Her rebuke came as councillors at last week's planning and regulatory committee meeting debated a report by consultant Beca, outlining the threat posed by sea level rise to Dunedin's harbourside and south city areas.
The report suggested measures including a network of pumps and wells would be needed over the next century to protect the area, which was home to 10,000 people and $4.3 billion worth of infrastructure and property assets.
Pumps would be needed first, perhaps by 2040, and could cost the city $10 million to install, while wells needed later, by 2090, could cost $65 million, initial estimates, which were subject to change, suggested.
Cr John Bezett said the eventual cost of defending South Dunedin had the potential to be ''an absolute disaster'' financially for the city, comparable to the Canterbury earthquakes.
He questioned whether councils should have to cover the cost, or whether they should be borne at a national level, by the likes of the Ministry for the Environment.
Council corporate policy team leader Maria Ioannou said that remained a ''grey'' area.
However, it was hoped an investigation into climate change adaptation, launched by the Parliamentary Commissioner for the Environment, could address the issue, she said.
Cr MacTavish said the government was showing ''a complete absence of leadership'' by leaving the issue to councils to address.
Protecting the city could be a costly exercise, particularly for a ''financially constrained'' council like the DCC, she said.
''We need to be putting pressure on central government to be better supporting its regions and its cities.
''It is an issue of national importance ... it's cross-party, it's cross-generation, and of significant economic importance and significant social importance for this country.''
The Beca report, prepared by Robert Crosbie, said the main threat to the harbourside and south city area from sea-level rise in the next 100 years would be from rising groundwater, forced up by the rising sea level.
Groundwater in the area generally sat about 40cm below the surface. Predictions were for the sea level to rise 30cm by 2040 and by 80cm to 1.6m by 2090.
Underground drains in lower-lying areas, pumping the collected groundwater into stormwater systems, could address a 30cm sea level rise.
When sea levels rose by 80cm, 70m-deep wells around the perimeter of the area could intercept incoming groundwater before it reached the aquifer and pushed the groundwater levels up, the report said.
Mr Crosbie, addressing councillors at last week's committee meeting, said the main message from what could be a ''highly emotive'' issue was that South Dunedin could be protected.
Exactly when each intervention would be needed would depend on symptoms showing themselves, such as more frequent flooding in the area, he said.
''There's time to deal with this issue.''
Dunedin would not be alone. Other parts of New Zealand, including eastern areas of Christchurch, were likely to experience similar problems, he predicted.
However, it was already too late to try to mitigate climate change and reduce the costs of adaptation to be faced in South Dunedin, he suggested.
''Slowing down sea level rise has got a huge amount of inertia,'' he said.
Councillors voted to continue the council's collaboration with the Otago Regional Council on the issue.
They also agreed to consider a programme of work, and necessary funding, needed for a more detailed investigation of the area during next year's long-term plan hearing.
Cr Neville Peat, who was among councillors who spoke in support of the work, said he was reassured the council was already planning for climate change and that South Dunedin could be defended.
