United States
Environmental Protection
Agency
Office of Policy, Planning
and Evaluation
(2111)
EPA 230-F-97-008h
September 1997
Climate Change And Delaware
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)
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
-1
±
r^ \ /
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 temperature in Dover.
Delaware, has increased 1.7°F, and precipitation has increased
by up to 10% in some parts of the state.
Over the next century, climate in Delaware 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 Delaware could increase by about 3°F
(with a range of 1-7°F) in spring and about 4°F (with a range or
2-9°F) in the other seasons. Precipitation is estimated to increase
15-40% in all seasons, probably slightly less in spring and fall.
and slightly more in winter. Other climate models may show
different results. The amount of precipitation on extreme wet or
snowy days is likely to increase. The frequency of extreme hot
days in summer would increase because of the general warming
trend. Although it is not clear how severe storms such as hurri-
canes would change, an increase in the frequency and intensity
of summer thunderstorms is possible.
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
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. Air
pollution also is made worse by increases in natural hydrocarbon
emissions during hot weather. If a warmed climate causes
increased use of air conditioners, air pollutant emissions from
power plants also will increase.
A 4°F warming in New York City, with no other change in
weather or emissions, could increase concentrations of ozone, a
major component of smog, by 4%. Similar increases could occur
in Delaware. Currently, ground-level ozone concentrations
exceed national ozone health standards throughout the state.
Wilmington and the northern part of Delaware are classified as
"severe" nonattainment areas for ozone. Ground-level ozone has
been shown to aggravate respiratory illnesses such as asthma.
reduce existing lung function, and induce respiratory inflamma-
tion. In addition, ambient ozone reduces crop yields and impairs
ecosystem health.
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. Mosquitos flourish in some areas around
Delaware. Some can carry malaria, while others can carry
Eastern equine encephalitis, which can be lethal or cause neuro-
logical damage. Incidents of Lyme disease, which is carried by
ticks, already occurs in Delaware. If conditions become warmer
and wetter, mosquito and tick populations could increase, thereby
increasing the risk of transmission of these diseases.
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 occurrence
and persistence.
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 coast of Delaware is an important resource with 381 miles
of shoreline. Delaware's coastline includes barrier beaches.
inland bays and productive estuaries, freshwater and salt marshes.
tidal flats, and several islands that dot the coast. Delaware Bay is
the chief spawning ground for the horseshoe crab and a nursery
for many coastal fisheries.
Future Sea Level Rise At Lewes
I^U
110
100
f\J
A)
n
5% Chance — •—
50% Chance — —
95% Chance _L
__ __
2100
Source: EPA (1995)
2200
Year
At Lewes, Delaware, sea level already is rising by 12 inches per
century, and it is likely to rise another 23 inches by 2100. Rising
sea levels, combined with possible decreases in summer stream
flows could increase the salinity of the Delaware River and Bay.
A 20-inch rise in sea level could inundate about 50% of the
wetlands in Delaware Bay.
As in many estuaries, the Delaware Inland Bays are already
affected by shoreline erosion. Rising sea levels will further erode
shores along the bay. Responses are likely to be increases in the
use of traditional techniques to combat erosion, such as building
bulkheads and revetments, which would threaten habitats of least
tern and other species depending on estuarine beaches. Public
access along the shore could also be diminished.
Other possible responses to sea level rise include allowing the
sea to advance and adapting to it, and raising the land (e.g., by
replenishing beach sand, elevating houses and infrastructure).
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 replenishment to protect the coast of Delaware from
a 20-inch sea level rise by 2100 is estimated at $34-$ 143 million.
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.
Most of Delaware drains to either Delaware Bay or Chesapeake
Bay. The state relies heavily on a relatively shallow groundwater
system for industrial and municipal water supply. Climate change
could increase summer evaporation and thus reduce summertime
recharge of aquifers, although some of this loss could be offset by
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increases in winter recharge if winter precipitation increases.
Many of Delaware's aquifers are contaminated by industrial
pollutants. Although the effects of climate change on the move-
ment of pollutants are not well understood, changes in infiltration
rates could affect the rate at which pollutants migrate throughout
an aquifer. Increased precipitation could contribute to ground-
water contamination by increasing the inflow of contaminants
into the state's aquifers.
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 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 Delaware, agriculture is a $600 million annual industry, three-
fourths of which comes from livestock, mainly broiler chickens.
About 10% of the farm acreage is irrigated. The major crops
in the state are corn, soybeans, and wheat. Grain yields could
fall by as much as 32% or rise by as much as 24%, leading to
changes in acres farmed and production. In Delaware, wheat
yields could rise while production falls because of a decrease in
wheat acres farmed.
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 prevail. Under these conditions.
forests could become more dense. These changes could occur
during the lifetimes of today's children, particularly if 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 forested areas
in Delaware could change little or decline by as much as 10-20%.
However, the types of trees dominating those forests are likely to
change. Mixed forests, dominated by southern pines and oaks.
would spread northward, replacing the predominantly hardwood
Changes In Agricultural Yield And Production
Irrigated Yield Production
Corn Wheat
Soybeans
• AT = 7°F; Aprecip. = 3%
Corn Wheat
Soybeans
AT = 9°F; Aprecip. = 10%
Source: Mendelsohn and Neumann (in press); McCarl (personal
communication)
forests currently found in the northern half of the state. Maritime
forests, important for their recreational and aesthetic value and
for their role in coastal hydrology, could be affected adversely
by changes in the frequency of large storms associated with
climate change (hurricanes in the late summer and fall.
nor'easters in the winter and spring). Coastal estuaries are the
breeding ground for important commercial fish and shellfish
species, and changes in the hydrology of upland forests in
Delaware and surrounding states could have profound effects
on these sensitive coastal systems.
Ecosystems
The most notable ecosystems of Delaware are the coastal
estuaries, marshes, and barrier islands. Delaware's coastal waters
are critical for many commercial species, game species such as
deer, and migratory birds, including bobwhite quail. The
Delaware estuary is an important habitat for migratory shore-
birds, waterfowl, migratory songbirds, fish, and other coastal
species such as horseshoe crabs. Approximately 35% of the
Delaware estuary's rare species live in or depend on wetland
habitats, and 70-90% of the state's commercial fish and shellfish
species either live entirely in estuarine habitats or use them as
nursery grounds. Delaware Bay has the second largest concentra-
tion of migratory shorebirds in the Western Hemisphere, with
approximately 1.5 million shorebirds passing through the bay
area each spring.
Small changes in sea level, freshwater inputs, and storm fre-
quency, intensity, and character, driven by climate change, could
affect these ecosystems substantially. The combination of human
activities and sea level rise could result in a net loss of coastal
wetlands and could increase the salinity of the waters of those
that remain. The result could be a sharp loss in the diversity of
these ecosystems and the species that depend on them, such as
shorebirds.
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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