Sea level rise to impact on New Zealanders – report

Flooding and erosion from rising sea levels are likely to significantly impact on New Zealanders in our lifetimes, warns the latest report from the Parliamentary Commissioner for the Environment.

King tide on Tamaki Drive, Auckland, in February 2014.
King tide on Tamaki Drive, Auckland, in February 2014.

Commissioner Dr Jan Wright released the report titled Changing climate and rising seas: Understanding the science this afternoon, which lays out the science behind sea level rise and how its consequences will affect New Zealanders.

Drawing on modelling of future sea level rise, the document paints a grim picture of what lies ahead. It says that the sea level is ‘locked in’ to rise by about 30 centimetres by 2050, which is enough to intensify king tides, storm surges, flooding and coastal erosion across New Zealand.

The second report from the Commissioner, due next year, will show which towns and cities are most vulnerable and assess the risk to infrastructure in those areas.

You can listen to audio from the report launch below.

[note: first section of audio missing]

The Science Media Centre rounded up the following expert comments in response to the Commissioner’s report. Feel free to use these quotes in your reporting. If you would like assistance or more information, please contact the SMC (04 499 5476;

Prof Martin Manning, Climate Change Research Institute, Victoria University of Wellington, comments:

“Dr Wright’s very readable review of the scientific basis for estimating future sea level rise is setting out an extremely important issue for New Zealand. How do we plan for major changes to our coastline when the rate at which these will occur is still not clear?

“The IPCC’s Fifth Assessment report set 66% likely ranges of sea level rise up to 1 metre but these do not cover all of the next 100 years, or set a risk based framework for planning purposes. Furthermore several recent studies are showing that those estimates did not cover everything. A major ice sheet in the northeast of Greenland that was assumed to be stable is now known to be moving, and more detailed studies of the East Antarctic ice sheet are showing it is much more vulnerable to sea water intrusions.

“But the commissioner’s report is also pointing out that this is already a major issue for New Zealand because of our lack of any clear response strategy. It is showing that delegation of responsibility to local governments to plan for major changes to our coastline, without the guidance or coordination that can be set by national standards, is just creating more problems.”

Rob Bell, NIWA Principal Scientist, Coastal and Estuarine Physical Processes, comments:

“The report provides an insightful commentary on the history behind assessing the impacts of a changing climate and in particular sea-level rise – when did it start to rise, by how much so far, why is it rising, and what are the projections?

“A further rise in sea level of 20 to 30 centimetres in the next few decades may sound minor. But the flow-on effect that will become obvious to coastal dwellers is a significant increase in storm-tide and wave events that inundate low-lying roads and properties, causing disruption and flooding at-risk properties.

“King high tides already fill harbours to the brim – based on the rise in sea level to date – so any storm that occurs on these red-alert tide days will more often flood the low-lying margins.”

Assoc. Prof Nancy Bertler, Joint Antarctic Research Institute, Victoria University of Wellington / GNS Science, comments:

“The report provides an excellent summary on the current knowledge of past and future sea level rise including the main drivers and the regional patterns. Dr. Wright highlights the concern of the scientific community on the possibility of substantial and abrupt future contributions from the West Antarctic ice sheet.

“Additional important considerations are that: worldwide over 200 million people live within one metre of sea level. The last time atmospheric carbon dioxide concentration was at 400 ppm (3-5 million years ago) the associated global temperatures caused the Greenland and West Antarctic ice sheets to catastrophically collapse – raising global sea level by around ten to twenty metres.

“The rate at which sea level will rise has important implications on our ability to adapt. New research suggests that sea level could rise as quickly as 4 metres per 100 years (or 1 metre per 25 years). Assuming even a modest global sea level increase of 50 cm by 2100 (IPCC scenario RCP 4.5), the frequency of coastal inundation in New Zealand is predicted to increase by a multiplier of 1000 times.

“Under such a scenario, an annual event becomes a daily event, a ‘100 year’ event occurs several times per year. As an approximation: every 0.1m rise triples the frequency of inundation events.

“Unfortunately, the Deep South National Science Challenge specifically excludes sea level rise and polar ice sheet dynamics from its research focus.”

Declared interests:
I am the Chief Scientist of the RICE ice core project (mentioned on page 6 of the ‘Changing climate and rising seas – Understanding the science’ report). This project focuses on the stability of the Ross Ice Shelf and West Antarctic Ice Sheet in warming world and implications for sea level rise.
I chair Antarctic Climate 21, a SCAR Research Programme, that aims to improve model projections on how Antarctica will respond and drive future climate change.
I am a contributor to the Deep South National Science Challenge.

Dr Paul Denys, Lecturer in Sea Level Studies, School of Surveying, University of Otago, comments:

“The report would appear to provide a concise and, from my point of view, an accurate assessment of rising sea levels given that the science is complicated and inter-related.

“My main criticism would be that there is too much emphasis on the historical context at the expense of relevant current day scientific results. It discusses the global (broad scale) science as documented in the IPCC (and other) reports and little is said about what is actually happening in New Zealand.

“How does the NZ situation compare with the global results? Given that the report makes the case that sea level rise is not uniform across the globe, how consistent or different is NZ compared with the global (averaged) results? For example, in my area of interest, recent SLR values based on NZ data are given in Hannah (2004) and Hannah and Bell (2012). Results from combined tide gauge and altimetry data are given in Fadil et al (2013). Sea level change based on salt marsh records are provided in Fadil et al (2013).

“The report mentions that vertical land movement that affects tide gauge sites and tide gauge data can be due to post-glacial rebound and tectonic activities. New Zealand straddles the Pacific/Australian tectonic plates and hence is affected by effects such as earthquakes. While this is a very important and significant effect, what is probably more significant in the NZ context is the effect of slow slip events (SSE) (sometimes called silent earthquakes). Most of the east coast of the North Island and the top of the South Island are being subducted under the Australian plate and this significantly affects vertical land movement and hence the effect of sea level rise on our coastlines.

“It is the extreme events that are going to make the general public and the government act. It is the slow and imperceptible effects that are difficult to mitigate for. For example, the situation in South Dunedin where sea level is only 30cm below ground level in some places.

“In my view, the problem of planning for sea level rise is too big to be delegated to the local authorities. Government needs to take a lead and be proactive at the national level.”

Declared interests:
I am involved in the measurement of SLR based on tide gauge records and in particular the measurement of vertical land movement in relation to sea level records.
I am a co-author on the paper Fadil et al (2013).

Dr Stephen Flood, Post-Doctoral Fellow, School of Geography, Environment and Earth Sciences, Victoria University of Wellington, comments:

“I think overall the report does a particularly good job of explaining the current science behind the complex mechanisms involved in sea level rise in a clear and lucid manner.

“Further detail could be provided on the tide gauges and their existing network to strengthen the science presented. For example, some of the content from the footnotes could be included in the main body of the text. Further emphasis could also be given on the exponential impact of the Ice-Albedo effect.

“I think the report’s examples of problems in Auckland and Christchurch illustrate the potential and importance of sea level rise/storm surge interactions.

“I think the fact that a small rise in sea level can lead to big impacts is a point that is delivered well in the conclusion and has particular relevance for planning. The insurance industry is mentioned but it could also be useful to explicitly mention the importance of a risk management approach.”

Dr James Crampton, Palaeontologist, GNS Science, comments:

“I think that the report does a very good job of placing modern sea-level rise in its long-term context and, in particular, it emphasises how far we are moving outside the stable environmental envelope of the past few millennia. The report also highlights the diversity of approaches and data that are required to understand and predict future rates of sea-level rise. The report makes it clear that we understand some aspects of the science rather well, but have very large uncertainties in other areas, such as likely instability thresholds and rates of change of the polar ice sheets.

“I think that the second report on impacts, to be released in 2015, needs to be clear that we should not be planning for an arbitrary AD 2100 end-game: sea-level rise will be on-going and, quite possibly, still accelerating by the end of the century. Our children’s children will be dealing with changes occurring after 2100.

“The report’s use of king tides and storm surges in Auckland along with subsidence and flooding in Christchurch as examples is a key point and totally appropriate: people have a chance to adapt to changes in the average state – what hurts society are the extreme events. Hence the ‘one-in-one-hundred-year event’ is forecast to become the one-in-ten-year event or even an annual event by 2100, and these are the events that will be causing harm to coastal communities. An absolutely crucial concept, although tricky to convey, is that the shape of the normal probability curve means that it is a mathematical inevitability that a relatively small change in the average climate state disproportionately increases the relative frequency of extreme events in the upper tail of the distribution. In other words, and using arbitrary numbers, a three degree Celsius warming will increase the frequency of extreme storms or flooding events several hundred-fold. This point can be illustrated with a diagram.

“The policy response taken to reduce the consequences from sea level rise needs to be negotiated jointly between decision makers, communities at risk, and science providers. Once an acceptable level of risk has been determined – or a framework to assess tolerable levels of risk has been developed – an appropriate response can be initiated. This may include a combination of mitigation, adaptation, and emergency management provisions. Economic interests (i.e. from landowners, councils, businesses, insurance companies, legal firms, developers, etc.) will play a driving role in this phase.”