures could make
remaining in compliance more difficult. Ground-level ozone has
been shown to aggravate existing respiratory illnesses such as
asthma, reduce lung function, and induce respiratory inflamma-
tion. In addition, ambient ozone reduces agricultural crop yields
and impairs ecosystem health.
Changing climate conditions also may affect human health
through impacts on terrestrial and marine ecosystems. In particu-
lar, warming and other climate changes may 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. Although dengue fever is currently uncom-
mon in the United States, conditions already exist in Florida that
make it vulnerable to the disease. Warmer temperatures resulting
from climate change could increase this risk.
Finally, sea surface warming and sea level rise could increase
health threats from marine-borne illnesses and shellfish poisoning
in Florida. 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. In
turn, algal blooms potentially can lead to higher incidence of
water-borne cholera and shellfish poisoning. Acute poisoning
related to the consumption of contaminated fish and shellfish has
been reported in Florida.
Coastal Areas
Global sea level rise is one of the most likely effects of global
warming. Along much of the Florida coast, the sea level already
is rising 7-9 inches per century. Because of local factors such as
land subsidence and groundwater depletion, sea level rise will
vary by location. For Florida, the sea level is likely to rise 18-20
inches by 2100. As sea level rises, coastal areas in Florida.
particularly wetlands and lowlands along the Gulf and Atlantic
coasts, could be inundated. Adverse impacts in these areas could
include loss of land and structures, loss of wildlife habitat.
accelerated coastal erosion, exacerbated flooding and increased
vulnerability to storm damage, and increased salinity of rivers.
bays, and aquifers, which would threaten supplies of fresh water.
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 and/or elevating
houses and infrastructure). Each of these responses would be
costly, either in out-of-pocket costs or in lost land and structures.
For example, the cumulative cost of sand replenishment to
protect Florida's coast from a 20-inch rise in sea level by 2100 is
estimated at $1.7-$8.8 billion.
Forests
Trees and forests are adapted to specific climate conditions, and
as climate warms, forests will change. Changes in tree species.
geographic extent, and the health and productivity of forests
could be expected with a warmer climate. 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 would lead to changes; trees that are better adapted to
warmer conditions, such as tropical 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 they are 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.
The mixed conifer/hardwood forests found in the northern and
panhandle sections of Florida are likely to retreat northward.
These forests eventually could give way to wet tropical forests
such as tropical evergreen broadleaf forests and dry tropical
savanna. These changes would be accompanied by a reduction in
forest density. The dry tropical savanna of the Florida peninsula
could become more of a seasonal tropical forest with a corre-
sponding increase in forest density. The potential dieback of
forests along the Gulf coast could adversely affect forest-based
recreation and commercial timber.
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.
Changes In Forest Cover
Current +10°F, +13% Precipitation
Broadleaf Forest
Savanna/Woodland
Grassland
Source: VEMAP Participants (1995); Neilson (1995)
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particularly in the summer. In addition, more intense precipitation
could increase flooding. If streamflow and lake levels drop.
groundwater also could be reduced.
A critical factor in Florida's development, especially in southern
Florida, has been water. Although south Florida receives an
annual average of 60 inches of rain, annual evaporation some-
times can exceed this amount. Rainfall variability from year to
year is also high, resulting in periodic droughts and floods.
Competing demands for water — for residences, agriculture, and
the Everglades and other natural areas — are placing stresses on
south Florida's water resources.
Higher temperatures increase evaporation, which could reduce
water supplies, particularly in the summer. Saltwater intrusion
from sea level rise also could threaten aquifers used for urban
water supplies. These changes could further stress south Florida's
water resources.
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
Hay Potatoes Oranges
Sugarcane Tomatoes Grapefruit
• DT = 6°F; Dprecip. = -3%
Hay Potatoes Oranges
Sugarcane Tomatoes Grapefruit
DT = 6°F; Dprecip. = 3%
Florida is one of the leading states in terms of cash revenue from
farming, with irrigated cropland accounting for the high value of
farm production. Yields of citrus fruits could decrease with
warmer temperatures in the southernmost part of the state
because of a lack of a sufficient dormant period. Changes in
cotton and sorghum production are unclear — increasing CO2
levels and rainfall would be likely to increase yields, but the
shortened growing season brought on by increasing temperatures
could result in plants producing fewer or smaller seeds and fruit.
which would decrease yields. Increases in temperature (about
6°F) and rainfall (10%) are projected to reduce corn yields
by 14%.
Unique Ecosystems: The Big Cypress
Swamp, The Everglades, And The Keys
Southern Florida has national treasures in the Big Cypress
Swamp, the Everglades, and the Keys. These three ecosys-
tems are interlinked and have a common history. The Big
Cypress Swamp is part of the broad, shallow river moving
fresh water south into the Everglades. The Keys mark the
last outposts of the Everglades lands. Once hummocks of
higher vegetation set in a prehistoric swamp, they have
struggled against the rising sea. Mangroves on their perim-
eters collect silt and organic material, building a barricade
secure against all but the most severe hurricane winds and
tides. In the Everglades and Big Cypress Swamp, there is a
strong contrast between the seasons. From early spring well
into autumn, they have ample rainfall, averaging 50 inches
per year. Winter is a time of drought and fire, and saltwater
penetrates farther inland.
Already stressed by water diversions, invading species of
plants and animals, and the natural phenomena of drought.
flood, and storms, these ecosystems will be stressed further
by climate change. A 20-inch sea level rise would cause
large losses of mangroves in southwest Florida. Increased
salinity, resulting from rising saltwater into the Everglades
from Florida Bay, also would damage freshwater ecosystems
containing sawgrass and slough. Communities of wet prairie
also would decline with the rise in sea level.
Climatic conditions in central Florida may become suitable
for subtropical species such as Gumbo-limbo, now confined
to subtropical hummocks in the southern part of the penin-
sula and the Keys. Theoretically, such species could move as
far north as Gainesville and Jacksonville, but agricultural
and urban development could preclude such migration.
Source: Mendelsohn and Neumann (in press); McCarl (personal
communication)
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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