Tuvalu - the touchstone of global warming and rising sea level

Does this show the island is rising? Just look at the inaccuracy. The commonsense interpretation of the sea level graphs is surely that Tuvalu, and 11 other Pacific Islands, are not sinking over the time span concerned. The sea level is virtually constant.

Similar manipulation of sea level data is described in Church and others (2006), who consider the tropical Pacific and Indian Ocean islands. Their best estimate for sea level rise at Tuvalu is 2 ± 1 mm/yr from 1950-2001. They wrote "The analysis clearly indicates that sea-level in this region is rising." Does this square with simple observation of the data in Figure 15? They further comment: "We expect that the continued and increasing rate of sea-level rise and any resulting increase in the frequency or intensity of extreme-sea-level events will cause serious problems for the inhabitants of some of these islands during the 21st century." The data in Figure 15 simply do not support this excessive alarmism.

Models and ground truth

Before getting on to the next part of the story I shall digress on to the topic of "models’ versus "ground truth’. The past twenty years might be seen as the time of the models. Computers abounded, and it was all too easy to make a mathematical model, pump in some numbers, and see what the model predicted. It became evident very early that the models depended on the data that was fed in, and we all know the phrase "Garbage in, Garbage out". But the models themselves do not get the scrutiny they should. Models are invariably simplifications of the natural world, and it is all too easy to leave out vital factors.

"Ground Truth’ is what emerges when the actual situation in a place at the present time, regardless of theories or models. It is a factual base that may help to distinguish between different models that predict different outcomes - just what did happen, and what can we see today.

In the case of Tuvalu’s alleged drowning, we are usually presented with a simple model of a static island and a rising sea level. As Webb and Knetch expressed it: "Typically, these studies treat islands as static landforms". "However, such approaches have not incorporated a full appreciation of the contemporary morphodynamics of landforms nor considered the style and magnitude of changes that may be expected in the future. Reef islands are dynamic landforms that are able to reorganise their sediment reservoir in response to changing boundary conditions (wind, waves and sea-level)".

In simple language we have to include coral growth, erosion, transport and deposition of sediment and many other aspects of coral island evolution. The very fact that we have so many coral islands in the world, despite a rise in sea level of over 100 m since the last ice age, shows that coral islands are resilient - they don’t drown easily.

The actual growth of islands in the past twenty years

Webb and Kench studied the changes in plan of 27 atoll islands located in the central Pacific.

They found that the total change in area of reef islands (aggregated for all islands in the study) is an increase in land area of 63 hectares representing 7% of the total land area of all islands studied. Thecmajority of islands appear to have either remained stable or increased in area (86%).

Forty three percent of islands have remained relatively stable (< ±3% change) over the period of analysis. A further 43% of islands (12 in total) have increased in area by more than 3%.

The remaining 15% of islands underwent net reduction in island area of more than 3%.

Of the islands that show a net increase in island area six have increased by more than 10% of their original area. Three of these islands were in Funafuti; Funamanu increased by 28.2%, Falefatu 13.3% and Paava Island by 10%. The Funafuti islands exhibited differing physical adjustments over the 19 years of analysis. Six of the islands have undergone little change in area (< ± 3%). Seven islands have increased in area by more than 3%. Maximum increases have occurred on Funamanu (28.2%), Falefatu (13.3%) and Paava (10.1%). In contrast, four islands decreased in area by more than 3%.