Dave Cull calls it a slow-moving disaster.

That might be a tired cliche to describe climate change - a quick Google search will find you more than 300,000 similar references - but Cull can use it with a great degree of candour.

The Dunedin mayor is already reckoning with the monster.

South Dunedin - home to about 10,000 residents, 12 schools, six rest homes and an aged wastewater and stormwater system - sits across a spread of low-lying flats between Otago Harbour and the Pacific Ocean.

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Even just 20cm to 40cm of sea-level rise will mean the suburb's water table will rise, exposing it to flooding after heavy rain that could damage roads, pipes, cables, buildings and parks.

"If you take a situation where there is possible retreat or coastal erosion, and it's affecting privately owned properties - in the case of South Dunedin it's rather a lot of them - then it's not imminent, but it's still kind of like a slow-moving earthquake."

Other hot spots include Haumoana in Hawke's Bay, where 2m of coastline was recently washed away in a week, and Matata in Bay of Plenty, which may have set one of the country's first climate-related precedents after the council removed the land rights of 34 at-risk seaside homes.

But if the sea level rose according to official projections, those localised issues would become a drop in the rising ocean.

Two-thirds of us already live in areas prone to flooding.

As more people and infrastructure concentrate in our largest cities, the risk would only grow.

The most recent national assessment found nearly 170,000 buildings sat within 3m of the mean high water spring, exposing them not just to sea level rise, but also storm-tide and wave flooding that could reach 1-2m in exposed places.

If all of those buildings were lost, they would cost $52 billion to replace.

About 68,000 buildings are below the 1m mark, carrying a replacement value of about $19b.

The report didn't include other assets or infrastructure on the damage bill, other than identifying the kilometres of road and rail exposed, and the number of airports.

Auckland, with about 1360 homes, 60 businesses and 56km of roads within 150cm of spring high tide, appeared better off than other places.

Flooding on Auckland's Tamaki Drive. Auckland has around 1,360 homes, 60 businesses and 56km of roads within 150cm of spring high tide. Photo / File
Flooding on Auckland's Tamaki Drive. Auckland has around 1,360 homes, 60 businesses and 56km of roads within 150cm of spring high tide. Photo / File

But tides and storm surges pose a big threat to our largest city.

If sea level rose by another 30cm in Auckland, the once-in-a-century January 2011 storm that put much of the Northwestern Motorway underwater would happen once every four years, and 40cm would make it a two-year occurrence. A 70cm rise would make it a monthly event.

"Who takes responsibility for compensation, how do you retreat property, who has the liability - none of that is clear," said Cull, speaking to the Herald as president of councils lobby group Local Government New Zealand (LGNZ).

What policy-makers urgently needed now was better science.

Narrowing it down

Our best reference is the Fifth Assessment Report, a sprawling synthesis of thousands of peer-reviewed studies published by the UN's Intergovernmental Panel on Climate Change (IPCC).

That told us the rise in sea level was fairly certain to be in the narrow range of 20cm to 30cm by 2050.

More than two metres of coastline was washed away at Haumoana in Hawkes Bay this year. Photo / File
More than two metres of coastline was washed away at Haumoana in Hawkes Bay this year. Photo / File

But by the end of the century, the uncertainty range of the expected rise would likely widen to between 50cm and 1m, depending on how global emissions track.

On a local scale, scientists still had huge knowledge gaps to fill.

Over the next five years, experts working under the NZ SeaRise Programme will try to create accurate estimates of the magnitude and rate of sea level rise for our coastal regions to the end of the century and beyond.

The study, which just received an $8 million MBie grant, would take into account the unique factors of vertical land movements related to ongoing natural ground subsidence.

In the lower North Island, subsidence alone might add an extra 20cm to 30cm of sea level rise on top of the IPCC estimates by the close of the century.

here was also the other elephant in the room - the melting of ice sheets in Antarctica and Greenland.

Flooding at Matata in 2005. More than a decade later some residents are being forced to vacate one at-risk area in the Bay of Plenty township. Photo / File
Flooding at Matata in 2005. More than a decade later some residents are being forced to vacate one at-risk area in the Bay of Plenty township. Photo / File

A lack of knowledge around the potentially unpredictable response of Antarctica's ice sheets to projected warming was driving urgent efforts to factor dramatic processes like ice-shelf disintegration and ice-cliff collapse into simulations.

With these, the models estimated an extra Antarctic ice sheet contribution of between 40cm and 80cm by 2100 for a worst-case scenario of no global effort to cut emissions.

In a recent report, using the new Antarctic ice melt estimates, the National Ocean and Atmosphere Administration estimated a plausible worse-case scenario of 2.5m sea-level rise along the US eastern seaboard, affecting major cities like Boston and New York.

Police deal with surface flooding along Tamaki Drive during a storm on January 21, 2011. Photo / File
Police deal with surface flooding along Tamaki Drive during a storm on January 21, 2011. Photo / File

The NZ Sea Rise research team would use the new projections to work out impacts here, which varied from storm surge to the incursion of salt water into our coastal aquifers and cherished estuaries and wetlands.

Detailed, high-resolution maps would be created for our largest sea-side cities, making vulnerability models much more accurate.

"One of the key things for New Zealand is, sea-level rise will be different depending on where you are," said Professor Tim Naish, a Victoria University glaciologist heading the work alongside leading scientists including Niwa's Dr Rob Bell and GNS Science's Dr Richard Levy.

"And the other thing to know, of course, is what's going to happen to the ice sheets - that science is changing a lot at the moment, and it's looking like the contribution from the Antarctica Ice Sheet has been under-estimated."

The latest research by Naish's colleagues even warned of a potential 40cm on top of the 1m of global sea-level rise predicted by the IPCC for its high emissions pathway by 2100.

Naish said that applied to the extreme upper end of the IPCC's projected climate models, which Bell recently used to draft worst-case scenario guidelines for planners in the new Ministry for the Environment coastal hazards guidance, which was leaked by the Greens before the election.

Scientists are urgently trying to quantify how much equivalent sea level rise melting ice sheets in Antarctica will contribute. Photo / File
Scientists are urgently trying to quantify how much equivalent sea level rise melting ice sheets in Antarctica will contribute. Photo / File

"If Antarctic ice melt has been underestimated for the next 100 years, and we do not achieve the Paris climate agreement emission reductions, then that changes the whole game, and we will have to start planning for a scenario that takes into account the revised estimates."

But it wasn't all bad news.

"These same models suggest that if the world is successful in limiting global warming to the Paris target of 2C above pre-industrial levels then we have a chance of preventing widespread Antarctic melt-down."

Some parts of the country would get better forecasts than others.

Glaciologist Professor Tim Naish. Photo / Supplied
Glaciologist Professor Tim Naish. Photo / Supplied

"For example, the major cities have Lidar data - that's very accurate land surface elevation information - whereas in some other parts of the coastline, we have to rely on topographic maps made with aerial photographs.

"But where most of the population is, and where the serious impacts and consequences will be, such as our coastal cities and infrastructures - we should be able to provide some really high-resolution visualised maps of inundation and associated impacts."

Councils under pressure

Climate change opened up a world of new problems for councils - and they weren't just worried about getting the hard facts.

Other headaches included rising water tables affecting property foundations, and public infrastructure wearing damage from storm surges, flooding and erosion.

More than 50 mayors and chairpeople signed a declaration singling out climate change as a serious issue facing communities.

LGNZ has tasked researchers with making a stocktake on assets in the firing line, working out how water services in low-lying areas might be affected, suggesting ways for councils to talk to their communities, and recommending better planning options.

Local Government New Zealand president and Dunedin Mayor Dave Cull wants more direction around climate change issues from central government. Photo / File
Local Government New Zealand president and Dunedin Mayor Dave Cull wants more direction around climate change issues from central government. Photo / File

That was a crucial element - 70 per cent of infrastructure in the world's cities wasn't yet built.

Cull said councils were further worried about a lack of direction from government, not enough funding to adapt to climate change, and the absence of any national campaign that encouraged fewer emissions.

"Much of the necessary on-the-ground climate change work will need to happen locally, but central government action is also critical."

The incoming Government could help by introducing a new climate-focused mandate in the Local Government Act - and a clear statement on responsibilities for adaptation actions that included fiscal responsibility and legal liability.

Salt water flooded into the grounds of the Waitemata Golf Club during a huge storm on January 21, 2011. Photo / File
Salt water flooded into the grounds of the Waitemata Golf Club during a huge storm on January 21, 2011. Photo / File

Was the pressure on councils already mounting?

"It's probably just starting, in terms of coming from our ratepayers and communities, but there is certainly a rapidly rising awareness, when you look at some of the comments from insurance companies.

"And certainly, whenever councils issue new hazard maps, or put anything on people's LIM reports especially, there is a reaction, because people are naturally very anxious about the value of their property and whether they can insure it."

Can we insure for climate change?

This year, New Zealand's industry sustained more than $230m in insured losses from extreme weather events, a figure well within its bounds to absorb.

While that appeared small compared with the more than $20b and $2b respectively paid out in the wake of the Canterbury and Kaikoura earthquakes, it was regularity that counted more.

"Extreme climate events are much smaller - but they are also far more frequent," Insurance Council of New Zealand (ICNZ) chief executive Tim Grafton said.

How the industry responded could vary but Grafton expected an "incremental and gradual transition" to meet issues around vulnerable properties.

The first might be to either increase excesses or premiums, or both.

Further down the track, companies might put exclusions in place, or withdraw coverage for some properties altogether.

"Having said that, a lot of coastal properties at the moment are not immediately at risk, but there are pockets of New Zealand where a combination of sea level rise and storm surges at high tide are affecting them even now."

More extreme weather events could lead to an increased pool of customers buying more insurance, which would in turn deepen the pool of insurance that was available.

But it could also make insurers more selective about the types of risks they took on if they had greater knowledge, Grafton said.

"Extreme climate events are much smaller - but they are also far more frequent," says Insurance Council of New Zealand chief executive Tim Grafton. Photo / File

Last year, the ICNZ released a report that included 15 recommendations to address risks from natural hazards - and, like LGNZ, it demanded more information, more funding and a nationally co-ordinated strategy.

The group has also been closely involved with the Deep South National Science Challenge, a collaborative effort that has launched a wave of new insurance-focused research projects.

Catherine Iorns, of Victoria University's Faculty of Law, will investigate the tipping-points at which insurance companies might decide to refuse insurance to coastal property owners - and what happened after.

Iorns also hoped to determine to what extent homeowners could or should rely on the Earthquake Commission (EQC), or on local or central government, to compensate them if their homes become uninsurable or uninhabitable because of climate change.

Another Victoria University researcher, economics PhD student Belinda Storey, would separately look at "insurance retreat", or where insurance became unavailable.

Escalating coastal hazards did not seem to be reflected in home-owners' decisions to buy and renovate coastal property, and further, climate risk was likely not incorporated into the price of residential coastal property.

Evidence from overseas suggested that high insurance premiums and the unavailability of insurance had a stronger impact on private decision-making than even the uncertain risk of extreme events.

Wellington's waterfront. The lower North Island has been subsiding at a rate of about 4mm per year. Photo / File
Wellington's waterfront. The lower North Island has been subsiding at a rate of about 4mm per year. Photo / File

Storey's project therefore explored how coastal housing markets might be hit, and would pinpoint those places around the country likely to lose access to insurance within the next few decades.

A third programme, run by Otago University's Associate Professor Elisabeth Ellis, would ask which players the risks around sea level rise should fall upon, and what option was the fairest. A fourth, led by Motu Economic and Public Policy Research Trust, looked specifically at the EQC's role.

Although that agency mainly helped households suffering earthquake damage, homeowners affected by extreme weather like storms, floods or landslips could also make EQC claims for some damages.

More frequent and more intense weather might therefore affect the EQC's long-term sustainability.

Over the past 20 years, the EQC had paid out more than $240m on more than 17,000 claims, to households affected by non-earthquake disasters.

Flooding in Edgecumbe in April. Our insurance industry has sustained more than $230m in insured losses from extreme weather events this year. Photo / File
Flooding in Edgecumbe in April. Our insurance industry has sustained more than $230m in insured losses from extreme weather events this year. Photo / File

Motu's Dr David Fleming would study these claims and compare them with government data to better understand how the EQC had covered households over time and across regions after extreme weather events - and what the future held.

Naish said the urgent demand for better information made it a "huge responsibility" for experts, who were also faced with the complicating fact that the science was changing every month.

"But councils have to start dealing with this now - so we need our own authoritative science, that is rigorously done and peer-reviewed, and that will stand up in court. It gives planners confidence and it gives the public confidence."

New Zealand and climate change

• Under present projections, the sea level around New Zealand is expected to rise between 30cm and 100cm this century. Temperatures could also increase by several degrees by 2100.
• Climate change would bring more floods; worsen freshwater problems and put more pressure on rivers and lakes; acidify our oceans; put even more species at risk and bring problems from the rest of the world.
• Climate change is also expected to result in more large storms compounding the effects of sea-level rise.
• New Zealand, which reported a 23 per cent increase in greenhouse gas emissions between 1990 and 2014, has pledged to slash its greenhouse gas emissions by 30 per cent from 2005 levels and 11 per cent from 1990 levels by 2030.