SEAN RUSH: New Zealand is planning for a climate future scientists now reject

New Zealand is planning for a climate future scientists now reject

And fixing it will require more than a policy tweak

New Zealand’s coastal climate change planning system is built on a simple legal standard: councils must plan for the likely effects of climate change, using the best available evidence.

But across the country, planning is being anchored to a future that scientists now say is implausible—and, legally, should never have been treated as “likely” in the first place.

Earlier this year, the international team responsible for the climate scenarios used by the Intergovernmental Panel on Climate Change (IPCC) concluded that the high‑emissions pathway SSP5‑8.5 has become implausible for the 21st century. That matters because this scenario has become deeply embedded in New Zealand’s planning system.  It sits behind national guidance.  It underpins the Ministry for the Environment’s coastal hazards framework.  It is reflected in the sea level projections used by councils nationwide using the 'SeaRise' online tool.  And it remains embedded in scientific studies relied on in the National Climate Change Risk Assessment—released only weeks ago.  It also likely at the root of extreme forecasts that have become part of the popular discourse,

The problem is not just scientific. It is legal.

“Likely” does not mean “worst case”

Under the New Zealand Coastal Policy Statement, councils must take account of the likely effects of climate change. The Climate Change Response Act uses the same test.

This is a mandatory legal standard. And it excludes outcomes that are merely possible—still less those now considered implausible.

Yet current guidance encourages planners to consider high‑end scenarios such as SSP5‑8.5. This risks introducing what administrative law calls an irrelevant consideration—a factor that distracts from the statutory test decision‑makers are required to apply.

There is a place for extreme scenarios. They are useful for stress‑testing infrastructure and exploring tail risks. But that is very different from using them as the basis for regulatory decisions.  In fact, only by artificially inflating the warming effects from this implausible climate scenario, are scientists and planners able to detect the climate signal from natural variability.  Let that sink in – only by manufacturing global warming are scientists able to tell the human caused effect from nature.  Climate sceptics have been banging this drum for decades.  Pat Michaels, the climate scientist for the state of Virginia for 27 years was heavily criticised for taking money from the fossil fuel industry (after being fired because he refused to toe the line). He self-described himself as a “lukewarmer.”  He accepted the radiative effects of greenhouse gases but could not support the activist narrative of catastrophe because in his view, the radiative effects were manageable.  It seems he was right.

A system built on the wrong assumption

There are real life consequences for continuing to believe in a scenario that IPCC lead author, and Canterbury University’s Professor Dave Frame, described as one “no one believes.”

In Kāpiti, modelling by consultants Jacobs Engineering—using high‑end assumptions based on SSP5‑8.5—identified thousands of homes as being at risk from coastal hazards. But when an independent review was undertaken by coastal scientist Dr Willem de Lange, using scenarios aligned with likely outcomes, the number of at‑risk homes fell to just 44.

That is not a technical quibble. It is the difference between targeted risk management and large‑scale planning intervention affecting entire communities.

Across New Zealand, similar approaches are being used by Councils to inform hazard mapping, LIM notations, and development restrictions. Tools like SeaRise continue to present projections derived from scenarios that no longer reflect what is considered plausible.

Unwinding that system will be difficult.

But leaving it in place is worse.

This will end up in court

Once planning decisions begin to impose large economic consequences, the legal position becomes unavoidable.

Developers, infrastructure providers and property owners will ask a straightforward question: how can an implausible scenario satisfy a statutory requirement to consider likely effects?

If there is no clear answer, judicial review will follow.

Courts will not decide climate science. But they will enforce the law. And the law requires decisions to be grounded in a rational evidential basis aligned with the statutory test.

The reset we now need

Fixing this will require more than a policy tweak.

It means re‑anchoring planning in plausible climate scenarios and revising national tools, such as SeaRise, and planning guidance.  New Zealand’s legal framework is already clear. Now the science is too. The only question is whether the planning system will catch up—or whether it will be forced to, in court.

Sean Rush is a former Wellington City Councillor and an expert reviewer for the Intergovernmental Panel on Climate Change. He holds a Master of Laws and a Master of Climate Change Science and Policy.