150 The impactsof climate change
level rise over the next millennium that might be expected with different
levels of temperature change at Greenland. A warming of 5.5◦C, for
instance, if sustained for 1000 years, would be likely to result in about
3 m of sea level rise.
The portion of the Antarctic ice-sheet that is of most concern is that
in the west of Antarctica (around 90◦W longitude); its disintegration
would result in about a 6-m sea level rise. Because a large portion of
it is grounded well below sea level it has been suggested that rapid
ice discharge could occur if the surrounding ice shelves are weakened.
Although studies are far from conclusive, current ice dynamic models
do not indicate that rapid disintegration is likely and suggest that, over
the next millennium, the contribution of the west Antarctic ice-sheet to
sea level rise will be less than 3 m.The impacts of sea level rise
A rise in average sea level of 10 cm by 2030 and about half a metre by the
end of the next century (typical values from Figure 7.1) may not seem a
great deal. Many people live sufficiently above the level of high water not
to be directly affected. However, half of humanity inhabits the coastal
zones around the world. Within these, the lowest lying are some of the
most fertile and densely populated. To people living in these areas, even
a fraction of a metre increase in sea level can add enormously to their
problems. Some of the areas that are especially vulnerable are, firstly,
large river delta areas, for instance Bangladesh; secondly, areas very
close to sea level where sea defences are already in place, for instance
the Netherlands; and, thirdly, small low-lying islands in the Pacific and
other oceans. We shall look at these in turn.
Bangladesh is a densely populated country of about 120 million
people located in the complex delta region of the Ganges, Brahmaputra
and Meghna Rivers.^6 About ten per cent of the country’s habitable land
(with about six millionpopulation) would be lost with half a metre of sea
level rise and about twenty per cent (with about 15 million population)
would be lost with a 1-m rise^7 (Figure 7.4). Estimates of the sea level
rise are of about 1 m by 2050 (compounded of 70 cm due to subsidence
because of land movements and removalof groundwater and 30 cm from
the effects of global warming) and nearly 2 m by 2100 (1.2 m due to
subsidence and 70 cm from global warming)^8 – although there is a large
uncertainty in these estimates.
It is quite impractical to consider full protection of the long and
complicated coastline of Bangladesh from sea level rise. Its most obvious
effect, therefore, is that substantial amounts of good agricultural land
will be lost. This is serious: half the country’s economy comes from