This page outlines the likely impacts of climate change on our coastal areas and how central and local government are preparing for these impacts.
About sea level rise
From 1880 to 2012, global average temperatures warmed by 0.85ºC, as reported in the Intergovernmental Panel on Climate Change’s Fifth Assessment Report [IPCC website].
The ocean is absorbing 90 per cent of the heat added to the climate system. This warming is causing an expansion of ocean water which, in combination with water from the melting of land-based ice, is causing sea levels to rise.
The global average sea level rose about 17 cm last century, at an average rate of 1.7 mm per year. From 1993 to 2010 the global average sea level rose at an average rate of about 3.2 mm per year.
Due to the influence of regional climate trends and gravitational effects, sea level does not rise uniformly around the globe. Sea levels in New Zealand rose by 17 centimetres last century and on average by 1.7 mm per year over the last 40 years.
The impacts of climate change on our coast
Much of New Zealand’s urban development and infrastructure is located in coastal areas. This makes it vulnerable to coastal hazards such as coastal erosion, inundation (flooding) by the sea and sea level rise.
Climate change is likely to bring the following changes:
- increased frequency, duration and extent of coastal flooding
- coastal defences are overtopped by waves or high tides more often
- severe storms increase in intensity and storm surge levels rise
- some sandy beaches may continue to accrete, but more slowly
- some gravel beaches are more likely to erode
- waves in Wellington could be 15 per cent higher by 2050 and 30 per cent higher by 2100
- in areas with smaller tidal ranges (eg, Wellington, the Cook Strait area and the East Coast) the historic high tide mark may be exceeded more often.
- the potential for saltwater to enter underground freshwater aquifers increases.
Planning for future sea level rise in New Zealand
It is important that we start planning for future sea level rise now.
The Ministry recommends the following projections of future sea level rise are used for planning.
Planning out to 2090–2099
For planning and decision timeframes out to 2090-2099 use a base value sea level rise of 0.5m relative to the 1980–1999 average, along with an assessment of potential consequences from a range of possible higher sea level rise values.
At the very least, all assessments should consider the consequences of a mean sea level rise of at least 0.8m relative to the 1980–1999 average.
Planning beyond 2100
For planning and decision timeframes beyond the end of this century use an additional allowance of 10mm per year.
Updates to this advice may result as part of the coastal hazards and climate change guidance update, due for release in the second half of 2016.
Central government response to planning for sea level rise and increasing coastal risk
The New Zealand Coastal Policy Statement 2010 (NZCPS) provides further direction on planning for development in the coastal zone.
Each regional council must prepare a regional policy statement, and this regional policy statement must give effect to the NZCPS. Other regional and district plans must also give effect to the NZCPS.
Under Policy 24 of the NZCPS, “Hazard risks, over at least 100 years, are to be assessed having regard to physical drivers and processes including… sea level rise…”
For further information, including a copy of the NZCPS, see New Zealand coastal policy statement 2010 [Department of Conservation website]
Local government response to planning for sea level rise and increasing coastal risk
Many local authorities have already started to plan for sea level rise. Some councils have completed coastal hazard assessments and have developed maps showing areas which are expected to be affected over the next 50-100 years.
Other activities being undertaken by local government include:
- restricting development in coastal erosion areas
- planning for managed retreat
- rejecting consents for alterations or extensions to existing buildings in the coastal zone
- discouraging the construction of defences such as sea walls.
Find out more
Preparing New Zealand for rising seas [Parliamentary Commissioner for the Environment website]