United States
Environmental Protection
Agency
Office of Policy
(2111)
EPA 236-F-98-007I
September 1998
Climate Change And Maryland
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 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
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 College Park.
Maryland, has increased 2.4°F, and precipitation has increased by
up to 10% in many parts of the state. These past trends may or
may not continue into the future.
Over the next century, Maryland's climate 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 climate model (HadCM2), a model that accounts
for both greenhouse gases and aerosols, by 2100 temperatures in
Maryland could increase by 3°F (with a range of 1-7°F) in spring
and 4°F (with a range of 2-9°F) in the other seasons. Precipitation
is projected to increase by 20% (with a range of 10-40%) in all
seasons, probably slightly less in spring and fall and slightly
more in winter. 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 or snowy days in winter 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 the
severity of storms might be affected, an increase in the frequency
and intensity of winter storms is possible.
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. Maryland, with its irregular, intense heat
Precipitation Trends From 1900 To Present
Source: Karl et al. (1996)
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waves, could be susceptible. One study projects that in Balti-
more, a warming of 3 °F could increase heat-related deaths by 50%
from the current 85 to 130, and in Washington, D.C., results
indicate slightly smaller increases (although increased air
conditioning use may not have been fully accounted for in both
estimates). This study also projects that winter-related deaths in
Baltimore should remain unaffected, but could increase by a third
in Washington, D.C. The exact reasons for these differences are
unknown. The elderly, especially those living alone, are at
greatest risk.
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. In the
eastern mid-Atlantic region, a 4°F warming, with no other change
in weather or emissions, could increase concentrations of ozone.
a major component of smog, by 4%. Currently, ground-level
concentrations exceed the national ozone health standard
throughout the state. Nearly all of Maryland is classified as a
nonattainment area for ozone. Serious to severe nonattainment
areas include Baltimore and the suburbs of Washington, D.C.
Ground-level ozone is associated with respiratory illnesses such
as asthma, reduced lung function, and respiratory inflammation.
Mosquitos carrying malaria, dengue fever, and St. Louis encepha-
litis are present in Maryland. Warm, wet conditions could
increase mosquito populations, increase biting rates, and reduce
the incubation rate of the viruses and parasites within them. The
incidence of Lyme disease could also increase as warmer tempera-
tures and increased precipitation enhance the habitat for ticks
and their rodent hosts. Warmer winters, warmer temperatures, and
heavy precipitation also can increase harmful algal blooms, that
is, red tides; reduce water quality; and increase the potential for
outbreaks of cryptosporidiosis and giardia. These impacts.
however, can be minimized through existing disease prevention
and control methods.
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.
Mary land has 3,100 miles of tidally influenced shoreline. It
consists of barrier islands such as Assateague Island, the highly
urbanized and developed oceanfront of Ocean City, and the
extensive eastern shore of Chesapeake Bay. The eastern shore of
Chesapeake Bay in Maryland has an extensive array of tidally
influenced freshwater and salt marshes, forested wetlands,
riverine wetlands, and open water.
At Baltimore, sea level already is rising by 7 inches per century.
and it is likely to rise another 19 inches by 2100. Human activities
such as impounding and dredging as well as sea level rise have
caused extensive losses of coastal wetlands and marshes in both
the Chesapeake Bay and Assateague Island regions. With higher
Future Sea Level Rise At Easton
\d)J
110
100
90
/U
n
5% Chance — •—
" 50% Chance — —
" 90% Chance _L
7
*
-
Year
Sources: Lyles et al. (1988); EPA (1995)
sea levels, Assateague Island is likely to migrate toward the
mainland as sand is eroded on the ocean side and deposited on
the mainland side, and the island's native plant communities.
which include some threatened species, are likely to change in
distribution and diversity. The 9-mile coastline of Ocean City.
which was nourished by a $30 million beach nourishment project
in the late 1980s, could be threatened by a rise in sea level.
The cumulative cost of additional sand replenishment to protect
Maryland's coastline from a 20-inch sea level rise by 2100 is
estimated at $35-$200 million. However, sand replenishment may
not be cost-effective for all coastal areas in the state and,
therefore, some savings could be possible.
Water Resources
Without increases in precipitation, higher temperatures and
increased evaporation would lower streamflows, lake levels, and
groundwater levels in the summer and fall. This could adversely
affect the many instream uses of water in Maryland, including
hydroelectric power generation, navigation, marine commerce.
commercial and sport fishing, and recreation. Water supplies for
the large and growing metropolitan areas surrounding Baltimore
and the District of Columbia could suffer from lower summer
streamflows. Drier summer conditions also could reduce ground-
water levels, which could be significant for parts of Charles and
Prince Georges counties in southern Maryland, which are already
experiencing declines in groundwater levels. Groundwater is also
the primary source of water for domestic use and irrigated
agriculture on the Eastern Shore. Additionally, low flows and
higher temperatures in the summer could affect water quality.
further aggravating problems with nuisance algae, low dissolved-
oxygen levels, and bacterial contamination in urban streams.
If, however, rainfall and runoff increase in the Maryland region.
the resulting higher streamflows could alleviate water supply
problems and dilute pollutants, although more flooding could
occur. Higher runoff also could increase erosion and levels of
pesticides and fertilizers from agricultural areas. These chemicals
reduce oxygen and limit the types of species that can live in the
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rivers. Increased runoff from farmlands would exacerbate this
effect. It also could increase erosion and pollution from urban and
strip mining areas. Although many sources of pollution into
Chesapeake Bay have been controlled, runoff containing nutri-
ents, heavy metals, and sediment remains a problem in many tidal
areas. Acid mine drainage is also a concern in westernmost
Maryland.
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 users.
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 Maryland, production agriculture is a $ 1.3 billion annual
industry, 60% of which comes from livestock, mainly cattle.
Very few of the farmed acres are irrigated. Climate changes could
reduce the farmed acres of major crops such as corn, soybeans.
wheat, and hay by 24-43%, in response to changes in yields and
resulting economic conditions. Projected changes in yields vary
widely, depending on how climate changes and whether land is
irrigated. For example, under severe conditions, corn and hay
yields could fall by 32% and soybeans by 38% as temperatures
rise beyond tolerance levels of the crop. Less severe changes.
however, could result in increases of 4% and 24%, respectively.
as soil moisture and carbon dioxide levels rise.
Changes In Agricultural Yield And Production
Dryland Yield
Production
Corn Wheat
Soybeans Hay
• AT = 7°F; Aprecip. = 1%
Corn Wheat
Soybeans Hay
I AT = 9°F; Aprecip. = 12%
Sources: Mendelsohn and Neumann (in press); McCarl (per-
sonal communication)
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 prevail. Under these
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 forested areas
in Mary land could change little or decline by as much as 5-10%.
However, the types of trees dominating Maryland forests are
likely to change. The warmer mixed forests, dominated by
southern pines and oaks, would spread northward, replacing the
predominantly hardwood forests currently found in the northern
and western sections 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
frequencies of large storms associated with climate change
(hurricanes in the late summer and fall, nor'easters in the winter
and spring). Coastal estuaries are breeding grounds for important
commercial fish and shellfish species, and changes in the
hydrology of upland forests in Maryland could have profound
effects on these sensitive coastal systems.
Ecosystems
The diverse habitats of Maryland's Chesapeake Bay (including
underwater grass beds, salt marshes, forested wetlands, and
upland forests) provide a home for more than 2,700 species of
animals and plants. The Blackwater Wildlife Refuge on the
eastern shore of the bay has the largest concentration of nesting
bald eagles on the east coast north of Florida, and is vital for
migratory waterfowl and shorebirds. These wetlands are also
important agents of flood control and water quality.
Chesapeake Bay has already begun to feel the effects of sea level
rise. Rising sea level enables saltwater to penetrate farther inland
and upstream, and the more than 150 streams and rivers that flow
into the bay could be affected. Intruding salt water and increasing
sedimentation are choking many marshes. Since 1938, the rising
sea has destroyed one-third of the marsh at Blackwater. Most of
the remaining marsh in this area is projected to disappear within
30 years. Inundation of lowland habitats surrounding the marshes
could result in the disappearance of habitat for migratory birds
and other species, for example, the endangered Delmarva
fox squirrel.
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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