Editorial: Report on sea-level rise will enable sensible planning
The new report about the threat to coastal areas in and around Christchurch from projected rising sea levels is timely but not a matter for immediate alarm.
The report prepared for the Christchurch City Council by geotechnical experts Tonkin and Taylor builds on an earlier study done in 1999 for the council which had similar results.
They reinforce the need for the council, as it is already doing, to take into account in its district plan the fact that changing sea levels are increasing the risk to some low-lying areas, particularly at South Brighton and around the estuary.
The coastline near Christchurch has been changing for many years. Photographs from a century or so ago show the spit at South Brighton, for instance, has changed shape and been encroached upon considerably.
The 1999 report, commissioned at a time when awareness in the change in global sea levels was growing, suggested that as the situation evolved there were areas for which the council would have to plan carefully in future.
The new report emphasises how important this will become in the coming century.
New and better information about how the sea level is changing, not just here but around the world, makes it clear that the original report underestimated how much the sea would rise over the next few decades.
The projections in the report are subject to some uncertainty.
Events of the last few weeks, with unprecedented heatwaves in Australia and equally unprecedented freezing blasts across the whole of the United States, whether they are related to climate change or not, show how unpredictable weather-related matters can be.
As the report says, the melting rate of the Greenland and West Antarctic ice sheets is the dominant factor in sea-level rise projections and what that rate will be is unknown.
The latest report by the Intergovernmental Panel on Climate Change, the United Nations body that provides consensus reports on the latest science on the matter, is due out this year and should give a better idea of what lies ahead.
Taylor and Tonkin's advice to the city council assumes a rise of one metre by 2115. But given what is at stake, it is plainly better to err on the side of caution rather than optimism.
Apart from that new information, a new report was necessary because of the changes to the landscape brought about by the earthquakes. The land around the estuary has subsided by as much as 0.5 metres. The full effects of that are not yet known.
The city council has already acted to cope with these changes. It has designated some areas as flood management areas and restricted development in them.
The Taylor and Tonkin report suggests that the extent of those areas should be reviewed. It also suggests that the minimum floor levels established for those areas may have to be raised to allow for the higher sea level.
Other work such as sea walls and flood walls and raising property and infrastructure are likely to be necessary.
It will all require a large amount of work but the time frame is a long one.
There is plenty of time in which to consult with all those affected and to get it done.
Problems caused by high and rising sea levels have been handled in other parts of the world without major difficulty, in many cases by assessing the issues early and addressing them.
One of the large benefits of the new report is that planning blunders of the kind that were revealed by the earthquake, where land was built on that should not have been, can be averted.
The report will also help ensure such work as needs to be done can be done efficiently and affordably.