Fresh from receiving a report on peak oil, which followed another earlier this year on climate change, the issues were clearly at the centre of Mr Cull's thinking as he put together his state-of-the-city address.
At the annual event, organised by the Lions Club of Dunedin Toroa and the Otago Chamber of Commerce, he also pointed to a more positive outlook for the residents of South Dunedin, who have been hit this year by reports of the area's vulnerability to sea level rise, and more recently, the possibility of liquefaction during earthquakes.
He said he believed the area must be maintained, as the city needed to remain "compact" in an era without cheap oil.
He pointed to the importance of the railway and port to the city, and the closeness of the harbourside industrial area, as accessibility might have an impact on plans to develop cafes and residences there.
Mr Cull was giving his first state-of-the-city address since winning the mayoralty in October.
Dunedin needed to be a liveable city that was accessible, both from outside and from within, he said.
While he did not like the word, it had to be "sustainable", or resilient and ready for whatever challenges arose.
It needed full employment, smart, contemporary businesses, and up-to-date building stock.
"We don't want to be the ghetto of the South," Mr Cull said.
One aspect of Dunedin was it was about as far away from the centres of economic and political power as it was possible to get.
"We've got an isolation issue, I guess."
And the Canterbury earthquake in September showed when there was a problem elsewhere in the country, it had an effect on Dunedin.
"Suddenly our supermarket shelves were empty."
Mr Cull said the challenges the city faced were: climate change, sea level rise, and a prediction in a report last week that by 2050 the city would have to cope with using just 50% of the petrol it was using now.
Climate change meant a drier east coast, with the possibility millions of dollars might need to be spent of water storage capacity.
With much of South Dunedin below the high tide mark, money might need to be spent there on facilities such as a sump that could collect water to be pumped away, or windmills to do a similar job.
"I don't think we can afford to say we can retreat somewhere else.
"In the long run, it's pretty important for us to maintain South Dunedin."
With the prediction for 2050, the city would need to remain "compact", and retain its railway and port.
"Having those next to an industrial area [at the harbourside] is a huge advantage."
Such infrastructure helped make up the "skeleton" of a pre-cheap-oil era city that it could return to in future.
The "mass of buildings" in the Crawford and Cumberland St areas could also come into play, being turned into residential buildings in future when oil became more expensive.
Mr Cull also noted the possibility of Dunedin becoming an oil support base, if oil drilling began offshore.
"The exquisite irony is we may be becoming the major oil support base for the South Island."
All those issues, Mr Cull said, the city should deal with "proactively", rather than waiting for their effects.
It was likely food production, more and more, would be occurring closer to where it was consumed, and the Taieri region was important in that regard.
Trolley buses had been suggested in the report on peak oil, and the Hillside workshops were a good place to build them.
"Dunedin has the potential for an enormously bright future."
