United States
I; -5 MB Environmental Protection
* W J=-1 Agency
August 2016
EPA 430-F-16-040
What Climate Change
Means ^Pennsylvania
Pennsylvania's climate is changing. The commonwealth
has warmed more than half a degree (F) in the last
century, heavy rainstorms are more frequent, and the
tidal portion of the Delaware River is rising about one
inch every eight years. In the coming decades, changing
the climate is likely to increase flooding, harm
ecosystems, disrupt farming, and increase some risks to
human health.
Our climate is changing because the earth is warming.
People have increased the amount of carbon dioxide in
the air by 40 percent since the late 1700s. Other heat-
trapping greenhouse gases are also increasing. These
gases have warmed the surface and lower atmosphere
of our planet about one degree during the last 50 years.
Evaporation increases as the atmosphere warms, which
increases humidity, average rainfall, and the frequency
of heavy rainstorms in many places—but contributes to
drought in others.
Greenhouse gases are also changing the world's oceans
and ice cover. Carbon dioxide reacts with water to form
carbonic acid, so the oceans are becoming more acidic.
The surface of the ocean has warmed about one degree
during the last 80 years. Warming is causing snow to
melt earlier in spring, and mountain glaciers are retreat-
ing. Even the great ice sheets on Greenland and Antarc-
tica are shrinking. Thus the sea is rising at an increasing
Increasing Temperature and Changing Precipitation
Rising temperatures and shifting rainfall patterns are likely to
increase the intensity of both floods and droughts. Average annual
precipitation in Pennsylvania has increased 5 to 10 percent in the
last century, and precipitation from extremely heavy storms has
increased 70 percent in the Northeast since 1958. During the next
century, annual precipitation and the frequency of heavy downpours
are likely to keep rising. Precipitation is likely to increase during
winter and spring, but not change significantly during summer and
fall. Rising temperatures will melt snow earlier in spring and
increase evaporation, and thereby dry the soil during summer and
fall. As a result, changing the climate is likely to intensify flooding
during winter and spring, and drought during summer and fall.
In 2011, Hurricane Irene caused the Schuylkill River to overflow its banks,
flooding a rail line, bike path, and other infrastructure in Philadelphia.
Credit: Sarah Clark Stuart, Bicycle Coalition of Greater Philadelphia.
Temperature change (°F):
-1 -0.5 0 0.5 1 1.5 2 2.5 3 3.5
Rising temperatures in the last century. All regions of
Pennsylvania have warmed. Source: EPA, Climate Change
Indicators in the United States.
Higher Tides Along the Delaware River
Sea level is rising more rapidly along Pennsylvania's shoreline than
in most coastal areas because the Delaware Valley is sinking. If the
oceans and atmosphere continue to warm, the tidal portion of the
Delaware River is likely to rise one to four feet in the next century.
Parts of Philadelphia International Airport and neighborhoods to the
north are within two or three feet above the average high tide on the
Delaware River. In downtown Philadelphia, Penn's Landing and the
Northeast Corridor railroad tracks at 30th Street Station are currently
in the 100-year floodplain. Along the Delaware and Schuylkill rivers,
a higher sea level could increase the extent of flooding caused by
either coastal storms or severe rainstorms, unless communities take
measures to hold back the rising rivers.

Tidal marshes like this one at Tinicum are vulnerable to destruction
and saltwater intrusion as sea level rises. Credit: Partnership for the
Delaware Estuaiy.
The tidal freshwater wetlands along the Delaware River are likely
to capture enough sediment for their land surfaces to keep pace
with rising sea level. But both rising sea level and increasing
drought enable salt water to mix farther up the Delaware River,
which could kill wetland plants. In places where that occurs,
wetlands might be replaced by either salt-tolerant wetland plants
or shallow waters. Higher salinity could also create problems for
Philadelphia's water supply during droughts, if salty water moves
upstream to the city's drinking water intake at Torresdale.
Inland Waters
Extraordinarily high river flows occasionally cause problems for
commercial navigation along the Ohio and Allegheny rivers,
and riverfront communities along the Susquehanna River and
smaller tributaries occasionally flood. Heavier storms and
greater river flows could make these problems worse. In 2011,
heavy rainfall caused record flooding on the Susquehanna and
the evacuations of Wilkes-Barre. Conversely, lower summer
rainfall and higher evaporation could leave some rivers too
shallow for navigaton during droughts.
One advantage of climate change is that warmer winters reduce
the number of days that ice prevents navigation on rivers and
in the Great Lakes. Between 1994 and 2011, reduced ice cover
lengthened the shipping season on the Great Lakes by eight
additional days. The Great Lakes are likely to warm another
3° to 7°F in the next 70 years, which will further extend the
shipping season. The impact of climate change on water quality
is less likely to be beneficial. Warmer temperatures tend to
cause more algal blooms, which can be unsightly, harm fish, and
degrade water quality. Severe storms also increase the amount
of pollutants that run off from the land into the water, further
increasing the risk of algal blooms.
Changing the climate threatens ecosystems by disrupting the
existing relationships between species. Wildflowers and woody
perennials are blooming—and migratory birds are arriving—
sooner in spring. Not all species adjust in the same way,
however, so the food that one species needs may no longer be
available when that species arrives on its migration. As a result,
for example birds in western Pennsylvania have had lower body
weights during warm years. Warmer temperatures allow deer
populations to increase, leading to a loss of forest underbrush,
which, in turn, makes some animals more vulnerable to
predators. Rising temperatures also enable invasive species to
move into areas that were previously too cold.
Changing climate will have both beneficial and harmful effects on
farming, but the net effect is unknown. Longer frost-free growing
seasons and higher concentrations of atmospheric carbon
dioxide would increase yields for many crops during an average
year, notably soybeans. But increasingly hot summers are likely
to reduce yields of corn, Pennsylvania's most important crop. The
earlier arrival of spring may increase populations of major crop
pests, such as the corn earworm and aggressive weeds. Higher
temperatures cause cows to eat less and produce less milk, so a
warming climate could reduce the output of milk and beef, which
together account for more than one-third of the commonwealth's
farm revenues.
Human Health
Hot days can be unhealthy—even dangerous. Certain people
are especially vulnerable, including children, the elderly, the sick,
and the poor. High air temperatures can cause heat stroke and
dehydration, and affect people's cardiovascular and nervous
systems. Warmer temperatures can also increase the forma-
tion of ground-level ozone, a key component of smog that can
contribute to respiratory problems. Rising temperatures may also
increase the length and severity of the pollen season for plants
such as ragweed.
The risk of some diseases carried by insects may also increase.
The ticks that transmit Lyme disease are active when tempera-
tures are above 45°F, so warmer winters could lengthen the
season during which ticks can become infected or people can
be exposed to the ticks. Higher temperatures would also expand
the area that is warm enough for the Asian tiger mosquito, a
common carrier of West Nile virus. The number of cases may or
may not increase, depending on what people do to control insect
populations and avoid insect bites.
The sources of information about climate and the impacts of climate change in this publication are: the national climate assessments by the U.S. Global Change
Research Program, synthesis and assessment products by the U.S. Climate Change Science Program, assessment reports by the Intergovernmental Panel on Climate
Change, ana EPA's Climate Change indicators in the United States. Mention of a particular season, location, species, or any other aspect of an impact does not imply
anything about the likelihood or importance of aspects that are not mentioned. For more information about climate change science, impacts, responses, and what you
can do, visit EPA's Climate Change website atwww.epa.gov/climatechanae.