Evidence doesn't support rapid future sea level rise
The Royal Society of New Zealand's recent study on sea level rise claims that, in the next 100 years, sea levels will surely rise by 0.3m and 1m is possible. It strongly recommends action should be taken now to deal with this.
The claim does not stand up to close examination.
First, the rise in sea level and New Zealand coast has been about 0.14m over the past 100 years, with no sign of a recent increase in the rate.
There is no solid evidence to indicate this steady rate will increase rapidly in the future. The Royal Society's claims are based on flawed climate models that predicted, by now, temperatures would be 0.5° higher than they really are and increasing faster and faster.
When this dubious data were fed into sea level models, they predicted rapidly increasing sea level rise. How surprising!
The predictions of a Russian climate model that assumes CO2 makes only a small contribution to global warming is the only one that matches recent temperatures. Perhaps it is right.
The Royal Society’s conclusions are a serious matter because many councils are now restricting building close to the sea and putting restrictions on existing houses that have substantially reduced their value.
It is strange the Royal Society has ignored the fact that, all around New Zealand, the land is rising or falling at different rates. So it is quite wrong to assign a single value of sea level rise to the whole country.
What is known about sea level rise?
The long-term record is from tide gauges spread around the world. The oldest records date back to the 1890s and the average rise for 225 tide gauges spread around the world is 1.48 mm per year. (Source: Sea Level Info.)
This is close to the generally accepted 1.72 mm per year for tide gauges.
In the 1990s, Australia set up a series of very accurate tide gauges all around Australia and on many Pacific Islands (BoM reports). These show that, for the majority of sites, the sea level rise since the mid-1990s was less than 2mm per year.
The Pacific Islands record shows, for instance, that the sea level in Tuvalu has hardly changed since 1992. As a result of the now-ending El Niño effect, the Tuvalu sea level is about 100 mm below the level in 1994-1997.
Research by Paul Kench, of the University of Auckland, has established that the area of most atolls is increasing because natural processes build up the islands. Without this, all the atolls would have drowned as the sea level rose at 30mm a year at the end of the last Ice Age.
According to Sea level rise – history and consequences, by Bruce Douglas, Mark T Kearney and Stephen P Leatherman, there has been no acceleration of the rate of rise during the 20th century.
Data are available from satellite observations since 1993. These show a rise of about 3.2mm per year with indications of a recent decline in the rate. Nobody seems to be able to explain why it is about twice the tide gauge rate.
Satellites v tide gauges
Many “climate scientists” have adopted the dubious practice of substituting satellite for tide gauge readings post-1993 so they can claim that the rate of rise is increasing.
Predictions of sea level rise from the more realistic of the IPCC computer models range from about 150mm to 600mm by 2100.
In 2011, NASA’s predictions range from 200mm to 700mm. The Ministry for the Environment and NIWA seem to have used an Australian prediction that cobbled the satellite record on to the tide gauge record and predicts a sea level rise of something like 0.5m to 0.8m by 2100.
The Royal Society of New Zealand leads the pack with a projected rise of 0.3m to 1m. This is more than anybody else and much more than the 0.125 m we would expect if sea level rise continued at its present rate.
So, there we have it. All the observational evidence indicates that the sea level is likely to rise 0.1 to 0.2 m by 2100. But the Royal Society, the government and other public bodies ignore this evidence and, instead, choose to believe the predictions of the computer models of climate and sea level that have never made an accurate prediction.
On the basis of this dubious evidence, they are devaluing coastal properties, preventing development in places where, in all probability, there would be negligible risk for hundreds of years and, on Auckland's northwestern motorway at least, spending millions of dollars on extra raising of the existing road to a level far above the likely sea level rise within its lifetime.
So, blind belief in flawed computer models overrules the evidence. Taxpayers and coastal communities bear the cost.
Solomon Islands report
On May 9, RNZ broadcast several news items about a professor in Queensland who claimed the sea level was rising rapidly in several of the Solomon Islands and that it was caused by man-made global warming – which he called “climate change.”
RNZ interviewed James Renwick (ex NIWA) and the Green Party, both of whom claimed it was evidence of climate change and criticised the government for not taking urgent action.
Remarkably, it seems that nobody in RNZ nor the people interviewed stopped to think: If they had done so, they would have realised that an apparent rise in sea level around a few islands is not evidence of a sea level rise worldwide.
The obvious explanation – which was not mentioned – was that these particular islands were slowly sinking beneath the sea. A few minutes with Google confirms this is the case and it has been going on for many years.
Sadly, this is typical of the reaction of the mainstream media to any story that can be construed to support the unproven and dubious hypothesis that man-made carbon dioxide causes dangerous global warming and that, in turn, this causes rapid sea level rise.
What we need is an independent examination of the evidence by people with open minds and practical experience of the New Zealand coastline and sea level rise, rather than a group of academics relying on computer models.
Willem de Lange, MSc DPhil, is a senior lecturer at the University of Waikato. His expertise includes tsunami and storm surge prediction and mitigation, wave-induced sediment transport, dispersal studies, climate change and oceanography.
Bryan Leyland MSc, FIEE(retired), FIMechE, FIPENZ. is an electric power engineer with experience in computer modelling and data analysis. He has had a long-term interest in climate change.
Tune into NBR Radio’s Sunday Business with Andrew Patterson on Sunday morning, for analysis and feature-length interviews.