Transcript Change In Sea Level

Change In Sea Level
Definition: Long term changes in sea-level are
brought about by Climate change. This not only
affects the type of processes but also rates at
which they operate.
How and why is the sea level changing?
• England and Wales are vulnerable to an increase in
flood risk from a rise in sea levels and other potential
changes in storm frequency and intensity.
• Over 8% of the land area of England are protected by
river and coastal defenses.
• Two processes contribute to sea level rise as a result of
global warming. As the temperature of the atmosphere
increases:
1) ice on land will melt and run into the sea
2) total volume of seawater will expand
• The greatest effect is from this thermal expansion of the
oceans as they warm. Sea level rise by thermal
expansion will continue for many centuries after the
climate has been stabilized because of the large heat
capacity of the ocean.
Areas at risk of flooding in England and Wales
•
•
1)
2)
How and why is the seal level changing?
The sea level is changing because there is expansion and
contraction of ice sheets.
The two different ways of expansion are:
Eustatic – this is where sea level changes are due to a
hydrological cycle caused by water held in storage on land in ice
sheets.
Isostatic adjustment – a more local change in sea level resulting
from the depression of the earth’s crust by the increased weight
imposed upon it by growing ice sheets.
Isostacy - The balancing of the downward force of the Earth's crust
and the upward force (buoyant force) of the Earth's mantle.
Features of emergent coastlines
• Raised coasts
• Common in areas that were glaciated
during the last ice age.
• Several ports now lie several kilometres
inland and now out-ports have had to be
built as a result.
Continued : Coastal plains
• The most typical raised coastlines are lowlands
or former coastal plains that emerged.
• As a result of emergence, a gently shelving
smooth and wide coastal plain develops.
• Coastal plains form rich farming land as a result
of the thick marine deposits that cover it.
• Offshore, in the shallow water, lagoons and
offshore bars may be common.
• E.G. south eastern coast of USA
Continued : Barrier Islands
• Barrier islands are a natural sandy breakwaters
that form parallel to flat coastlines.
• Between the islands which may extend several
kilometres and the mainland is a tidal lagoon.
• Barrier islands make up 13% of the world’s
coastline.
• They develop on coasts with
relatively high energy waves and
a low tidal range.
Features of submerged coastlines
Fjords
~ they are located where glaciers were able to erode below
sea level.
~when the ice has melted valleys surrounding them were
flooded by the rising sea to form long, deep, narrow
inlets with precipitous sides and hanging valleys.
~Example is North-west Scotland, Alaska, Norway, British
Columbia in Canada and south island of New Zealand.
~ Description= Long, narrow inlets with high, cliff like sides,
very deep except at the shallow entrance.
Rias
• During the ice age, when the ice melted and sea level
rose the valleys cut by rivers and its tributaries were
drowned to produced sheltered, windy inlets, called Rias.
• Description= Long, Winging inlets with low,gently sloping
sides. They are generally shallow, with their depth
increasing towards the sea.
• Examples= Parts of south-west england, Walse and
Ireland, also Brittany in France and north-west spain.
Fjards
• They are low land areas which have been glaciated and
drowned.
Global warming
• The earth is being warmed by short wave
radiation during the day from the sun
• During the night it is cooled by longer wave
infrared radiation. We need a balance between
these two.
• However, incoming radiation is passing out
through the atmosphere but outgoing radiation is
trapped by a blanket of trace gases.
• As they trap heat like a greenhouse, they are
called greenhouse gases.
Continue…. Global warming
• During the twentieth century, global temperatures
increased by 0.6ºc.
• A further increase of between 1.6ºc and 4ºc is expected
by 2100.
• It has caused the sea level to rise by 110-25 cm in the
last 100 years. The Intergovernmental panel on climate
change (IPCC) forecasts a further rise of 50 cm by
2100.
• These changes will increase the hazards of coastal
flooding and erosion.
• 100 million people are living in low lying coastal areas
and could be at risk.
Continue…. Global warming
• During the twentieth century, global temperatures
increased by 0.6ºc.
• A further increase of between 1.6ºc and 4ºc is expected
by 2100.
• It has caused the sea level to rise by 110-25 cm in the
last 100 years. The Intergovernmental panel on climate
change (IPCC) forecasts a further rise of 50 cm by
2100.
• These changes will increase the hazards of coastal
flooding and erosion.
• 100 million people are living in low lying coastal areas
and could be at risk.
Response
•Miami , Florida, suffer hurricanes every 7 years.
•People have responded by spending 30 million
pounds to make Miami beach hurricane proof.
•This includes a widen beach, evacuation routes,
artificial mounds 6 metres above sea level for all new
buildings.
•As Japan and Hawaii are prone to tsunamis they
have developed seismographs to detect shock
waves.
•These can be used to warn people of danger and so
evacuation can take place.
Past, Present and future references
•This is not the first sea level change, it is occurring
constantly all over the world. It usually occurs over
long period of time.
•When there is a new change new cliffs and beaches
are created.