2014 - February

My co-author, Prof Philip Woodworth, on our Global and Planetary Change paper produced a briefing note for the BIOT Science Advisory Group entitled:

An Update on Past and Future Sea Level Changes at Diego Garcia and Remarks on the Need for Chagos Regional Ocean Modelling

Using a further two years data from the tide gauge at Diego Garcia, Woodworth reported an updared value of mean sea-level rise of 3 mm yr^-1. This compares with the earlier trend of 2.2 mm yr^-1 from satellite altimeter data. The earlier analysis of the tide gauge data had been restricted to two separate time periods because of an unresolved datum shift. This remains the case and Woodworth used the earlier estimation of the likely datum shift in order to re-align the two separate time series for his updated analysis (Note: caution is therefore needed when quoting this new value of 3 mm yr^-1).

From the tide gauge Dunne et al (2012) had estimated rates of rise of 5.12 mm yr⁻¹ for 1988-2000, and 6.9 mm yr⁻¹ for 2003-2010 but both had very high variability, meaning that they could not be sure that the rate of rise was 'real' (this is a method of statistical validation).

These are all rates for Diego Garcia. To the north, where the islands of Salomon and Peros Banhos are situated the rates were smaller ~ 1.5 mm yr^-1.

The main purpose of Woodworth's note is to demonstrate the need for detailed ocean modelling so that we can understand better the dynamic regional processes which have to date caused a depressed rate of sea-level rise compared with the global mean.

For now we must assume that the future for the Chagos is that sea level will indeed rise in this region. Our best 'guess' must rely on the values for the global mean in the latest Inter Governmental Report on Climate Change (AR5). I will not go into that here because the choice of the Representation Concentration Pathway (RCP) dictates the outcome.

Nor is life that simple, because these are islands which have been formed at different sea levels to those today and which rely on storms and sediment for their existence. If you want to venture into that field I would suggest you read the published work of Prof Paul Kench who is one of the leading experts on this subject.

POSTSCRIPT

The Chagos Conservation Trust posted Philip Woodworth's briefing note on their website (see: CCT News) and somewhat enthusiastically announced this in headline terms "New paper revises sea level estimates in the Chagos Archipelago". It does not, the whole picture remains that described in the Global and Planetary Change Paper.