EXRACT: The New Zealand climate minister tells every council to stop planning around RCP8.5
“It is quite interesting that even these rather abstract scenarios have such consequences as well in daily decisions”
– RCP scenario architect upon learning that they harm real people in 2026
The retirement of implausible baseline climate scenarios is now starting to have real-world consequences as decision makers realize they’ve been making decisions that have had unnecessary real-world, negative impacts on their constituents and clients.
In a letter shared 1 July 2026 with local communities across New Zealand, the country’s Minister of Climate Change, Simon Watts, has asked public officials to reconsider using RCP8.5 and other retired scenarios in their planning decisions.
Councils, the letter states, have used these implausible emissions scenarios in a way that, “results in unnecessary costs being imposed on ratepayers, businesses, and communities.”
The letter also instructs councils that they “should not automatically” continue to treat these scenarios “as the central or most likely future when making decisions that affect infrastructure investment, land use, property rights, or rates.”
A first hand look at what the impact of RCP8.5 looks like in New Zealand can be seen in Managed Out, documentary on “managed retreat” from the coasts filmed before the minister’s letter.
On the Kapiti Coast, residents describe hazard notations stamped onto their property files that are based on a consultant’s report built on futures projected under RCP8.5. One local resident complained:
“They’re using RCP 8.5 which is the most extreme outcome. House prices are on the way down, insurance prices are sky-rocketing, because they have put notations on all of our LIM reports [Land Information Memorandum, which assesses hazards] which uses the extreme modelling.”
A former Wellington city councilor in the film argues that the problem lies in:
“the use of the IPCC 8.5 model that is supposed to be used only for stress-testing and not for policy-making.”
These residents are experiencing the unintended consequences of the use of a scenario that scientists built originally for exploratory earth system modeling to inform global climate negotiations turning up in the price of their homes.
Using RCP8.5 to predict coastal hazards in New Zealand — or anywhere else — and thus serve as the basis for home pricing and insurance is simply a misapplication of science (that may have had valid uses in research in other contexts).
How things went cattywampus
A baseline scenario — also called business as usual or a reference scenario — is according to the IPCC, a “scenario used as starting or reference point for a comparison between two or more scenarios.”
Climate policy analyses, including cost-benefit studies, typically start with a baseline scenario as a representation of where-we-are-headed and then compare that to other scenarios in which policy is introduced within the scenario. Such scenarios are typically called policy (or mitigation) scenarios.
Such a comparison, in principle, allows decision makers to evaluate the expected effects of implementing a policy versus not implementing that policy.
Based on the IPCC’s official AR6 baseline scenarios — RCP8.5, SSP5-8.5, SSP3-7.0 — New Zealand councils had drawn hazard lines across property titles, adjusted infrastructure plans, and shifted insurance and lending exposure, with real economic consequences for New Zealanders.
Thanks to the correct decision by the CMIP7 scenario committee, we now know that all of these decisions and consequences have been based on a scenario now officially recognized as implausible.
In a recent interview with Alistair Harding in New Zealand, Detlef van Vuuren — the Dutch scientist who helped to lead the development of the 2011 RCP scenarios (including RCP8.5) as well as the new 2026 CMIP7 scenarios that officially retired RCP8.5 — was asked if it was ever a fair description of RCP8.5 and the like as business-as-usual (BAU) or a no-mitigation future.
His answer:
“No, that was always a wrong way to describe it.”
And yet, as has been carefully documented here at THB, the set of three baseline scenarios has — for fifteen years — been characterized as a BAU or baseline or reference scenarios throughout climate research and policy. That designation trickled down to land use decisions in coastal New Zealand.
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Correcting course is just starting
Regarding the RCR Van Vuuren interview — he expresses sympathy for those in the country whose fortunes have been compromised because of the unwitting use of RCP8.5 as a baseline scenario for current land use planning and regulation (emphasis added):
“If I was owning a house somewhere and there is a risk in 2150, I think it [RCP8.5] is useful information. But I would expect that my mortgage being out 30 years or so, that it would be completely unfair that the value of my property would be so much determined by something that is uncertain and way out.”
Van Vuuren suggests that, from his perspective, the RCP scenarios were never really intended to be used in local decision making:
“The way that I normally use these scenarios is in climate negotiations. It is quite interesting that even these rather abstract scenarios have such consequences as well in daily decisions…”
Interesting, indeed.
The mistakes made in New Zealand in using RCP8.5 as a scenario depicting an expected future, a forecast even, is understandable as a cascade of confusion and conflicting intent for the role of scenarios in climate research. However that cascade has had material consequences for real people in real places, reaching far beyond New Zealand.
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To read Professor Roger Pielke JR’s full article, please click HERE.