Government Guidance on Sea Level Rise is Grossly Conservative – Urgent Review Required

The Ministry for the Environment (MfE) Guidance to Local Authorities on Coastal Hazards was published in December 2017 and contains excellent advice for councils on climate change adaptation.  Unfortunately, similar guidance just published in California demonstrates that sea level rise scenarios in the MfE Guidance are already grossly conservative and out of date and must be reviewed urgently. 

The MfE sea level rise projections are outdated partly because the previous National Government withheld the draft MfE guidance for over a year, but also because the Guidance relies heavily on IPCC sea level projections from 2014, and these, in turn, are based on data gathered several years prior to 2014. 

MfE has promised that there will be annual reviews of the Guidance.  The pressing need for an immediate review became even more obvious this week when the California Climate Commission released its draft 2018 Guidance on Sea Level Rise

As can be seen from the comparative tables below, under the Medium – High Risk Aversion scenario the California Guidance states a sea level rise of 2.1 m by 2100 should be considered, whereas the New Zealand Guidance requires consideration of just 0.79 m by that date under the roughly equivalent median NZ RCP 8 scenario.

CCC Sept 2018 Table SLRwithm

Under the California Extreme Risk Aversion scenario, which is roughly comparable to the NZ RCP8 H* scenario in the New Zealand Guidance – consideration should be given to 3.1 m of sea level rise by 2100 compared to just 1.05 m in the New Zealand guidance.

The comparison of sea level rise projections for 2150 is even more stark.  The California Guidance recommends consideration of a sea level rise of 3.9 m under the Medium/High scenario and 6.7 m under the Extreme Risk scenario.  This compares with just 1.41 m in the New Zealand Guidance for the median scenario and 1.88 m under the extreme H* scenario.

The California Guidance has taken account of the very latest scientific studies including the possibility of rapid ice sheet loss from West Antarctica and has not been constrained by the IPCC 2014 projections.  MfE must urgently review its guidance on sea level rise, taking account of this latest science.

As an example of why this urgent review is required – consider a new development the Thames Coromandel District Council is actively pursuing – a $25 million sub-regional aquatic centre on low-lying coastal land near the airfield as Thames.  The council has commissioned a report from Tonkin and Taylor on coastal hazards relating to the site. 

That report considers just 1.36 m of sea level rise by 2120 under the extreme H* scenario from the New Zealand Guidance tables.  Even under the Medium/High California scenario, 2.6 m of sea level rise should be considered by 2120, and under the equivalent Extreme scenario the California Guidance recommends that 4.3 m of sea level rise be considered at 2120 for projects (such as a major aquatic centre)  “with little to no adaptive capacity that would be irreversibly destroyed or significantly costly to repair.”

Unless the New Zealand Guidance is urgently reviewed, local authorities will continue to assess risky coastal greenfield subdivisions and development projects like the proposed Thames Coromandel aquatic centre using grossly conservative sea level rise projections.


The California Guidance describes the Medium-High Risk Aversion scenario as the 1-in-200 chance (or 0.5% probability of exceedance) and states it should be used for projects “with greater consequences and/or a lower ability to adapt.”

The Extreme risk aversion (H++): accounts for the extreme ice loss scenario (which does not have an associated probability at this time) and states it should be used for projects “with little to no adaptive capacity that would be irreversibly destroyed or significantly costly to repair, and/or would have considerable public health, public safety, or environmental impacts should that level of sea level rise occur.”