Local authorities told to throw out flawed sea level estimates

Coastal property groups are recommending the government urgently update its faulty advice to local authorities on sea level rise.

They say too many local authorities are using inflated sea level rise calculations and unnecessarily disadvantaging thousands of homeowners living along New Zealand’s coastline.

Local authorities are required to use likely sea level rise in their planning for coastal hazards. The Ministry for Environment instructs them to use projections developed by the United Nations’ Intergovernmental Panel on Climate Change (IPCC). The IPCC prepares a range of these based on different assumptions about carbon concentrations in the environment over the next 100 years. The highest IPCC projection is known as SSP7-RCP8.5.

The Ministry guidance recommends including this projection for planning purposes.
However, the most recent report from the IPCC, titled AR6, states that this highest projection is unlikely, referring to it as “implausible” and explaining that it is included in their reports as a “counterfactual” for research purposes only.

Coastal Ratepayers United Chair Salima Padamsey says families living near the beach realise councils need to plan for the future, but they expect them to use good science.

“We have already been hit by councils using science that was found to be unfit for purpose in their knee-jerk attempt to face climate change, but they should pay attention to the expert scientists,” she says.
She says beach property owners are more willing to work with local authorities to plan for future sea level changes when councils are realistic rather than alarmist. To put in the vernacular IPCC’s recent report suggest that RCP8.5 sea level rise is almost 50% higher than its most likely scenario.
Warwick Schaffer of the Christchurch Coastal Residents United says the RCP8.5 projection has never been likely, and clearly is not intended for the purpose of planning. He welcomes the fact that the IPCC has finally clarified this matter.

“Using this scenario has significant impact,” he says, pointing out it would lead to many more homes and businesses being designated danger areas and not being able to expand, rebuild, or develop their sections.

“I challenge anyone to tell me this level is likely and something we should use,” he says.

The Ministry for the Environment’s guidelines to local authorities was issued in 2017, and CRU has asked it to update them based on this new information and advice from the IPCC.

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For more information contact Salima Padamsey at cru.kapiti@gmail.com

The ICPP report: https://www.ipcc.ch/report/ar6/wg1/#TS ref. Section 1.6.1.4 and Section 4.2.2
The CRU website: https://www.cru.org.nz/
https://doi.org/10.1038/d41586-020-00177-3 is a useful resource to help in the understanding of the SSP/RCP scenarios and the “unlikely” issue

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