THE INTERGOVERNMENTAL Panel on Climate Change (IPCC) is a highly-regarded group of the world’s leading climate scientists.
At their meetings in 2007 and 2011 they stated that “it is beyond scientific doubt that human action is the key driver in the current and ongoing warming of the earth’s atmosphere”.
One consequence of this warming of atmosphere is an inevitable rise in sea-levels.
The world’s sea levels were basically stabilised about 1200 years ago.
The Pacific Ocean level has been rising very gradually since about 1800 (since 1900 it has risen 15cm).
Recent history of sea-level rises in the Solomon Islands group varies slightly.
From 1993 to 2010 the following rises were recorded by the Solomon Islands Meteorological Services (SIMS):
Santa Cruz (in the east) – 7 to 8mm
Guadalcanal & Malaita – 8 to 9mm
Central & North Islands – 9 to 10mm
This variation is caused by the west to east rotational force of the earth.
The eastern Pacific (on the coast of South America) is about 450mm lower than the western Pacific.
So the difference of 2 to 3mm between the east and west of the Solomon Islands, over 1300 kilometres apart, is consistent with that ocean-wide variation.
Predictions are that the sea-level at Honiara will rise between 5 and 15cm by 2030 and between 35 and 40cm by 2100.
Other, similar predictions, have a rise of 9cm in 15 years, 19cm in 40 years, and up to 40cm in 75 years.
It is significant that both these predications have a reasonable level of scientific confidence and they are fairly consistent.
So sea-level at Honiara will, almost certainly, be 9 to 10cm higher by 2030 and 18cm higher by 2050.
That is not much, it can be accommodated with simple foreshore works.
But – and it is a big but – when these minor rises are accompanied by king tides and/or storm surges the combined result makes the necessary sea wall defences a more serious engineering project.
Work such as that done on the breakwater near the Breakwater Café or the seawall of the Pacific Hotel/Casino at Kukum are examples of such works.
What are often called ‘king tides’ are officially known as Mean Higher High Water (MHHW) events.
Between 1974 and 2011 there have been ten such top events at Honiara with rises of 390 to 495mm.
60 percent of these rises occurred during La Nina events, 30 percent during Neutral events and only 10 percent during El Nino events.
Top ten MHHW events measured at Honiara (39 to 49.5cm)
| La Nina events: November 30, 1974
June 10, 1975 December 4, 1975 May 8, 1985 April 8, 1989 April 10, 2008 |
Neutral events: April 18, 1984
April 12, 1986 April 17, 1991
El Nino event: December 8, 1976 |
So the worst-case scenario is a combination of long-term sea-level rise and a Mean Higher High Water event, with the resulting, occasional sea-level rise at Honiara being 49cm by 2030 and 68cm by 2050.
While such rises may seem alarming, they would occur only once every 3 or 4 years on average.
It is interesting to note that the MHHW event of April 12, 1986 came less than a week before Cyclone Namu struck Malaita, Guadalcanal and other Solomon Islands.
Despite the future sea-level rises most of the sand or pebble beaches of the Solomon Islands should gradually and naturally build up beach levels to give some protection for most villages and roads close to the shore-line.
In places where higher water levels result in scouring out of existing sand/pebbles there may be a need to undertake subsurface, off-shore, reef-like deposits to positively influence beach-sand build-up.
Within the Solomon Islands group there are many scattered low-lying islands. Some low-lying islands are insignificant but several, such as Rennell and Bellona Islands, Utupua and Duff Islands in the Santa Cruz Group and parts of the New Georgia and Shortland Islands Groups will need specific investigation to see if adequate protection from sea-level rise can be provided economically.
Where this cannot be done, resettlement programmes within the Solomon Islands will have to be sensitively handled.
Engineering works to save some islands, or the costs to resettle populations from other islands will need significant funding from national and international sources.
It is not too soon for diplomatic activity to start applications for such funding.
In the meantime, investigations should be commenced to identify those islands that may retain their population following shore protection works, and those where populations will have to be relocated.
[Published with thanks to SIBEPA – Solomon Islands Built Environment Professional Association]
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