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Climate Change, Sea-Level Rise, and the Chesapeake Bay
Sea-level rise and global warming result from natural climatic cycles, which usually
occur over very long time periods. Current and historical data show that we are in a
warming trend, and therefore, sea levels are rising—and that they will continue to rise.
Sea level has risen roughly four to eight inches over the past 100 years. Within the
Chesapeake Bay, the rate of sea-level rise is about twice the global average. What
does this mean for the Chesapeake Bay, the more then 16 million people who live in
the Chesapeake Bay watershed, and the multitude of terrestrial and aquatic organisms
that coexist within the watershed?
History
During the most recent ice age, which peaked about 18,000 years ago, sea level was
much lower. The Chesapeake Bay did not exist; the Susquehanna River flowed across
the continental shelf and emptied directly into the Atlantic Ocean many miles east.
The Earth’s last ice age was followed by a warming period, which featured was melting
ice caps and rising sea levels. Slowly, about 10,000 years ago, the Susquehanna River
was flooded by rising waters that led to the formation of the Chesapeake Bay. We are
still in that warming period, and the Earth continues to get warmer. With increasing
temperatures, global ice caps will continue to melt, contributing to rising sea levels
worldwide.
The Greenhouse Effect
The effects of global warming and sea-level rise seem simple: As the Earth warms,
glaciers melt and the seas rise. But the science behind the Earth’s atmospheric
greenhouse gas effect and forecasting changes in Earth’s climate is very complex.
The natural greenhouse effect is a critical part of our Earth’s climate. About 2%
of our atmosphere is made up of greenhouse gases (water vapor, carbon dioxide, ozone,
and methane). The gases help trap heat radiated by the Earth’s surface and prevent it
from escaping our atmosphere. Without these gases, our planet would be uninhabitable
for life as we know it because it would be too cold.
Since the Industrial Revolution in the 1750s, however, human activity has increased the
levels of greenhouse gases greatly. Carbon dioxide levels have increased by more than
30% since 1750, compared to a relatively constant level for the preceding 750 years.
Most of the carbon dioxide increases can be linked to the burning of fossil fuels
including wood and petroleum products to power factories, run our cars, heat our
homes, and support other activities. The increase of greenhouse gases in our atmosphere
has caused our atmosphere to trap more and more heat, resulting in global increases in
both air and sea-surface temperatures.
How Does This Affect the Chesapeake Bay?
The natural cycles of climate change on Earth occur over very long time periods. When
this change happens slowly, humans, animals, and even the land can adapt to it. But
the rapid rate of sea-level rise in the Chesapeake Bay is about twice the global
average. If this trend continues, water levels in the Chesapeake could rise as much
as 15 to 40 inches over the next century. This might not seem like a lot to many people,
but much of our coastal area would be flooded  by a
one-and-a-half-meter (just under five feet) rise.
More than humans will be affected by global warming and sea-level rise. Levels in bays
and tidal rivers will rise because there will be more ocean water in the Chesapeake Bay.
That also means there will be more salt water in these areas, which are not accustomed
to high-salinity water. Both air and water temperature increases will force plants and
animals into different distributions. All species have certain preferences for where
they like to live based on conditions like temperature, salinity, availability of food,
etc. When those conditions change, plants and animals will shift in response.
Following is a list of some of the changes that are likely to accompany sea-level rise
in the Chesapeake Bay, which will be superimposed upon continued population growth
and development in the coastal environment.
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As sea level continues to rise, valuable coastal habitats will be threatened. Wetlands
will continue to retreat, increasing the erosion of shorelines. Aside from property
losses, shallow waters will become more turbid, making it difficult for SAV
(submerged aquatic vegetation—underwater grasses) to survive.
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An increase in water temperatures could alter local fisheries in favor of subtropical
forms (Wood et al. 2002). Cooler-water species such as striped bass would be replaced
by warmer species, such as brown shrimp.
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While warmer temperature may increase the growing season of species such as oysters,
other factors could be compromised. The early onset of diseases may occur with
warmer temperatures. For example, MSX and Dermo, devastating diseases of oysters,
are associated with warmer temperatures (Scavia et al. 2002).
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Harmful algal blooms have also been associated with temperature extremes.
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Changes in river flow would affect nutrient and sediment loadings to the Bay, as
well as alter dissolved oxygen levels (Wood et al. 2002; Scavia et al. 2002). With
increased flows come increased nutrients and sediment loadings, with the potential
to change salinity distributions and estuarine circulation.
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Increased water temperatures favor low dissolved oxygen levels. This would further
degrade coastal water quality and likely reduce overall system productivity
(Wood et al. 2002).
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Less-desirable gelatinous plankton would continue to dominate Bay waters, outcompeting
economically important species for limited resources.
These predicted changes compete with ongoing restoration efforts in
the Chesapeake Bay. Therefore, the more we can do now to prepare
ourselves and the coastal region for these changes, the better. We
can all do our part to release fewer
greenhouse gases  by driving less, reducing our electricity usage whenever
possible, reducing usage of aerosol products, and more.
Becoming more informed on why climate change is happening—and what it
means for the Earth—can help you play a more active role in conserving our
environment and analyzing the potential effects of sea-level rise in the
Chesapeake Bay.
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