Sealevel rise still set to be serious issue

PLEASE don’t think that sealevel rise may not be as bad as you think.

Malcolm Taylor (ODT, 7.2.19) notes a figure of 1.32mmperyear rise at Dunedin, and projects this to give a relatively low rise by the year 2100.

However, the average rate around New Zealand is 1.7mm per year (and this may now be out of date). Lyttelton has a rate of around 2mm per year, but also has the mild advantage of being raised a few centimetres by the Christchurch earthquakes. Dunedin was not so fortunate. Further, I believe the estimation of sealevel rise at the Dunedin tide gauge has a number of difficulties and is not as reliable as that at Lyttelton.

The New Zealand tide gauges do not show the acceleration in rate of sealevel rise shown around the world, as yet — ongoing records will no doubt do this. Meaning that the current rates of rise will themselves rise in future. A linear extension will not predict the future.

Mr Taylor discusses the range of possible rises by 2100 given by Nasa and Niwa. He notes that the newspaper article he is reacting to states the words ‘‘even under a 1m rise . . .’’ implying to him a low probability, an extreme. This would be so if a single computer model of future rise was run many times giving lots of results near the average, and few at the extremes.

However, the Nasa and Niwa results are those of a number of different models each with its own set of assumptions regarding the major influences on level rise. The high results come from one particular model, with perhaps more probability than the others. As studies continue to be carried out and new information becomes available, I tend more to a realistic pessimism.

Also remember that the year 2100 has no specific importance — the sea will continue to rise long after that. Steve Moynihan

Cromwell ...................................

BIBLE READING: Defend the cause of the weak and fatherless; maintain the rights of the poor and oppressed. Rescue the weak and needy; deliver them from the hand of the wicked. — Psalm 82:34.