New state government sea level rise guidelines will make it easier for people to fortify their homes against the effects of climate change, but local councils said the policy would lead to ''ad hoc'' walls of sandbags that will not hold back the sea.
The policy, unveiled last weekend by the Special Minister of State, Chris Hartcher, overturns the previous strategy of ''managed retreat'' that sought to limit new developments in low-lying coastal areas.
Large areas of Sydney are expected to face more frequent inundation as sea levels creep up. They include Collaroy, Caringbah, Kurnell and Manly Vale, as well as low-lying parts of inland suburbs such as Marrickville, federal government maps show.
But Mr Hartcher said the rate of sea level rise predicted by the United Nations' Intergovernmental Panel on Climate Change - an average of up to 90 centimetres along the NSW coast by the end of the century - contained too much uncertainty for the government to give general advice to local governments.
''The new policy recognises that there are a range of IPCC sea level rise projections,'' he said. ''Because of this uncertainty, the government does not consider it appropriate to recommend specific statewide sea level rise projections or benchmarks for use by councils.''
Instead, there will be recommendations on a case-by-case basis, and more relaxed rules on fortifying the coastline with sea walls. The change ''will allow landowners to more readily place large sandbags as temporary coastal protection works to reduce erosion impacts from minor storm events'', he said.
The Sydney Coastal Councils Group, representing 15 councils, said the new policy added to confusion about how to adapt to climate change. ''The last thing we need is individual councils having different management policies up and down the coast,'' the group's chief executive, Geoff Withycombe, said.
''If you build a sea wall somewhere, then all you're doing is redirecting the sea's energy somewhere else.'' Mr Withycombe said councils wanted ''clear direction'' from the government in order to make planning and public works decisions.
''The press release is rather confusing, and we are unsure what it's supposed to mean. There's been no consultation that I'm aware of in relation to this,'' he said.
A coastal management consultant and a former chairman of Engineers Australia, Doug Lord, said building local sea walls of the type preferred by the state government would be ineffective.
''What they are doing is allowing people to think they are doing something useful to protect their property, but it won't have any impact at all,'' he said. ''That type of sandbag protection doesn't work.''
The policy will ease restrictions on local sea wall construction with one-tonne bags of sand.
''These works are currently permitted under the Coastal Protection Act and the reforms will relax some of the requirements relating to placing these works,'' Mr Hartcher said.
''Councils are encouraged to only consider planned or managed retreat as a last-resort option.'' He cited a review of sea level rise science, conducted by the NSW chief scientist and engineer, Mary O'Kane, to support the argument that there was too much uncertainty around the IPCC's predictions.
Professor O'Kane's report found that existing forecasts on sea level rises were appropriate, given present levels of knowledge, and that more specific predictions could be made in future as more research was published.
''I probably shouldn't comment on whether the policy change is appropriate, but I will say that the science is evolving and the models have become more sophisticated,'' Professor O'Kane said.
''It's harder than ever to set a single benchmark across the whole of the NSW coastline,'' she said.