United States
Environmental Protection
Agency
Office of Policy, Planning
and Evaluation
(2111)
EPA 230-F-97-008II
September 1997
Climate Change And Pennsylvania
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. Of these, 1995 was the
warmest year on record, suggesting the atmosphere has re-
bounded 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
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^ V /
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, the average temperature in Harrisburg.
Pennsylvania, has increased 1.2°F, and precipitation has in-
creased by up to 20% in many parts of the state.
Over the next century, climate in Pennsylvania may change even
more. For example, based on projections made by the Intergov-
ernmental 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 Pennsylvania could increase by about 4°F (with
a range of 2-9°F), slightly less in summer and fall, and slightly
more in winter and spring. Precipitation is estimated to increase
by about 10% in spring, by about 20% in winter and summer, and
by as much as 50% in fall. Other climate models may show
different seasonal changes in rainfall. 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
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
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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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.
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. Pennsylvania, with its irregular, intense
heatwaves, could be especially susceptible.
In Philadelphia, one study projects that by 2050 heat-related
deaths during a typical summer could increase 90%, from
close to 130 heat-related deaths per summer to over 240
(although increased air conditioning use may not have been
fully accounted for). Similar but smaller increases have been
projected for Pittsburgh, from about 40 heat-related deaths
to 60, or a 50% increase. Winter-related deaths could drop from
85 in Philadelphia per winter to about 35 if winter temperatures
warm. In Pittsburgh, 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. 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 preliminary modeling study of the Midwest, which included
the area around Pittsburgh, found that a 4°F warming, with no
other change in weather or emissions, could increase concentra-
tions of ozone, a major component of smog, by as much as 8%.
Currently, ground-level ozone concentrations exceed national
ozone health standards in several areas throughout the state, with
the Philadelphia area classified as a "severe" nonattainment area
for ozone. Ground-level ozone has been shown to aggravate
respiratory illnesses such as asthma, reduce existing lung func-
tion, and induce respiratory inflammation. 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 Pennsylvania. Some can carry malaria, while others can
carry encephalitis, which can be lethal or cause neurological
damage. Incidents of Lyme disease, which is carried by ticks.
have increased in the Northeast. If conditions become warmer
and wetter, mosquito and tick populations could increase in
Pennsylvania, thereby increasing the risk of transmission of
these diseases.
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.
Pennsylvania's Susquehanna River drains much of the eastern
two-thirds of the state, and the Allegheny and the upper Ohio
rivers drain most of the western third. A warmer climate would
lead to earlier spring snowmelt, and could result in higher
streamflows in winter and spring and lower streamflows in
summer and fall. However, changes in rainfall also could
have significant effects on streamflow and runoff and, if
summer precipitation falls, could affect adversely downstream
uses such as navigation on the Ohio River. Increased precipi-
tation in winter or summer could offset losses from increased
evaporation, but also could lead to increased flood risk. Some
of the most intense flooding on record in the United States has
occurred in Pennsylvania.
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
Changes In Agricultural Yield And Production
Irrigated Yield Production
Corn Hay
• AT = 7°F;Aprecip.=
Corn Hay
AT = 10°F; Aprecip. = 13%
Source: Mendelsohn and Neumann (in press); McCarl (personal
communication)
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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 Pennsylvania, agriculture is a $3.8 billion annual industry.
two-thirds of which comes from livestock, most of which is dairy.
About 6% of the crop acreage is irrigated. The major crops in the
state are corn and hay. Climate change could change crop yields
very little or by as much as 39%, leading to changes in acres
farmed and production. For example, hay yields could rise while
production falls because of a decrease in hay 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 oaks
and 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 acceler-
ated 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 of forested areas in
Pennsylvania could change little or decline by as much as
15-25%. However, the types of trees dominating Pennsylvania
forests and woodlands are likely to change. The maple, beech.
and birch forests found in northern Pennsylvania would retreat
northward. Forest areas would become dominated by oak, ash.
hickory, and pine, and the brilliant autumn foliage associated with
maples would be diminished. In areas where richer soils are
prevalent, southern pines could increase their range and density.
Changes In Forest Cover
Current +10°F, +13% Precipitation
• Conifer Forest
Broadleaf Forest
Savanna/Woodland
Source: VEMAP Participants (1995); Neilson (1995)
and in areas with poorer soils, which are more common in
Pennsylvania's forests, scrub oaks of little commercial value
(e.g., post oak and blackjack oak) could increase their range. As
a result, the character of forests in Pennsylvania may change.
Ecosystems
Ecosystems in Pennsylvania consist of forests, woodlands.
wetlands, peatland, and riparian habitats. The Two Mile Run
wetlands in the Pocono Mountains are the largest undisturbed
peatland ecosystem in Pennsylvania. This is also the site of the
largest and healthiest native spruce forest in Pennsylvania. The
peatlands are an important habitat for black bears, which use
them for denning and feeding. Snowshoe hare, osprey, beaver.
river otter, and waterfowl also live in the Two Mile Run wetlands
area. Climate change could alter the range and location of these
habitats, and fragmented land use patterns could impede
migration of plants and animals.
Climate change could adversely affect ecosystems such as the
Erie National Wildlife Refuge and French Creek, which flows for
117 miles through northwestern Pennsylvania. This area provides
habitat for approximately 70 species offish and 25 species of
freshwater mussels. Many of the aquatic species in French Creek
(for example, the clubshell mussel) are already endangered. The
refuge system also provides important habitat for birds, including
the threatened bald eagle.
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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