Editorial: Falling land data should be a tipping point for action

New projections show the largest sea level increases  would happen around the southeast North Island, along the Wairarapa coast. Photo / Gordon Wyeth, File

OPINION

The true realisation of what global warming will do to New Zealand should be sinking in.

Subsiding land and rising oceans could push sea levels in  our two biggest cities and many other parts of the country to double that generally projected – much sooner than we earlier thought.

The NZ Searise programme has factored the role of undulating land movements into calculations for rising sea levels and, as a result, the projections change dramatically for places such as Wellington, Auckland, Napier, and Marlborough/Nelson.

As anyone who has lived in New Zealand long enough to feel a decent earthquake knows, this island country moves, sometimes in large shifts. The Searise scientists calculated the longer impacts of smaller and larger seismic events and found subsidence in many parts of New Zealand could double the effect of a rising sea level.

Co-leader of the programme, Professor Tim Naish from Victoria University, says rises in sea level mean some parts of New Zealand could be inundated by twice the global average. He says international climate commitments anticipate global oceans to climb by about 60cm before this century's end. "However, for large parts of Aotearoa, this will double to about 1.2m due to ongoing land subsidence."

The data has been built into a website, showing location-specific sea level rise predictions to the year 2300, for every 2km of the New Zealand coast. Shortly after going live, the website was shut down, allegedly by cyber attack, although massive interest from New Zealanders was also understandable.

Most local territorial authorities contacted by RNZ about the data had either already viewed it, or were interested in seeing it. Many expressed concerns about the costs to councils for mitigating against the worst of the impacts and revising plans.

The consensus has it that climate change and warming temperatures are causing sea level to rise, on average, by 3.5mm per year. This sea-level rise is caused by thermal expansion of the ocean, melting glaciers, and melting of the Greenland and Antarctic ice sheets.

In a rational world, the research would inform zoning decisions and steer development away from the more prone sites. However, under the Resource Management Act, councils cannot prevent people from building on private land. Insuring such sites will become increasingly prohibitive.

Naish says once-in-a-century floods could be occurring annually within 20 years. It is not only homes at risk, it's the infrastructure of water supplies, wastewater treatment, power and roads.

NZ Searise was set up with an $8m government grant in 2017 as a five-year programme to discern accurate estimates of the magnitude and rate of sea-level rise for our coastal regions to the century's end. Annual releases of projections from the programme have caused pockets of concern but these have often ebbed away as other priorities arose.

The inclusion of land movement projections has provided a whole new picture.

Could this be the point where the majority sit up and take notice of the sea change that is about to crash over us? It's to be hoped so.