“
The source of our increasing problem is the rise in sea
level, which is caused largely by an increase in global
temperatures as well as some land subsidence.
The problem for Charleston and other coastal cities, not
to mention Kiawah Island, is that the number of nuisance
floods is increasing. In the 1970s there were only about two
days each year on which nuisance flooding occurred. In 2015
Charleston had 38 days of tidal flooding, and in 2016 there
were 50 days of flooding. Predictions are that there could be
as many as 180 days of flooding per year in the 2040s. The
National Oceanic and Atmospheric Administration (NOAA)
reported that nuisance flooding has increased between 300
and 925 percent since the 1960s. A NOAA report states, “The
extent of nuisance flooding depends on multiple factors,
including topography and land cover.”
Charleston is not the only city with this problem, of course.
Annapolis, Maryland leads the way with an annual average
of 40 days of flooding in the period 2007-2013. Baltimore
and Atlantic City follow close behind as well as Sandy Hook,
New Jersey, and Port Isabel, Texas. Charleston is number 7
on the top-10 list with 23.3 days annually in that time period
followed by Washington, D.C., San Francisco, and Norfolk.
The source of our increasing problem is the rise in sea level,
which is caused largely by an increase in global temperatures
as well as some land subsidence.
• • During the 20th century, the mean global sea level (MGSL)
rose an average of seven inches per 100 years based on tide
gauge observations. As the sea level rises, tides higher than
normal can lead to flooding.
• • Charleston has one of the oldest continuous sea level
measuring stations in the country. Since 1920 to the present
the station has recorded an increase of about 3.15 mm per
year.
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”
• • According to NOAA, the problem is likely to worsen
because, during the last 25-year period, mean global sea
level rose 13 inches on a 100-year basis. Based on satellite
data, roughly one-third was due to the expansion of
warming sea water, and the other two-thirds was from
melting land-based ice.
• • In November 2012 NOAA issued a report on “Global
Sea Level Rise Scenarios for the United States Climate
Assessment” (Technical Report OAR CPO-1). The report
stated, “We have very high confidence (> 9 in 10 chance)
that global mean sea level will rise at least 0.2 meters
(about 8 inches) and no more than 2.0 meters (about 6.6
feet) by 2100.” That wide range of estimates is because
NOAA considered a series of scenarios based on potential
carbon emissions into the atmosphere and the resultant
atmospheric and ocean warming.
NOAA has published estimated sea level changes going
forward for various locations based on tide gauge data.
Realizing that it is impossible to predict sea level rise with
absolute confidence, NOAA has given a range of possibilities
based on the rate of change in carbon emissions (largely
CO 2 ), ice melt rate, release of methane into the atmosphere
from warming of permafrost in the Arctic, and other sources.
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