South-West Pacific
There is concern that sea level rise might threaten the existence of some small island communities. Since the start of the 1990s the Australian Meteorological Bureau has run the South Pacific Sea Level & Climate Monitoring Project. Every month the tidal centre publishes an update on their work. Figures 1-12 show the 12 island groups involved in the study (see below):
In these graphs we present
values of monthly average sea level relative to a local
datum for each of the sites. The numbers were obtained by
digitising graphs of the sea levels as the reports do not
give data values. We estimate that the error in any
individual month is of the order 5 to 10 mm, not
significant relative to level changes of the order of
100s of millimetres. We have also plotted values of the
Southern Oscillation Index (SOI). The index used by the
Bureau of Meteorology is based on ten times the monthly
anomaly of the difference in mean sea level pressure
between Tahiti and Darwin, divided by the long-term
standard deviation of that difference for the relevant
month. For both sea levels and the SOI we also plot 12
month moving averages.
What all of these graphs show is that there are
significant variations in sea level and that these are
very much influenced by the atmospheric pressure, as
indicated the SOI. For many of the measuring sites the
lowest levels occurred in 1998 and the large pressure
anomaly in 1997. This is also a feature, seen most
clearly in the moving average plots; the effect the SOI
on sea levels is only seen after a period of 6 to 9
months. The same anomaly was also related to the El Nino
of 1997 which was followed by a world-wide temperature
increase. The graphs also show that for the period of
record sea levels are tending to increase, though the SOI
has also tended to increase over this period and may be
responsible for at least part of the level increase.
The Bureau of Meteorology estimates the rate of rise to
be in the range of 3.3 to 9.4 mm/year for the islands
except for the Federal States of Micronesia which has a
short record. They advise caution in interpreting these
figures which are based (in terms appropriate for sea
level change) on short records.
One of the stations is for Papua New Guinea where there
is record for Rabual in Papua New Guinea in the file
prints.rlr from the Proudman Oceanographic Laboratory
(POL). Figure 13
shows data for the 1975 to 2009 from two records, the
above and the one from POL. For a few months there were
missing values but the period of missing data was never
more than one month and this case the average of the
previous and following month was used. The values of the
early record were adjusted to have the same average as
the later record for the 21 month period of overlap. This
graph confirms the importance of variations in
atmospheric pressure on sea level. It also confirms the
general tendency of sea levels to rise.
Data Sources
Data for the 12 South-West Pacific were extracted from: http://www.bom.gov.au/ntc/IDO60101/IDO60101.200906.pdfThe file was downloaded in August 2009 and has data up to June 2009.
The data for the Rabual were extracted from the file “prints.rlr” downloaded from www.pol.ac.uk/psmsl/pub/prints.rlr .
