154 The impactsof climate change
wetlands and mangrove swamps currently occupy an area of about a
million square kilometres (the figure is not known very precisely), equal
approximately to twice the area of France. They contain much biodi-
versity and their biological productivity equals or exceeds that of any
other natural or agricultural system. Over two-thirds of the fish caught
for human consumption, as well as many birds and animals, depend on
coastal marshes and swamps for part of their life cycles, so they are
vital to the total world ecology. Such areas can adjust to slow levels of
sea level rise, but there is no evidence that they could keep pace with
a rate of rise of greater than about 2 mm per year – 20 cm per century.
What will tend to occur, therefore, is that the area of wetlands will ex-
tend inland, sometimes with a loss of good agricultural land. However,
because in many places such extension will be inhibited by the presence
of flood embankments and other human constructions, erosion of the
seaward boundaries of the wetlands will lead more usually to a loss of
wetland area. Because of a variety of human activities (such as shoreline
protection, blocking of sediment sources, land reclamation, aquaculture
development and oil, gas and water extraction), coastal wetlands are cur-
rently being lost at a rate of 0.5–1.5% per year. Sea level rise because of
climate change would further exacerbate this loss.^19
To summarise the impact of the half-metre or so of sea level rise
due to global warming which could occur during the twenty-first cen-
tury: global warming is not the only reason for sea level rise but it is
likely to exacerbate the impacts of other environmental problems. Care-
ful management of human activities in the affected areas can do a lot to
alleviate the likely effects, but substantial adverse impacts will remain.
In delta regions, which are particularly vulnerable, sea level rise will lead
to substantial loss of agricultural land and salt intrusion into freshwater
resources. In Bangladesh, for instance, over ten million people are likely
to be affected by such loss. A further problem in Bangladesh and other
low-lying tropical areas will be the increased intensity and frequency
of disasters because of storm surges. Each year, the number of people
worldwide experiencing flooding becauseof storm surges is estimated
now at about forty million. With a 40-cm sea level rise by the 2080s this
number is estimated to quadruple – a number that might be reduced by
half if coastal protection is enhanced in proportion to gross domestic
product (GDP) growth.^20 Low-lying small islands will also suffer loss of
land and freshwater supplies. Countries like The Netherlands and many
cities in coastal regions will have to spend substantial sums on protec-
tion against the sea. Significant amounts of land will also be lost near
the important wetland areas of the world. Attempts to put costs against
these impacts, in both money and human terms, will be considered later
in the chapter.