“You have a long coastline and part of the coast is very mildly sloping” and is therefore susceptible to erosion, said Michalis Vousdoukas, a coastal oceanographer at the European Commission and the paper’s lead author.
“Melbourne is worse than Sydney,” Dr Vousdoukas told the Herald and The Age, adding Brisbane and Adelaide’s beaches fell between the two in terms of vulnerability to erosion.
The researchers said global sea levels had been increasing “at an accelerated rate during the past 25 years and will continue to do so with climate change”.
So far, most of the increase had come from the thermal expansion of warmer water but, by mid-century or so, the increase in sea levels would likely come more from melting ice sheets, Dr Vousdoukas said.
Following the lower emissions pathway would prevent about 22 per cent of the projected coastal retreat by 2050 and 40 per cent of it by 2100. “This corresponds to a global average of around 42 metres of preserved sandy beach width by the end of the century,” the paper said.
Some nations would be harder hit on a relative basis than Australia, with Suriname, Pakistan, El Salvador and Guinea-Bissau among those countries facing the loss of more than 80 per cent of their sandy coasts.
Carribean states, for instance, could see beach retreats of more than 300 metres, with “substantial implications” for economies dependent on tourism, the paper found.
Kathleen McInnes, head of CSIRO’s coastal extremes group, said the paper was “useful at a macro level”, and noted its own limitations such as an exclusion of “backshore” infrastructure such as sea walls that would limit beach retreat in built-up areas.
The paper’s assessment, though, that the impacts of big storms would tend to be a “second-order effect” compared with the background effect of remorselessly rising sea levels “was a very plausible finding” and in line with CSIRO’s own research, Dr McInnes said.
Still, major storms – which climate scientists predict will become more intense as the atmosphere warms – can be important.
“Storm erosion is typically followed by beach recovery but some events may leave a footprint that takes decades to recover [from], if at all, while the additional shoreline retreat renders the backshore more vulnerable to episodic coastal flooding and its consequences,” the paper said.
Peter Hannam writes on environment issues for The Sydney Morning Herald and The Age.