Background
With respect to the South Pacific Ocean, the authors indicate that there are few reliable tide gauge records with data predating 1950, writing that "for the last two decades the assessment of relative sea level trends in New Zealand has been solely derived from the sea level records obtained from the four main port tide gauges of Auckland, Wellington, Lyttelton and Dunedin, where the only long-term (>70 year) data sets exist." In addition, they say that "at a regional (Australasian) level, there are only three other long-term gauge records," and they note that for the entire Southern Hemisphere, in fact, there are less than ten sites with pre-1940 records.

What was done
In an attempt to improve this data-sparse situation, Hannah and Bell say that "an investigation was undertaken to determine whether historical data from other tide gauge sites could provide additional spatial coverage of relative sea level trends around New Zealand." And in their paper they describe the "data rescue and mining process" they conducted that enabled "new relative sea level trend estimates to be derived for a further six tide gauge sites in New Zealand at Whangarei, Moturiki, New Plymouth, Nelson, Timaru and Bluff."

What was learned
When all was said and done, the two New Zealand scientists report that "the average relative sea level rise calculated from the six newly derived trends was 1.7 ± 0.1 mm/year," a result that they say "is completely consistent with the far more rigorous and conventional analyses previously undertaken for the four main ports using long-term tide gauge records." And they write that "in a global context, this average trend in relative sea level rise is also consistent with the results of Church and White (2011), who find a global average linear trend in secular sea level rise of 1.7 ± 0.2 mm/year from 1900-2009."

What it means
The results described above provide no evidence for a large acceleration in global sea level rise over the past couple of decades, in contradiction of oft-repeated climate-alarmist claims to the contrary. Church and White (2011), however, do report a mean global sea level trend of 1.9 ± 0.4 mm/year since 1961; but this result is not statistically different from that of the entire 1900-2009 period. As for whether or not it ultimately will become significant, the old adage must suffice: only time will tell.

Reference
Church, J.A. and White, N.J. 2011. Sea-level rise from the late 19th to the early 21st century. Surveys in Geophysics 32: 585-602.