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article imageGRACE satellites, paleo data predict sea level rise of 5 metres

By Paul Wallis     Nov 22, 2009 in Environment
A new finding that the eastern Antarctic ice sheet is losing a lot more ice than previously thought has re-ignited debate over projections for sea level rises. The ice sheet, if it disappeared, could add 5 metres to sea levels.
The eastern Antarctic was thought to be comparatively stable, but since 2006 has been losing coastal mass at roughly half the rate of the western ice sheet, which lost ice at a rate of 132 billion tons per year.
It’s not clear exactly how the winter re-freeze affects the aggregate loss of ice. The science has also been rather vague about the margin for error, which is cited as a few billion tons or up to 100 billion tons. Nor is there a publicly stated time frame for this melt scenario.
The significance of this information is that it comes from the GRACE satellites, gravity measuring satellites. Mass movements affect gravity, which they can measure to quantify ice loss.
This study by professor Jianli Chen of the University of Texas also found that in a previous inter-glacial period called the Eemian, global temperatures were 6C higher than today, with CO2 levels roughly the same. The Eemian temperature was also 3C above previous estimates.
The glacial/interglacial periods are regular events, occurring every 100,000 years in recent history. The inference from studies is that the current period is the beginning of the end of an interglacial period.
The problem is that at the end of the Eemian, sea levels were 5 metres higher than they are now.
In Australia, an example where settlement is mainly coastal, local councils and state planners are currently looking at scenarios for sea level change and coastal erosion. This is a very big issue, because the capital value of Australia’s coastal cities and settlement is in the trillions of dollars. Although some parts of the coast are well protected by high cliffs, low-lying areas include Sydney, Brisbane, and Melbourne.
Melbourne and Sydney have been looking at London-style barriers, which are feasible if expensive mainly because of the restricted access to the sea through Port Phillip Heads and the Sydney Harbor entrance, which is basically a channel surrounded by massive cliffs.
Elsewhere on the Australian coast, severe erosion is occurring in some areas during king tides, and the effect looks like a California mudslide. Sandy soils are under cut and these areas collapse. Some New South Wales and Queensland residential areas are already experiencing notable coastal cutting.
Island nations on Pacific atolls are already experiencing record tides. Many have been asking for assistance, and relocation talks and programs have been under way for some years.
The net effect of a 5 metre rise in sea levels would alter the entire configuration of coastal settlement. Most big cities are about 1-2 metres above sea level. That includes a lot of infrastructure, and huge populations.
Backwash and ocean encroachment on river deltas will also affect those systems, where submerged water tables are likely to be significant issues, changing drainage patterns affecting cities and agriculture.
The information about historic sea level rises changes the paradigm for global warming. This data suggests it was always going to be a “when”, rather than an “if”.
All scenarios for sea level rises anticipate major costs in remedial work and relocation. “When” is now the issue.
More about Antarctic, Interglacial periods, Sea level rise
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