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Vanuatu sea levels: how much did they contribute to cyclone damage?

Posted By Joanne Nova On March 19, 2015 @ 6:59 pm In Global Warming | Comments Disabled

Sea levels are part of the scare campaign, but how many journalists ask, and how many scientists admit, that sea levels in the South Pacific are noisy data that changes as the ground moves and the ocean slops back and forward? The Pacific averages 4 km deep. Is it any wonder that slight changes in winds and currents will shift the top 10cm, just 0.0025% , around? Long term sea level changes are difficult to assess. But this is not what we hear much in the media:

“Rising sea levels making island nations such as Vanuatu more vulnerable to storms and amplifies the impact of tropical cyclones” –The Guardian

“Coastal flooding is a sleeping giant,” it says. —  The Climate Council (News.com)

The good recent data shows big rises and falls that don’t correlate with CO2

A very neat high-quality network of SeaFrame equipment was installed around South Pacific Islands in 1992 to measure both land and sea movements. This is called the Pacific Sea Level Monitoring Project. It is maintained by the Australian BoM. The geodetic observations are done by Geoscience Australia.

These tide gauges show that sea levels are rising and falling around Vanuatu over the last 20 years (feast your eyes, there is a 30cm range on that graph below). Where is that CO2 signal? Seas around Vanuatu have been falling since 2008. Getting long term trends out of short data with large natural swings is misleading. Slightly different start or end points will change the rate dramatically. In 2009 the  rate of sea level was listed as 6.5mm/yr since 1993. By 2011, the trend was 5.2mm/yr.2 There is no newer report, but clearly it would be even lower now.

Vanuatu Sea level  |  Source: Ref 3

The anomaly chart shows sea levels increase for a while, then decrease for a while. There is no connection with steadily rising CO2.

… |  Source: Ref 3

The surface temperature of water around Vanuatu cycles up and down by 5 degrees C like clockwork every single year. There is no trend visible at all. Then again, if seas are rising by 0.03 C per year, we aren’t going to see it on this graph, or measure it with this equipment. Marvel that last year the corals around Vanuatu coped with a five degree Celsius rise over just a six month period (like they do every year). But put on your panic-hat at the thought of them surviving a fraction of degree over a century.

Spot the effect of massive emissions of CO2?

Sea levels, south pacific

Vanuatu sea surface temperature |  Source: Ref 3

Reader Steve writes in with a paper from 1987 showing that the corals around Vanuatu are regularly baked in the sun, “emerging” above the seas and going back underwater:

Using coral growth bands, we can determine the year coral surfaces died due to emergence. We interpret four major coral emergence events as coseismic uplifts that occurred near the epicenters and rimes of large shallow earthquakes on January 5,1946 (Ms = 7.3), August 11, 1965 (Ms = 7.5), October 27, 1971 (Ms = 7.1) and December 29, 1973 (Ms = 7.5).

Vanuatu is in motion, and it’s been the same for a century:

At various places in 1957,1969-1970.1977, and 1978-1981 there was about 5-10 cm of emergence not  associated with major earthquakes, which may indicate nonseismic tectonic uplift. However,  oceanographically lowered sea levels, as in El Niños, may have determined the times when corals died and recorded these events. Nevertheless, the accumulation of emergence, its persistence, the limited geographic  extent of each event, and occurrence in areas of rapid Holocene uplift suggest that the causes of the uplifts are tectonic. These events suggest that in some areas a third or more of the total accumulated uplift in central Vanuatu takes place as aseismic motion. However, in some areas we find only coseismic emergence. In  central Vanuatu, contemporary coseismic vertical deformation, Holocene uplift, and topography have  remarkably similar patterns. This suggests that the mechanisms and processes causing vertical deformation have varied little over the last 106 years. Apparently, the topography, structure, and seismotectonics are controlled by the subduction of the d’Entrecasteaux ridge, a major bathymetric feature underthrusting this part of the arc. The influence of this ridge may have been especially extensive because it migrates very slowly along the arc trend, and thus it interacts for a long time with a single portion of the arc system. Our previous studies of reef terraces indicated the existence of at least four seismotectonic arc segments or blocks along the Santo-Malekula interval of the arc, and our present results further support this conclusion. Each block has uplifted at different times, by different amounts, at different rates, and tilted in a different direction.

Source: Reference 4

Confidence Intervals?

In Figure 6 of the 2009 report (Ref 1) the confidence intervals for linear mean sea level trends are plotted. With 20 years of data the range is nearly plus or minus 3mm, based on NOAA tide gauges in the USA. But I suspect the real answer is that we don’t have long enough data to even calculate the confidence intervals properly. Vanuatu is not the USA. It is close to the Pacific Rim, which probably explains why it is so mobile.

The big picture

Whatever is happening with sea levels and crustal plates near Vanuatu, sea levels in most of the world are not accelerating, and not correlated well with CO2 either (they started rising long before CO2 did). If we use tide gauges, estimates are in the range of 1mm a year (see here as well). If we use satellites it’s 3mm a year — but only after the original raw data was adjusted.

REFERENCES

1. Pacific Country Report, Sea Level & Climate: Their Present State, Vanuatu, December 2009, South Pacific Sea Level and Climate Monitoring Project [BoM, Australia]. A program sponsored by AusAID. Table 4, page 12.
2. Sea Level Data Summary Report: Jul 10–Jun 11, South Pacific Sea Level and Climate Monitoring Project [BoM, Australia]. A program sponsored by AusAID. Table 2. p 28.
3. Graphs from the Australian BoM: South Pacific Sea Level and Climate Monitoring Project  Monthly Data Reports 2014 Aug
4. Taylor, Frohlich, Lecolle, Strecker (1987)  Analysis- of Partially Emerged Corals and Reef Terraces in the Central Vanuatu Arc: Comparison of  Contemporary Coseismic and Nonseismic With Quaternary Vertical Movements, JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 92, NO. B6, PAGES 4905-1933, MAY 10. 1987


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