Subject: [Homestead] Oceans rise one-half meter by 2100
Date: Mon, 13 Sep 2004 18:12:52 -0700
Not to worry, the Planless President will go right on draining the
economy of megatrillions of dollars in flood damage year after year,
year after year, decades after decades as a true pseudoconservative
would do. When I was a kid in the Great Depression, when the treads
started showing, we would recap a tire at a cost of $6.00. Preventive
Maintenance is a lot cheaper than cleaning up toxic dumps or climate at
the tipping point. Pseudoconservatives don't care---it will be the
problems of our grandchildren..
Key text
------------------------------------------------------------------------
Getting into hot water – global warming and rising sea levels
------------------------------------------------------------------------
/The 20th century saw the greatest increase in temperature of any
century during the last thousand years, and the 1990s was the warmest
decade since records began. As the temperature rises, so does the sea
level – with profound consequences for us all./
------------------------------------------------------------------------
Printer-friendly version of complete topic
<http://www.science.org.au/nova/082/082print.htm>
In its 2001 assessment of global warming, the Intergovernmental Panel on
Climate Change (IPCC)
<http://www.science.org.au/nova/082/082glo.htm#ipcc> projected that
global mean sea level is expected to rise between 9 and 88 centimetres
by 2100, with a 'best estimate' of 50 centimetres.
*Higher temperatures lead to higher sea levels*
A warmer world will have a higher sea level because as the land and
lower atmosphere of the world warm, heat is transferred into the oceans.
When materials are heated they expand (thermal expansion). So the heat
that is transferred causes sea water to expand, which then results in a
rise in sea level.
In addition, water from land-based ice such as glaciers and ice sheets
<http://www.science.org.au/nova/082/082glo.htm#ice%20sheet> may enter
the ocean, thus adding to the rise. A point to remember is that no extra
water is added to the oceans when ice floating in the ocean melts. As
floating ice melts, it only replaces the volume of water that it
originally displaced.
*Melting or expansion?*
Which contributes the most to sea-level rise – melting ice or the
thermal expansion of water? The answer depends on the time-scale you're
interested in. Warmer temperatures could lead to the following scenarios:
* /*Non-polar glaciers*/
If non-polar glaciers such as those in New Zealand and Norway
melted, they would release water that may enter the ocean and
contribute to a sea-level rise. Glaciers are rather sensitive to
climate change and they could melt rapidly.
* /*Greenland ice sheet*/
In Greenland, ice increase from snowfall is balanced by ice loss
from melting and the discharge of glaciers. Projections indicate
that increased melting from higher temperatures would exceed any
increases in precipitation. This change in the ice balance would
add water to the ocean.
* /*Antarctic ice sheet*/
Nearly all of Antarctica is covered by an ice sheet that is, on
average, 2.5 kilometres thick. If all the land-ice covering
Antarctica were to melt – that's around 30 million cubic
kilometres of ice – the seas would rise by over 60 metres!
However, in the Antarctic it is so cold that even with increases
of a few degrees, temperatures would remain below the melting
point of ice. In fact, warmer temperatures could lead to more
snow, which would increase the amount of ice in Antarctica.
* /*Thermal expansion*/
While thermal expansion is a less obvious process than melting ice
(mainly because you can't see it happening) the IPCC projects that
thermal expansion will be the main component of expected sea-level
rises over the 21st century.
*Uncertainty in estimates*
It is difficult for scientists to be more precise with sea-level
projections because there are a number of uncertainties:
* /*Greenhouse gas concentrations*/
While scientists agree that the levels of greenhouse gases
<http://www.science.org.au/nova/082/082glo.htm#greenhouse%20gas>
are rising, future increases depend on many factors, including
population growth, energy use and the development of new
technologies.
* /*Climate sensitivity */
Climate sensitivity is the amount of atmospheric warming that
results from a doubling of atmospheric carbon dioxide
concentrations. It depends on the presence of greenhouse gases,
and on feedback
<http://www.science.org.au/nova/082/082glo.htm#feedback> processes
from clouds, water vapour and ice. This is a significant source of
uncertainty in projections of long-term climate change.
* /*Ocean heat exchange*/
Heat moves between the atmosphere and the ocean's surface. The
temperature at the surface at any one time is influenced by what
is going on in the ocean. Quite small changes in the transport of
heat or salt can have large effects on surface temperature, and
ultimately on climate. Ocean models have developed rapidly over
the last two decades but accurately representing the most
important ocean features remains a challenge.
* /*Ice*/
There is uncertainty about the response of the ice sheets in
Greenland and Antarctica to hundreds of years of warmer
temperatures. Scientists are concerned that there could be a rapid
disintegration of the West Antarctic ice sheet, causing a rapid
rise in sea level.
As well as these global uncertainties, the rate and magnitude of
sea-level change will vary from place to place in response to changes in
ocean currents and vertical movements of the land itself. In some areas,
sea level may actually fall.
*What is the impact of 50 centimetres?*
On average, it is expected that by 2100 sea levels will have risen in
most places by around half a metre. Reduced to a raw number like this it
doesn't sound like too much. What impact does 50 centimetres have on
anything? Maybe you'll just have to build your sandcastles a little
higher up the beach.
The reality promises to be a little grimmer. In many places, 50
centimetres would see entire beaches being washed away, together with a
significant chunk of the coastline. For people living on low-lying
islands such as Tuvalu, Kiribati or the Maldives, where the highest
point is only 2-3 metres above current sea levels, an extra 50
centimetres could see significant portions of their islands being washed
away by erosion or covered by water. Even if they remain above the sea,
many island nations will have their supplies of drinking water reduced
because sea water will invade their freshwater aquifers
<http://www.science.org.au/nova/082/082glo.htm#aquifer>.
While these islands have sizeable populations, they're insignificant
compared to the tens of millions of people living in the low-level
coastal areas of southern Asia. These include the coastlines of
Pakistan, India, Sri Lanka, Bangladesh and Burma.
*Australian coasts*
Each centimetre of sea-level rise will lead to increasing impacts on
low-lying coastal land. Modelling predicts the inundation would cause
sandy beaches on the Australian coastline to recede by the order of 100
times the vertical sea-level rise. For example, if the sea level rises
by a metre, the coastal beaches could retreat by about 100 metres unless
some preventative action is taken. Given that about 85 per cent of
Australia's population lives within an hour's drive of the coast, this
is particularly relevant.
Floods already cause more damage in Australia than any other natural
disaster, in terms of cost to the community. CSIRO researchers believe
that damage costs associated with coastal flooding would more than
double in southern Queensland and northern New South Wales if sea levels
were to rise by 40 centimetres.
Low-lying coastal ecosystems, such as the freshwater wetlands that make
up about 90 per cent of the coastal zone of Kakadu in the Northern
Territory, are also vulnerable. Hundreds of species of birds, reptiles
and amphibians depend on these freshwater areas. Intrusion of salt water
is already a major management issue in Kakadu. If sea levels around
Australia rise by about 50 centimetres, these freshwater wetlands will
become saltier. A 1-metre rise in sea level would transform lowland
Kakadu almost totally into mangrove forest.
Future planning should take global warming and consequent sea-level
rises into consideration. For example, building protective sea walls and
restricting coastal development in areas at risk are planning measures
that could minimise damage from rising sea levels over the next century.
*A changing world*
Even if greenhouse gas emissions could be stabilised by the end of the
21st century, sea-level rise from ocean thermal expansion may only have
reached half its eventual level by the year 2500. To minimise the
impacts of climate change, we need to start changing our habits as soon
as possible – Australia is one of the largest per capita greenhouse gas
emitters in the world. The longer we delay, the less effective our
actions will be.
------------------------------------------------------------------------
External sites are not endorsed by the Australian Academy of Science.
------------------------------------------------------------------------
Posted March 2004.