Received from Malcolm McQueen
Wed, 20 Apr 2016 at 8:44 p.m.
█ Planning for South Dunedin in the face of the rising sea level
The floods last year in South Dunedin have provoked discussion as to what are appropriate policies that Dunedin should adopt regarding planning for this area.
Concern that rising sea levels as a result of global warming brings urgency to consider this problem.
The area is low lying and even a modest rise in sea level may make the frequency of flooding a serious problem at some time in the future, possibly to the extent that the area becomes unviable as a residential area. A rise of 300mm may increase the danger of severe flooding to an unacceptable level.
A timely but not precipitate response is required. The cost of the response may be huge in both financial and social costs for the city if a solution such as “a retreat from the sea” is undertaken.
But predictions are predictions, they are not yet actual.
We are fortunate in Dunedin to have an accurate and reliable record of sea level. Indeed the safety record of our port attests to this. This record indicates that the sea level in Dunedin is rising at the rate of 130mm per century. Figure 1 shows the sea level as measured at Port Chalmers taken from the “PSMSL Data Explorer” http://www.psmsl.org/data/obtaining/map.html. And note that there is no observable increase in the rate of rise over time.
At this rate it will be 230 years before a 300mm limit is reached, well beyond our planning horizon, say 2100.
Figure 1. [click to enlarge]
However, claims are made that the rate will greatly increase and so pose a threat that we must consider immediately. But note that in order to reach a 300mm rise before 2100 the rate of sea level rise would have to increase by a factor of 270% above that currently observed.
It would be irresponsible in the extreme to undertake extreme action without carefully examining the validity of the claims.
We must consider if and when a response is required. What reasons do we have to expect such a catastrophic rise?
I address four points as to why I do not consider the predictions of catastrophic sea level rise to be well founded.
Validity of predictions
1) As discussed above, the available sea level data gives no indication of an impending catastrophic sea level rise.
2) Rising sea levels are a claimed consequence of rising temperatures. Thus for the prediction of rising sea levels a precondition is that temperatures should be rising. That this should be so is confidently accorded to by the IPCC. However, reality is not quite so simple.
Figure 2 shows the average temperature as recorded at the Musselburgh Pumping station by NIWA in its CliFlo database. http://cliflo.niwa.co.nz/
Figure 2. [click to enlarge]
Although this is a local measurement and rising sea levels are claimed to be a consequence of rising global temperature, the absence of significant warming and no evidence for any increase in the rate of warming must cast doubt on predictions of imminent catastrophic sea level rise.
3) The track record of predictions regarding climate change does not give rise to confidence in the validity of those predictions.
For instance in 2007 the Australian Climate Commissioner, Tim Flannery, claimed that Sydney was “facing extreme difficulties with water”, in 2008 that: “The water problem is so severe for Adelaide that it may run out of water by early 2009.“ and others regarding an endless Australian drought.
These claims were influential in the decision to construct desalination plants in Australian seaboard cities at a cost of about $10 billion. His predictions have not come true, the drought broke and the plants have not been needed. This expense is probably not a complete waste as the plants do provide insurance against future droughts which are sure to occur.
Other predictions that have been made:
– from the UN in 2005, “50 million climate refugees by 2010”
– from Dr David Viner, of University of East Anglia, who confidently asserted that within a few years winter snowfall will become “a very rare and exciting event”.
– and many others too numerous and many too silly to comment on.
All these predictions have failed to eventuate.
I suggest that we should not take at face value the predictions of claimed experts without corroborating evidence such as trends in the historic record or the success of previous predictions.
4) Sea level rise is largely due to melting of continental ice sheets exceeding their gain from snowfall. This is not an easy measurement to make accurately. It has been assumed that melting exceeds accumulation thus contributing to sea level rise. However, recent satellite measurements by NASA cast this in doubt. In fact they indicate that the opposite is the case.
It is critical that we should have a high degree of confidence in the predictions of sea level rise before committing ourselves to very expensive and socially destructive remedial or mitigation policies.
The issue at hand is not one of the reality or otherwise of global warming, we need make no commitment on that issue before deciding the fate of South Dunedin. The climate has changed over the millennia and will continue to do so. The issue is the making of a timely and appropriate response to its flooding problems.
The points I make above are intended to show that the confidence in alarmist predictions is misplaced and are insufficient in themselves to provide a sound basis for planning.
It is clearly unnecessary to address this problem immediately but continued attention is required so that appropriate actions can be taken if the situation is observed to change.
Fortunately in New Zealand the data relevant for making decisions such as that posed by planning for South Dunedin’s future is publicly available and of high quality. Citizens should avail themselves of this the opportunity of consulting the data themselves to draw their own conclusions rather than rely on second hand interpretations.
“You don’t need a weatherman to tell which way the wind blows” Bob Dylan.
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Posted by Elizabeth Kerr