Geography Reference
In-Depth Information
8
Coastal erosion
Tom Spencer
is still widely found in the literature, but current
'best guess' estimates for this period are 49 cm, a
considerable downward revision on earlier figures
(see Warrick
et al
. 1996 for detailed discussion and
French
et al
. 1995a for geomorphological and
ecological implications). However several caveats
should be applied to this apparently comforting
reduction. First, very large uncertainties remain in
the predictions of global environmental change.
Second, it is not clear how the primary effect of
sea level rise might influence a range of secondary
effects, such as changing tropical cyclone
magnitudes and frequencies and mid-latitude
wave climates, which might in themselves have
greater impact on coastal communities than sea
level
rise per se
. Third, although the expected sea
level rise for the next 100 years is now much lower
than previously envisaged, it still represents a
significant increase on the previous 100 years. The
magnitude of expected sea level rise converts to
an average rate of sea level rise of 4.5 mm a
-1
.
Although it is difficult to provide a single figure
for the rate of sea level rise over the last 100 years,
Warrick
et al
. (1996) suggest an average rate of rise
of 1.8 mm a
-1
. Thus future rates are currently
expected to be 2.5 times those of the last 100 years.
Any future sea level change will be played out
against the backdrop of the second set of major
processes to affect the world's coastlines. This is
the creation of highly modified, 'artificial'
shorelines as a result of long-continued, but now
larger-scale, human modification and utilisation of
the coastal zone. Typically 30-40 per cent of open
coasts in developed countries (e.g. USA, England,
Japan) have protection against flooding, erosion
INTRODUCTION
In 1985, Bird reported on a project undertaken by
the International Geographical Union's
Commission on the Coastal Environment: this
found 70 per cent of the world's sandy coastline
undergoing net erosion. As 60 per cent of the
global population (or nearly 3 billion people) live
in the planet's coastal zones, and two-thirds of the
world's cities with populations of 2.5 million or
more are located in open coast or estuarine
locations (Viles and Spencer 1995), Bird's (1985)
statistic identifies a major environmental issue. It is
an issue already strongly imprinted on many local,
and national, consciences. Strong conflicts can
arise in the tackling of coastal erosion between
local residents; local, regional and national
regulatory bodies and interest groups; and
consultant scientists: the interaction of physical
processes and economic, social and political forces
makes coastal erosion a strongly geographical
problem. Furthermore, any coastal study must take
account of the great diversity of coastal settings
and of the role of environmental change over the
last 10,000 years in determining contemporary
shoreline morphology (see Box 8.1). There has
been a growing concern in the last decade that
coastlines are at risk and under pressure. Two broad
sets of processes, both potentially accelerating, have
been identified.
The first set concerns the impact of sea level
rise over the next 100 years consequent upon
human-induced global climate change. The figure
of
c.
100-150 cm of sea level change by AD 2100
