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The Effects of Global Warming on Wetlands
Introduction
Wetlands are highly productive ecosystems. Wetlands include
marshes, estuaries, bogs, fens, swamps,
deltas, shallow seas, and floodplains. Wetland habitats support
a vast range of plant and animal life, and
serve a variety of important functions, which include water
regime regulation, flood control, erosion
control, nursery areas for fishes, fish production, recreation,
plant production, aesthetic enjoyment, and
wildlife habitat. Wetlands account for about 6% of the global
land area and are among the most
valuable environmental resources.
The Problem
The potential impacts of climate change on wetlands are of great
concern. Increasing atmospheric
concentrations of carbon dioxide and other greenhouse gases
released by human activities are generally
expected to warm the Earth a few degrees (C) in the next century
by a mechanism known as the
"greenhouse effect." Such warming could raise sea level by
expanding ocean water, melting mountain
glaciers, and eventually causing polar ice sheets to side into
the oceans. Among the coastal areas of
greatest risk in the United States are those low-lying coastal
habitats that are easily eroded and which
occur along the northern Gulf of Mexico and southern Atlantic
coasts of the U.S. These coastal wetlands
are especially vulnerable to direct, large-scale impacts of
climate change, primarily because of their
sensitivity to sea-level rise.
Observational records indicate that sea level has already risen
between 10 and 25 cm globally over the
past 100 years. In addition, the Intergovernmental Panel on
Climate Change (IPCC) has projected a sea-
level rise of 15-95 cm as a consequence of global warming.
Sea-level rise will also increase the depth of
coastal waters and increase inland and upstream salinity
intrusion, both of which affect fresh and
brackish water wetlands. Sea-level rise has the potential for
increasing the severity of storm surges,
particularly in areas where coastal habitats and barrier
shorelines are rapidly deteriorating. These direct
consequences of global- and regional-scale changes will increase
the vulnerability of coastal wetlands
which are already heavily impacted by human activities.
Analysis of sites in five coastal states indicate that many
marshes and mangrove ecosystems receive
adequate mineral sediments to produce enough organic sediment
and root material to remain above
sea level at the present rate of sea-level rise (1-2 mm per year
globally). However, three of the twelve
wetlands studied were not keeping pace with the current rate of
sea-level rise. If sea-level rise
accelerates, some additional sites would also begin to slowly
deteriorate and submerge.
An increasing body of evidence indicates that increasing
concentrations of greenhouse gases could
cause sea level to rise one or two meters by the year 2100. Case
studies of South Carolina and New
Jersey marshes indicate that a two-meter rise would destroy 80
to 90 percent of the coastal marshes,
depending on developmental practices.
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In Florida, Louisiana, and South Carolina, submergence and/or
salt water intrusion have been implicated
in the decline in productivity, and death, of certain coastal
forests. However, restoration of salinity-
impacted baldcypress swamps, for example, may be possible by
cultivating more salt-tolerant strains of
baldcypress. Studies in Texas have also shown that changes in
global climate would affect forests of the
coastal plain by possibly influencing patterns of disturbances,
such as fires or storms, and by altering the
regional moisture balance. Such changes would affect resources
in both preserved and commercial
forests of the coastal plain.
The Solution
Future losses of wetlands from sea level rise could be reduced
by
* slowing the rate of sea level rise
* enhancing wetlands' ability to keep pace with sea level
rise
* decreasing human interference with the natural processes by
which wetlands adapt to sea level rise
* holding back the sea while maintaining the marshes
artificially
Humans could slow down sea level rise by limiting the projected
increase in concentrations of
greenhouse gases. A study has shown that reducing CO2 emissions
with bans on coal, shale oil. and
synfuels would delay a projected two degree (C) warming from
2040 to 2065; because of the thermal
delay of the oceans, the resulting thermal expansion of ocean
water would be delayed ten to fifteen
years. Although limiting the rise in sea level by limiting
greenhouse gases seem the logical thing to do, it
can be very costly. The world's nations would have to agree to
replace many industrial activities with
processes that do not release greenhouse gases.
Wetland protection officials are also considering measures that
would enable wetlands to adapt to rising
sea level. These measures include marsh building, enhanced
sedimentation, and enhanced peat
formation, and would not have to be implemented until sea level
rise has accelerated. However, these
proposed activities are not very cost-effective.
Allowing wetlands to adapt naturally to sea level rise would not
prevent a large reduction in acreage,
but might allow the ecosystems themselves to survive. This
option would consist primarily of removing
human impediments to sedimentation and the landward migration of
wetlands.
Finally, it might be possible to hold back the sea and maintain
wetlands artificially. For small amounts of
sea level rise, tidal gates might be installed that open during
low tide but close during high tide, thereby
preventing saltwater intrusion and lowering average water
levels. For a larger rise, levees and pumping
