Bondi beach will shrink to a thin ribbon of sand and extreme storm surges would reach the top of its concrete sea wall, research commissioned by the local council shows.
The latest report from the Intergovernmental Panel on Climate Change, released on Friday, found the sea level would rise and could be expected to be up to 80 centimetres higher by the end of the century.
As scientists warned of dire global consequences from climate change at the report's release in Stockholm, residents in Sydney are grappling with the practical implications.
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In the case of an 80-centimetre rise in sea levels, high tides would regularly flood parts of many Sydney suburbs that are close to water, including sections of Annandale, Mosman, Marrickville, Brighton-le-Sands, Sylvania Waters, Five Dock and Narrabeen.
In Bondi, critics say local authorities are ignoring rising sea levels that threaten millions of dollars' worth of planned waterfront works - a claim strongly contested by the council.
The beach, which pulls 1.8 million visitors a year, is poised for its biggest overhaul in decades after the council proposed an underground car park, beachfront parks and a new waterfront promenade. It follows the unveiling last week of the $7 million North Bondi surf lifesaving clubhouse.
Waterfront works planned: Bondi beach. Photo: Janie Barrett
But NSW Greens MP David Shoebridge said the plans ignored the council's own research, which shows Bondi beach is set to recede dramatically - by about 20 metres in 2050 and 45 metres in 2100. The research is contained in a 2011 report, commissioned by the council, by consultancy WorleyParsons.
Council figures show the north and south ends of the beach presently measure about 60 metres, widening to 120 metres at the centre.
They also show the ocean would surge over the sea wall during a one in 100-year storm event, swamping waterfront parks and coming within metres of the proposed car park entrance.
''This kind of wilful blindness on planning for climate change is simply unacceptable … and the public [is] not being told the truth,'' Mr Shoebridge said.
He said the sea wall should be moved back to allow the beach to retreat.
A draft 10-year plan for Bondi concedes the shrinking sand ''will decrease the overall amenity'' of the beach and erosion may undermine the sea walls and risk their stability during storms.
Rob Brander, a senior lecturer at the University of NSW specialising in coastal geomorphology, said Sydney's coastal regions faced significant impacts from rising sea levels.
''If a beach shifts landward, it hasn't got many places to go,'' Dr Brander said. ''Beaches will get narrower and low-lying coastal properties will face damage.''
Major storms in 1974 are an indication of what the future will look like.
''It's not the sea-level rise that's going to damage all the properties,'' he said. ''It's those storms superimposed on the higher sea levels that's really going to do the damage.''
But Waverley's Liberal mayor, Sally Betts, said the risk to Waverley's coastline remained ''low''.
''The sea wall currently protects the promenade and park from any wave impact or flooding and is expected to continue to do so in the future,'' she said.
The 2011 WorleyParsons report was ''widely circulated'' and the council had plans to adapt buildings and landscapes to future climate conditions and reinforce infrastructure where necessary, Cr Betts said.
''Waverley Council … has always taken climate change extremely seriously and will monitor any reductions in beach width and take action accordingly,'' she said.
Sydney Coastal Councils Group chief executive Geoff Withycombe said Bondi was far less vulnerable to sea-level rise than other parts of Sydney, such as the northern beaches or low-lying areas around Botany Bay. The impacts of sea-level rise on groundwater and stormwater infrastructure was a far more pressing concern for councils, he said.
But Mr Withycombe said that a state government decision last year to scrap specific statewide sea-level rise projections for use by councils had created uncertainty around local planning and public works decisions.
A member of the Wentworth Group of Concerned Scientists, Bruce Thom, said Bondi was ''very resilient'' because its sand remained inside the bay during storms and was not lost to the sea.
Potential measures such as ''nourishment'', which replaces sand that has been washed away, meant forecasts about the loss of sand were ''hypothetical'', he said.
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