CDA United States	AugUSt2016
Environmental Protection
Agency	EPA 430-F-16"022
What Climate Change
Maryland's climate is changing. Most of the state has
warmed one to two degrees (F) in the last century, heavy
rainstorms are more frequent, and the sea is rising about
one inch every seven to eight years. Higher water levels
are eroding beaches, submerging low lands, exacerbating
coastal flooding, and increasing the salinity of estuaries
and aquifers. In the coming decades, changing the climate
is likely to increase coastal and inland flooding; harm
marine, wetland, and inland ecosystems; disrupt fishing
and 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 retreating.
Even the great ice sheets on Greenland and Antarctica are
shrinking. Thus the sea is rising at an increasing rate.
Temperature change (°F):
-1 0.5 « O.SI 1.5 2 2.5 3 3 5
Rising temperatures in the last century. Except for western
Maryland, the state has warmed more than most of the nation.
Source: EPA, Climate Change Indicators in the United States.
Increasing Temperature and Changing Precipitation Patterns
Rising temperatures and shifting rainfall patterns are likely to increase the intensity
of both floods and droughts. Average annual precipitation in Maryland has increased
about 5 percent in the last century, but precipitation from extremely heavy storms
has increased in the eastern United States by more than 25 percent since 1958.
During the next century, average annual precipitation and the frequency of heavy
downpours are likely to keep rising. Average 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
Rising Seas and Retreating Shores
Sea level is rising more rapidly in Maryland than in most coastal areas because the
land is sinking. If the oceans and atmosphere continue to warm, sea level along the
Maryland coast is likely to rise sixteen inches to four feet in the next century.
As sea level rises, the lowest dry lands are submerged and become either tidal
wetland or open water. The freshwater wetlands in the upper tidal portions of the
Potomac, Patuxent, Choptank, and Nanticoke rivers build their own land by capturing
floating sediments, and they are likely to keep pace with the rising sea during the
next century. But most salt marshes elsewhere in the state are unlikely to keep
pace if sea level rises three feet. The wetlands along the Eastern Shore south of the
Bay Bridge are even more vulnerable, and likely to be lost if the sea rises two feet.
Wetlands in Dorchester County are already being submerged by rising sea level.
Beaches also erode as sea level rises. A higher ocean level makes it more likely that
storm waters will wash over a barrier island or open new inlets. The United States
Geological Survey estimates that Assateague Island is likely to be broken up by new
inlets or lost to erosion if sea level rises two feet by the year 2100. Eroding beaches
along Chesapeake Bay and its tributaries are likely to be squeezed between the
advancing water and stone revetments erected to protect development along the
shore. Even towns with "Beach"' in their names are seeing their beaches replaced
with hard shore protection structures.
Sea level rise threatens coastal wetlands like this marsh at Blackwater Wildlife Refuge, along
with the ecosystems and fisheries they support. ©James G. Titus; used by permission.

Saltwater Intrusion
As sea level rises, salt water can mix farther inland or upstream in bays,
rivers, and wetlands. Because water on the surface is connected to
ground water, salt water can also intrude into aquifers near the coast.
Soils may become too saity for the crops and trees that currently grow in
low-lying areas.
Homes and Infrastructure
Storms can destroy coastal homes, wash out highways and rail lines,
and damage essential communication, energy, and wastewater manage-
ment infrastructure. In 2003, the storm surge in Chesapeake Bay from
Hurricane Isabel flooded downtown Annapolis, North Beach, and several
communities on the Eastern Shore, causing about $400 million in dam-
ages. While recent hurricanes have had minimal impacts on Ocean City,
about 25 percent of its structures are vulnerable to flooding. On the lower
Eastern Shore, communities like Hooper's Island, Smith Island, and parts
of Crisfield are so low that water in ditches along the streets rises and falls
with the tides. These towns will become more vulnerable to storms and
erosion as sea level rises.
Although hurricanes are rare, their wind speeds and rainfall rates are likely
to increase as the climate continues to warm. Rising sea level is likely to
increase flood insurance rates, while more frequent storms could increase
the deductible for wind damage in homeowner insurance policies.
Downtown Annapolis the day after Hurricane Isabel struck the Atlantic coast
on September 18, 2003. © James G. Titus; used by permission.
The loss of tidal marshes could harm fish and birds that depend on a
marsh for food or shelter. Small insects and marine organisms that feed in
the marsh are a key source of food for crabs, rockfish, and other commer-
cially important fisheries. Striped bass, bluefish, sea trout, and summer
flounder also move into and out of the marsh for feeding and shelter.
The most vulnerable marshes along Chesapeake Bay are inhabited by
great blue heron, bald eagle, American black duck, and snowy egret.
The marshes near Ocean City and Assateague Island provide forage for
shorebirds, such as sandpipers and plovers, and several species of ducks
and geese spend the winter in these marshes.
The loss of bay beaches would remove key habitat for diamondback
terrapin that nest on these beaches. Other species that depend on bay
beaches include horseshoe crabs, tiger beetles, sand fleas, snails, and
several crab species. The loss of those species would remove important
sources of food for birds.
Changing temperatures could also disrupt ecosystems. If water tem-
peratures exceed 86°F during summer, eelgrass could be lost. Blue
crabs would lose an important hiding place during spring when they are
changing shells and vulnerable to predators, and the sea turtles that feed
on those crabs in the eelgrass might lose that food source. 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.
Fishing and Farms
Parts of Maryland's fishing and agriculture sectors may suffer as
the climate changes. Blue crabs and other shellfish are vulnerable
to increased acidity in the water, especially during early life stages
when acidity impairs their ability to build shells. As sea level rises, the
Chesapeake Bay region is expected to lose some of the wetlands that
fish and shellfish depend on for nursery grounds. Warmer waters are
expected to increase harmful algae, lower oxygen levels, and change the
mix of species that thrive in the bay.
Climate change may also pose challenges for agriculture: some farms may
be harmed if more hot days and droughts reduce crop yields, or if more
flooding and wetter springs delay their planting dates. Other farms may
benefit from a longer growing season and the fertilizing effect of
carbon dioxide.
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 formation of ground-level ozone, a 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.which has already been observed in other regions.
The risk of some diseases carried by insects may also increase. The ticks
that transmit Lyme disease are active when temperatures 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. 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, and 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
at vmw.eDa.aov/climatechanae.