Sea level rise in NZ

The Parliamentary Commissioner for the Environment has released a report:

New Zealand needs to better prepare for the impacts of a rising sea on its coastal towns and cities, warns the Parliamentary Commissioner for the Environment.

In a major new report released today, Dr Jan Wright called for an overhaul of the way New Zealand is preparing for sea level rise.

“Homes, businesses and infrastructure worth billions of dollars have been built on low-lying land close to the coast,” Dr Wright said. “Rising sea levels will have major impacts in many places. In time, some coastal land will become uninhabitable.”

The Commissioner found that councils and communities face a very difficult task in planning for sea level rise. On the Kapiti Coast and in Christchurch City, for example, the process has been particularly adversarial.

“Perhaps the most difficult aspect is the impacts on people’s homes, which for many are much more than financial security. Councils must use science that is fit for purpose, and engage with communities in a measured way and with empathy.”

One key finding of the report is that preparing for sea level rise is very much a work in progress and that the Government needs to do more to help. There is a need to take some time to develop a better approach.

“We must plan for sea level rise, but there is time to do it carefully”, Dr Wright said. “There are a few cases where action is required soon, but in most cases it is more important to do it well than to rush.”

The report contains eight recommendations to the Government. The first seven are focused on improving the direction and advice given to councils. These are to the Minister for the Environment and the Minister of Conservation.

The last recommendation is to the Minister of Finance and is focused on the fiscal risks of sea level rise.

I’ve read the report and it is well done. Many reports scaremonger about 10 metre rises, while this one does not. It focuses on the possibility of a 50 cm rise, and identifies 9,000 homes that could be impacted by that.

Sea levels have been rising slowly but steadily for the last century and there is no reason to think this will stop. The question is whether the rate of increase stays the same, or quickens.

The increase since 1900 has been around 20 cms globally and locally. So the long-term rise rate has been around 2 mm a year.

But since around 1990 the rate has been around 3 mm a year. So the most conservative estimate of future increase would be to remain at 3 mm a year.

So what could be the extent of any rise in say 50 and 95 years? I use those time periods as 50 years is probably the outer limit of impacting a current owner of a house. The 85 year period covers economic impact, even if not current owner impact.

In 2065, at 3 mm a year, the increase would be 15 cm or half a foot. This is unlikely to have a huge impact.

However the upper boundary of the most pessimistic scenario of the IPCC has more rapid rise, which would be 40 cm by 2065. In that scenario around 9,000 homes are affected.

So the likely range is 15 cm to 40 cm by 2065. They are not equally likely – the 40 cm is the current top estimate. As we get better data and information over the next decade, projections may change.

How about out to 2100? Well at 3 mm a year that is an increase of around 25 cm or almost a foot. But what under the most pessimistic IPCC scenario?  That is almost a metre. Again that is the upper end of the scenario. The midpoint for that scenario is around 70 cm.

So over close to 100 years the likely range is one foot to three feet.  Obviously if it is at the upper end, that will have a significant impact on coastal properties.

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