Homestead mailing list

[Tvoivozhd <tvoivozd AT infionline.net>]

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
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 Getting into hot water – global warming and rising sea levels

        Published by

<http://www.science.org.au/aashome.htm>
Australian Academy
of Science

                Sponsored by

Commonwealth Bank Foundation <http://www.commbank.com.au/foundation/>

This topic is sponsored by the Australian Greenhouse Office 
<http://www.greenhouse.gov.au/>.

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/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./
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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.

*Related site: Climate change and Australia's coastal communities 
<http://www.dar.csiro.au/publications/CoastalBroch2002.pdf>*
An overview of the impacts of sea-level rise and more extreme weather. 
(PDF file)
(CSIRO, Australia)

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.

*Related site: Sea level rise projections and planning in Australia 
<http://www.coastal.crc.org.au/coast2coast2002/proceedings/Theme3/Sea-level-rise-projections.pdf>*
Looks at different local planning options to cope with projected rises 
in sea level. (PDF file)
(Coast to Coast 2002, Australia's National Coastal Conference)

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.

*Related /Nova/ topic:*

Enhanced greenhouse effect – a hot international topic 
<http://www.science.org.au/nova/016/016key.htm>

CREDITS <http://www.science.org.au/nova/082/082cred.htm>

Printer-friendly version of complete topic 
<http://www.science.org.au/nova/082/082print.htm>

        KEY TEXT <http://www.science.org.au/nova/082/082key.htm>
GLOSSARY <http://www.science.org.au/nova/082/082glo.htm>
ACTIVITIES <http://www.science.org.au/nova/082/082act.htm>
FURTHER READING <http://www.science.org.au/nova/082/082fur.htm>
USEFUL SITES <http://www.science.org.au/nova/082/082sit.htm>


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