Wednesday, October 29, 2008

We won't lose our beaches as sea level rises!

Various media outlets and some otherwise scientifically sound climate change spokespersons claim that Perth's beaches will be lost forever if and when sea level rises and engulf them. The following letter to the editor of The West Australian wasn't published but it outlines what will actually happen.

"A major sea level rise of the Indian Ocean will not 'destroy' most of Perth's beaches (West, October 23, 2008, page 56). A rise in sea level along a sandy shoreline will move the shoreline inland in a ratio of about 1:100. For Scarborough and most other sandy beaches, a one metre rise will create a new beach some 100 metres inland. For some of the smaller 'pocket' beaches trapped within rocky coastlines such as around Trigg, these beaches will disappear completely unless large volumes of sand are washed northwards or artificial replenishment from inland occurs.

In the face of rising sea levels, we really only have two options: withdraw or defend. We can remove buildings and other structures so that a new beach is allowed to form inland of the old one. Alternatively, we can protect existing structures with massive engineered walls if the assets under threat are worth a lot more than the cost of their protection. Gold Coast sea defences cost up to $15,000 a linear metre or $15 million per kilometre. One consequence of seawalls is that they deflect wave energy seaward, causing the beach to be washed away. The resulting concrete structure with deep water immediately offshore is far less attractive than a natural sandy beach."

On a similar theme, The Sunday Times printed the following letter in reply to the statement that some Pacific island countries are threatened by sea level rise:

"Not all low lying countries like Tuvalu are threatened by sea level rise (Sunday Times, October 5). As a geologist, I know that many parts of the world are sinking as a result of tectonic movements deep in the earth. Many remote atolls are built on ancient volcanoes which are sinking, so it is inaccurate to state that sea level rise is the only or even the main threat to these countries.

Even so, the end result is the same and developed countries like Australia will have to address the question of what to do with the thousands and millions of people who will need to find a new home over coming decades."

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