Geoscience Reference
In-Depth Information
ectly linked to the sea-surface temperature. As hurricanes can only start to form if the sea-
surface temperature is above 26°C it would seem sensible that in a warmer world there
would be more hurricanes. Yet the formation of hurricanes is much rarer than the oppor-
tunities for them to occur. Only 10 per cent of centres of falling pressure over the tropical
oceans give rise to fully fledged hurricanes. Other considerations, such as wind shear to
start the rising air spinning, need to be considered when understanding the genesis of trop-
ical storms. In a year of high incident, perhaps a maximum of 50 tropical storms will de-
velop to hurricane levels. Predicting the level of a disaster is also difficult as the number
of hurricanes does not matter, it is whether they make landfall. For example, 1992 was a
very quiet year for hurricanes in the North Atlantic Ocean. However, in August, one of the
few hurricanes that year, Hurricane Andrew, hit the USA just south of Miami and caused
damage estimated at $26 billion. Hurricane Andrew also demonstrates that where a storm
hits is equally important: if the hurricane had hit just 20 miles (~32 km) further north it
would have hit the densely populated area of Miami City and the damage bill would have
more than doubled.
In terms of where hurricanes hit in developed countries, the major effect is usually eco-
nomic loss, while in developing countries the main effect is loss of life. For example, Hur-
ricane Katrina, which hit New Orleans in 2005, caused over 1,800 deaths; Hurricane
Mitch, which hit Central America, killed at least 25,000 people. Hurricane Katrina was
not the worst storm that has hit the USA; a storm that hit Miami in 1926 was 150 per cent
larger but did little damage because Miami Beach was yet to be developed. In the USA,
coastal population has doubled in the last ten years. So in terms of climate change, mitiga-
tion policies will have little effect on the costs in the developed world, while adaptation of
coastal regions will be essential. But in the developing world mitigation would have a
large impact in reducing the total loss of life and preventing regional economic melt-
down. For example, the immediate economic impact of Hurricane Katrina was over $150
billion, but its subsequent effect on the US economy was to boost it slightly, by 1 per cent,
that year due to the $105 billion injected by the Bush administration to help the recon-
struction of the region. Compare this with Hurricane Mitch, which set back the economy
of Central America by about a decade.
As can been seen from the case of Hurricanes Katrina and Mitch, storms and floods have
the ability to destroy major cities and towns. In most cases it is the flooding that causes
the worst disasters. Many major cities around the world are vulnerable to flooding be-
cause they were built close to rivers or the coast in order to facilitate trade via the oceans.
London is one such city. At the moment, London is protected from flooding by the
Thames Barrier. The Thames Barrier was built in response to the catastrophic floods of
