This is the edited transcript of questions by Jamie Morton of the NZ Herald, answered by Prof Tim Naish on Friday 29 April 2022, prior to the NZ SeaRise webtool going live.
How much of a step-change is this new data from our previous understanding of sea-level rise around Aotearoa New Zealand?
Before the launch of the NZ SeaRise web tool there was only one set of sea-level projections (essentially based on global mean sea-level) for the entire country. Users were advised to consider local land movements, but there was no research to base this on.
Having a geological background, we (Dr Richard Levy and Prof Tim Naish) realised that even in between earthquakes the coast of Aotearoa is dynamic, sinking and rising millimetres every year. This is because we are the “shaky isles”, sitting astride a major tectonic plate boundary on the “pacific ring of fire”.
With funding from the MBIE Endeavour Fund and with national and international partners we have worked with the Ministry for the Environment to provide a set of location specific sea-level projection spaced every 2km around the coast of the motu. These sea-level projections extend out to 2300 and are based on the most recent IPCC report for how global sea-level is changing and also includes vertical land movements (VLMs).
We have used the same methodology as the IPCC developed by our close American collaborator at Rutgers University, Prof Bob Kop. However, we have worked with Bob and the land deformation experts at GNS Science to innovate a methodology that accounts for very local changes in VLM. These local changes are measured by satellites at 10m-scale resolution and calibrated to the GNS GeoNet GPS network around Aotearoa New Zealand. This is a world first and provides a critical tool for assessing the impacts and risks of sea-level rise for nations like Aotearoa (e.g. Japan and Chile).
The timing could not be better with Minster Shaw announcing on Wednesday last week the public release of the Draft National Adaptation Plan for consultation. The impacts and risks of sea-level rise are big for Aotearoa New Zealand and are poorly defined at the local level. So our new web-based toolkit will be of immediate use to local government planners, infrastructure providers, communities, and the business sector who are grappling with adaptation to sea-level change at the local level.
How instrumental do you expect it to be for council and Govt planners as they have to grapple with things like re-zoning and managed retreat?
We expect the web-based sea-level projections tool, hosted by Takiwā, a Maori-owned data analytics and spatial-data analysis company to be the go-to national tool for assessing sea-level rise impacts and risks. We have already tested and trialled it extensively with Councils and infrastructure providers such as Waka Kotahi. With legislative changes currently happening to the resource management act and the new climate change adaptation act council planners will need this information. It will help them make decisions around zoning and with finding the best and most equitable solutions to coastal adaptation.
The website also has a community section where members of the public can zoom in on a map to a stretch of coastline near them and find out what they are in store for over the coming decades with sea-level rising.
Of the scenarios in the tool, which do you feel is the most realistic, or likeliest we'll face this century?
The tool presents two sets of sea-level estimates for the future climate scenarios, or pathways, outlined in the latest IPCC report. These pathways span a range of potential futures from achieving dramatic emissions reductions in line with the Paris climate agreement through to unabated fossil-fuel driven climate change.
We are currently on a pathway where global warming could be stabilised at about 3°C above pre-industrial levels. However, if each country honours the emission reduction pledges made at the recent COP26 meeting in Glasgow, then we could limit global warming to below 2 degrees.
So coming back to the tool and the two sets of projections, what does that mean for Aotearoa New Zealand?
In the first set of projections we use estimates for Antarctic ice sheet melting that are known with “moderate confidence” out to 2150 (the same as the IPCC). Using the tool, users will see the lowest sea-level rise for New Zealand is 30 cm of sea-level rise by 2060 and 60 cm by 2100. However, because the land is sinking at the same rate sea-level is currently rising in many places, some locations will get up to double the global average. This means 60cm by 2060 and 1.2 m by 2100. This is true for Wellington, Auckland, and Napier, along with stretches down the coast of the eastern and southern North Island, and in Marlborough and Nelson.
So, if you’re a coastal dweller or user you have half the time you thought you had before sea-level impacts become disruptive. An example of this is that, with 30 cm of sea-level rise, the 100-year coastal storm surge and flood will become an annual event for many places. In these regions where the land is going down at more than 3mm per year (such as parts of Wellington and Auckland) this threshold will be exceeded as soon as 2040. This means Councils need to put serious plans for adaptation in place right now.
The second set of estimates extends to 2300 and includes rapid Antarctic melting, which is possible, but known with lesser confidence. These estimates are scientifically plausible and is why the IPCC says “2 m of sea-level rise cannot be ruled out” by the end of the century.
If you have long-lived assets and infrastructure such as airports, roads, wharves, or ports on the coast and a low tolerance for risk, then you may consider the low chance but high impact projections which involve rapid collapse of the West Antarctic ice sheet.
Understanding the future behaviour of the Antarctic ice sheet in response to global warming is one of the biggest scientific challenges we face. It leads to “deep uncertainty” for decision and policy makers and here in New Zealand the Antarctic Science Platform is trying to improve this knowledge working with international partners.
For NZ users the take home message is “Global sea-level will go up 25-30 cm by mid-century. The new sea-level rise tool will show you how much vertical land movements will add to that for a place near you. The impacts and risks associated with this locked-in sea-level rise can be planned for now. However the plans need to be flexible beyond 2060 and allow for a high emissions, warmer world where the Antarctic ice sheet melts quickly.”
What are the next steps for the programme?
If we receive funding, we aim to take into account earthquake risk and improve the resolution of the tool to a scale that encompasses individual buildings. We also want to work on our community engagement and encourage the government to fund a coastal adaptation platform.