United States
Environmental Protection
Agency
Office of Policy,
Planning, and
Evaluation
EPA230-F-92-004
May 1992
Climate Change
Discussion Series
In the next 100 years, the "greenhouse
effect" could lead to rising seas and
dramatic changes in the world's coastal
zones. These changes would affect eco-
systems and human development
alike, and in some regions, valuable
natural, economic, and human re-
sources could be lost entirely. There are
policies that could reduce the impact of
sea level rise on the various coastal re-
sources while still allowing human uti-
lization of the coastal zone.
Global climate change could raise sea
level by expanding ocean water and by
increasing the amount of water in the
ocean. The more certain impact is ther-
mal expansion. As a molecule of water is
warmed, greater energy is imparted to
the molecule and its movement in-
creases. As a result, the space between
molecules grows, and the volume of a
given amount of water increases. Warm-
ing of the atmosphere in the next cen-
tury will increase ocean temperatures
enough to raise sea level about 30 cm.
Although the oceans contain most of
the world's water, there is enough
Sea Level Rise
fresh ground water to raise the sea 20
ft. and enough ice resting on land to
raise the sea over 200 ft. No one has es-
timated the likely impact of future in-
creases in irrigation, although the im-
pact over the last century is only a few
centimeters. In the near term, the larg-
est impact would probably be moun-
tain glaciers, which could melt and
add about 30 cm to sea level.
Over the long term, the polar ice sheets
could raise the sea significantly. In
southern Greenland, warmer air tem-
peratures could lead to
increased melting during
the summer; in West Ant-
arctica, warmer water tem-
peratures could gradually
melt the floating ice that
prevents the large ice sheet
from sliding into the ocean.
Although the combined
impact of these polar ice
sheets is likely to be less
than 50 cm in the next cen-
tury, over the next few cen-
turies the rise could be sev-
eral meters. At least part of
this rise will probably be offset by in-
creased snowfall accompanying the
wanner polar temperatures.
Current estimates range from 30 to 110
cm of global sea level rise by 2100. At
first glance, a meter or more of sea
level rise in a century may seem en-
durable, but the coastal zone is a dy-
namic environment and can be sub-
ject to rapid change with little prov-
ocation. Listed below are the primary
effects of sea level rise on the coast-
al environment.
How Much Will Sea Level Rise?
120
2100
Primaiy Effects of Sea Level Rise
Erosion One foot of sea level rise can erode beaches 50 to
300 ft. A one meter rise could cause underdeveloped bar-
rier islands to break apart.
Inundation Low-lying sheltered shores not subject to ero-
sion would still face inundation as the sea rises.
Infrastructure Costs The combined effects of erosion and
inundation from a meter of sea level rise could force gov-
ernments to spend $100 to $300 billion to protect coastal
property in the United States, if nothing is done to plan for
sea level rise.
Storm Surges As sea level rises, the amount of coastal area
subject to flooding from any size storm will increase.
Wetland Loss Many wetlands would not be able to keep up
with even a half-meter rise in sea level. Some would
be inundated and lost, but others might be able to migrate
upland as sea level rises, if the upland zone is not occupied
by development. If wetlands are allowed to migrate up-
land uninhibited, a one-meter rise in sea level could still
mean a 26 to 66 percent loss in U.S. coastal wetlands.
Salt Water Intrusion Thesalhvater wedgeof an estuary will
migrate upstream as sea level rises, shifting marine
ecosystemsupriver. If the upstream conditions are un-
suitable, ecosystems will be lost. Groundwater will be
affected, too. Some coastal communities will lose their
water supplies as brackish water infiltrates aquifers
supplying drinking water.
NOTE: Climate change refers 10 potential modification of the earth's climate resulting from increasing atmospheric concentrations of greenhouse gases such as carbon
dioxide (C0:). methane (CH4), nitrous oxide (N;O). andchlorofluorocarbons (CFCs). Through a naturally occurring process known as the "greenhouse effect." these
gases act to warm the earth by trapping heat in the atmosphere. This process plays an important role in maintaining the earth's current temperature and climate. By
increasing concentrations of greenhouse gases, human activities are trapping more heat in the atmosphere and potentially changing the earth's climate.
£j Printed on Recycled Paper
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Planning for Sea Level Rise
States can respond to sea level rise either
by holding back the sea or by adapting to
a natural retreat of the shorelines. In the
next few decades, the impacts of sea level
rise will be relatively minor in most of the
nation. There is little need to build dikes
or fortify beaches in anticipation of a
problem that is decades away, because
these projects can be implemented in a
few years.
Changes in land use, however, are only
cost-effective if enacted decades in ad-
vance. Thus, if communities do not de-
velop long-term plans for rising sea
level today, holding back the sea may
be the only viable option for much of
the coast. For densely developed areas,
this result is reasonable. For many
moderate and low density areas, how-
ever, the failure to plan could result in
both unnecessary coastal protection
costs and a loss of marshes, swamps, and
other natural shoreline ecosystems.
New tools for coastal management are
necessary because existing policies, if
applied to all areas threatened by sea
level rise, would almost certainly in-
volve unconstitutional seizure of pri-
vate property. Moreover, most people
would find it unreasonable to prohibit
development in the 7000 square miles
that would be inundated from a one
meter rise in sea level
Fortunately, planning tools are available
that would permit shorelines to migrate
landward without requiring seizure of
private property (see box). The key differ-
ences between these approaches and tra-
ditional regulatory approaches are that
the regulatory approaches tell the prop-
erty owner how to meet the environmen-
tal constraint and has immediate restric-
tions, which can cause large reduc-
tions in property values while the new
approaches simply set the constraint and
allow the market to decide how to com-
ply. The new approaches also defer the
restrictions until they are actually neces-
sary, and when discounted to the present,
the impact on property values is trivial.
Planning for sea level rise is necessary,
"not because there is on impending catas-
trophe, but because there are opportuni-
ties to avoid adverse impacts by acting
now, opportunities that may be lost if
the process is delayed." (LPCC)
Examples of Potential Policies for Sea Level Rise Planning
Beach Nourishment Pumping sand onto beaches not only
protects development from erosion, but has the attributes of
maintaining beaches and allowing flexible response to sea
level rise. The total cost of nourishing US. beaches for a one-
meter rise in sea level could be over $50 billion. Decisions by
localities depend in part on whether they can rely on state
funding of beach nourishment If state financing is likely to
be limited, states should provide localities the authority to
raise the necessary revenues.
Prohibit Development Statutes or regulations could be
used to prevent construction in areas with extreme sensi-
tivity to human activity.
Buy Coastal Land Government agencies or conservancies
could purchase land onto which wetlands could migrate as
sea level rises.
Prohibit Bulkheads Do not interfere with private activities
today, but explicitly notify property owners that as sea level
rises they will not be allowed to construct bulkheads to
protect their property.
Leases Do not interfere with private activities today but
convert (with compensation if necessary) property rights
of current owners to long-term leases which expire after 99
years, or conditional leases, which expire whenever the
sea rises enough to inundate the property. Underlying
ownership could belong to the public, or a private conser-
vancy group.
Public Trust Doctrine In many states, the public is as-
sumed to have an easement along the shore for recre-
ational, commercial, and environmental purposes. Court
tests are necessary to determine whether this easement
moves inland as sea level rises, and whether a permit for a
bulkhead relinquishes this easement.
Land Titles The common law "rule against perpetuities"
prevents people from ensuring that donated coastal property
reverts to nature when the sea rises. State laws exempting
charity-to-charity conditions from this rule could be expanded
to include an exception for climate change.
Louisiana Navigation, flood control, and other projects have
increased the vulnerability to the point where even current
trends allow the Gulf to reclaim 50 square miles pCT year. Only
by restoring the natural processes that once enabled the
wetlands to keep pace with rising sea will this delta survive
the consequences of global warming. Possible options in-
clude allowing a natural diversion to the Atchafalaya River
and shifting ocean-bound navigation away from the main
channels of the Mississippi River toward alternate routes.
Intergovernmental Panel on Climate Change. Climate Cliange: Tlie IPCC Scientific Assessment. Cambridge, UK: Press Syndicate of tht University of
Cambridge. 1990.
Titus et al. "Greenhouse Effect and Sea Level Rise: Potential Loss of Land and the Cost of Holding Back the Sea." Coastal Management. 1991 fVol 2).
Titus. "Greenhouse Effect and Coastal Wetland Policy: How Americans Could Abandon an Area the Size of Massachusetts at Minimum Cost.
Environmental Management, Volume 15.1991.
Report of the Coastal Zone Management Sub-Group of the Intergovernmental Panel on Climate Change.
EPA's Climate Change Outreach Program is designed to raise awareness about climate change and provide assistance to state and local
governments, industry, and non-governmental organizations in the evaluation of cost-effective response strategies. For further information
about this program, please contact Joel Smith at 202/260-8825.
US. EPA Climate Change Discussion Scries 1992
Global Climate Change Sea Level Rise
Adaptation to Transportation
Climate Change Energy
Forestry Water Resources
Agriculture Biodiversity
Order from: CUMATE CHANGE INFORMATION
U.S. EPA
Office of Policy Analysis
Climate Change Division (PM221)
401 M Street. SW.
Washington. DC 20460
USA
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