High
Seas Set To Become Higher
23rd May
GWA Correspondent
We’ve
all read about it, worried and wondered about rising sea levels
due to melting glaciers and polar ice caps. That’s part
of it, but thermal expansion as the surface layer of the sea heats
up is viewed by the IPCC * as likely to have the greater effect
on sea levels over the 21st century. The oceans around us are
a heat sink and after all cover 71% of the earth’s surface.
We are surrounded by 1.36 billion cubic kilometres of the stuff.
Crank up the temperature and the oceans are going to expand, although
by exactly how much is far from certain.
Because
of the variables such as layer mixing, models used are quite subjective.
The surface layer, taken to be from 0-200 metres deep, mixes the
most readily.
Below that the layers are fairly stable. It has been calculated
that ‘new water’ at the ocean floor would take a thousand
years to reach the surface. So the upper 200 metres is the layer
which absorbs the heat and thus expands the most.
This
table gives the thermal coefficient of water by volume.
| water,
liquid (4 °C) |
0 |
| water,
liquid (10 °C) |
88 |
| water,
liquid (20 °C) |
207 |
| water,
liquid (30 °C) |
303 |
| water,
liquid (40 °C) |
385 |
| water,
liquid (50 °C) |
457 |
| water,
liquid (60 °C) |
522 |
| water,
liquid (70 °C) |
582 |
| water,
liquid (80 °C) |
640 |
| water,
liquid (90 °C) |
695
|
In
1990 the average temperature of the blanket of air surrounding
the earth was 15 degrees C, which was the highest on record. Since
then it has increased even more and in doing thermal expansion
has lifted the sea levels. By how much?
Over
the last 100 years sea levels have risen by 6-35 centimetres.
Taking the IPCC* predictions for the next 100 years as gospel
this translates out to a further 15 and 95 centimetres rise.
Doesn’t
sound like much? Low lying cities like Portsmouth and Southsea
could be flooded and many of Bangladesh’s inhabited islands
would disappear forever. Tuvalu’s population in the Pacific
is already being evacuated to their new home in Auckland, New
Zealand. Coupled with storm surge the effect is going to be devastating
to coastal cities and communities.
As
a general rule, for every 1 centimetre rises in sea level a metre
of coast line is lost. Not the end of the world exactly but if
the IPCC’s predictions come in at the high end of their
estimates it will spell the end for a lot of our coastal communities.
* Intergovernmental Panel on Climate Change.
